Non-stop Air While Bleeding Brakes

[1981]

Help, my vette needs some fixing, poor thing can't seem to catch a break!

While bleeding the left rear caliper I get fluid during most of the brake pedal movement then about 1 inch from the floor I get air. This happens with every pump of the pedal. It just does not stop.

The right caliper is great, nothing but fluid. dirty, but fluid.

I am sure the left caliper is bad, so my next step will be to check the rotor, then check my bearings.

I put her back together and the brake light only comes on when I get about 1 inch from the floor, which means I am going below 450 psi in the braking system?

What is the least expensive way to fix the caliper.

I will worry about the cost of the rotor and/or bearings when I troubleshoot it down to that tomorrow.

Had my U-joint at the spindle of this wheel go bad about 3 months ago. Got a brake light at this time also which led me to change this caliper then find the bad U-Joint.

1981

 

[DDLS3]

You have mentioned a couple of problems. Dirty brake fluid is likely contaminated with moisture and corrosion. Bleed you brake system completely to flush all the old crap out and force new fluid in. Are you bleeding with the engine running? If so, don't. Are you keeping the master cylinder full while bleeding so as not to introduce more air? These cars are tough to bleed as well, be patient and keep bleeding, the rear is the worst by far. If all else fails, have your brake system power bled a a brake shop. This by far the easiest way to flush the system and introduce new fluid. Once everything is done you will need to reset the brake light switch by practically jumping onto the brake pedal hard.

 

[MidShark]

Try putting a 2x4 under the pedal while bleeding. Sounds like the piston in the MC is going too far. The pedal doesn't have to go down to the floor in order to bleed the brakes. Give it a shot.
Dick

 

[1981]

DDL-81

Are you bleeding with the engine running?

No

Are you keeping the master cylinder full while bleeding so as not to introduce more air?

Yes

MidShark

Sounds like the piston in the MC is going too far. The pedal doesn't have to go down to the floor in order to bleed the brakes.

So you are saying the MC could be bad? That the piston is shot letting air into the line when the pedal gets close to the floor? I can see what you are talking about, but I do not know exactly how the system works at the MC. Since the problem occured I have been able to push the pedal to the floor. Only when the pedal gets about 1 inch from the floor does the brake light come on, then as the pedal is raised the light goes out, and the hydraulic brakes seem to work about 70%. If I drive the car for longer than 30 minutes the light stays steady, and the brakes work about 40%, no hunker down when put in gear. I know this because I drove it in this condition from Houston.

Thanks,
1981

 

[81LT4]

BRAKES

Are you bleeding both valves in the rear caliper.
It is best to bleed your brake's with a hand help vac pump.
there is no foot pumping.

 

[1981]

81LT4

Are you bleeding both valves in the rear caliper.

Yes, I bled the outer valve first and just kept getting air, must have bled about 2-3 cups of fluid through with lots of air. Never could get the air to stop so I closed this valve up and continued on suspecting this side of the caliper to be worn out. I then bled the inner valve and not much air came through. Some but not nearly as much as the outer valve. Could not get this side to stop either, but never got much air out. Closed it up after about 2-3 cups through system. Suspect this side damaged, just not as bad as the outer side.

I bled the right rear valves (both) and got nothing but fluid. This caliper and part of the system suspected good to go.



Should I replace the whole left rear caliper or should I do a rebuild myself? I have never done a rebuild but I have changed a caliper on a 1983 Nissan truck, back in 1989. I could do a rebuild if I had directions. Let me search.

I will be looking at the rotor and the bearings today.

1. If the rotor is warped, can this be fixed by turning? If not, do I just replace the rotor? Do I order the rotor and hub with rivets, or just the rotor? Basically, any help on what parts should be replaced with the rotor?

2. If the bearings need to be replaced, any help on what parts should be replaced there too? i.e. bearings and/or wheel bearing kit to include (inner/outer rear bearing with race and seals). Should I buy shims? should I do both rear wheels at the same time? How hard is this to do by myself? I am mechanically inclined, just never done this job before.

