LemonChips

Hi,

In the process of changing my brake pads (1975 corvette stingray) my brakes wouldn't bleed. It's the very first bleed that I cannot get (Right Rear). I've tried pumping it and pumping it and pumping it but no pressure builds up at all. Before starting the new bleed I drained all of the Brake fluid (Extremely dirty) and replaced it with new Brake fluid. Now I cannot get a drop out of the line. I also replaced the rear brake line/hose with new ones. I haven't checked to see if the other sides (left rear, front etc.) are doing this as well. I did leave the line open for approximately one day to take the calliper off and have a mechanic remove a stubborn stripped bleeder valve. I was thinking It's either my lines corroded from within or my master cylinder went bad. Those are just ideas though. I do know how to bleed brakes but I'm no pro. Any help will be greatly appreciated. Thanks O ya and doing a regular old fashioned bleed (pump a couple of times, hold on last pump, open bleeder valve, close bleeder valve, repeat process until air is gone). and another thing i just realized is that if I remove the line from the caliper no fluid comes out either. O one last thing I did purchase some new speed bleeders so that I could begin to do the job myself and not purchase anything else, but I removed them and nothing is flowing.

Easy Mike

Chassis service manual says to bleed the left rear first. Try that. Inner half first, then the outer. Then move to the right side.

Same drill; inner half first, followed by the outer.

If you still have no brake fluid, the differential switch may need to be reset.

LemonChips

I'll try it that way. Won't hurt. The differential needing to be reset may be true, but the fluid should still flow. The differential is basically a sensor with no control/shut off valve right?

noonie

No, on a 75 it will try to block off front or rear system.

Easy Mike

The switch only detects an imbalance between front and rear. Just the same, they can stick in an in-between position.

noonie

That is incorrect.
This info isn't in the AIM.

Here is a pic of the block with proportioning valve from a 75.
The valve spool with seals will block off 99.9% of the flow from either the front or back system when it is in the off center position.
The idiot lite switch turns on when the switch pin is not in centered in the deep "vee" of the valve spool.

You may have a lot of crud built up in the valve, but since the parts are all brass, I doubt that pedal pressure will not force fluid thru. Either way, you will have fluid from either front or rear, no matter what. They can be taken apart to be clean/resealed.

leadfoot4

I haven't bled a C-3 in ages, but for some reason, maybe because I bought the tool to do it, I remember one of my other late 70s GM cars needed to have the plunger in the differential switch held in the "out" position. I don't remember if that's the case with a C-3, but I'll toss it out there as something to try...

scottyp99

If you drained all the brake fluid from the entire system, you may just need to prime the master cylinder. Remove it from the brake booster, and push the piston all the way in a few times. Make sure there is brake fluid above the cylinder, don't let any air in. Once you have the air out of the master cylinder, it'll flow. If you have already done this, I don't have any other ideas, sorry.


Keep the shiny side up!
Scott

dburgjohn

my 81 would not bleed until I bought a Motive power bleeder. So much better IMHO