Come August just on a pre-MOT check there was discovered to be a leak in the back of the master-cylinder. Although this did not affect the braking, it would have been enough to give a fail. So new seals were obtained and fitted. Now began the problem.
It was impossible to achieve full braking. Bleeding the brakes removed all air but on a road test, although the first two pumps produced good stopping the pedal would then “go to the floor”. The power would recover after a while and good stopping would once again be achieved. The brakes were once again bled with no difference. It was decided that the cause was that the piston was not returning fully and was staying in the depressed position, possibly due to the seal rotating in the barrel. The master cylinder was again removed and stripped, this time also having the barrel honed and the piston polished as well as another set of seals being inserted. At the same time, on the assumption that the spring might be weak, a new sprig was made and inserted. No change! The operation was gone through again (by this time I was getting quite adept in removing the MC – 25 minutes to remove including lifting the car and 20 to replace to wheels on the ground!) and this time a much stronger spring was inserted. You’ve guessed – no change.
So it was decided, even though there was previously good braking with the mix of the P4 wheel cylinders to P3 MC, that the mix might be the fault and to fit the slightly larger P4 MC. Worked a dream but now we were at the end of the season and the car only did about 50 miles over the rest of the year.
No fault in the breaking right up till early summer this year, in fact did one trip of over 140 miles in a day and all the time no braking problem. However, I had noticed a damp spot on the garage floor in the area which would be below the MC. Checked it out and the “new” MC was leaking at the back! So, new seals were obtained and fitted. You guessed right. Exactly the same problem. So the question is what is happening? None of the “experts” I speak to has any suggestion of the cause beyond what I have determined above. Has anyone a suggestion as to what I might have done or what can be done or has anyone had this problem on a P3?
