How to check that disc brake swap was done correctly?
jim larson said
Jun 25, 2020
Someone added power disc brakes tp my 66. Not sure if it came with manual or power drum. It is not stoping like I think it should. I might add I have no experience in this area. But brakes don’t lock up an don’t feel as good at stoping as my SS with power drum brakes.
How do I begin checking things were done correctly?
Lost in the 60s said
Jun 26, 2020
If the car was originally manual brakes, I've seen many instances where the installer connects the booster rod back in the manual hole of the pedal arm. With power, the rod needs to be in the lower position hole.
Also, they may have a manual master cylinder. If there are any casting numbers on the master, that should be easy to research on the www
Have you swapped the weight springs and vacuum advance canister to your distributor yet ?
jim larson said
Jun 26, 2020
Working on the dizzy. Timing now set at 18* and some improvement. VC plugged. Bob has me taping the springs to see if that is adding timing at idle. Moving from 14 to 18 has allowed my to reduce some idle rpm and made shifting better. Untapped springs and car still starts good and runs good with no pinging.
now going to bump timing up to 22* with Springs taped and see if I can get idle down more and shift even better. When done with that, plan is to limit dizzy so total timing is 34-36. Then adjust CV so i’am up near 52@ cruise.
just starting to check Brake components are correct. So far 11” original Delco Morain booster and Delco MS 5470409 From an early 70’s chevelle.
so I take it this hole is under the dash and part of the pedal assembly? Are the different rods? Could my Vacuum issue also be a problem?
i am thinking I should take the car over to Derek’s and have him drive it so he can evaluate how he thinks it is working. It’s a nice 30 mile county drive on tar.
-- Edited by jim larson on Friday 26th of June 2020 09:20:35 AM
Derek69SS said
Jun 26, 2020
There should be 2 holes in the clutch pedal under the dash. Upper hole is for manual brakes, lower hole is for power brakes.
Bobs_Place said
Jun 26, 2020
I don't know that you could get the push rod on the upper hole as the booster points the rod and lines up correctly with the lower hole, the boosters have an angled bracket. If you could put the push rod in the upper hold there would be less peddle pressure needed to stop the car do to better mechanical advantage.
I noticed a very big improvement in braking when I installed the Impala 11" rears. Both Mitch and Chris P installed 11" from I think later mid size cars.
The master cylinder that you have is probable a 1 1/8 bore for power brakes, you can get a manual Corvette master with a 1" bore . The 1" would give better stopping with the same peddle pressure than the 1 1/8 bore. I have about 7" at idle vac., part of the problem.
The 70 Chevelle and other mid sized cars came with a proportioning valve on the rear brakes with power discs. The valve is mounted on the rear cross member. In later years the proportioning was incorporated in the combination distribution and front limiting/proportioning valve. Most disc brake upgrades, the rear proportioning is not installed, with larger than stock rear tires you could gain some better braking by removing it if it had been installed. If its part of the distribution block it would not be easy to remove it.
jim larson said
Jun 26, 2020
Rod is in lower hole. I think the rear brake line is original to the 66. I will look for a distribution valve by the rear cross member. How would you determine if it is up front? That distribution fitting up front is definitely different than what’s on the 66 SS. I think this upgrade was done in 1997.
At first when applying pressure the brakes seem pretty good. Then when you think it should stop it goes about another 20- 30 feet. Seems like the corvette 1” cylinder might be a good option. What about replacing all the fluid.
jim larson said
Jun 26, 2020
Regarding the larger rear brakes. I have 15x8 rally rims, so would that be relatively easy? I see there is an aftermarket kit, everything included for about $600.
jim larson said
Jun 26, 2020
There is some kind of block mounted to rear crossmember. Caliper and rotor on one side appear to be gm, other side aftermarket.5
-- Edited by jim larson on Friday 26th of June 2020 12:53:24 PM
-- Edited by jim larson on Friday 26th of June 2020 12:55:39 PM
Dot 3 or 4 "should" be flushed every 2 years, but who does that, I try to bleed them as often as I can but still ends up 4,5,10 years between.
Don't know how you would know if the valve is a rear proportioning or not without taking it apart or doing a brake pressure test.
As for that last 20-30 feet try down shifting. that will raise the vacuum.
If you go to the Corvette master, be sure to get a non power/manual brake master, also compare the push rod depth in the old vs new, I'm sure it will inter change on my car and should on yours with that master, check it just to be sure.
jim larson said
Jun 26, 2020
Just sent you a photo of the valve. Has a part # that is kind of hard to read. It has an inlet and an outlet, then on the top it looks like something else possible screwed in.
A Fluid drain with the new Master cylinder should not be t wo expensive and comparitibfe easy.
-- Edited by jim larson on Friday 26th of June 2020 01:30:07 PM
Bobs_Place said
Jun 26, 2020
jim larson wrote:
Regarding the larger rear brakes. I have 15x8 rally rims, so would that be relatively easy? I see there is an aftermarket kit, everything included for about $600.
