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MG MGB Technical - third clutch throw-out bearing

I am about to change my clutch throwout bearing for the third time in less than 800 miles on my 77 mgb. I am suffering the same clutch judder symptoms when I depress the clutch. The first time I changed the bearing and clutch, the second time I just changed the bearing, since the clutch had no wear. I'd hate to do this yet again, (after this time) and am looking for some advise as to what it could be. I can tell you the second time the throwout bearing did not swivel on the fork easily so I filed the fork so that it would swivel. Could it be that I got a bad clutch replacement, the first time around? Not sure how it could be bad. (Borg and Beck). Anyway I am looking for any advise as to what components I should replace so I do not have to pull the engine yet a fourth time. Thanks
r schwartz

Did you get a heavy duty clutch? Heavy duty clutches are good for two applications - racing and eating throwout bearings. I had a heavy duty clutch in our MGB and went through throwout bearings at a great rate. I finally got smart and switched to a standard clutch and have not changed a throw out bearing in 5 or 6 years. Cheers - Dave
David DuBois

I am pretty sure it was a standard clutch ordered from Brit-tek
r schwartz

Do you mean judder as the clutch starts to take up the drive? Or vibration through the pedal? If the latter is the vibration just as you operate the pedal, or while you are holding it down?
Paul Hunt

r,

Sorry if you already know about this, but the bearing will wear out very quickly if you keep your foot on the pedal. If waiting at lights, you must change into neutral, take your foot off and wait. If you keep it in first with the clutch disengaged you'll kill the bearing.

David
D Balkwill

Yep, already knew about not keeping your foot on the clutch pedal other than shifting, (I didn't want to go through yet another engine pull). I took the car around the block so I could answer Paul's question accurately. Even when I am stopped, when I press on the clutch pedal, I get a grinding noise, and vibration felt through the pedal. Same symptom appears when I am moving but press on the clutch pedal.
r schwartz

That sounds like a bad throwout bearing, one where the carbon portion as been destroyed and there is metal to metal contact between the bearing and the pressure plate.

As others have noted, this rapid bearing wear is unusual with a standard B&B clutch kit.

Two things come to mind. I have seen some of the more recent kits packaged with the throw out bearing in with the other clutch parts, its only protection a piece of oiled paper. Such bearings are frequently cracked when examined closely and would not hold up well in use.

Second thing is the clutch fork itself. Seldom examined, almost never replaced, the clutch forks will wear over time in the areas that contact the two round extensions of the bearing. They will develop a degree of slop which allows faster bearing wear. On the GT I an putting back together, with a new clutch kit installed seven years ago, the bearing face was worn at an angle and one of the bearing retainers has come loose. Fortunately, the fellows helping me with the job were professional MG mechanics, immediately noticed the problem and we changed out the clutch fork before installing a new bearing. But, even then, the bearing has lasted for seven years in a daily driver and there was no metal to metal contact between the bearing and the pressure plate.

You need to find out what is wrong with the system and causing the accelerated bearing wear. Also, check out the hydraulic system especially the flex hose. If the pressure is not fully releasing, rapid bearing wear would be expected as an indication.

Les
Les Bengtson

In 1960 I took a factory course at Wolfsburg Germany on the VW beetle. Typically Germans do not have a sense of humor but in thw VW service manual there is one bit of levity. It pertains to clutch throwout bearing failures.
Fist thing was to install a roller bearing type in lieu of a carbon one.
If that failed they suggested to tell your driver to find another foot rest.
The same things apply to our carbon throw out bearings,
Find another foot rest.
Sandy
conrad sanders

Like Les grinding and vibration through the pedal when depressed is pointing to problems with the release bearing and/or fork. My roadster had that for some time before one side of the release bearing casting wore completely through and broke. I have no idea why so much wear should have occured just on one side, it's now been 40k and 14 years and so far so good. It's not something silly like the friction plate on the wrong way round? I know this causes problems but not what they are. I've just changed a clutch on another car and was so paranoid about that I actually removed the cover plate after fitting to double-check. There is another current problem with carbon bearings and that is some have the carbon pinned into the casting instead of being bonded. These are very poor and cause the carbon to break up very rapidly. Someone else had one of these fail in about 8000 miles and there was nothing but carbon dust in the bell-housing. They are very easiy to spot, clearly having a roll-pin in the side of the casting see http://www.mgb-stuff.org.uk/wn_clutchframe.htm click on 'Release Bearing' and scroll down to the update.

