I have replaced the rotors,calipers, and soft hoses on my 79 front and rear. I bled the front first since I pulled them first and got a better pedal. Then when I pulled the back and started to bleed them I had my wife pump the pedal like 10x and no air or fluid. A friend of mine told me to smack the side of the master cylinder with a hammer to unstick the piston and the bleeding went fine with a forceful squirt. Then I did the passenger side and accidently forgot to refill the reservoir and bled them nearly dry. After I refilled it I never got it to squirt with any force unless I smacked the m.c. and the next release of the bleeder screw it just dripped out. I now have nearly no pedal. I am thinking the m.c. needs replacing. But I read where the c3s are pains to bleed right. Any advice would be appreciated.

 

I used a power bleeder. I'm told that some vettes require to be gravity bled overnight to get all of the air out. Just let the fluid drip through the system. It would require some set-up to keep the MC full and a lot of brake fluid. I had similar problems until I used the power bleeder. I had four different MC's and they all were soft. I replaced the proportioning valve too. I have heard it could create problems, but I have not figured out how.

 

Really, Vette's are no more difficult than other cars, same basic priciples apply to the bleeding process, the only difference is that the rear calipers have 2 bleeders. Before you replace the master cylinder, I would try to get the system working as is. You replaced everything, so it will take time and patience to get all the air out. Let the system gravity flow for a few hours, but don't let the master cylinder go dry, keep checking it until fluid is dripping out of every bleeder. To bleed the system, you must start with the furthest brake from the master cylinder and work your way closer (RR, LR, RF, LF). Also, you must not let the master cylinder go dry, or you'll have to start all over.

Start at the right rear. Rear calipers have 2 bleeders, bleed the inner first then the outer. Open the bleeder and have someone push the pedal to the floor. Have your wife push the pedal to the floor and hold it there. Have her tell you when the pedal is on the floor, snug the bleeder, and tell her to release the pedal. Do not release the pedal with the bleeder screw open, you'll suck air back in. Do this procedure until you get clear fluid from the inner bleeder, then move to the outer bleeder and do the same process. You can lightly tap the caliper with a rubber mallet to loosen air bubbles during and between pedal movements. Refill the master before starting another bleeder. Check all of the fittings for leaks, because leaks will suck air back into the system. You may have to do all 4 calipers 2 or 3 times, but it will work, and should take you 1 to 2 hours. Good Luck.

 

Thats the way I did it. Only thing I believe my manual said to do the rear driver side 1st then the pass. But we did spend a lot of time pumping and releasing the pedal. We got all the initial air out and got to the new fluid but we never got a good pedal or a squirt of fluid with any pressure unless I tapped the master cylinder. When I did the front ones they had good pressure and gave me a good pedal feel. Now all I get is a slight bit of pedal pressure and none when the car is on.

 

The master cylinder is the highest point in the system, so air will collect there, and by tapping you probably released some air. If the piston is stuck, you would feel it in the pedal. Don't worry that you don't have a firm pedal right away, as you get air out, the pedal will firm up. It may get firm, and go back to nothing, it's just part of the process.

 

Ok so you dont think I have a master cylinder problem, well thats good. Yeah I know it is a tedious process but it seemed like it wasnt draining much fluid. But You guys know these cars better than me. So thanks for the help I guess I'll put off on replacing the master cylinder and just keep pumping/bleeding. What baffles me though is when I get a good burst of fluid followed by a slow pouring on the next release.

 

If you're not getting a shot of fluid when pumping the brakes, and have to the M/C, I believe you may have more issues than just bleeding. How old is the M/C? Any signs of internal rust/goo? Perhaps bench-bleeding the M/C would help.

 

It is original. 41k miles but only 1k since 81 been sitting a long time. To bench bleed does that mean just unhook the lines at the MC? It may be a stupid question but I just consider myself a parts replacer and Im using the vette to attempt to learn more. Since a rebuilt mc is only $15 before my discount I'll probably just replace it.

 

Sometimes "troubleshooting" an issue is fun & satisfying, but, when you're only talking a few skanools, R&R is the way to go.

Disclaimer: Do not rely totally on my advice! I am not an exceptional mechanic (half-arsed at best). You could have a myriad of other problems and replacing the M/C may not help.

 

What else could it be with new calipers and no visible leaks? The MC is the only other link in the system besides the booster but it has no control on the hydraulics right?

 

If I Remember Correctly...the booster could be toast and/or the plunger rod that activates the M/C could be rusted/sticking...also the proportioning valve could be an issue.

Someone with more experience will chime in here if you wait long enough...

 

I typically blame a soft pedal on air in the system. If my pedal is firm but then bleeds down I change the mc. I think a bad booster only gives a hard pedal much like if you disconnect the vacuum to the booster.

 

A couple of points come to mind. Have you had your helper pump the pedal 3-4 times before holding it down? That can help build pressure to move the fluid better.

Don't have your helper push the pedal to the floor. That pushes the pistons in the MC into an area of the cylinder they've never been before. A used MC is going to have pits and crud in the cylinder's unused area that can tear up the seals and ruin a MC that was working fine before. Push the pedal down only halfway.

 

Double check the sequence. This one is the old standard for MOST cars. Vettes are different. Check your shop manual. I believe it is LR, RR, LF, RF; that is off my memory as I am at work. It is NOT farthest to closet from the MC on Vettes. Do it this way and you may bleed for hours without success. I had a race car builder with out club swear to me I was dead wrong when we were doing an emergency brake job on a club outing. We couldn't get a hard pedal. I called my daughter at home, led into the manual and had her read back the bleed order. Hard pedal one pass. My own '78 I apent over two hours trying to get a hard pedal using the old standard bleed sequence. Once I cracked the manual and got the proper sequence I got a hard pedal in one pass. A Chevy mechanic explained it on here once, and it was something to the effect that because of the brake system design you simply keep pushing air bubbles back and forth at the portioning valve. You never allow the bubble to move out to the calipers.

I will reiterate, and a number of you will tell me I am wrong, but I know better, the C3 Corvette bleeding sequence is not done like standard cars. It is NOT farthest to closet from the MC. I am fairly confident it is LR, RR, LF, RF. Check the GM shop manual to be sure. I have seen more posts over brake bleeding over the last few years than anything else. Almost always I ahve seen improper bleed sequence I have seen people say you have to pressure bleed, gravity bleed, etc. etc., but if you use the right bleed sequence you will get a hard pedal.

 

Yeah thats what my manual says. I tried it that way and never got the good pedal or a good squirt of fluid.

 

Here is a question: I have never done this before when bleeding brakes. What about the bleeder valves up near the master cylinder? When/are these ever opened? If they are never used, why are they there?

 

Well I replaced the master cylinder and that was the problem. But after one round of bleeding I still have air in the lines. I believe my father in laws method wasnt forcing the air out enough. Is it better to release the screw then push the pedal down and hold it while the screw is tightened up or is it quicker/better to pump the pedal multiple times holding it down on the last pump and then releasing the screw and tightening it before releasing the pedal. I have used the later before but he had me use the first method. If I can just get these dang brakes squared away I can get tires plates and insurance and get it on the asphault where it belongs!

 

When you say "open" the bleeder......does that mean take a wrench to the fitting and turn it until it opens? I was wondering because i'm really not sure how to bleed the brakes and i thought maybe I was supposed to take the pointy cone shaped attachment that came with my vaccum bleeder and just push it into the fitting hole.

Just wanted to make sure before I dive into this.

Thanks

 

yes, turn the bleeder with a wrench about a 1/4 turn from closed, if it turns freely, it's probably open

 

Thanks!