The disc and calipers look original GM not an aftermarket kit.
Was going to get pictures of the brake valves on my car but the camera battery is dead, charging now.
Bobs_Place said
Jun 26, 2020
jim larson wrote:
Just sent you a photo of the valve. Has a part # that is kind of hard to read. It has an inlet and an outlet, then on the top it looks like something else possible screwed in.
A Fluid drain with the new Master cylinder should not be t wo expensive and comparitibfe easy.
-- Edited by jim larson on Friday 26th of June 2020 01:30:07 PM
The photo looks like the proportion valve, same as mine. I'm not sure if the valve limits brake presser during all braking or just heaver braking to prevent rear wheel skids. The 70 manual is not clear on that, in a 74 manual, the proportioner, part of the combination valve only reduces brake presser to the rears in extreme braking situations. I think it is possible the that valve could be seized and limiting rear BP.
Early 70 to 76 on the master, I think Auto Zone had them for on $40 or so. I'm planning to put one on my car sometime this summer.
jim larson said
Jun 26, 2020
Bobs_Place wrote:
jim larson wrote:
Just sent you a photo of the valve. Has a part # that is kind of hard to read. It has an inlet and an outlet, then on the top it looks like something else possible screwed in.
A Fluid drain with the new Master cylinder should not be t wo expensive and comparitibfe easy.
-- Edited by jim larson on Friday 26th of June 2020 01:30:07 PM
The photo looks like the proportion valve, same as mine. I'm not sure if the valve limits brake presser during all braking or just heaver braking to prevent rear wheel skids. The 70 manual is not clear on that, in a 74 manual, the proportioner, part of the combination valve only reduces brake presser to the rears in extreme braking situations. I think it is possible the that valve could be seized and limiting rear BP.
Early 70 to 76 on the master, I think Auto Zone had them for on $40 or so. I'm planning to put one on my car sometime this summer.
Drove the car early this afternoon. I went in reverse at about 25 mph and slamed the brakes. Then going forward on hard braking the rear pass would lock up; but not the drivers side. So I took both drums off for inspection. Looks like good pad left, drums looked good with no ridge. No leaking cylinder. I adjusted driver side up a bit and will test again tomorrow.
i suspected an issue with front drivers side, so I pulled that side outer bearing. Looked good, felt good and sounded good. So reassembled. Did not look at inner bearing or spindle shaft, probably should have as I am hearing noise from there; may be caliper not releasing enough. To be continued.
Bobs_Place said
Jun 26, 2020
Here are the brake valves
Distribution block
The rear proportioning valve mounted on the rear cross member just ahead on the rear axle.
This is the front metering valve, It delays front brakes until rear brake shoes are extended out to the drums
My proportioning valve on the rear frame looks the same. The valve up front is similar but not thinking the same. Has 2 lines in and 3 out. MC look different with no front metering valve. My line out goes directly to the front distributio block and not through a valve mounted on the booster. I think it is a 1/8” bore as you suggested.
Based on the size difference the brakes should be about 21% better and a 21% longer peddle stroke with the 1" master over the 1 1/8 master. If I did the math correctly.
jim larson said
Jun 27, 2020
Bobs_Place wrote:
The area of a 1 1/8 cyl. is .994.
The area of the 1" cyl is .785
Based on the size difference the brakes should be about 21% better and a 21% longer peddle stroke with the 1" master over the 1 1/8 master. If I did the math correctly.
Sounding like a master cylinder change. Where do you find the math formulas? There is also a little leakage between the MC & Booster. Probably due for a fluid change. Is that extra valve on the front line necessary or something yo u added?
As long as we are on disc brakes, if caliper are hanging up, is there a fix?
jim larson said
Jun 27, 2020
Thinking the rear brakes are working as they should now. Not so sure on front. Right front seem ok. I think there is a problem with drivers side. Car wants to dive right when breaking hard. Also I think the drivers side might be hanging up a little ( noise seems to come from there). Don’t want to start sticking a whole lot of &’s into the brakes now. Might there be a problem with the piston, the hose, or the slide pins? I have watched a few videos, Eric the car guy seems the most complete. I think I might try to evaluate the drivers side. Wondering if there is a good Reasonable shop in mn to recondition calipers?
Bobs_Place said
Jun 28, 2020
The formula for the area is Pi x radius squared, so for a 1" bore the radius is .5. Than 3.1416x.5x.5=.7854
Than .7854/.994 (the area of a 1 1/8 bore) =.790. That is, the area of the 1" cyl is 79% of the 1 1/8 cyl. So with equal peddle pressure, the hydraulic brake pressure should be 21% higher.
With a vacuum booster, the longer stroke needed with the smaller cylinder may consume more vacuum. Would the brakes be better or worse. I think the brakes will be better but it could depends on how much vacuum the engine is making at the point the brakes are being applied.