Roller-bearings were recommended for the MGB at one time and in fact I used one, but they are a waste of money as I wouldn't leave an old one in there when I next changed the clutch. They don't seem to be available any more, but they are standard on the V8 and 1500 midget/Spitfire.
Paul Hunt

All of the above but also. Are you certain the clutch driven/pressure plate is centred? If off-centre, even by a very small amount, it may produce the 'judder' sensation you are experiencing. The workshop manual specifies that the accuracy of the alignment of the face of the plate must be within 0.015 inch (0.38mm).

In the same area, the bush is sound?

I know that would necessate an engine out to service but you will probably have to do that in any event.

Not sure about the results of filing the bearing holding arm surfaces. I'd make sure you had a good fit there with any new cup.

Regards
Roger
Roger T

I have seen many times - a Hillman release bearing with holes in the end of the pivots. These are too wide for the MGB fork. As he said he has filed the fork to ease it a bit. Has he fitted thelate the wrong way round. This will cause a grinding noise when starting to engage & will more than likely judder as well. If the bearing is wearing away to quickly perhaps the spring in the master cyl has broken & therefore not releasing properly as the bearing will always be under pressure.
Garth
Garth Bagnall

If the master piston isn't coming back far enough it won't clear the bypass hole and as the fluid heats up and expands it will press harder on the release bearing that it should, and this will cause rapid wear. This could be due to a problem in the master itself, but there should be a spring on the clutch pedal pulling the pedal and master push-rod, at least, all the way back.

But bear in mind the spring in the *slave* cylinder is always pushing the release arm, release bearing and cover plate into contact to take up play and give a consistent release and biting point. This *isn't* a problem.
Paul Hunt

I second Paul's comment re ensuring that the friction plate is in the correct way - the hub is offset axially. Centering of the plate is not usually of concern - if you can get the splined shaft in then it is close enough and will certainly centre completely once the clutchis first depressed.

Good luck and keep us informed of progress as this is always a learning experience for all.

Regards,

Barry
BJ Quartermaine

Thanks everyone, I read through the thread, some of the things I am thinking, and really I am just testing my logic.

1. Can't be the clutch disc in backwards, it ran several hundred miles and clutch oeprated smoothly. I figure that if I installed the clutch disc backwards, this would have been obvious at the onset
2. Can't be the flex hose to the clutch. I can see not being able to disengage the clutch, because the flex might balloon, but I can't see how a bad hose could prevent the slave cylinder from going to the home position
3. Now from a visual inspection, it seems like the slave operates freely, and responds well to the pedal, so I am discounting a bad spring in the master. If the spring was bad I assume the slave would not retract as readily

Maybe I'll find a pinned throwout bearing. As I said, not sure if I am correct on all the above points, appreciate any challenges on my logic
r schwartz

I have also had a few carsin where the clutch hose had perished inside & bits had blocked the bleed off hole in the master cyl. Check to see if the slave piston can be easily pushed back.
Garth
Garth Bagnall

Can't fault your logic, but do as Garth says. If you can push the pushrod and hence piston further into the slave cylinder with steady pressure (I wouldn't say easily, it does need some force and only moves slowly) then it isn't the hydraulics. Watch out you don't push the slave piston back so far that the master overflows.
Paul Hunt

r,

I've never seen it happen myself, but have often heard of brake hoses failing on the inside, and then causing a brake to drag. The failure mode is not that it balloons, it is the inner wall of the hose failing and then operating like a check valve that doesn't let the fluid return. I think it is unlikely, but I wouldn't rule it out with out checking.

Charley
C R Huff

Indeed, and not being able to push the slave piston further into the cylinder would reveal that.
Paul Hunt

I used to think that the deteriorating brake hose was a myth, but on my daughter's Dodge Neon of all cars a bad hose caused the caliper to stick on heating up the wheel so much that it melted the plastic wheel cover! A guy in our local MG club had to replace 3 release bearings in about 2500 miles. In the end he discovered that a replacement slave cylinder push rod from Moss was about 1/4" longer than the original after he was comparing everything on the 3rd time out.
He put the original back in and no more problems. Maybe it was causing the piston in the slave cyl. to bottom out in its bore? Just as a matter of course I would change the flex hose anyway this time, they are not that expensive.

Ralph
Ralph

Paul,

Yes, indeed. I'm with you. I just wanted to make the reasoning a bit more clear by connecting the dots.

Charley
C R Huff

Thanks everyone, I was able to push in the slave, manually, so seems like it can depresurize OK. Off to buy a clutch, the fork, a B&B clutch set, and a hose. Thanks again for the help.
r schwartz

This thread was discussed between 06/07/2008 and 17/07/2008

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