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Post Info TOPIC: I need a little lesson in Brake Hydraulics.
jim larson


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I need a little lesson in Brake Hydraulics.
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My car has power drum brakes.  The original wheel cylinders had a 1 1/8" bore in the front and a 15/16" bore in the rears.

Whats the advantage or dis-advantange in going to wheel cylinders of a different size?  Somtime in the past someone put rear cylinders on  that had  a 1" bore that I replaced with the original 15/16" bore size.  Wondering if I should have stayed with the 1" size?

I haven't determined what I have on the front,  I will have to take the brake  springs off to get the part numbers as I can't read what is cast into the housing.  But I suspect it is the original 1 1/8" size.  I am thinking I might change these, since I don't think they are exactly correct, even though they fit and are a 1 1/8" bore, as I can only get an open end wrench on the bleeder  (Ive just about round it off completely); because of the size of the bleeder and also where it sits in relationship to the arm of the spindle.



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Jim L

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The bleeders are very poorly positioned behind the spindle arm and you really need a dedicated box end bleeder wrench to prevent what you are doing with the open end. I'm heading out to the shop now and will get a pic of the tool in a while.
You should be able to buy replacement bleeders and replace the damaged ones. I'm pretty sure NAPA has them on the "HELP" rack. I would think O Reilly's would too ?? They may have the bleeder tool too, but it may be special order, since there isn't any demand for them now.

As for bore size, going bigger can create the need for more pedal pressure, the reasoning being it takes more stroke and pressure to move the increased capacity of fluid. A change of 1/16th in the rear wouldn't be much more fluid and I can't imagine you would notice much, if any, pedal/braking difference.

You are trying to remedy a hard pedal ?? all this started after the master and booster work ?? Did you also change the shoes at that time ?? Shoe composition can make a huge difference in pedal pressure and stopping ability. Were the drums turned, were the shoes arched to match the drums, yada, yada. There are many variables to the brake system working well.

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Mitch D.   River Falls, WI

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1966 Chevelle SS 396 M20

1970 Chevelle SS 396 M20

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Here's the wrench on the bleeder. The correct size of the hex is 5/16. The one on the other side is a replacement with 3/8 hex and I can barely get the wrench on that one.



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Mitch D.   River Falls, WI

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1966 Chevelle SS 396 M20

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Derek69SS


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Smaller bore needs more pressure to exert the same force, so the pedal should now be firmer, but take more effort to do the same work.

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Derek Kiefer - Mantorville, MN

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SShink


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Different off topic than brakes (sorry Jim)... but Mitch I'm curious about your anti-sway bar end link bushings.  The bushings don't appear to be compressed to the same diameter as the cup washers.  I thought the proper torque technique was to 'squash' the washers down tight enough that the bushings were the approximately same diameter as the washers, similar to the process for shock absorber bushings?  headscratch

 

In other words, it looks like the end link could be tightened a little more?



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Lost in the 60s


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SShink wrote:

Different off topic than brakes (sorry Jim)... but Mitch I'm curious about your anti-sway bar end link bushings.  The bushings don't appear to be compressed to the same diameter as the cup washers.  I thought the proper torque technique was to 'squash' the washers down tight enough that the bushings were the approximately same diameter as the washers, similar to the process for shock absorber bushings?  headscratch

 

In other words, it looks like the end link could be tightened a little more?

 Those are urethane bushings, they don't squash like rubber...tsktsk



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Mitch D.   River Falls, WI

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1966 Chevelle SS 396 M20

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jim larson


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Lost in the 60s wrote:

Here's the wrench on the bleeder. The correct size of the hex is 5/16. The one on the other side is a replacement with 3/8 hex and I can barely get the wrench on that one.

 Thanks Mitch, the bleeders that I have are both 3/8th on the front.  I picked up a couple of the 5/16th bleeders from NAPA yesterday and will install them the next time I have the front end up in the air and the tires off.  I will have to get one of those wrenches.  I also will have to get some wrenches to help with the spring removal/re-assembly for the brakes.  It's a pain using a screw driver.

I just bought a bleeder wrench like yours Mitch.  Would you care to recommend a brake spring removal wrench?



-- Edited by jim larson on Wednesday 17th of September 2014 09:29:04 AM

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Jim L

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image_12531.jpg

The pliers tool is for the return springs. The black end is to remove them by using the tip to catch the open end of the hook and rotating the tool to pop the spring off the top stud. Use the other long end to put them on. You place the open hook on the tool and then use the divot at the end to hold the tool on the pivot and simply lift the tool upright and the spring will slide down and onto the pivot head.

 

The red handled tool is to push, twist and release the shoe hold down springs/cups.

I don't recommend HF tools, I just happened to find this pic with both tools. NAPA should have better quality tools like this.



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Mitch D.   River Falls, WI

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1970 Chevelle SS 396 M20

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For all my advise on how to gravity bleed, I am up against the same wall with the GTO. Every piece of the brake system to the backing plates is NEW and I can't get the rears to bleed. I removed the master this morning and believe the pushrod is too long, holding the internal valve slightly compressed. That would prevent fluid from getting from the reservoir to the piston again. I spaced the master out 1/4" and got a little free space on the pedal, but it still won't bleed by gravity. I'll leave the right rear bleeder open all day and see if it gets going....banghead



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Mitch D.   River Falls, WI

Lifetime member of the "Cars apart Club"

1966 Chevelle SS 396 M20

1970 Chevelle SS 396 M20

1967 Camaro SS/RS 350 M20
jim larson


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I read somewhere about special bleeder valve  that won't allow air back in; but my bleeders are so old i doubt they are of that type.  I bought an NOS MC repair kit when I rebuilt my MC last year.  When I bleed the MC, it wouldn't work to just open the bleeder valve on the MC.  I had to also push in on the piston from the rear  to get air out and fill the piston area of the MC with fluid.   When I looked at the old parts, it made sense that I had to push on the piston to force air and then fluid eventually out the bleeder valve.  There was some kind of rubber seal that would hold the air or fluid in.

I think the kit I bought didn't have that kind of a seal, so I just reused to old seal.



-- Edited by jim larson on Wednesday 17th of September 2014 11:46:21 AM



-- Edited by jim larson on Wednesday 17th of September 2014 11:51:49 AM

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Jim L

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I bought a set of those check valve bleeders and threw them away because they didn't work.

The master is spankin' new....not rebuilt and I did bench bleed the bejeepers out of it. I did have trouble getting all the air out of the rear compartment and am wondering if there is a still a bubble in there being a PITA.

I was just at NAPA and they have 3 different spring pliers from $7-23. The middle one for about 9 dollars looks like a good tool. thumbsup



-- Edited by Lost in the 60s on Wednesday 17th of September 2014 01:06:49 PM

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Mitch D.   River Falls, WI

Lifetime member of the "Cars apart Club"

1966 Chevelle SS 396 M20

1970 Chevelle SS 396 M20

1967 Camaro SS/RS 350 M20
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