If the left caliper is hanging up the rotor will get worm/hot, than that side will fade and won't brake as well as the other side.
Calipers are not that expensive, or if the piston is good they can be rebuilt.
I have had bad lines, they caused the brakes to be slow to apply and slow to release. Change them if they old or look bad.
Lost in the 60s said
Jun 29, 2020
Your left front flex hose appears to be quite new. I wouldn't suspect that as the issue. Very common for the calipers to stick in the bore over time. Since these aren't original to the car, no sense having it rebuilt. You can get rebuilt calipers from NAPA, and other sources and just swap out. There should be a casting number on the caliper and an internet search will show what vehicle it came on, to get a replacement. To be honest, I would replace both as "loaded", with new pads too. If you have a local place to turn the rotors, I would have that done as well and you will have new front brakes. I would do this before messing with the master, to compare the brake performance. You may be happy with the 1 1/8" master then, BUT... You WILL need to replace the master, at some point, for the leakage at the booster. That leakage is, often, the rear seals failing on the master piston. It could be a leaking cap seal too, but you should see fluid down the back side of the master casting from that.
SShink said
Jun 29, 2020
Lost in the 60s wrote:
Since these aren't original to the car, no sense having it rebuilt. You can get rebuilt calipers from NAPA, and other sources and just swap out. There should be a casting number on the caliper and an internet search will show what vehicle it came on, to get a replacement. To be honest, I would replace both as "loaded", with new pads too. If you have a local place to turn the rotors, I would have that done as well and you will have new front brakes. I would do this before messing with the master, to compare the brake performance. You may be happy with the 1 1/8" master then, BUT... You WILL need to replace the master, at some point, for the leakage at the booster. That leakage is, often, the rear seals failing on the master piston. It could be a leaking cap seal too, but you should see fluid down the back side of the master casting from that.
I had bought the disc conversion parts from Denny at Auto City Classics for the '71 Malibu and never got them installed before I sold it (imagine that...lol), so will be installing them on the '69 this week (I promise). Part of the kit are the 'loaded' calipers that also have a nice zinc look finish on them, so I don't believe they will rust. Anyway, reach out to Denny at ACC if you want a price for just the 'loaded calipers' since I bought them as a kit.
And yes, I know some people have had issues with the ACC conversion kits, but if I do I know Denny will stand behind the parts.
The formula for the area is Pi x radius squared, so for a 1" bore the radius is .5. Than 3.1416x.5x.5=.7854
Than .7854/.994 (the area of a 1 1/8 bore) =.790. That is, the area of the 1" cyl is 79% of the 1 1/8 cyl. So with equal peddle pressure, the hydraulic brake pressure should be 21% higher.
With a vacuum booster, the longer stroke needed with the smaller cylinder may consume more vacuum. Would the brakes be better or worse. I think the brakes will be better but it could depends on how much vacuum the engine is making at the point the brakes are being applied.
If the left caliper is hanging up the rotor will get worm/hot, than that side will fade and won't brake as well as the other side.
Calipers are not that expensive, or if the piston is good they can be rebuilt.
I have had bad lines, they caused the brakes to be slow to apply and slow to release. Change them if they old or look bad.
On your formula Bob, the volume of fluid the piston moves is Pi(r)(r)(H). I don't know the stroke of the MC of the manual vs the hydraulic, so I didn't understand if you were saying manual or hydraulic MS was better. If same stroke then Hydraulic is 21% better. I think I misinterpreted what you were saying in a previous post. Though you were saying a 1' manual was better than a 1 1/6" power cylinder.
jim larson said
Jun 29, 2020
Regarding replacements, most likely leaning that way now. I am think fix the leaking MC first, then new fluid. The new loaded calipers and turn the rotors. But those caliper and rotors sure look nice Stan. One thing though in looking at the calipers it looks like new coper washers for the brake hoses, I have heard that steel are better. I wonder if that is true?
Lost in the 60s said
Jun 29, 2020
I've never seen steel sealing washer and can't imagine they would compress and seal better than copper.
My reasoning for saving the master for last, is, if the replaced brakes work as you want/expect, then replacing with the same size master would be OK. If you replace the master now, are you going to go to a smaller size ?
All this talk about pie is making me hungry...
Bobs_Place said
Jun 29, 2020
jim larson wrote:
Bobs_Place wrote:
The formula for the area is Pi x radius squared, so for a 1" bore the radius is .5. Than 3.1416x.5x.5=.7854
Than .7854/.994 (the area of a 1 1/8 bore) =.790. That is, the area of the 1" cyl is 79% of the 1 1/8 cyl. So with equal peddle pressure, the hydraulic brake pressure should be 21% higher.
With a vacuum booster, the longer stroke needed with the smaller cylinder may consume more vacuum. Would the brakes be better or worse. I think the brakes will be better but it could depends on how much vacuum the engine is making at the point the brakes are being applied.
