Bottom Line Up Front - change your brake fluid regulalry

I've been doing my own mechanical work on my cars (including brakes) for 30 years. This is the first time I've ran into this problem. When the brake pad wear sensor light came on, I replaced pads front and rear. The old pads were very thin. The new pads (ceramic) were uber thick. I used a c-clamp to squeeze the front caliper pistons all the way in and pryed the rear pistons (one at a time) all the way in to get the new pads to fit. I did not open any bleed valve or line hose. Of course the master cylinder over-ran due to the large amount of fluid being squeezed out of it. No prob, just rinsed and cleaned it up.

Took it for a test drive and noticed right away the pedal went to the floor and there was very little braking. Pedal was soft and spongy. It would stop, but would not come close to locking the brakes and a panic stop would be dangerous.

So I bled the brakes. The original fluid (2005) had never been changed and came out green. As far as I can tell, no air bubbles came out (used clear hose). Bled it until new clear fluid came out (1 pint). Brakes came back! Pedal was firm and impending lock-up caused ABS to activate.

So although it's baffling in that I'm convinced no air had been introduced, I feel the old brake fluid being pushed back the the M/C is the culprit. The oldest fluid is at the calipers (topping of at the M/C with new fluid over time). I am guilty of not changing it. But in the "old days", never had to. Did this same procedure many times over the years and have not had a problem. But listening to the "experts", nowadays they tell you to replace the fluid every year or 2. I used to blow them off as B/S. I'm now a believer.

 

My guess is that you pushed the pistons too far in and a seal contacted an area on the piston that was either dirty or corroded and allowed air to get past the seal.

The dirt or corrosion can be the result of a damaged boot, and this can lead to a damaged seal and leaks. keep your eyes open for any future leaks which can be contained behind the boot for a while. All seals leak, it's the amount that's the concern.

I did this once and I had to change the whole assembly, these days I only push the piston in enough to just get the new pads on.

If no oil has ever been added to the MC reservoir then pushing the pistons in the minimum amount will not lead to an overflow.

A daily driver is subject to more wear and tear all over than my garage princess, so a change in oil is recommended more often.

 

I have read on other manufacturers' instructions concerning ABS systems, you should open the bleeder on the caliper you are pushing the piston back in. That way, you are just pushing fluid out, rather than pushing fluid back against the ABS system components.

Just a thought. James

 

You the man James....exactly...

 

The Repair Manual does not mention this though, it just says pry the piston back.

 

Makes sense to me James.

 

we did the coupe in that way....didn't have any problems...

 

I saw that, only after the fact while looking for an answer. In the future, that will be my procedure.