New calipers installed and can't get pedal. Ahh, but read on - there's more.

Two things: I did Brake & Front End for 10 years so I'm not a newbie at caliper swaps. Also, I've bled the system on this car three times over the years, each time with great success.

So last week I got brand new calipers for the system Stainless Steel w/O-ring design from Van Steel. Master Cylinder is a year old, and was installed brand new as well. To note, there were NO master cylinder symptoms from the car at all last week; the reason for buying new calipers was only because one of them was leaking. Always had a hard pedal before the update, and never had a problem doing a short stop or locking up wheels if/when I had to.

Now I can't. If I sit at a stop, the pedal stays high. Normal stops are no problem; she sails down from 60 to 0 straight and smoothe.

-BUT- try a short stop and only then will you see that you can't. AT ALL. The master cylinder bottoms out, leading me to believe that there's air in there still.

Twice, I've re-bled all six bleeders in the system to get rid of air. Not a bit to be had. I tried first, bleeding in the sequence I used on the car in the past: Right Rear outer first, then inner. Next I went to Left Rear Outer, then inner. Then RF and finally the LF.

This time, I tried swapping the inner rears for the outer; last time I did the outers first. Today I ran another whole quart of fluid through it starting with the inners in the rear then the outers. Pedal felt good again, until I test drove it and made a short stop. Or tried to at least.

Then I tried the hammer trick on the calipers. I used a 2x4 block of wood to cushion the hammer blows, and rebled them trying to knock loose an air bubble. Not a bit of air.

Wow I said, NOW WHAT? Still, no signs of pedal sinking as if it was a bad master. Just the sensation that the master bottoms out, if you hit the pedal good & hard. It will not lock up any of the four at any speed.

 

MY C4 started doing the same thing and I was told it was the seal in the Master. Sometimes it would hold, sometimes it wouldn't. When you put hard pressure on it, the seal swells and holds, when you put lighter pressure on it, it leaks through. Just a thought.

 

sounds like you still have a little air somewhere.

 

May be the right time to upgrade to stainless flex lines. Sounds like you may have a weak line in the system.

Dan

 

While it's certainly possible, it seems that it would have exhibited this same behavior with the old calipers too - if that was true.

 

If all you did was install rebuilt calipers then suspect the calipers. Eliminate the calipers as a problem by finding some adapters so you can put a bleeder onto on the flexible hose ends. If that works then attach the calipers...if you get the problem that you described then it's the calipers...one or the other. Normally, you can tell which caliper by checking for air coming out when you bleed.

One thing to keep in mind is that when pressure is released by letting off the pedal then air will bleed out of the system automatically through the fluid inlet valves. Which is why most manuals suggest starting with the wheel cylinder which is furthest away from the master cylinder. But, if one of those valves is plugged then air will not escape...and consequently fluid will not be getting in either.

 

These are brand new, from Van Steel. Not reman.

 

It does not matter if you bleed the front first or last since they are independent systems.
A better sequence is to bleed the wheel that is closest to the master clyinder first:
LF than RF
Than Left rear inner than Left wheel outer
Than Right inner than right outer.
By doing it in this order you eliminate the possibility that air in a line close to the master cylinder may enter a line farther away after it has been bled.
If this fails than check the master cylinder, PG.

 

With 10 years experience at brakes I doubt I doubt I could suggest anything new.

Anyway, the rule of thumb I go by:
With power brakes car running, manual doesn't matter
Pump brakes a bunch of times relatively quickly and hold on the last pump with a lot of foot pressure

If the pedal gets higher and harder and the pedal stays up, then you have air in the lines.

If when holding it hard for a minute, the pedal slowly goes down, then the master cyl has a small internal leak.

I use a pressure bleeder and do the longest line front and rear first to make sure any air is past the prop valve. I also use a lot of fluid to flush and go around a 2nd time.

Adding new fluid might have cleaned the master a small amount and made it's age show. They are cheap enough.