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MG MGB Technical - Clutch Bearing: carbon-faced or roller?

Which is better for a 1980 MGB, a carbon-faced or roller bearing system?

I've only had carbon-faced in my MGB and midget, and was wondering if I should try roller-bearing when my engine comes out in the coming month. Thanks...
Kevin

Kevin. I have not tried the roller bearing myself. I have, over the last several years, read about them on this BBS and that information should be available in the archives. What I remember is that, if one is to use the roller bearing, you need the positive retraction kit as sold by Doug Jackson. If not, the roller bearings are in constant contact with the pressure plate and wear far more rapidly than the carbon throw out bearing. Having driven MGs for something over 25 years, I have learned not to keep the clutch pedal depressed at traffic lights, stop signs, etc. Hence, the carbon bearings have lasted me for many, many years. I purchased a new 79 B in November of 79. I drove it for about 65K miles and, when sold (a bone of contention, even today, between my wife and I) the clutch and throw out bearing were working fine. My older daughter learned to drive on an MGB and, when the engine cracked an exhaust valve and had to be pulled, the carbon throw out bearing was still in good condition. As a result, I have kept using the carbon throw out bearings and will continue to do so in my own cars.

As a note, if you are going to buy a "clutch kit", do so from Brit-Tek. The current packaging of the kits, from the manufacturer, is such that the throw out bearing is not padded and oil can get onto the clutch plate from the pressure plate. I spoke with Moss about this and they tell me that the manufacturer is packaging them this way. Brit-Tek is re-packaging the kits to protect the bearing. (One kit from Moss had the bearing in pieces and contamination on the clutch plate.) Also, use some form of cleaner on the clutch plate, like brake cleaner, to make sure it is perfectly clean. The pressure plate also has to have the bearing area cleaned before installing it. Les
Les Bengtson

Kevin,

I have a roller release bearing, without the retraction kit, and as yet it hasn't failed. However seeing as the carbon ones last the life of a clutch and come free with the kit, I would probably fit the carbon one next time.

fwiw.
--
Olly
Oliver Stephenson

Hi Les,

I think you are right on about not keeping the car in gear and clutch depressed while at a stoplight. I have retrained myself to put the car in neutral and leave the clutch alone until I need it to engage a gear, throw out bearings,clutches and slave cylinder seals seem to last longer. Good point ... got my vote.

Alan
Alan

I have long since learned to put the car in neutral at red lights -- just pop it outta gear as you coast into the light. But I must say I don't understand, having only had the clutch out once, years ago. What is coming into contact with what that makes the MGB's clutch bearing more susceptible to wear than it would be in most any other car?
Ted

Ted. I cannot speak for your car. As I remember it, you have a V-8 conversion, a subject on which I have no experience. On the four cylinder cars, the only "return" system is the pressure plate. There is no spring to pull the clutch fork backwards as you will find in most roller bearing systems. Hence, the pressure place, when the clutch pedal is released, forces the carbon throw out bearing backwards, forcing the clutch fork to pivot which causes the actuating rod of the slave cylinder to move the slave cylinder piston backwards into the bore. However, this system can only move the throwout bearing back far enough to maintain light contact with the pressure plate. Not a problem as the graphite bearing is self lubricating and the small amount worn away is insignificant. This is why the clutch system is "self adjusting" rather than having the mechanical ajustment required of the roller bearing type. As the throwout bearing wears, the rod is not forced back quite so far as it was previously.

This is the reason given for problems with the roller bearing. (Again, let me point out that I have no personal knowledge of the roller bearing system and can only pass on what others have written.) The roller bearing is designed to be withdrawn from contact with the pressure plate by some form of spring mechanism. It is not designed to run in constant contact, even light contact, with the pressure plate. Hence, we are told, the constant contact keeps the bearing spinning far beyond its intended design and, without some form of modification, such as is sold by Doug Jackson, will begin to seize up. Not having a face of self lubricating design, it will then wear the pressure plate excessively and cause a loud squeeling sound. This is the theory and the posted experiences as I remember them. I also remember a couple of people who used the roller bearing, without any form of adaptation, and reported no problems. However, since I know the carbon bearings will hold up to over five years and 65K miles of severe usage (I was a lot younger then), I recommend the carbon bearings unless one is willing to experiment and, possibly, have to pull the engine and tranny to replace the clutch and roller bearing in a relatively short amount of time. Les
Les Bengtson

