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MG MGB Technical - loss of clutch fluid

Hi Guys,
Is it posssible to have a slow loss of hyddaulic fluid through the clutch master cylinder cap? Clutch failed to disengage after some months storage in garage and found reservoir empty. No oil on garage floor ,no sign of fluid on cockpit carpet and slave cylinder is dry of any oil leak. In fact no sign of a leak anywhere.
However i found the the cylinder cap was cracked across the thread and was not tightening down properly, although not really any sign of a great deal of oil.Have topped up , fitted new cap and seem to have full pressure now . Quite bizarre !
Any ideas please ?
ps, have a '72 mgb

Thanks ken
k proud

Jonathan Creek case??
Allan Reeling

Or Jeremy Clarkson.
Steven Rechter

very helpful guys :-).
Have'nt they both retired ?
ken
k proud

I can't provide an answer to your loss of fluid, but it's most unlikely that it all evaporated through the cap. Keep an eye on it. Have you peeled back the slave cylinder rubber boot? It should be completely dry inside it.
Mike Howlett

Ken, it maybe also worth looking at the clutch slave cylinder flexi hose. I have known rubber hoses in the past to develop a fine spit allowing fluid to come out under pressure in a fine spray. When not under pressure - no leak!

Andy
Andy Robinson

Sorry for the levity Ken. I presume DOT 3 or 4, not silicone!
As Mike said "it's most unlikely that it all evaporated through the cap". In fact evaporated in general. I can't believe it has gone "without trace", especially after only "some months storage". Wouldn't trust the system though, it will let you down.
Allan Reeling

It has to be either the flex hose or the slave cylinder, unless the hardline has failed, unlikely, or a very slow leak past the master cylinder end seal. This would show up as a puddle underneath the clutch pedal itself. The most likely scenario is that the fluid level was low when you put the car into storage and what was left leaked past the seal in the slave cylinder. It must have been so low that it was almost invisable to see on the floor. RAY
rjm RAY

Thanks for being a good sport.

I agree with the others that it's not a gravity leak but a leak occurring during pressurization.

Have you tried having someone pump the pedal while examining the system for leaks?
Steven Rechter

Thanks guys , i
am going to order a new slave & hose, i agree it seems most likely. Havent had a chance to prize cap off the cylinder yet.
thanks again .
ken
k proud

I have found in the past that hydraulic fluid that drops on a concrete floor does dry out stroke evaporate over time.

If it failed to disengage after several months storage, and did work properly before, then almost certainly it is a gravity leak and not a pressure leak, as off the top of my head I can't think of any part of the 'wet' side that will only be affected by pressure. If, for example, it WAS a weak point that only opened up when you tried to disengage the clutch, then the leak would have been obvious as it would only just have occurred and still be 'fresh'.

The fix will almost certainly be the same in any event. Impossible for it all - or even a significant part - to evaporate through a cracked cap, which are ventilated anyway.

Changing the flex hose will be fun, the fixings at the chassis end are a beggar to get to. Also in my experience what you put back will very likely need different spanners to what you took off. Fit the slave to the bell-housing first, then screw the hose into the slave. Only tighten the chassis end pipe fitting and clamp nut of the hose then.

More fun in prospect for bleeding, much in the archives about the trials, tribulations and tricks for this.
Paul Hunt

This thread was discussed between 22/03/2016 and 24/03/2016

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