Brake Bind Issue

[TomZupra]

Had an issue with my brakes on the weekend, I started to notice a loss of power and engine temps rising, coasted to the hard shoulder and stopped quite rapidly.

I checked the rear drums and they were fine, front discs were very hot though (pro tip: don't touch disc brakes you suspect to be hot). Rang a friendly member here to check I hadn't changed anything whilst working on the car and he recommended opening the bleed nipples which sure enough got the brakes off and home with a bit of a soft pedal.

So some facts, have Supra (MA70) servo and master cylinder, original 260z proportioning valves and piping and silvermine 4 pot upgrades at the front (new), reconditioned drums at the rear. Brakes were not pulling either direction, I have had this issue before in hot ambient temperatures but not when cold which makes me think its (partially) temperature related. I believe my problem is I can increase braking hydraulic pressure but not relieve it.

Possible causes:
1) Brake lines are expanding or collapsing (worn) and acting as storage
2) Master cylinder fault
3) Boost non-return valve malfunction
4) Brake servo issue (return spring worn, atmospheric valve damaged)

My moneys on 4 at the moment, wondering if anyone has had any issues with front brake binding with engine swaps or general advice? Would love to fault find this without replicating the conditions if possible

 

[Mr.F]

Check servo push rod length - may be expanding and acting on back of the master cylinder.
Had this problem on my V8 240Z back in the '80s, but never really got to the bottom of it. Ended up with a Jaguar master cylinder which proved more compatible than the original!

 

[tel240z]

my mony's on the master cylinder free play to tight as it seems the hydraulic pressure cant get back to the reservoir and causing a hydraulic lock or the cylinder is shot, think you might need to replicate it diagnose the fault by cracking off the brake lines from the master cylinder to the callipers to see where the lock is, bit of luck if it releases at the master cylinder then you have found the culprit, I also think Tom you need to do a check on how your hybrid brake system has been plumbed as I thought dual circuit brakes work diagonal

 

[pmac]

Check servo push rod length - may be expanding and acting on back of the master cylinder.
Had this problem on my V8 240Z back in the '80s, but never really got to the bottom of it. Ended up with a Jaguar master cylinder which proved more compatible than the original!

If the system had just been recently put together then I buy your pushrod scenario. That is a common issue when adapting a late S130 Master cyl to fit a S30 servo./pedal box.
If the car has been OK for a long time in this configuration then my chief suspect is an internal master cylinder fault..
Swapping it out might be a useful test