The brakes on my 1992 Townace 2.0 diesel turbo Super Extra stop the car excellently. However when stopped at traffic lights, and holding the car stationary on the footpedal, after a minute or so the footpedal starts to fall away. Pump the pedal once and the pressure is back as before. What is the problem. Is it master cylinder?

- (#8478) David Powell, 11 Feb 04 07:35

More likely to be vacuum loss.

- (#8478) Clive (Bristol), 11 Feb 04 08:09

David. The symptoms do indicate that the problem might be with the master cylinder but, there are other areas which you might check first. I assume that the reservoir is full because if the level has fallen, you should have had a "low level" light illuminating on the dashboard. Have you bled the brakes recently? Air in the system, which will compress under load, will give similar symptoms and this should be completely bled off. Also, after hard driving and frequent braking, water in the fluid which, because of the fluid's hygroscopic nature, will attract and absorb it, can boil off, and the vapour, still in the system, will compress under load and give the symptoms which you describe. Have you checked the front flexible hoses and, is there a slight weep of fluid from a minute hole in these hoses or, possibly, around any of the connections?
Before you attempt the laborious job of removing the master cylinder, it would pay to do a thorough inspection of the braking system and check ALL of the cylinders for leakage, especially the rears. Doing a thorough brake bleed, and fluid change at the same time, will help but,if you bleed the brakes manually, put a block under the brake pedal to limit the "stroke" of the piston, and avoid tearing the seals on the unused and corroded part of the master cylinder bore.
If all this fails to eliminate the problem then, yes, it is time to re-seal the master cylinder

- (#8478) John Davis, 11 Feb 04 08:17

Are you sure it's not a simple case of the alternator belt slipping.

The belt drives the alternator that has the vacuum pump bolted on the rear.

I had loss of brake vacuum last year which was a bit scarey as I only noticed when I was slowing down, perhaps at the lower revs the belt is slipping sufficiently to reduce the vacuum.

Just another simple thing to check before ripping your dashboard apart.

- (#8478) Mark, 11 Feb 04 13:43