Thanks,
1981

 

[1981]

Just as information:
At no time does the brakes shudder or vibrate the pedal. The car stops straight with no pull left or right. Wouldn't a vibration or shuddering be the sure sign of a warped rotor or bad bearings?

So is it safe to say I may not have a rotor or bearing problem?

Myabe the piston in the MC is bad letting air into the system when braking? But why then while doing the left rear bleeding do I get air when the pedal is about 1 inch from the floor? Then when I do the right rear I get no air at all? This would tell me the left rear caliper is bad and not the MC. But what caused the left rear to go bad? Man this is kicking my butt. And the local machanics are not helping. It is ashame that out of 4 different shops they all have 4 different opinions as to where they want to look first. 3 told me out right that the rotor and the bearings can not cause pulsating pistons in the calipers introducing air into the system.

But it is funny how I have destoyed two left rear calipers on the last two trips I have made going long distances (highway about 200 miles one way).

Help, I am lost and the local mechanics are totally useless except for the fact they have nice lifts!

When I build my house in about 2 years I will have a 20 x 20 third garage with a 2 post lift, air compressor, and all of my tools I have and will keep getting with each project I undergo with this vette. My goal is to rebuild a 1964 corvette and turn it into a Grand Sport. But for now I am liftless, except for my four jack stands and floor jack. I could not survive without them. They are the work horses of this shade tree corvette mechanic.

Thanks,
1981

 

[DDLS3]

1981,

In defense of the mechanics that you spoke with, if they ain't worked on corvette brakes, then they don't understand the problem. C3's used a fixed caliper, with 4 live pistons and was very susceptable to air pumping with only a few thousands run out on the rotor. This brake caliper was not used on other vehicles, thus the lack of wide spread knowledge on the subject. I attempted to rebuild one of my calipers. Getting the piston in straight was a mojor challenge. I would suggest a rebuilt O-ring style caliper from a reliable rebuilder such as Vette Brakes. The O-ring piston seal is less susecptable to to air pumping than the standard lip seal. You still may have another source of air, although I'm not at all sure about the master cylinder theory. Rotors are not real expensive to replace and are readily found at most major auto parts stores. I would replace before I would machine, just my 2 cents worth.

 

[BeaterShark]

I'd rebuild the caliper. My guess is that you have a leak in the caliper. This would explain how the upper is worse than the lower bleed valve.

You should be able to find a rebuild kit for about $6. I'd also check the runout of the rotor.

 

[Robin7TFour]

"81" you should consider buying the new bleeder valves with the check ball in them. will make it much easier to bleed ,if done the tradional way


robin

 

[81LT4]

1981

You have to bleed both valves in the rear at the same time.
I do mine with a vaccum pump (HAND HELD) auto zone
$40.00. when I first got my car it sat for a long, when i bleed the brakes I did one vale at a time on the rear, that was wrong.
All i got was air air air. the vac pump is a one man/woman
system, and you'll never go back to foot pumping (EVER)
make sure you have no sign of fluid on you wheel's or tire's,
if so then you will need to rebuild the caliper/caliper's.
If you need more info,PM me with your phone # I will further
help you.

 

[WhalePirot]

two good vendors

I liked both:

http://www.muskegonbrake.com/ and

http://www.vettebrakes.com/

 

[Rip]

Check out this site for brake troubleshooting.
http://www.mpbrakes.com/troubleshooting.htm

Down at the very bottom they discuss possible problems with trapped air in the calipers. Not sure if this applies to your prticular problem, but maybe worth a look.

Rip

 

[wipeout48]

Hi,

Had the same problem with my vette, kept shooting out air in the right front caliper. Took me awhile to figure it out but when I looked at the flex hose the rubber was split right open. Whenever I would bring the pedal back it would just suck air back in thru there.

So I would check your flex hose.

Hope this helps.