If the left caliper is hanging up the rotor will get worm/hot, than that side will fade and won't brake as well as the other side.
Calipers are not that expensive, or if the piston is good they can be rebuilt.
I have had bad lines, they caused the brakes to be slow to apply and slow to release. Change them if they old or look bad.
On your formula Bob, the volume of fluid the piston moves is Pi(r)(r)(H). I don't know the stroke of the MC of the manual vs the hydraulic, so I didn't understand if you were saying manual or hydraulic MS was better. If same stroke then Hydraulic is 21% better. I think I misinterpreted what you were saying in a previous post. Though you were saying a 1' manual was better than a 1 1/6" power cylinder.
The stroke of the 1" master should increase by approximately 21% over the 1 18" master. The brake system needs the same amount of pressure to stop the car whether you have a 1" or a 1 1/8 master, however, there is no free lunch, so with the 1" you don't have to push on the peddle as hard, the trade off is a longer stroke. The stroke is the result of the rest of the brake system. If you were to install larger rear cylinder for example, the peddle stroke would increase.
Disc brakes consume very little fluid during a brake application, the rear drum brakes shouldn't consume much fluid ether with good working adjusters and properly bleed system, so the brakes will be better if the booster can Keep up. If however the engine does not create much vacuum at idle, and with an auto trans, and depending on speed, the RPM drops to were the booster would run low on vacuum for the next brake application. The check valve should maintain the vacuum for the initial application.
I believe there are a lot of the cars that are up graded with a 1" master without any problems.
Have you tried down shifting to see if the last 20-30ft stops better?
jim larson said
Jun 29, 2020
Yes I tried the down shift think, drive into second, It did seem a hair better; but you know about the placebo effect on taking a pill.
Now I am on the same page as you regarding 1.125 bore to 1.0 bore. You need a longer stroke on the smaller bore to get the same pressure. But your saying a smaller effect but over a longer distance. I think it may abe kind of iffy with my vacuum issue.
Can you get new seals to install so the MC doesn't leak. You hardly notice the leak. But on a new booster that would be upsetting. As for other plumbing issues it on to installing a taller toilet.
-- Edited by jim larson on Monday 29th of June 2020 03:05:07 PM
-- Edited by jim larson on Monday 29th of June 2020 03:06:04 PM
jim larson said
Jun 29, 2020
What is the purpose of the two proportioning valve on Bobs photos, the one mounted to the booster and the one at the rear fram crossmember? I though there was only one used, wrong again.
Lost in the 60s said
Jun 29, 2020
The round one at the booster is a hold off valve. It holds back the front brake fluid for a second, to let the rear drums start expanding, so the car doesn't want to skid on the fronts alone.
The rear prop valve would limit the amount of pressure to a pre-determined amount, probably to control brake lock up. Never seen one on a Chevelle, they were somewhat common on first gen Camaro's. I'll have to look at my '70 SS tomorrow and see if it has one.
Bobs_Place said
Jun 29, 2020
jim larson wrote:
Yes I tried the down shift think, drive into second, It did seem a hair better; but you know about the placebo effect on taking a pill.
So if braking is not much better the booster must be getting enough vacuum, the trans in second will also help slow the vehicle.
Now I am on the same page as you regarding 1.125 bore to 1.0 bore. You need a longer stroke on the smaller bore to get the same pressure. But your saying a smaller effect but over a longer distance. I think it may abe kind of iffy with my vacuum issue.
Your close, it not the longer stroke that give better braking its the smaller bore. You have to push the same amount of fluid regardless the cylinder, it's just easier with the smaller bore but the plunger must go farther. I plan to go to a 1" cyl on my car.
Can you get new seals to install so the MC doesn't leak. You hardly notice the leak. But on a new booster that would be upsetting. As for other plumbing issues it on to installing a taller toilet.
Brake fluid absorbs moisture, so if the fluid has not been changed/flushed in several years the master may be corroded. Or, when the disc brakes were installed, did the master get rebuilt, did they hone a corroded cylinder, so the pitting from the corrosion would still be there, the seals then would not last. My guess is the cylinder needs to be replaced.
-- Edited by jim larson on Monday 29th of June 2020 03:05:07 PM
-- Edited by jim larson on Monday 29th of June 2020 03:06:04 PM
jim larson said
Jun 30, 2020
I did have good luck on the 66ss old MC. It was rusty. I cleaned and JB weld the pits and honed it out. Has not leaked in the last 10yr or so. But this cylinder is not a numbers match to the car. I see them on eBay from around $75 to $300.
-- Edited by jim larson on Tuesday 30th of June 2020 06:48:42 AM
Lost in the 60s said
Jun 30, 2020
Again, NAPA master cylinders are very good. I have a number of them on cars.
My '67 Camaro had manual drum brakes on it until a year ago. I put a rebuilt NAPA master on it 16 years ago that cost $12 and it was still working good and not leaking when removed for disc upgrade.
