BRAKES!! Really?? Need some help... - Corvette Forum : DigitalCorvettes.com Corvette Forums

GS81vett · 06-16-2012, 04:07 PM

Ok 81 stock brakes. Front calipers have been rebuilt with O rings. Master Cylinder has been replaced. All worked great. Then she sat for a while. Year or so. Then no pedal. So I thought new MC and I wanted a Wilwood anyway so I put it on. Still no pedal. So I rebuilt the rear calipers with O rings and put them on and bleed that sucker good! Used a vacuum bleeder and did it the standard way. STILL NO PEDDAL....WTF Man it is not that complex system. So can the proportioning valve be the issue here? Or are my calipers done? Any help...I feel like an idiot!

gtr1999 · 06-16-2012, 09:04 PM

Did you bench bleed the M/C before installing? I recommend using a Motive bleeder as well, works the best IMO. You can also use it to test for leaks in the system.

I would start by checking the M/C and be sure you have the correct one, they were different between manual and power and later in the run.

The O ring calipers are more forgiving with rotor runout and are supposed to last longer, I can't say since I always used lip seal calipers and have great brakes.

GS81vett · 06-16-2012, 09:35 PM

Gary I did bleed the MC before it was used. I called Wilwood and asked for the correct one and it fit and I did the bleeding in the car just to test. All I can come up with is maybe the calipers are failing the front that is being is sat so long even they were rebuilt about two years ago.....Very frusterating...Any other thoughts?

wan2run · 06-16-2012, 09:41 PM

How's the vacuum from the booster?

GS81vett · 06-16-2012, 10:15 PM

Good but the car is not running right now this is all with no vacuum and still pedal to the floor.

GS81vett · 06-16-2012, 10:16 PM

Good but the car is not running so no vacuum and still the pedal goes to the floor

7TRoadster · 06-16-2012, 10:32 PM

Are you sure the master cylinder is engaging? It sounds like it is but just enough to let you bleed the rear.

I recently installed a new Power Booster and Master Cylinder on on my 1970. The booster came with two rods for engaging the master cylinder. A short one and a long one. Wondering if you have the short one installed and your new master cylinder is designed for the longer one.

Just a thought.

GS81vett · 06-16-2012, 10:52 PM

Good thought I am open to anything. The only issue is this no pedal started before I changed out the MC. And it did come with a rod and it feels like it is engaging... Like I said I am stumped on this on

7TRoadster · 06-16-2012, 11:35 PM

Hmmmmmmmm, I assume you don't have a large pool of brake fluid under the car or brake fluid running down the inside of the front tires. If the calipers are bad they would likely be leaking.

Doesn't make sense to me either, my best guess was the actuating rod. Second guess as mentioned earlier in another post is master cylinder bleeding.

After that I am out of ideas, as you stated it's a simple system.

GS81vett · 06-17-2012, 02:30 PM

No no puddle andI have looked. I am at a loss here...

iburke · 06-17-2012, 08:12 PM

Forget the power bleeders... Get back to basics. get a helper to pump the peddle, and open one of the caliper bleeders, do you have fluid coming from it, if yes move to the next. If you have fluid coming from all calipers, then you have air in the system or a leak.

If you have no fluid movement back up to the master cylinder, plug the ports and see if you can get a peddle, if not you have a bad MC or the mechanical linkage is screwed up.

GS81vett · 06-18-2012, 08:46 AM

THANKS! I did not think to isolate the MC. And I did bleed the old fashion way after the power bleeder just to be sure. I have my stupid hat on this week my daughter is in the hospital trying to give birth so things are a bit crazy here.

iburke · 06-18-2012, 12:36 PM

OK keep us posted...

GS81vett · 09-28-2012, 12:43 PM

Ok guys this issue is still a bit challenging. As stated I put in a new Master Cylinder and now I have put in new calipers and new braided lines to replace the rubber ones in the rear. I also put in new rotors and followed Gary's advice on the run out......I try to bleed them and still get foamy fluid out of both rear. I did as Iburke suggested and disconnected the MC and got good tough peddle telling me it was not the issue. Instead of acting like a tech I acted like a shade tree and started changing parts...So I put my thinking hat on and took the rear breaks apart again and started vacuum testing each part. I disconnected the MC rear and had my partner put his finger over the line and pulled a vacuum from the caliper and then the break line and then the break line before the flexible and tested each piece and got good vacuum on each. Then I go to the driver side rear and did the same thing. Now I put my vacuum hose on the line before the flex line and could NOT get a vacuum. I have stopped here but I am next going to disconnect the line from the proportioning valve and test it. My thought is the Prop valve is bad BUT the strange part is there is no leakage when the peddle is pushed but air is pulled in when a vacuum pump is used???? So am I missing anything? Does this type of leak make sense? Anyone heard of this air going in and fluid not coming out? Any thoughts?

GS81vett · 09-28-2012, 03:03 PM

Well I did not realize the left rear block was also where the split took place for both rear wheels so when I pulled the vacuum on the right side the left was apart so that would explain were the leak in this case was. I have ordered new steel lines for both rear sides so I can get a good solid connection and will replace the brass washers on the steel braided lines and test again. Question for anyone reading this long thread has anyone seen a prop valve go bad and allow air in and not push fluid out?