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MG TD TF 1500 - Front Brake Cylinders

The front brakes were locking whilst the car was parked and recently there has been a loss of brake fluid. The locking would indicate that the pistons were seized in the cylinder. Examination showed that the cylinders (front) were leaking fluid and causing the lock up. The pistons are made from brass or gun metal which stops the reaction between piston and cylinder with the standard pistons.

Examination found that the gun metal or brass pistons were badly scored on one side at the top edge. This would indicate that the pistons were a bad fit in the cylinder or, as has been suggested the pistons distort under hard breaking.
Has anyone else had similar problems

Bob Marshall
R J Marshall

Bob, I can think of no circumstance where a leaking cylinder causes a lock up. It takes hydraulic pressure to expand the cylinders to activate the brakes. The hydraulic pressure is not sufficient to distort a metal piston. Are you sure you don’t have a bad master cylinder that won’t release and leaky wheel cylinders, 2 separate problems with your brake system?
I think I have read of issues with deteriorating flex lines or brake cylinder seals that can trap fluid keeping pressure on the wheel cylinders.
Do you know the age of your brake system components and the type of fluid you are running?

Regards, Tom
tm peterson

My front brake locking was caused by horribly old and deteriorated flexible lines that prevented the fluid from being able to return so the wheel cylinders couldn't relax. I don't know how old the flex lines were but I suspect many, many years. Simple to replace, relatively inexpensive and completely solved the problem.

Jud
TD 25009
J K Chapin

The master cylinder is new so it was not that that was causing the problem. Clearly there had been unacceptable side movement of the piston within the cylinder to score the piston. This lateral movement could well have caused the lock up which only happened when the car was left in the garage. I never use the brakes when parking nor do I leave the handbrake on; not has this any effect of the front brakes.

The leak was/is very worrying for , the 60 years that I have had the TF I never had problems with brake lock up. I have had problems with seized pistons with the original cylinders where there is a metal piston and an aluminium cylinder.

The brake lines are a possibility but if they were causing the lock up, the fluid would not be getting to the cylinder and leaking out.

The UK YF Guru had problems with these cylinders and they now reside on his shelf.

Bob
R J Marshall

Bob, what happens with old collapsed flex hoses is that the fluid can get to the cylinders under pressure but can't return when the pedal is released. You may be suffering from both bad cylinders and bad hoses.

Just my thoughts 'cause that's what happened to me.

Jud
J K Chapin

The master cylinder is new, did you check that you have free play at the pushrod,
I have found quite a variance in position of the piston to the mount bolt holes altering the clearance.This can cause the seal to cover the recuperation hole in the master cyl.
Also do you have brass pistons in ally cylinders ?
Ray TF 2884
Ray Lee

Yes brake fluid on the linning CAN cause the brakes to lock when going forewards, very rare but it can happen.Push the car backwards to confirm andunlock the brakes.
Len
Len Fanelli

This thread was discussed between 19/01/2023 and 26/01/2023

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