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MG MGB Technical - lack of clutch and brake function

I had to store my 67 BGT for some years and pulled it out recently to find out that clutch and brake pedal felt soft with slight resistance but no function. I figure the master brake cylinder and one of the clutch cylinders should leak. The fluid reservoirs, however, are full and there are no stains on the floor. What to check first?
A Roehrborn

For a start you should change the fluid in both systems, you may well find they need bleeding. But after 'some years' the bores could be badly corroded with water adsorption by the fluid, seals perished, and all sorts.
Paul Hunt

PS. Someone somewhere asked about using DOT 5 i.e. silicone fluid instead of DOT 3/4. I came across this http://www.american-auto-club.co.uk/aac_articles/index.php?task=show&id=70 which virtually says don't touch it, don't flush your systems with spirits if you do, certainly don't change back if you do change, and it is on the way out anyway. My local parts place doesn't stock DOT 5 anymore, just DOT 4 and 'Super' DOT4.
Paul Hunt

Interesting points, Paul. I have enough DOT 5 on hand to last me the rest of my life, I happen to use it only in the TD. Aside from the surface area at the top of the MC, I'm at a loss as to how copious amounts of water will end up in my TD's brake fluid. So far (one full year and over 7,000 miles of driving) my TD brakes are excellent. I don't plan on flushing them. If I need to remove the DOT 5 from the system for moisture contamination, I'll do it the way I made the switch to DOT 5, i.e. complete flushing off-car of all pipes, new wheel cylinders and rebuilt MC, new hoses.

When I redo the B I'll probably go with the new DOT 4... although I really, really like the DOT 5, but I'll need to save it for the TD!

warmly,
dave
Dave Braun

A friend had DOT 5 silicon in his MGB braking system for 17 years (he's now sold the car) and never had a moment's trouble. What's more, his brake hydraulics never needed attention in all that time.
Mike Howlett

Thanks for your advice. The brake fluid is certainly too old now. I donīt know what type of stuff is in there, but it worked fine for the years I drove the car, except for the fact that dics without booster feel somewhat strange today.
My understanding of old brake fluid is, that it is hygroscopic and therefore the water content can generate air bubbles when boiling under driving conditions. I noticed the problem with the car in the garage, though. Can it really be the fluid under these circumstances?
Thanks for your help again!

Ansgar
A Roehrborn

Funnily enough it is said that DOT5 silicon aerates very easily i.e. develops air bubbles at ambient temperature. But you have to be careful when taking about DOT5, the later non-silicone fluid is to spec DOT5.1 and either this or Super DOT 4 could be on the container. I'm glad I never bothered changing to silicone.

Wondering about the fluid is pointless, surely changing it as a matter of course is a no-brainer? If the master pressure seals have failed then they will leak back into the reservoir, which doesn't result in visible leaks. You could go through the systems changing all the seals before refilling, but personally for the sake of a bit of fluid I'd change it first, bleed fully, and see what happened. After that it would be a case of careful use, then examining the slaves, calipers and masters carefully, like peeling back the boots on the slaves, looking for any leakage.

Brakes are easy to tell from the pedal whether there is any loss of or reduced function, clutches less so, only trying to engage reverse will tell you. If it doesn't grind it is fine. I've never understood why people talk about a 'spongy' clutch, it is supposed to go to the floor after all. 'Very light' maybe, but not spongy, but the reverse test is the only valid criteria. I changed a clutch and slave cylinder for a pal and he got in and said 'it isn't working' because it was lighter than he was used to, but it engaged reverse just fine.
Paul Hunt

Drain the fluid and dismantle ALL the cylinders - it is the ONLY way to go - brake failure can cost you your life ...
Chris at Octarine Services

This thread was discussed between 14/10/2009 and 16/10/2009

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