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MG MGB Technical - White smoke from exhaust

Hi, My next door neighbour has a G (1969) reg MGBGT. He has been having problems with the loss of brake fluid.

He has replaced the master cylinder, checked all the pipes and wheels but still there is a loss of brake fluid.

he has looked at the servo and checked the diaphram and it seems okay.

He has gone on some of the less knowegable sites who seem to say his servo is broken. I told him I would ask people I trust.

So guys, is his servo toast or what?

Regards

Edd
E McGee

With the two symptoms of white exhaust and loss of brake fluid, its the servo. The engine is sucking the fluid out and burning it.

Herb
Herb Adler

Not really the servo. It is the master cylinder leaking fluid into the servo. If this is a remote servo, it is still the servo cylinder leaking, not the big servo diaphragm. It rebuilds just like a master cylinder. The kits were supplied as cylinder kit, air valve kit, and servo vacuum kit.

FRM
FR Millmore

As a UK 1969 I'd expect it to be a remote servo.

"Not really the servo" Eh??

It *is* the servo that's at fault, and hence as Herb describes, and it will be either the push-rod seal leaking directly into the main diaphragm chamber, or the air-valve piston seal leaking via the air valve housing. If you remove the air-valve cover and the diaphragm and support that is under that and see fluid there, it is probably the latter seal, otherwise probably the former.
PaulH Solihull

Paul-
Semantics.
Yes it likely is a remote servo; I was thinking of US cars where we rarely see (or saw) remote servos on MGB, so the integrated ones are what I usually think of.
That is why I added sentence two.
It is my experience that while "servo" is commonly used to refer to the entire assembly, when referring to remote units, it is the vac chamber that actually provides the servo force, so "servo" is correct for that unit alone. On the integrated units, "servo" always means that part not the master cylinder. When it comes down to fiddling with it, people tear into the vac cylinder expecting to find a problem, when the problem is actually in the hydraulic bit.

FRM
FR Millmore

In aprticular, it is the seal around the pushrod between the vacuum chamber and the hysraulics which is leaking.

There could be a problem in replacing it: original remote servos were 7/8" slave cylinder, 1.6:1; there was also a 5/8 version of the same unit with a correspondingly higher boost ratio - used on Hilman Hunter amongst others. Most seal kits seem to be for the 5/8" rather than for the 7/8". If my memory serves corectly, the faulty seal in question is a differnt size between the two. But that might just be the nive bollte of wine we had for dinner talking ...

What I'm really trying to say on the seal replacement is check very carefully what people are trying to sell you to make sure it's the right one!
Paul Walbran

The MGB servo also had two levels of boost, increasing in May 1970 (Clausager).
PaulH Solihull

Thanks guys - I'll let him know the answer - he'll probably buy an replacement servo -I know he has replaced the brake cylinder.

Regards

Edd
E McGee

This thread was discussed between 03/02/2013 and 10/02/2013

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