I own a 1974 oldamobile catlass suprime 5.7L
While I replaced the brake fluid, when I bled the rear brakes I needed to step with two legs on the pedal. On both sids only small quantity of fluid came out of the bleeders, so I think that the fluid pressure is low. On the front, there was no problem to bleed, and it seems like the front wheels are able to lock when I step on the brake pedal, on a drive test. The rear kept on spinning. I did not see any problem on the brake pipes. Could it be that the master cylinder gives fluid pressure to the front caliper only? Will replacing the master cylinder solve the problem?

 

I would first try before and after the rubber hose that connects to the rear end.

 

If you are basing this "low pressure" on the size of the stream coming out of the bleeder screws, you are likely mistaken. The most likely cause of low flow from the bleeders is rust blocking the bleeder screw or the port inside the wheel cylinder. Remove the bleeder screws completely and see if anything comes out. Probe the bleeder screw ports with a piece of wire (or, just replace them). Also, when you bled the system, it is very possible that you pushed the differential pressure piston in the combo valve off to one side. This would also restrict flow. Finally, yes, it is possible that the M/C piston seals are worn and leaking internally, but as always, I prefer to do no-cost troubleshooting BEFORE spending any of my hard-earned cash.

 

The bleeder screws where plugged. I cleand it with a wire and was able to bleed the rear
Brakes. But only when i pressed the pedal. Almost nothing came out by gravitation. I checked the. brakes on a road and the front wheels only where able lock. The rear kept on spinning. When i checked it on dirt road the left rear wheel seemed to lock but not the right one. Are the rear brakes suppose to lock the wheels completely, and what can cause the the imbalance between the two sides?

 

When was the last time you adjusted your rear brakes?

- Eric

 

I just did. I'll try to streach it a bit more

 

And all of the internal components were in good shape? Shoes not excessively worn? Adjusters free, with star wheels not worn down?
You adjusted them to where they just begin to catch, and then back out a hair?

You can usually lock your rear brakes, especially on a dirt road, but drums do not self-adjust and self-balance the way disks do, so they won't always lock up exactly equally front to back or side to side (though, ideally, they should).

- Eric

- Eric