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MG MGB Technical - Slipping clutch

I have a 69 B roadster with 133k miles or so on the clock. About two years ago we replaced the clutch and pressure plate with a "high performance" or "high strength" clutch and pressure plate, throwout bearing, the works. The clutch and pressure plate now have about 15,000 miles on them. On a trip home three weeks ago I found that I could make the clutch slip by giving the engine a little more throttle than I was using to cruise(it would break loose and the engine would begine to almost rev freely!) This only seemed to happen occasionaly at first but it has gotten progressivly worse. Sometimes I can take off and accelerate at full throttle with no problem, but other times it is almost impossible to get the car up to speed with partial throttle. The slave cylinder was rebuilt at the same time we did the clutch and the rubber line was replaced. The engine is all origional except for an intake manifold, K&N air filters, electronic ignition, and free flow exhaust system.
Any ideas or suggestions on why this may be happening and how do I stop it.
--Robert
Robert

Sounds like the classic symptoms of a worn clutch. You haven't said how you drive it. Sometimes high performance gear wears quicker than stock, because the material is softer, as in brake pads. Grips better, but not as long.
R. L Carleen

I wouldn't say I drive the car extremly hard, I think we may have 4 or so Autocross sessions on the clutch. I very rarely dump the clutch at high RPMs but it has been done. I never felt like the clutch was performing properly. It is very close to an on/off switch. Either it is in or out and it will allow a little bit of slippage when pushed in partialy. Since new it would only grab in the top 1/4 or so of pedal travel.
Thanks
--Robert
Robert

The "high performance" clutch is known to
have an "on-off" characteristic as you note,
Robert.

However, the slipping could be due to
an oil leak from the rear engine seal, or less likely
front transmission seal. Do you have more than
one or two oil drips out of the bellhousing after
a run? I doubt that the clutch disk could have
worn enough in 15K miles to cause slipping, but
who knows.

I don't know if this is possible, but the clutch
hose could act as a one-way valve if the inside
was disintegrating. Replacing the clutch hose
is cheap if it is more than a few years old.
Ronald

Robert. Brand is important. The Q-H clutches have a general reputation for causing problems. The B&B brand have a much better reputation. However, B&B seems to have been bought out a couple of years ago by another group. I got two "clutch kits" from Moss (pressure plate, driven/clutch plate and throwout bearing) which had been packed in a most inappropriate manner. The pressure plate was heavily coated with some form of oil, the pressure plate made contact with the driven plate and, in one case, the loose throwout bearing was cracked into several pieces. E-mails to other suppliers indicated that this was the common practice with the new manufacturer (Phoenix Associates?) and that they were also having significant problems. Since you seem to have installed your new clutch about the time this problem was taking place, could you have a contaminated clutch/driven plate? I clean mine with brake cleaner before installing and have few problems after doing so. However, the first one I installed mimiced the problems you describe. One supplier told me that 75% of the throwout bearings in the clutch kits were damaged when received from England.

Thus, while in no way definitive, your indications might indicate a contaminated driven/clutch plate.

If this is not the case, I would look for free movement in the clutch fork (bearing), free movement in the slave cylinder (as caused by a bad flex line) or a clutch master cylinder problem. Les
Les Bengtson

Robert.
The one thing I am glad to see, is that someone is actually
auto crossing their MGB.
As I am as well.
Safety Fast
Dwight
Dwight McCullough

If the slipping is noticeable more in 4th than 1st then the clutch is slipping. With oil on the clutch of a Mini it made it much fiercer than normal, rather than slipping.
Paul Hunt

I do believe that I will have a look under the car tonight as this is driving me nuts. I don't remember who made my clutch kit, I will have a look though.
Thanks
--Robert
Robert

Well, as luck would have it, my rear main seal seems to be blown. The bell housing has oil slung around inside it covering about everything. If anybody has any secrets or ideas on how to stop a leaking rear main seal without pulling the engine I would love to hear them.
Thanks again
--Robert
Robert

The only way I know to stop a leaking rear main seal without pulling the engine - is to sell the car!
Chris Betson

I pulled the engine today, turns out that it is actualy the front transmission seal. So I am going to replace that and the clutch disk (pressure plate has about 15k miles on it, looks good). The 34 year old engine and transmission mounts will get replaced also. With any luck the engine seal won't start leaking anytime soon since my Father doesn't want to replace it(it is his car, he is buying the parts, I do the labor)
Thanks for all your help
--Robert
Robert

Rear engine seal is about 5 quid iirc, plus another 2 or so for a backplate gasket. It should be you not wanting to change it, you have to take the flywheel and backplate off :o)

ttfn,
--
Olly
Oliver Stephenson

This thread was discussed between 17/07/2003 and 20/07/2003

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