QuestionSubject: BRAKES - PROPORTIONING VALVE?
Question:
Servicing brakes front brakes and leaky master cylinder on a 1984 Oldsmobile model 98 with 5 liter gas engine w/A/C I noticed that the rear brakes were not operating at all.
Serviced front brakes [new calipers, pads and hardware]. Replaced mastercylinder and power brake booster (leaking brake fluid damaged diaphrams in the booster). Primed new calipers, bench bled mastercylinder at level. Installed master and fully bled system.
Brake pedal feels firm but, no rear brakes function.
Serviced rear brakes. Brake shoes did not show any significant wear nor any significant dust in drum. Suspect rear brakes not been operating for some time. Installed new cylinders [old were lightly pitted] and hardware. Pre-adjusted rear shoes to drum size.
[By measurement and got slight brake drag when you turn the drums by hand (with wheels dismounted).]
Re-bled entire system. Still no brakes in rear. Removed and flushed brake lines. Flow to rear hydraulic system appear limited. Re-bled entire system. [Yes I tried with the combo valve pin held in, held out, and left alone. Also tried full bleed farthest wheel first , then tried full blead nearest wheel first.]
No rear brakes function. Did gravity blead on system. Still no rear brakes function.
Is it time for a proportioning valve? I am a shade tree mechanic so I'm not up on all the tricks of the trade. In nearly 40 years, I've never seen one go bad, but that seems like the only thing left. Have I missed something?
AnswerI agree with you Bill. Never saw a proportioning valve bad, but sounds like you did everything else.
Crack the line at the prop valve coming from the master cylinder, and see if fluid doesn't squirt out there ok.
Possible a piece of something is plugging a line.
Van