Derek69SS said
Jun 30, 2020
I have 0 experience with keeping drum brakes in the rear... didn't the Corvettes by that time all have 4-wheel discs?
How does the fluid volume requirements of rear drums compare? Are you running an adjustable proportioning valve?
Lost in the 60s said
Jun 30, 2020
Derek69SS wrote:
I have 0 experience with keeping drum brakes in the rear... didn't the Corvettes by that time all have 4-wheel discs? How does the fluid volume requirements of rear drums compare? Are you running an adjustable proportioning valve?
Yep, you are correct and he would need the adjustable prop valve.
I looked at the few manual disc/drum combos GM offered in 1969-1974 and they are all 1.125. Gonna be easier to just replace with the larger bore.
Bobs_Place said
Jul 1, 2020
ACDELCO18M27{#18030269, 19176423} are 1" search these pt#s.
Also Raybestos PT# MC36367
67-76 Corvette with manual brakes original PT# is 18001118
Lost in the 60s said
Jul 1, 2020
Bobs_Place wrote:
ACDELCO18M27{#18030269, 19176423} are 1" search these pt#s.
Also Raybestos PT# MC36367
67-76 Corvette with manual brakes original PT# is 18001118
Yes, I found 1" masters too, but as Derek pointed out, the master will be designed to operate 4 wheel discs. The line pressure may be too high for the drums in the rear and the residual pressure too low to retain the wheel cylinder cup "preload" of 10 lbs. Disc residual is typically 2 lbs.
The adjustable prop valve can reduce the pressure to the drums, to reduce/eliminate the tendency to lock up, but you will, also, need an in-line residual valve to hold the necessary 10 lb preload on the cups. THIS may be the purpose of the valve at the rear crossmember on your '70 and yes, mine has it too. It MAY be to hold higher residual pressure, but I can not find any information to conclude that.
Jim does have an issue with the left caliper and not enough brake force to operate properly, but this is all a bandaid for the root cause of the low vacuum to assist with braking...the engine is worn out. There is a constant stream of blue smoke out the right tail pipe at idle and there is so much blowby, that it is actually pressurizing the intake and reducing vacuum. When I pulled the pcv out of the valve cover and plugged it with my finger, the rpm went down, and the vacuum gauge went UP a few pounds. The internal pressure is so high that it blows smoke out the valve cover about 12" and I can FEEL pressure when putting my hand over the pcv hole. Even with the valve unplugged and out of the cover, the vacuum went up. Put the valve back in the cover and the vacuum went down from the internal pressure in the engine.
His disc "conversion" seems to be a cobbled mess of used parts and he needs to reseal or replace BOTH calipers, to eliminate in-adequate and uneven braking and the master for leaks. At that point, I believe the brakes will be as good as they are going to get until the vacuum issue is resolved.
After driving the 66 SS with power drum brakes last night , I feel I will be driving the convertible less than I planned before winter. It really feel like the vacuum is an issue regarding the disc brakes more than anything else. Brakes feel pretty good from 80mph down to about 15mph and then they fell like their gone and it take to long to finally stop. With all the messing with the distributor idle is down to 900rpm and sift feel OK.
Dave Seitz said
Jul 10, 2020
Brake pads do make a huge difference on how it stops. Even on my wife's minivan she complained the brakes were bad after I put in cheap pads. My truck I had to change out the pads after about two months because the cheap pads were so bad,
Replaced with top of the line pads and the brakes would throw you through the windshield. No you don't need the race only pads just the best quality pads available.
jim larson said
Jul 18, 2020
Well I just finished following Mitches suggestion regarding caliper. I just installed a Napa caliper on the drivers side which I though was the problem. Being a little on the frugal side I re-used the brake pads, didn't resurface the rotors, and left the pass side alone. Car stops real good and no caliper noise. Now I think I better take care of the leaking MC as there is a little clean-up and occasional topping off the fluid. I did keep the Deco caliper from 70 and will probably use it a a learning opportunity.
Someone added power disc brakes tp my 66. Not sure if it came with manual or power drum. It is not stoping like I think it should. I might add I have no experience in this area. But brakes don’t lock up an don’t feel as good at stoping as my SS with power drum brakes.
How do I begin checking things were done correctly?
Also, they may have a manual master cylinder. If there are any casting numbers on the master, that should be easy to research on the www
Have you swapped the weight springs and vacuum advance canister to your distributor yet ?
Working on the dizzy. Timing now set at 18* and some improvement. VC plugged. Bob has me taping the springs to see if that is adding timing at idle. Moving from 14 to 18 has allowed my to reduce some idle rpm and made shifting better. Untapped springs and car still starts good and runs good with no pinging.
now going to bump timing up to 22* with Springs taped and see if I can get idle down more and shift even better. When done with that, plan is to limit dizzy so total timing is 34-36. Then adjust CV so i’am up near 52@ cruise.
just starting to check Brake components are correct. So far 11” original Delco Morain booster and Delco MS 5470409 From an early 70’s chevelle.
so I take it this hole is under the dash and part of the pedal assembly? Are the different rods? Could my Vacuum issue also be a problem?
i am thinking I should take the car over to Derek’s and have him drive it so he can evaluate how he thinks it is working. It’s a nice 30 mile county drive on tar.
