Brake Demons

[NSFIAT]

Hi all - I'm hoping someone here will have an 'ah-ha!' moment and be able to point me in the right direction.

I have an '81 Fiat Spider and started doing some brake work on it last year. Everything at that point was 'functional' but certainly worn out and in need of some TLC. I replaced the booster, master cylinder, swapped the rear rubber lines over to braided steel lines, replaced a caliper that was leaking and replaced some of the old hard line that was corroded.

When all was said and done I was able to bleed the brakes and take the car for a drive. About 10 minutes in I noticed that the front driver's side caliper had clamped down and wasn't releasing. The smell was terrible. To release the caliper I loosened the associated line at the master cylinder and bled off some fluid - the caliper released right away and I was able to limp home after repeating the process again.

A few side projects tied me up and I wasn't able to return to the car until this spring. The MVI was due so I decided to have it towed to a local shop and have them replace the two rubber brake lines at the front with braided steel lines, thinking that they had started to collapse. Four springs, a drive-shaft bearing, a universal joint and two braided lines later I was finally able to pass MVI (it's never simple, right?) and figured I'd be good to go.

The ride was amazing - love the lower stance with the springs from AR and everything was buttery smooth .... until about 10 minutes in when the front driver's side caliper froze up again. The shop had serviced all four brakes and had checked all of the lines - everything had seemed fine. But here I am, having to release brake fluid at the master cylinder in order to release the caliper.

The process of the brake clamping down is gradual - from a fresh start the brakes feel great, the stopping power is fine and the pedal is nice and firm. But after a while I'm in trouble. Is anything jumping out at anyone? I can certainly take it back to a mechanic, but perhaps it's something silly / stupid that I've overlooked. The push rod on the booster was set to it's proper depth and the cylinder was bled beforehand.

[spider2081]

I have not experienced this problem but:

But here I am, having to release brake fluid at the master cylinder in order to release the caliper.

seem very strange. If the caliper releases when you loosen the brake line at the master cylinder it would seem to me the master cylinder has some sort of blockage in it.

[So Cal Mark]

the pushrod in your power booster is mis-adjusted. Pull the mc forward and you can adjust the pushrod

[NSFIAT]

Thank you Mark, that's something that I can easily tackle in the interim! Is there a set point that I should be looking at (ie, how far out or in that rod should be?) I had followed a guide from an online vendor last year but can't seem to find it again.

[NSFIAT]

I did keep the old booster, and when depressed all the way in the push rod barely peeks past the edge of the booster body. If memory serves me correct I installed the new one the same way, but I could be wrong. I'll know more tomorrow morning when I have a chance to get at the car again.

[divace73]

the pushrod in your power booster is mis-adjusted. Pull the mc forward and you can adjust the pushrod

I'm thinking the same thing...

Where the calipers completely overhauled at all?

[NSFIAT]

Yes, all four calipers have been serviced. I'll take a look at the booster push rod in the morning and compare it to the old one. Fun times!

[micbrody]

I agree with Mark: pushrod is adjusted too long.
I replaced my brake booster with the one from AR. I screwed down the nut and lock washer that came with unit all the way down. It did extend past the body of booster , but it looked to be within the 2mm that manual states.
When I started driving , everything felt great ; but within a few minutes , the braking became "super great"....I was realizing that my wheels were in constant braking condition. I theorized that initial driving was tolerable, but master cylinder must have been depressed slightly , trapping brake fluid in non-braking situation . As I continued to drive, the slight caliper pressure heated up brake fluid ; fluid expanded ; and more pressure placed on caliper.
I disconnected master cylinder from booster; pulled pushrod out. I removed the lock washer; and just screwed down rod with rounded end nut as short as it would go. Re-installed . Everything now works great

[NSFIAT]

Hello all - thank you for the help on this one. I did as suggested and removed the lock nut. The push rod is now threaded in as far as it will go and there have been no issues since.