car rolls fine in neutral with engine off but in reverse or drive brake pressure keeps car still unless a lot of throttle. I noticed today that the driver front wheel, on jacks, will completely lockup if I run the car in park and tap the brake pedal once. is this my booster ? e brake cables release ok.
I'm betting it's the booster. You could test that -- on level ground, unplug the booster hose from the intake manifold, and put a cap over the nipple [usually on the vacuum tree at the back of the intake manifold]. Then see if it still wants to apply brakes. Note, you will not have power brakes, and it will be very hard to stop the car with the pedal; this just to test the idea that it's the booster. Also could be the master cylinder itself. If that protruding rod has been adjusted longer, then set it back to proper length [1" on my '71].
been working long days, car sitting on blocks in the driveway with front driver wheel off. yesterday it was locked tight but this afternoon I could spin the wheel hub with one hand. the pressure from the brake line decreased and the caliper backed off the disc just enough, but it looks closed on the disc just by looking at it. I want to try the sugestions above tomorrow after work and report back. stupid question: shouldn't the master cylinder suck back the line pressure once vacuum is stopped when the engine is off? no vacuum equals no booster? could this be an impeded return valve/port in the master?
Yes ... the MC would be my 2nd choice. It's also possible you have a caliper piston that is sticking?
Could also be an internally ruptured brake hose(flexible hose that attaches to caliper). Good luck. Todd
I have had junk in the brake lines act like checkvalves. When the brakes were depressed the junk would allow flow to the brakes but when letting off the pedal the junk would jam up against a fitting and not allow the fluid to flow back to the MC. Wore me out, went through new MC's and rebuilds a couple of times before it was found. Purged out the system real well, changed hoses and put in new fluid helped me out.
does anyone know the size if the hex key on the screw holding the retaining clip one must remove to get the brake caliper off the disc? It's a bit rusted and I fear stripping it, seems vey hard to remove due to rusting.
If you haven't taken it apart yet check something first. Have it jacked up where you can see if both front wheels can be turned by hand. If they can be turned then hit the brake hard then see if one is still locked. While it is still locked reach behind the wheel and crack open the bleeder screw. If that releases the wheel and gives you a good sized squirt of brake fluid instead of just a dribble of fluid you have a bad hose. Your Ranchero is old enough to need new hoses all around, all three probably need replaced.
Sticky brakes You might consider the master cylinder residual pressure valve. If you are not familiar with it, it's function is to maintain slight pressure on the front discs when the brakes are released. This is to keep the discs clean while driving or sitting.road crap or rust can accumulate and cause rapid wear or grabbing. This causes a slight drag but hardly noticeable. But it can stick, and hold too much pressure , and lock the front brakes. Drag racers and mileage contestants remove it to gain a tiny bit of performance. Look into the holes where the tubing connects.you will see a screw in insert in one of the holes. Remove it temporarily (Probably torx or Allen wrench). If this cures the problem, replace it with a new valve. Don't just leave it out. You will regret it!!!! Hope this helps Regards Dan
IIRC, the only time a residual valve is used for the front disc brake circuit is when a 4 wheel disc master cylinder is mounted below the calipers(like in a street rod, under the floor pan, usually a 2lb valve is specified). Rear drum brakes usually require a residual valve (up to 10lb value)so the shoes do not fully retract away from the drums as spring tension works on them, they retract just far enough to allow the shoes to have a very slight drag placed on the drums so the operator does not have to pump the brakes to take up the distance between the shoes and drums as the shoes wear. Here is a good website concerning brake hydraulics, including MC's. Hope this helps. Todd http://www.piratejack.net/ Click the tech support tab, very informative.
