Brake Master Cylinder

[Ben Magoo]

Hi all

I have had a bit of a search for this but not really found much; brake master cylinders.

My 81' city is on drums all round, running a yellow tagged front rear split system which had decided to play me up since I had the front hub assembly off to do the wheel bearing. It wouldn't bleed properly and felt like there was a "notch" half way through the pedal travel.

Initially I thought maybe the seals in the master cylinder had gone as it had taken about a week for me to fanny about with the bearing on my tea breaks etc.

Changed the seals and flushed the system, now it won't bleed at all and the pedal hits the floor with no resistance.

There are no apparent leaks and the fluid level stays topped up, the whole system is less than 6 years old with exception of the master cylinder and the pressure valve.

How likely is it that the master cylinder is simply worn to the point where the seals won't seal against the side walls any more?

Is there a much simpler - cheaper issue I'm missing here?

Thanks for any help or advise in advance

Ben M

[Cooperman]

This is have one of the tandem vertical master cylinders. They are a complete bloody nightmare and the symptoms you have are very common. Basically there forms a step in the cylinder and the old seals fail when pushed past this step to bleed out the system. then the new seals won't 'take' either and the cylinder is, basicaly, scrap. The only solution is to get a new cylinder, but they are not cheap. It does seem to be the tandem cylinders for the drum braked cars which are particularly bad for this happening, as I recently did an '86 Mayfair with discs and the system bled out fine. Maybe it was dodgy Austin-Rover quality at that time.
It's the braking system, so my strong advice is to take no chances with attempting to hone out and fit a seal kit, get a new cylinder.
Whilst on the subject of the braking system let me remind everyone that the cars with the large brake compensator valve mounted on the front bulkhead, as opposed to the rear sub-frame mounted pressure relief valve, have METRIC THREADS into the compensator, but UNF threads into the master cylinder and wheel cylinder ends. This, from my perspective as a former aerospace engineer, is the most dangerous sort of folly that could ever be designed into a safety-critical system.

[Ben Magoo]

Thanks for the help

It is as I suspected, not too much hassle tbh - it's only two bolts, two unions and a pedal pin

A good bleed and flush through should see me on my way , cos it will be that easy

Cheers once again

Ben M