3 replies to this topic

[Kevster2]

Hi all, new to this forum.

I have a problem on my sons mini which has stumped me.

A 92 mayfair with a new type 3 non servo master cylinder, dual brake lines & 4 pot calipers in which the pistons are free to move OK. After a 4 or 5 mile run the brake pedal goes hard with no freeplay , the calipers & discs are very hot with a burning smell. from the symptoms I presume that brake fluid is being prevented from returning to the master cyl, but why ? any ideas ? could it be the compensating valve.

PS servo system was removed due to engine mods

Thanks in advance Kev

[Gr4h4m]

Brake hoses, they can collapse inside and act as a one way valve?

[tiger99]

I would say 99% to the pedal having insufficient free play to uncover the reservoir ports in the master cylinder. Typically caused by defective servo, trying to apply brakes lightly all the time, broken or missing pedal return spring (very important part, often forgotten), sticky pedal pivot, rogue carpet, or just a tolerance build up netween pedal, pedal box, bulkhead cross member and master cylinder. Shims are available for non- servo models. For a servo, a quick test is to blank off the vacuum and run without servo assistance. After a few pedal presses the residual vacuum will be gone. If that clears the fault, blame the servo. If not, check everything else.

[MRA]

What type of master cylinder is it ?  what is the thread diameter of the pipe ends into the master cylinder ?