Technical All four brakes sticking badly when hot

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Technical All four brakes sticking badly when hot

Luckor10

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Hello! It was so long ago I posted here, I've forgot my username, password and what email address I had at the time. You may wonder if I've forgot my name too ... Well, new account and a new world ...

I replaced the master brake cylinder on my X1/9 before putting the car away for winter rest last year, I then noticed some sticking tendencies but nothing alarming. After picking up the car for this year's warm season the sticking has become quite extreme. On one short trip I could barely manage to get the car home, all four wheels were so badly stuck. I had to drive on first gear with full turbo boost (Uno Turbo engine) the last few meters to my house.

Then, after cooling down, everything worked as normal again. I've read somewhere that the brake pedal rod pushing the master cylinder piston needs to have a significant play, I never checked that when replacing the cylinder. For the moment the car lacks radiator so I cannot go for a testdrive right now.

Please, tell me that the problem is this simple to solve, please do ... Actually, I've never experienced anything like this on any car before, and I've owned many oldies ...

Stefan in Sweden
 
I think this is due to water contaminated /old brake fluid. Have read a similar case recently on a fiat cinquecento. So hopefully changing the brake fluid will sort it?
 
Thanks, but since I replaced the master cylinder prior to the sticking effect the fluid is naturally brand new and bleeding is performed thoroughly. At the same time I upgraded the front brakes to Uno turbo calipers and discs. But, as mentioned, the problem occurs on all four wheels. I find this quite strange.
 
I've encountered this on a couple of Fiats.

One case was where the master cylinder had been renewed. This car was fitted with a brake servo and the pushrod on the servo had not been checked/adjusted. There was a dimension given for protusion of the pushrod in relation to the master cylinder mounting surface. Iirc, essentially it meant that the pushrod had to move approx. 2mm? before it started to push the master cylinder piston.

Second case was where the stoplamp switch had been renewed and was incorrectly adjusted thereby holding the brake pedal slightly down and taking away the pedal freeplay.

You could check if you have some free play at the brake pedal, 2mm on the actuating rod will equate to approx 10 - 12mm? at the pedal. Try pushing the pedal with your fingers.

Al.
 
Thanks for your help. I sure hope that it has to do with insufficient play of the pushrod. Or even the brake light switch sitting too tight! Both easy fixes. I didn't think of checking these when replacing the cylinder. I will have a check tomorrow.
 
FYI: I was lucky, I just needed to slacken the tension of the pushrod a bit, now everything works fine.
 
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