-- Edited by jim larson on Friday 26th of June 2020 09:20:35 AM
I don't know that you could get the push rod on the upper hole as the booster points the rod and lines up correctly with the lower hole, the boosters have an angled bracket. If you could put the push rod in the upper hold there would be less peddle pressure needed to stop the car do to better mechanical advantage.
I noticed a very big improvement in braking when I installed the Impala 11" rears. Both Mitch and Chris P installed 11" from I think later mid size cars.
The master cylinder that you have is probable a 1 1/8 bore for power brakes, you can get a manual Corvette master with a 1" bore . The 1" would give better stopping with the same peddle pressure than the 1 1/8 bore. I have about 7" at idle vac., part of the problem.
The 70 Chevelle and other mid sized cars came with a proportioning valve on the rear brakes with power discs. The valve is mounted on the rear cross member. In later years the proportioning was incorporated in the combination distribution and front limiting/proportioning valve. Most disc brake upgrades, the rear proportioning is not installed, with larger than stock rear tires you could gain some better braking by removing it if it had been installed. If its part of the distribution block it would not be easy to remove it.
There is some kind of block mounted to rear crossmember. Caliper and rotor on one side appear to be gm, other side aftermarket.5
-- Edited by jim larson on Friday 26th of June 2020 12:53:24 PM
-- Edited by jim larson on Friday 26th of June 2020 12:55:39 PM
Dot 3 or 4 "should" be flushed every 2 years, but who does that, I try to bleed them as often as I can but still ends up 4,5,10 years between.
Don't know how you would know if the valve is a rear proportioning or not without taking it apart or doing a brake pressure test.
As for that last 20-30 feet try down shifting. that will raise the vacuum.
If you go to the Corvette master, be sure to get a non power/manual brake master, also compare the push rod depth in the old vs new, I'm sure it will inter change on my car and should on yours with that master, check it just to be sure.
Just sent you a photo of the valve. Has a part # that is kind of hard to read. It has an inlet and an outlet, then on the top it looks like something else possible screwed in.
A Fluid drain with the new Master cylinder should not be t wo expensive and comparitibfe easy.
-- Edited by jim larson on Friday 26th of June 2020 01:30:07 PM
The disc and calipers look original GM not an aftermarket kit.
Was going to get pictures of the brake valves on my car but the camera battery is dead, charging now.
The photo looks like the proportion valve, same as mine. I'm not sure if the valve limits brake presser during all braking or just heaver braking to prevent rear wheel skids. The 70 manual is not clear on that, in a 74 manual, the proportioner, part of the combination valve only reduces brake presser to the rears in extreme braking situations. I think it is possible the that valve could be seized and limiting rear BP.
Early 70 to 76 on the master, I think Auto Zone had them for on $40 or so. I'm planning to put one on my car sometime this summer.
Drove the car early this afternoon. I went in reverse at about 25 mph and slamed the brakes. Then going forward on hard braking the rear pass would lock up; but not the drivers side. So I took both drums off for inspection. Looks like good pad left, drums looked good with no ridge. No leaking cylinder. I adjusted driver side up a bit and will test again tomorrow.
i suspected an issue with front drivers side, so I pulled that side outer bearing. Looked good, felt good and sounded good. So reassembled. Did not look at inner bearing or spindle shaft, probably should have as I am hearing noise from there; may be caliper not releasing enough. To be continued.
Here are the brake valves
Distribution block
The rear proportioning valve mounted on the rear cross member just ahead on the rear axle.
This is the front metering valve, It delays front brakes until rear brake shoes are extended out to the drums
My proportioning valve on the rear frame looks the same. The valve up front is similar but not thinking the same. Has 2 lines in and 3 out. MC look different with no front metering valve. My line out goes directly to the front distributio block and not through a valve mounted on the booster. I think it is a 1/8” bore as you suggested.
The area of a 1 1/8 cyl. is .994.
The area of the 1" cyl is .785
Based on the size difference the brakes should be about 21% better and a 21% longer peddle stroke with the 1" master over the 1 1/8 master. If I did the math correctly.
Sounding like a master cylinder change. Where do you find the math formulas? There is also a little leakage between the MC & Booster. Probably due for a fluid change. Is that extra valve on the front line necessary or something yo u added?
As long as we are on disc brakes, if caliper are hanging up, is there a fix?