Last July 4th my carbon faced throw out bearing failed with less than 30K miles (Iwas told) on it. I had only owned the car for the last 2000 of them. In hind sight, I had no apparent problems except engaging reverse, which sometimes proved difficult. Being my first MG, the previous owner told me this was typical, which I have learned isn't true (with a new bearing & clutch assy.) The day the bearing completely failed I was on a 130 mile long trip with no problems for the first 120 miles. When I had removed the engine, the bearing had worn off all the carbon and had dug into the steel backing, cracked the contact area of the pressure plate and destroyed the springs on the clutch. The clutch had a lot of material left ot it. I don't know how the PO drove the car, I know I will follow the advise in this posting and use neutral at each stop light. I wasn't sure about the roller vs. carbon bearing last July, so I went with the tried and true. Hopefully with good habits, I will reach another 60K miles. I met someone this week who is only on his third clutch in a '67 B with over 400 K miles. The body is beat (He drives in snow and sleet in New England) but he swears the motor hasn't been rebuilt, and has owned the car since 1970. Amazing!
Joe

“Not having a face of self lubricating design, it will then wear the pressure plate excessively and cause a loud squeeling (squealing) sound.” The throw out roller bearings I have used do have a wearing carbon surface. You should have no problems with the roller bearing.
Bob Ritter
Ribert Ritter

Thanks to everyone for their responses... I think I'll stay with carbon faced for my next clutch.

Fortunately -- well unfortunately, really -- I learned the out-of-gear trick after going through my Midget clutch when I was 16 and learned to drive a stick shift on the car!

Have a great weekend all,
Kevin
80 MGB
Kevin

I've pulled about a dozen roller release bearings from various B's over the years, and only a couple of them were really quiet when pulled. I recently had one go bad after less than 500 miles with the standoff kit installed. It began whining when engaged from the beginning, then screeched for a dozen or so shifts, then locked up on the way home. The carbon faced release bearing it replaced was still serviceable after 80k miles, and there was no play in the fork bush, so I attributed it to a bad decision and won't use one again. The roller bearing had a black teflon facing which probably saved the pressure plate. I haven't seen a carbon faced roller-style bearing such as Robert describes.
I've pulled at least a couple hundred carbon release bearings in the past 40 years, and only a handful ever made any noise, or gave any warning of failure - imminent or otherwise.... some had worn down to the point where the release fork was acting as the bearing, and had been ground to a razor edge - One owner had inserted an extra piston in the slave cyl to get the additional extension to keep the car going until he could get it fixed.
With good driving technique and a bit of luck (leak-free seal) there's no reason that a good quality clutch and release bearing can't go 125k trouble free miles miles or more. My 86 Trooper has gone 150k since the last reman clutch change - it shows no sign of slipping, and hasn;t needed an adjustment in a couple years. I don't off road, but I do pull an occassional 30 foot horse trailer, and every saturday we load 1000 pounds of feed in the back, so it's not exactly babied....
mark

Factory V8s do have the roller-bearing release bearing as standard, 4-cylinders cars didn't. The last time I changed my clutch I fitted one (whether of the same design as the V8 one or not I don't know) and it started squeaking just as pressure starts to build in the fluid line after just a couple of thousand miles. It's been alright ever since, and it does act as an audible warning if ever I happen to rest my foot on the pedal while stationary, but I would never bother again. Why not? I just can't imagine reusing an old release bearing, even the roller type, when I change the clutch, and I have never had one go *before* the clutch needed replacing anyway. It's a complete waste of money.
Paul Hunt

My '68 B had the roller bearing installed by DPO. When I yanked it, there were substantial grooves worn into the diaphragm spring, and it was noisy.

My '67 B still had the carbon bearing, but it was worn lopsided, so that one edge was real close to base metal. Since there was non-concentric wear on the spring, I decided it was due to extreme wear of release fork pin and bushing. My advice is to make sure you replace the pin and bush if at all suspect.

In both cases I replaced with carbon, but haven't had to go into either as yet. So, don't have any hard results. But no noise and no problems so far.
Terrence Goodell

This thread was discussed between 03/01/2003 and 06/01/2003

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