Brakes ‘holding on’ after a longish drive

[ujimaflip]

Hi, I noticed my brakes holding on a bit if I drive for > 20 miles or so. No problem on short runs. Initially the thinking was seals had gone on the calipers - but these have now been replaced. Thoughts now turning to servo or abs. Anyone got any recommendations as to what to look at first?

[Tractor Dave]

Have you got original brakes? Did you replace the slide pins when you did the seals?

[ujimaflip]

thanks for responding.
The brakes are porche 996 upgrade I think a lot of us have. To be clear the binding only occurs after driving. Sitting an pumping the brakes causes no issue - only once I’ve driven for a while.

[Tractor Dave]

Have you done a servo brake upgrade?
I did one for a friend a while back. Car drove fine with me on a small test drive. When it arrived with him after a short drive all the brakes locked on. The rod to servo needed adjustment.

[ujimaflip]

I’ve not touched the brake system for years (maybe 15 years) other than pads and disks. These problems surfaced after last disk change. We thought it might be the seals, but the problem persisted. Any advice on how I could check the rod/servo adjustment other than try and see?

[Tractor Dave]

I think it's unlikely to be the rod length if you haven't touched it. Are all the brakes binding? Take the car for a gentle drive and try not to brake at all. After a few minutes, stop and feel each disc for heat (carefully).

[ujimaflip]

A bit more that might help with diagnosis: I put the car on the local ramp, before driving all four wheels freely spinning. After pumping brakes all still fine - short drive no problem. Long drive, both fronts significant bind (but even - no pulling left or right).
I’ll try the short drive and heat test. If they are warm - what is this indicating?

[Tractor Dave]

It just indicates a binding brake. It will be very hot.
As it's both front brakes, were the new discs too thick?
Or maybe the new pads were too thick?
As the discs warm up they will expand slightly.
Did you replace the calipers pistons? Again, might be slightly too long and as they heat up will expand.

[ujimaflip]

With the new brakes on and the pistons pushed back there is still a bit of clearance between the brakes, if they were too big I'd suspect it too bind all the time.

After a drive, if you crack off the brake line to the caliper immediately they stop binding. So it appears it's holding pressure in the line after a drive. Any thoughts?

[Bowie69]

Could be failing brake hose or master cylinder, keeping pressure on.

[Jamin]

I've had the brakes locking on, the master cylinder had rust inside due to lack of fluid changes and was rolling the seal over causing it to jam.

[sal_s2]

I had this problem, it was the brake master cylinder

[ujimaflip]

Will have a go at taking the master cylinder out. Any advice on where to find a rebuild kit? Or failing that where to source the part?

[steverrquattro]

I’d also go for the brake master cylinder.

[ujimaflip]

Hi all, master cylinder taken off and there are no signs of rust or other particulate. I could go ahead and order a new cylinder. Anyone think it could be the abs pump?