I'm 100% naive when it comes to the brake system on a car. Well, maybe 80%...
I currently have a master cylinder and a brake booster from what I believe was a 70's Monte Carlo. The master cylinder has a marking stamp of 29966-0
(image attached).
I know this duo was used on a front disk / rear drum system, as that was what my truck had before I swapped out the rear axle for a limited slip from a Ford Explorer with rear disk brakes.
My question is: Can this duo be used for a front/rear disk brake system, or do I need to buy a new cylinder?
Happily as a general rule, rr calipers tend to be sized to use the same master cylinder bore as drums. If there is a "residual valve" in the rr system, necessary to keep a little pressure in there for the drum's slave cylinder to be up against it's springs, that must be removed for the disc pads to not drag.
I put a disc brake 8.8 in our Jeep Cherokee last year, replacing a drum brake 8.2, and it works excellent...but dang if I could find any such thing as a residual valve to remove, it may have not even had one. If so that would explain why previously that vehicle went through front brakes so bad, or who knows what was going on.
In any event and just as a report of what our experience was, brakes work much better now and the master was not changed.
One problem you may run into here with the 78-88 A/G-body master you have is being able to mount the whole works on the approximately 15° angle needed to get the master cylinder reservoir level.
An S-10 Master cylinder will solve this problem, as they mount level and have equal size cavity's in the reservior(or swap the S-10 reservoir to your master's body...but you may just end up with a leaker).
The S-10 master will be aluminum, and look cleaner.
Thanks for the info on leveling the master cylinder. Without a doubt that is a detail that would have never occurred to me since the original owner didn't bother to level it.
I had a master cylinder on my 37 Chev that looked like yours. It was mounted on the frame and was suppling front Mustang II disc and Ford 9" Granada rear disc. System has residual pressure valves and a adjustable proportioning valve. The master cylinder was not suited for use with Disc/Disc. You had to pump brake pedal once to get good brake because of a lack of volume.
I got a "Corvette" style aluminum master cylinder with SS insert from Speedway that was suitable for Disc/Disc. This solved all my brake issues. I believe the master cylinder was about $100. I went with the aluminum/with ss insert because of concern about heat as mine is mounted above an exhaust pipe. I added shields and cover and no heat issues.
. The S.S. insert is to prevent bore rust and corrosion in vehicles sitting/stored unused for long periods of time... and needed in aluminum units to prevent premature wear (like plagued Buick aluminum oil pumps)... of course, it's a nice upgrade for any vehicle...
. I seem to recall GM and Ford using different pressure standards for brakes... like 1,000 psi in one and 2,000 psi in the other... and different diameter brake lines...
. I thought residual pressure valves were only needed when the master cylinders were mounted down low, like mounted under the body old-school, allowing brake fluid to drain back into them by gravity...
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