Master Cylinder Failure

[dfyates]

All of a sudden, after starting the car, brake pedal to the floor, not even spongy, no resistance whatsoever. Fluid level is ok, sounds like M/C seals are gone?

Before attacking the M/C one question : my car is equipped with a lockheed servo, when bleeding the brakes, should the engine be running?

[bmcecosse]

Yes - it should be running - check to see if the servo is 'drinking' the fluid...... Master cylinders rarely fail..... Look in the chassis leg - is there any fluid to be seen? Yes - I know you say the fluid level is ok........ I would also pull all 4 wheels and check for leaks before going anywhere near the master cylinder....which is a relatively horrible job.....

[MarkyB]

Even a pin hole sized leak will give this type of failure, when the master cylinder goes it is normally a very progressive failure, lots of warnings.

[rayofleamington]

From your description the m/c/ primary seal has failed (or it's a fault in the servo).
A failed primary is very rare but not unheard of.

Master cylinders rarely fail..... Look in the chassis leg - is there any fluid to be seen? Yes - I know you say the fluid level is ok........

That relates only to the secondary seal failing (which is very common).

[dfyates]

Found the problem. The person who fitted the servo fed the servo from the side M/C outlet union, and plugged the rear M/C union (which normally feeds the rear brakes) by squashing the copper pipe. The copper pipe has become unsquashed! Chassis channel is full of fluid. While on the subject of master cylinders, I can understand the purists not wanting to turn the M/C bolts around for risk of the nuts nicking the torsion bar..... however....these bolts only see shear load and the nuts can be replaced with thin BSF nuts, with no fear of touching the torsion bar.

Will let you know whether I managed to bleed without engine running, answers to my question vary so much!

[bmcecosse]

Top job - squashing the 'copper' pipe. You assured us the level was ok ?? I sincerely hope NOT copper - since not suitable for car brake piping... There's no risk of the m/c nuts touching the T bar - the bolt ends may be close - but can be easily shortened - or simply put a washer under the bolt head. Bleeding depends also on how the servo has been installed - it must be 'nose high' ... but really - there is no need for a servo anyway on a wee car like a Minor. Just make sure the brakes are in good condition. Simples!

[moggiethouable]

"The more youve got,the more youve got to go wrong son"
Kenny Baker 1974.

[dfyates]

Yes but.....the servo's in so I'm not taking it out!

Upon dismantling the M/C I noticed the dished metal washer was missing. Is this important? wouldn't know where to get one anyway as it doesn't come with the seal repair kit.

By the way, the rear wheel cylinders were also leaking and need replacement. The apparent 'full' brake fluid level was in the remote bottle, appears to be an air bubble in the feed hose as the M/C was fairly empty.

[dfyates]

You can tell I'm redoing my brakes!!

Any useful tips for unscrewing the union on the wheel brake cylinder without twisting the copper pipe? heat? penetrating oil hasn't worked.

[bmcecosse]

You must not use 'copper' for brake pipes!! And can I guess that you have disc brakes fitted at the front - hence the servo ( ) and remote reservoir? If disc brakes - then the 'top hat seal' will have been removed from the mastercylinder.

[dfyates]

I'm aware of the requirement to remove the top hat seal, the previous owner obviously was too. As for copper pipes they were on when I bought it and I'm not ready to rip it all out.

On the other hand what does the dished washer do that I was talking about? Don't know where to buy one without getting a new M/C

[bmcecosse]

Copper work hardens and fractures - you see what has already happened with the crimped over pipe...... Sorry - no idea about dish washer - I value my life too much to ever re-seal a master cylinder.......

[JOWETTJAVELIN]

A lot of garages use copper now for replacement brake pipes. Can the original piping material - kunifer or whatever it was - still be obtained? If so why isn't it used now?

[bmcecosse]

The 'original' pipe was Bundy tubing - plated steel...rusts in time of course. Kunifer IS the stuff to use - no rotting and no work hardening. I rather hope that the 'copper' people refer to is in fact Kunifer....

[dfyates]

Upon redoing the rear brakes I noticed there were no 'beehive' springs. Come to think of it, on all the Minors I have had, some had the springs, some hadn't.

Anyone any idea if they were abandoned at any stage in production, and if so, why?

[bmcecosse]

'Everyone' has abandoned them post production......not necessary.

[les]

With one exception! ---------- Mentioning hammering over brake pipes, I once was taken for a test drive in a cooper and when returning was informed that the nearside wheel cylinder had been leaking but it was ok now because the pipe going to it had been beaten flat! They say there are more lunatics out than in.