Discussion Forum - Northstar Chevelle Club

Lost in the 60s · President

Front disc swap advice needed

67ss · 1K+ Club

That is the exact same setup I have on my camaro and my brakes work mint without having any other proportioning valve. If you were running 4wd discs it would be a different story.

Lost in the 60s · President

Thanks, Chris. All these parts are exact replicas of the factory setup for the 4 piston calipers. I didn't think the master or hold off valve cared how many pistons they were controlling..... wink

Derek69SS · Founding Member

Which MC are you using, and which calipers? If there's a bore size difference between 4-piston and single-piston, you might run into problems by mixing parts. I don't have any experience with 4-piston stuff, so I don't know what the MC bore size and caliper piston surface area is, but caliper piston surface area and MC bore size need to be sized to work together.

If the piston surface area is smaller, it takes less volume, but more pressure to do the same amount of work... so, if you're taking a MC designed for a big surface area, and using a caliper with a small surface area, your pedal will be very firm and you'll have high line pressure in the front before the rear starts to really do much... Other way around, and then you have too much mechanical advantage, so the pedal stroke will be very long & soft, and the rear brakes likely will lock up first.

If you're not mixing 4-piston and single-piston parts, then I wouldn't worry about it. :)

67ss · 1K+ Club

I have single piston calipers on mine, I forgot to mention that before.

Lost in the 60s · President

67ss wrote:
I have single piston calipers on mine, I forgot to mention that before.

Me too, they will be single piston calipers.
Not sure on the bore size but aren't the masters for single piston's on a 69-72 1 1/8th ? I'll see if I can get the specs on mine. It came from Inline Tube.

Derek69SS · Founding Member

Yeah, 1-1/8" sounds right...

Tony Hoffer · Moderator

How heavy of braking are you going to be doing. Autocross? drag race? road race?
Its my understanding all the hold off valve does is allow the shoes to come in contact with the drum before the front brakes are applied. I seem to do fine with my stuff using a stock 72 proportioning valve.. I think this had the holdoff function built in.

Lost in the 60s · President

Just talked to Inline and the bore is the same and they use this master for other applications using the single piston calipers... smile

The shape of the master changed in '70 but the internals are the same between the 2 styles.

Tony, yes bt '72 GM had eliminated the separate hold off valve and incorporated that function into the distribution/ prop valve.

No road course work for this car for a long time, if ever. It'll take years before the body is in complete paint, let alone a worthy chassis. I just want better brakes than 4 wheel manual drum. It could see a wee bit of "street performance" though..... wink

-- Edited by Lost in the 60s on Friday 7th of January 2011 12:30:05 PM

Chris R · 2K+ Club

You can just take your factory spindles and modify them to allow the caliper to bolt on with the proper caliper bracket and that would take care of the front discs. Looks like you already have a master and booster assembly. Your 75% there already.

Lost in the 60s · President

Chris R wrote:
You can just take your factory spindles and modify them to allow the caliper to bolt on with the proper caliper bracket and that would take care of the front discs. Looks like you already have a master and booster assembly. Your 75% there already.

That modification involves machining which I can't do and would cost money. I have a complete spindle set-up off a 68 Camaro ready to blast, paint and install. All I really need are 2 steel lines and new flex hoses to make the system complete....

Chris R · 2K+ Club

It actually doesnt require any machining. Providing you have the stock 66 drum spindles. You just grind off a certain amount of meterial off a small machined nipple area of the spindle using something like a die grinder and your good to go. You dont need to do this since you already have the parts. But it can be done without having to buy another set of stock spindles and you only have to get disc brake caliper brackets.

Just an abservation. Not that there is anything mechanically wrong. But I noticed the 2 front brake lines cross each other and wont hurt anything. It just looks different is all.

Lost in the 60s · President

Chris R wrote:
I noticed the 2 front brake lines cross each other and wont hurt anything. It just looks different is all.

Moving the distribution block to the top of the frame changed all the front line locations. I will most likely put a 90° fitting in the block for the left front brake and run that line outside the z bar bracket instead of under it. Then the 2 lines will run parallel. That was just a mock-up to see what I needed and what I liked and didn't. It will be cleaner once I decide on a final design. I'm kind of anal that way.

Chris R · 2K+ Club

I have the exact same way you did it on mine and ran the left facing outlet to the left wheel and the right towards the line running along the frame over to the right wheel. The line coming from the master cyl enters the block from the front. It looks pretty good and tucks under Z bar nice and neat.

Lost in the 60s · President

Chris R wrote:
I have the exact same way you did it on mine and ran the left facing outlet to the left wheel and the right towards the line running along the frame over to the right wheel. The line coming from the master cyl enters the block from the front. It looks pretty good and tucks under Z bar nice and neat.

That is a neat way to plumb it. I would have to cut off the nut from the master to move it to the front as it is a different size or see if there is a reducer adaptor available.

Chris R · 2K+ Club

Napa has big cabinets with tons of drawers with tons of fittings and blocks like these and I just went through thier selection until I found one with the correct sized fittings I needed. Just so I wouldnt have to screw around with adapters on the lines.