Thinking the rear brakes are working as they should now. Not so sure on front. Right front seem ok. I think there is a problem with drivers side. Car wants to dive right when breaking hard. Also I think the drivers side might be hanging up a little ( noise seems to come from there). Don’t want to start sticking a whole lot of &’s into the brakes now. Might there be a problem with the piston, the hose, or the slide pins? I have watched a few videos, Eric the car guy seems the most complete. I think I might try to evaluate the drivers side. Wondering if there is a good Reasonable shop in mn to recondition calipers?
The formula for the area is Pi x radius squared, so for a 1" bore the radius is .5. Than 3.1416x.5x.5=.7854
Than .7854/.994 (the area of a 1 1/8 bore) =.790. That is, the area of the 1" cyl is 79% of the 1 1/8 cyl. So with equal peddle pressure, the hydraulic brake pressure should be 21% higher.
With a vacuum booster, the longer stroke needed with the smaller cylinder may consume more vacuum. Would the brakes be better or worse. I think the brakes will be better but it could depends on how much vacuum the engine is making at the point the brakes are being applied.
If the left caliper is hanging up the rotor will get worm/hot, than that side will fade and won't brake as well as the other side.
Calipers are not that expensive, or if the piston is good they can be rebuilt.
I have had bad lines, they caused the brakes to be slow to apply and slow to release. Change them if they old or look bad.
Your left front flex hose appears to be quite new. I wouldn't suspect that as the issue.
Very common for the calipers to stick in the bore over time.
Since these aren't original to the car, no sense having it rebuilt. You can get rebuilt calipers from NAPA, and other sources and just swap out. There should be a casting number on the caliper and an internet search will show what vehicle it came on, to get a replacement.
To be honest, I would replace both as "loaded", with new pads too. If you have a local place to turn the rotors, I would have that done as well and you will have new front brakes.
I would do this before messing with the master, to compare the brake performance. You may be happy with the 1 1/8" master then, BUT...
You WILL need to replace the master, at some point, for the leakage at the booster. That leakage is, often, the rear seals failing on the master piston. It could be a leaking cap seal too, but you should see fluid down the back side of the master casting from that.
I had bought the disc conversion parts from Denny at Auto City Classics for the '71 Malibu and never got them installed before I sold it (imagine that...lol), so will be installing them on the '69 this week (I promise). Part of the kit are the 'loaded' calipers that also have a nice zinc look finish on them, so I don't believe they will rust. Anyway, reach out to Denny at ACC if you want a price for just the 'loaded calipers' since I bought them as a kit.
And yes, I know some people have had issues with the ACC conversion kits, but if I do I know Denny will stand behind the parts.
On your formula Bob, the volume of fluid the piston moves is Pi(r)(r)(H). I don't know the stroke of the MC of the manual vs the hydraulic, so I didn't understand if you were saying manual or hydraulic MS was better. If same stroke then Hydraulic is 21% better. I think I misinterpreted what you were saying in a previous post. Though you were saying a 1' manual was better than a 1 1/6" power cylinder.
Regarding replacements, most likely leaning that way now. I am think fix the leaking MC first, then new fluid. The new loaded calipers and turn the rotors. But those caliper and rotors sure look nice Stan. One thing though in looking at the calipers it looks like new coper washers for the brake hoses, I have heard that steel are better. I wonder if that is true?
I've never seen steel sealing washer and can't imagine they would compress and seal better than copper.
My reasoning for saving the master for last, is, if the replaced brakes work as you want/expect, then replacing with the same size master would be OK. If you replace the master now, are you going to go to a smaller size ?
All this talk about pie is making me hungry...
The stroke of the 1" master should increase by approximately 21% over the 1 18" master. The brake system needs the same amount of pressure to stop the car whether you have a 1" or a 1 1/8 master, however, there is no free lunch, so with the 1" you don't have to push on the peddle as hard, the trade off is a longer stroke. The stroke is the result of the rest of the brake system. If you were to install larger rear cylinder for example, the peddle stroke would increase.
Disc brakes consume very little fluid during a brake application, the rear drum brakes shouldn't consume much fluid ether with good working adjusters and properly bleed system, so the brakes will be better if the booster can Keep up. If however the engine does not create much vacuum at idle, and with an auto trans, and depending on speed, the RPM drops to were the booster would run low on vacuum for the next brake application. The check valve should maintain the vacuum for the initial application.
I believe there are a lot of the cars that are up graded with a 1" master without any problems.
Have you tried down shifting to see if the last 20-30ft stops better?
Yes I tried the down shift think, drive into second, It did seem a hair better; but you know about the placebo effect on taking a pill.
Now I am on the same page as you regarding 1.125 bore to 1.0 bore. You need a longer stroke on the smaller bore to get the same pressure. But your saying a smaller effect but over a longer distance. I think it may abe kind of iffy with my vacuum issue.
Can you get new seals to install so the MC doesn't leak. You hardly notice the leak. But on a new booster that would be upsetting. As for other plumbing issues it on to installing a taller toilet.
