I read the stickes and the current posts. I still can not get a firm brake petal

I have new front hard lines.
4 new oring calipers
new master cylinder - bench bled
all new rubber lines

I have tried everything to get a good petal but as soon as i turn the car on the petal goes to 1/4" from the floor.
I am running out of dot 3 in my country it has all been bled through my lines.
with the car off the petal is rock hard at the top. as soon as i turn it over the petal goes to the floor.
I have no leaks on the new lines - I am using fresh carboard to make sure.
I put tape on the bleeder threads so no air can get back in.
I can pump my mighty vac up to 10psi with no air bubbles

I am going to pinch off each rubber line and try that. Should my petal be hard at the top with the car on and the lines clamped?

any other suggestions?
how does a caliper leak internally?

 

Are you bleeding the rear calipers by doing the inboard bleeder first then the outboard bleeder?

 

Check for clearance in the booster/master rod.

A caliper cannot leak internally. It may take a little time and fluid to pass the dust seal though.

 

The caliper can't leak internally. If it's leaking then you have fluid coming out or air coming in. Check all of the connections carefully. It's also possible that you got a bad master cylinder. It happens more often than you'd think.

 

Don't feel bad.I started out with the mighty vac and gave up and went to the motive power bleeder.from there I tried the pedal method.Im waiting on a new set of o ringed calibers before I go back to this crazy headache.

 

ruger, i saw your post I feel your pain

how do I test for a bad master cylinder?
I still have the old one that was working fine...

 

hello
From reading many of the recent brake bleeding threads I have found that there are two different combinations of master cylinder and brake booster combinations that can be mixed or interchanged due to the design change around 1976 or 1977. Others can help find the year this changed.

Their is a long rod and a short rod brake booster. This matches to the correct deep bore or short bore master cylinder. A correct early year setup will use the long rod brake booster with the deep bore master cylinder. A later year will use the short rod brake booster with a short bore master cylinder. It is not possible to mix the long rod brake booster with the short bore master cylinder, because it should not be able to bolt together. However, you can install an early year deep bore master cylinder with a later year short rod brake booster. What will happen is the pedal will have to travel a long distance before the rod actuates the master cylinder.

If you have replace many of the components check the rod coming out of the brake booster. It should either stick out about 1 inch, or 1/4 inch from what I have seen with various photos posted on this subject.

Brake Booster Master Cylinder comments
long rod deep bore correct combination
short rod short bore correct combination
long rod short bore should not be able to install
short rod deep bore possible to install but problems
with pedal travel

OK. This is just my guess at the various combinations. I am having my own brake bleeding issues and am waiting to install my calipers after I rebuilt them.

kdf

 

I also had a hard time bleeding brakes on my current C-3, a 1980. Do not remember having trouble in the past on other C-3s. Anyway, I finally got all the air out by pumping the brake pedal very slowly to build up the pressure, then slowly, and I mean slowly push the pedal to the floor while a helper operates the bleed screw. This worked for me after I tried every other possible method. I also bench bled the master cylinder before I did the caliper bleeding. When you bleed the master cylinder, make sure the front of the cylinder is pointing down at a slight angle, this will get all the air out of the bore. Good luck.

 

That doesn't apply since he said he has a rock hard pedal with the engine not running.

I am referring to a rod that may be less than 1/8” from the correct length.
With the lines pinched off and the engine running (vacuum at booster), you can depress the pedal about 1”.

Just to confirm with the OP, does the pedal go to 1/4” of the floor by itself when the engine is started and the pedal is not touched or are you pushing the pedal down?

 

Sounds like a sure sign of air.



I went through two one time before I resolved the problem. They were rebuilt and I'll only use new from now on, that's what fixed it.

Also, I believe that a motive power bleeder is the only way to go.

 

 

The OP said he has a hard pedal without the engine running. If it’s hard and holds with the engine off, then his NEW master is OK.

 

Hello Noonie,
Would that mean his brake booster is ok, or the master cylinder.

kdf

 

The OP didn't answer the question I posted earlier and some other info would be really also be usefull.
It would help to know how far the pedal moves before it becomes rock hard at the top and if it stays there no matter how hard you push. May still have air in it.
He may have a 1" bore master instead of the 1-1/8" which would give much further pedal travel.
He may have the rod improperly adjusted or an incorrect length rod.
He may have a booster with a bad valve in it (not a bad diaphragm).

And as far as a firm pedal, that's subjective. No way will these old boosters give the more firm feel of a modern booster. They were designed to be very soft in those days, but that's different than being 1/4" off the floor.

 

Just a shot in the dark here, and not sure if it could happen on a c3. But folks that have replaced their calipers on c5 and c6 often install them in the wrong side. Resulting in the bleed screw being at the bottom vs top of the caliper and air is trapped in the caliper.

 

sorry for the delay.

the petal is at the top and rock hard with engine off
the petal travels to 1/4" from the floor when I stomp on it with the engine on. before was halfway max.
the calipers are on the correct sides.


I am not sure why this is so difficult. every thing points to air in the system. I am not a rookie on this stuff.

I have not yet pinched off each caliper, I think this will tell the story.

zero air bubbles from the system when i gravity bleed.

 

Either way, still sounds like air to me.

 

At least air.

 

I'd start looking for leaks. Starting with the back of the master cylinder. Then each connection, and calipers. You may even have a line rubbed through somewhere that you can't easily see. When you use the "old school" method of pumping up the pedal, holding it and breaking the bleeder, does the pedal pump up firm and hold, or does it leak down as you hold your foot on it? If it does, you've got a leak somewhere. If the pedal holds firm, you've still got air in the system.

You can use a small hose connected to the bleeder, then into a clean container to catch the fluid you bleed and re-use it. That might save you the problem of running out of fluid.

 

you cant use a mity vac on calipers that have lip seals in them.....for the same reason that a rotor out of round sucks in air from the lip seal the mity vacs sucks in air from the lip seal.....you have to use either a presure bleeder or do it the old fashion way and pump ....i have used the mity vac for all of my brake bleedings for years....that is until i got the vette it just doesnt work on lip seals. maybe your O rings are not sealing right and have the same problem?