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MG MGB Technical - clutch issues

A few years ago I restored my 64 B, Since then I have removed the engine and tranny twice for the same issue. The clutch starts chattering. The first time the throwout bearing was cracked. The second time there was nothing wrong, just cleaned and but it back together. It is doing it again. I already replaced the spigot bearing. It seems to do it more when it is hot and have driven it for an hour or so. Any ideas before I pull the motor again.
Andrew DeCandis

Are you getting any oil on it from the rear main? Oil on the clutch will cause it to chatter unless it is so much that it will just slip. If you haven't done it in the past it may be worth having the flywheel ground.
John H

I agree with John.
Reface the flywheel. Many years ago I had a Porsche 356. About every 3-4000 miles the clutch would start chattering. On pulling the engine I would find four discolored spots on the flywheel clutch face. A slight surace cut and all was well. Much later on another chattering I took a close look at the flywheel spots and found that they were actually blued from heat and surrounding each 1" spot were extremely small stress cracks radiating outwards for about 3/8".I replaced that flywheel and had no further trouble.
I was in the airforce at that time and had access to a testing lab. They found that there was a great difference in the actual hardness of the metal that was blued from heat.The possibility of improper steel used was suggested as it could have been contaminated at the smelter.I put over 200,000 miles on that car till the metal moths got it. Too much salt from up north.
Sandy
Sandy Sanders

Is this just audible chattering or is it clutch judder i.e. there is visible vibration in the power train? The clutch my roadster cam with had no judder. Then the release bearing broke so I replaced the whole thing and after that the new clutch tended to judder when manouvering at low revs. So I just slip the clutch a bit more as that stops it. Other have said that using *higher* revs when manouvering causes theirs to judder, so they are all different. If you can find a way of using the clutch so it doesn't judder, then I'd do that in preference to taking the engine out again. Either that or *do* take it, but replace the clutch again and reface the flywheel. But it is worth that effort and expense, I'd be asking myself.
Paul Hunt

It may be in your transmission input shaft or gear lash. If you put a lumpy cam in it that could cause you to hear the gear lash. If so increase your idle speed until it does not "cam" as much. If you have a smooth idle then it probably isnt that though. The sound can carry all through the bellhousing. I chased a noisy clutch once to find all I needed was to set my idle at 1000 instead of 800.
Bill

I have destroyed the throw out bearing in my 71 MGB and have replaced it with the kit from moss it looks like its on its way again. i did shave the fly wheel to take some weight off it. does anyone make a GREAT bearing so i dont have to keep doing this or does someone have a short cut to pulling the engine? Thanks, Don Baker
dab donald a baker

Don, Doug Jackson at mgamgb.com makes an adjustible pulloff kit.It allows you to set the clearance between the throwout bearing and the pressure plate so that the two are not is constant contact which leads to early failure. I have been using this kit for several years on a supercharged B with a heavy duty clutch and roller bearing with very good results. These roller bearings are unfortunatly NLA. RAY
RAY

Thanks for the advice. Just to followup the pressure plate was resurfaced. The chatter seems to be felt down the drive shaft and you can fee the rear wheels sort of bouncing. Rear springs and all bushings were replaced during the restoration so I dont think it is a rear end issue. I would be interested in hearing more about the adjustable pull off kit that ray mentioned.
Drew

Drew,

"The chatter seems to be felt down the drive shaft"

Do you know if the driveshaft is balanced? If you or a PO have replaced universal joints or flanges the shaft should have been re-balanced. Of cours, a thrown balance weight could cause the same symptoms.

Not sure if that would cause the rear wheels to 'bounce', but a badly balanced shaft could throw enough force to give that impression.

Regards
Roger
Roger T

Drew, The above mentioned kit allows the slave cylinder to be moved forward or aft to allow for clearance between the throwout bearing and pressure plate. It mounts externally and is an easy installation of less than a half hour. RAY
RAY

Just as brakes can squeal and cause a fuss if they aren't used very hard (they get a glazing on them), clutch discs can get similar problems.

Before you tear it all down and buy new parts and pay a machinist, do something like this:

Pull up to a curb, set the handbrake. Put the trans in second or third gear. Let the clutch out enough to get it kinda hot, keeping the revs up a little and making sure you don't jump the curb. Do this a few times if you need to.

You may find that the clutch works much smoother now. If not, you had fun.
Tom

This thread was discussed between 28/05/2008 and 03/06/2008

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