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MG MGB Technical - Clutch Judder

Hi

Can anyone offer any advice please? I think I may know the answer to this issue but the advice from you oracles is worth it's weight in gold! I have a '76 GT and it drives and runs well although I have noticed that as the car has warmed up and after constant use, I will get quite severe clutch judder and either pull away in 2nd gear or keep revs as low as possible to try and prevent it. Running from cold, there is no judder at all till warmed up. The car does have a leak (has done since we bought it) and I have read in previous threads that it could be oil contamination onto the clutch plate/flywheel? Does anybody have any other possible explanations for this that I could possibly investigate? Many thanks for all of your help.

Regards

Martin.
Martin Clegg

Oil contamination is the prime suspect, but first check all the engine and gearbox mounts. If they are loose or much to soft because of (the same?) oil contamination your clutch will also judder.
Willem vd Veer

I just pulled the engine and transmission out of our MGB to replace the clutch, which was also exhibiting judder on start up, particularly in reverse. I expected to find soft rear mounts from oil soaking, but to my surprise, they were good and solid. I did find a clutch disk that was almost completely worn out and with the sheet metal disk between the two side of the lining broken in a couple of places in addition to the throwout bearing worn down to the metal. The real surprise find was that the bolts holding the U joint to the rear flange on the transmission were all loose in spite of having used self locking nuts. Cheers - Dave
David DuBois

Most likely oil contamination on the clutch disc. Have the flywheel machined, when you go to replace the clutch assembly. Failure to do so will result in a job that needs re-doing. Be sure to replace the rear main seal. Take a close look at the crank shaft surface, where the seal contacts it. If if looks questionable, install a Speedysleive over the crankshaft. Also, clean and inspect the input shaft of the transmission. Any excessive movement or leaking oil indicates that the bearing and seal need attending to. RAY
rjm RAY

Agree with oil contamination as the first likelihood, especially if there is oil dripping out of the bell-housing drain hole (which can also come from a leaking gearbox seal). However I had a new clutch that tended to judder from the start which was disappointing as the old one hadn't, no leaks, mounts sound. I got round that by using low revs for manouvering as you mention. However some 20 years and 50k later I suddenly realised it had stopped, or at least got much better. The problem with clutches is how far do you go? Changing one for a pal more recently we just did the minimum i.e. no flywheel skimming, spigot bearing, crank or gearbox seals on the principle of least interference, and it has been fine.
PaulH Solihull

Hello again Gents

Thanks very much for all of your input. It's as I guessed, good old oil leak! I'm not planning on pulling the engine and gear box anytime soon as it's going to be an expensive job and I really don't have the space in my garage to do at home so it will be a professionals job, and only if the clutch/gearbox fails. The leak isn't excessive so I'm not overly concerned. I always have it routinely checked when it goes in for MOT anyway. I think it's a case of hoping it gets better and just keeping low revs when pulling away. I will, however, take Daves' advice and check the engine/gearbox mounts this weekend just in case this could be the culprit. Many thanks again all, your knowledge is invaluable!

Regards

Martin.
Martin Clegg

Ray's advice is spot on, whoever does the job. I also like to replace the welch (core) plugs at the back of the motor at the same time. Or better still all welch plugs. Nothing is worse than having to do it twice in quick succession.
Ian Buckley

With 'The Betson Bolt' you can change the rear one in-situ.
PaulH Solihull

If an oil leak is causing the judder, it's likely from the rear of the engine, not from the transmission. My 80 LE was the king of transmission seal leaks. Not drops, but a puddle. One way to check is place some paper underneath and look at the leaked oil. If it's clean and mostly amber, it's likely the transmission. If it's blackened from combustion, then it's the engine. I just pulled my transmission and replaced the seals. It was loaded with oil in the front, but the clutch mechanism and the rear of the engine were completely dry and clean. Thus, not affecting the clutch. Looks like you have a leak to fix anyway, but the clutch judder may or may not be associated with the leak. I'm curious that it occurs mostly when warmed up. That could be a mechanical issue. If the clutch material is severely worn down, the clutch disc may be thin enough to distort when heated up and cause the judder.
Rick Penland

Hi all

Once again, thanks for all of your comments! Rick, further to your post, the oil is blackened so it is definitely engine oil. Could this be contaminating the clutch to cause the judder, if the rear seal needs replacing? It does judder ONLY when warm and yes, it's curious! I don't have a huge amount of history of the car but I did find a receipt for the gearbox which was recon'd in 1996 (nearly 15 years ago!) and I don't know if anything has been replaced since?

Regards

Martin.
Martin Clegg

Because of the car's most common direction of travel (forward) and the slight downward incline of the engine to the rear, an engine oil leak can travel down the transmission front shaft and disperse into the clutch. A leak in the transmission will mostly seep into the front of the transmission, but not flow upward against the car's motion and incline of the shaft into the clutch mechanism and rear of the engine. However, the relationship of the judder to the temperature created by use and friction indicates wear of the clutch lining is very likely the cause of the judder. That means you can't do one of those "overnight" clutch lining and release bearing replacements that many of us have done along the way to get to work in the morning and drive several thousand more miles afterward. The clutch disc has probably worn to the point that the pressure plate will need replacing and the flywheel will need resurfacing as well. Along with repairing the engine oil leak, there's some work involved. Few MGB owners get spared this task along the way. I don't know if there is an actual mileage average for clutch wear. It depends on type of driving, driver habits and so on. I would expect about 75K to be very long life on an MGB clutch.
Rick Penland

Sixty thousand miles is considered the norm for the life of a B clutch, mostly due to the design of the throwout bearing. Oil, leaking past the rear main seal, is the most likely culprit for your judder. Expect to replace the entire clutch assembly, as well as the rear main seal. The flywheel should really have a small amount of material removed from it to ensure that you are starting out with everything in perfect order. RAY
rjm RAY

Superb gents, an expensive job then! On my list of things to do then, money permitting! Thanks for all of your help.

Martin.
Martin Clegg

This thread was discussed between 21/02/2011 and 03/03/2011

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