TR4 brake master cylinder failure?

[mikeh]

Well, it’s been an interesting day today………I took the TR4 for its MOT and all was going fine until the brake test. The rear brakes were on the rollers and the tester was just taking the readings when the pedal went to the floor. No sign of any leaks whatsoever, the fluid level in the master cylinder hasn’t altered and the brakes had been fine beforehand with no hint of sponginess.

 

The car is now in the garage at home, having been rather ignominiously trailered back. Thank heavens though that this happened where & when it did. The alternatives don’t really bear thinking about and the incident does highlight the risks inherent with single line systems.

 

Provisional diagnosis is that the internal seal in the master cylinder has failed but I’d be interested what thoughts the combined wisdom of the forum has on the matter.

 

By way of background, I’ve recently removed the after-market servo which was fitted when the car was restored some 20+ years ago. The reason was that I had found it was intermittently causing the brakes to stick on slightly. I’m just wondering whether the resultant change of operating conditions in the master cylinder has been the last straw for the seal, straws & camels’ backs, etc.

 

Any advice on i) the problem/diagnosis and ii) where to source a replacement (it’s the later 0.70” version).

 

Thanks in advance

Mike

[RogerH]

Hi Mike,

that's an interesting one.

With the servo it only needed light pressure. The MOT gives it plenty of welly. This probably was just too much.

Look for dirt/muck on the bore walls in the area of the bore that would not have been normally used prior to the MOT.

 

Maybe with normal use it would have degraded and you would have spotted it before complete failure.

 

Revingtons do the smaller size. If not I'm sure I have one that I bought 2 years ago that you can have (I wonder where it is).

 

Roger

[harlequin]

I would suspect that the cylinder had a wear ridge at the end of what was the piston travel and when you removed the servo the travel increased so that the seal was crossing the ridge every time you used the brakes with the inevitable result

 

George