-- Edited by jim larson on Monday 29th of June 2020 03:05:07 PM
-- Edited by jim larson on Monday 29th of June 2020 03:06:04 PM
What is the purpose of the two proportioning valve on Bobs photos, the one mounted to the booster and the one at the rear fram crossmember? I though there was only one used, wrong again.
The rear prop valve would limit the amount of pressure to a pre-determined amount, probably to control brake lock up. Never seen one on a Chevelle, they were somewhat common on first gen Camaro's. I'll have to look at my '70 SS tomorrow and see if it has one.
I did have good luck on the 66ss old MC. It was rusty. I cleaned and JB weld the pits and honed it out. Has not leaked in the last 10yr or so. But this cylinder is not a numbers match to the car. I see them on eBay from around $75 to $300.
-- Edited by jim larson on Tuesday 30th of June 2020 06:48:42 AM
Again, NAPA master cylinders are very good. I have a number of them on cars.
1970 corvette w/manual brakes, 1" bore
NEW, casting has "Made in USA" in it ?? $60... https://www.napaonline.com/en/p/NMAM1922?partTypeName=Brake+Master+Cylinder&keywordInput=master+cylinder
Reman... $50... https://www.napaonline.com/en/p/NMBP1922?partTypeName=Brake+Master+Cylinder&keywordInput=master+cylinder
My '67 Camaro had manual drum brakes on it until a year ago. I put a rebuilt NAPA master on it 16 years ago that cost $12 and it was still working good and not leaking when removed for disc upgrade.
How does the fluid volume requirements of rear drums compare? Are you running an adjustable proportioning valve?
Yep, you are correct and he would need the adjustable prop valve.
I looked at the few manual disc/drum combos GM offered in 1969-1974 and they are all 1.125. Gonna be easier to just replace with the larger bore.
ACDELCO 18M27 {#18030269, 19176423} are 1" search these pt#s.
Also Raybestos PT# MC36367
67-76 Corvette with manual brakes original PT# is 18001118
Yes, I found 1" masters too, but as Derek pointed out, the master will be designed to operate 4 wheel discs. The line pressure may be too high for the drums in the rear and the residual pressure too low to retain the wheel cylinder cup "preload" of 10 lbs. Disc residual is typically 2 lbs.
The adjustable prop valve can reduce the pressure to the drums, to reduce/eliminate the tendency to lock up, but you will, also, need an in-line residual valve to hold the necessary 10 lb preload on the cups.
THIS may be the purpose of the valve at the rear crossmember on your '70 and yes, mine has it too. It MAY be to hold higher residual pressure, but I can not find any information to conclude that.
Jim does have an issue with the left caliper and not enough brake force to operate properly, but this is all a bandaid for the root cause of the low vacuum to assist with braking...the engine is worn out. There is a constant stream of blue smoke out the right tail pipe at idle and there is so much blowby, that it is actually pressurizing the intake and reducing vacuum. When I pulled the pcv out of the valve cover and plugged it with my finger, the rpm went down, and the vacuum gauge went UP a few pounds. The internal pressure is so high that it blows smoke out the valve cover about 12" and I can FEEL pressure when putting my hand over the pcv hole. Even with the valve unplugged and out of the cover, the vacuum went up. Put the valve back in the cover and the vacuum went down from the internal pressure in the engine.
His disc "conversion" seems to be a cobbled mess of used parts and he needs to reseal or replace BOTH calipers, to eliminate in-adequate and uneven braking and the master for leaks. At that point, I believe the brakes will be as good as they are going to get until the vacuum issue is resolved.
https://www.speedwaymotors.com/Right-Stuff-BR02ZDC-Disc-Brake-Rotors-Drilled-Camaro-Nova-Pair,122471.html
https://www.speedwaymotors.com/Right-Stuff-DBMC01-1-125-Inch-Bore-Master-Cylinder-1970-79-GM,122421.html
https://www.speedwaymotors.com/IMCA-69-77-GM-Loaded-Brake-Caliper-Kit-w-Super-Stopper-Brake-Pads,411769.html
$15 less with different pads.
After driving the 66 SS with power drum brakes last night , I feel I will be driving the convertible less than I planned before winter. It really feel like the vacuum is an issue regarding the disc brakes more than anything else. Brakes feel pretty good from 80mph down to about 15mph and then they fell like their gone and it take to long to finally stop. With all the messing with the distributor idle is down to 900rpm and sift feel OK.
Replaced with top of the line pads and the brakes would throw you through the windshield. No you don't need the race only pads just the best quality pads available.
Well I just finished following Mitches suggestion regarding caliper. I just installed a Napa caliper on the drivers side which I though was the problem. Being a little on the frugal side I re-used the brake pads, didn't resurface the rotors, and left the pass side alone. Car stops real good and no caliper noise. Now I think I better take care of the leaking MC as there is a little clean-up and occasional topping off the fluid. I did keep the Deco caliper from 70 and will probably use it a a learning opportunity.