Much Thx DesertXL
Since I sent the booster out to be restored, we assume the push rod is adjusted right, but we agreed to recheck. The master came attached to the booster so assumed that ok too, I guess recheck that too. Rear shoes are good and all original part to my knowledge. Part #s match up to car after researching.
Fyi, when lines out master are blocked off pedal is hard.
Car has 1/2 pedal with pressure then after 3 stops red brake light comes on and proportioning valve thumps and shuts system down.
After reading you overhaul, do you recommend using the GM Disc/Disc combination valve in my case?
Thanks again,
PDM
Hello PDM,
OK so you've listed some crucial information here. If you've blocked off both ports on the master and have a firm pedal right at the top you can forgo the booster, booster pushrod and master cylinder pistons.
From your statement of 3 stops the shuttle valve shifts and the hydraulic failure warning lamp comes on, this sounds like either
1.) The RPV is missing and or bad, plus the shoes aren't adjusted close to the drum. Either of these scenarios usually is not enough to trip the shuttle valve, but both would be.
I illustrated how to check for an RPV in my post. So that's something that needs to be done, if it's knackered or missing, you'll have to add an external one or try another new master that has one built in. The rear shoes adjustment is simply adjusting the star adjuster on each side till the shoes are in light contact with the drum. Also the drum needs to be true and smooth on the inside, if not have machined or replaced.
2.) The valving (shuttle and or rear proportioning) are compromised and leaking. As I mentioned in my post the proportioning valve uses specially moulded seals that are unobtanium. Unless it's a show car, do not try to use any of it. I would replace it with whatever you feel comfortable with. Me personally I like the reproduction GM Disc Disc combination valve. Just make sure you get the connector (most times it's sold separately). But it could be shrunk/hard seals pulling in air for the rear or just plain leaking. Even the seals in the shuttle valve can do this. Or it's making it impossible to properly bleed the rear brakes.
As a side note, it's not necessary to use an adjustable proportioning valve. The factory does a really good job of balancing the front and back gross brake bias. Now if you have the wrong inner diameter rear wheel cylinders (there are different sizes for a rough bias adjustment) or have wider tyres on the rear or have different size factory shoes or changed the weight on the car, then an adjustable rear proportioning valve may be in order. But honestly I wouldn't bother as cheap ones are going to be problematic, and the really expensive ones are still another failure or leak point with the adjustability, plus in my opinion they are unsightly.
Hope that helps.
Cheers
. The previous mechanic installed an adjustable valve but was removed recently and replaced with original system.
