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MG MGB Technical - Roller clutch release bearings

Read a great deal about these online and there seems to be a mixed feeling about them, particularly the plastic mounted versions currently available.
I am in the process of removing my engine gearbox, mostly to address the wear in the gearbox but also to freshen up the engine.
while its out I'll sort out and service all the extransous bits, including changing the clutch and bearing.
Its it worth changing it to roller and if so which one?
Neckieman

If you have a roller bearing throw out you will need to have a pull back spring to insure that the bearing is not in contact with the clutch thrust surface. Without that, the roller bearing is spinning constantly and has a rather short life.
Cheers,
DW DuBois

Our Heavy Duty clutches are supplied with roller bearings, we have had no failures reported and we have been using them for around five years on all engines now. Some folk keep the old carbon thrust, others use the new plastic mounted roller release bearing.
There was a period a few years ago when some standard clutches were supplied with pegged carbon thrusts which broke up, hopefully all these have been sorted now. We never had the problem with Borg and Beck or AP clutches.

Peter
Peter Burgess Tuning

Don't bother. I fitted one with a new clutch about 20 years ago and it has given me nothing but trouble, almost from the word go. I read about the need for a pull-off spring, asked the supplier (MGOC) and they said it didn't need it and they hadn't had any problems reported before.

In theory they SHOULDN'T need a pull-off spring, V8s and midget 1500s have roller bearings as standard, and they don't have them. If you do have a pull-off spring, then you also need to have a stop to limit how far it can pull the release arm back or you will find the biting point very close to the floor if not below it.

My problems have been a slight wittering noise just as the pedal started to apply pressure to the bearing and hence the cover plate, and just as it released pressure. That went on for years, until suddenly I noticed it didn't do it any more. Then two years ago it started making more of a shriek while the pedal was partially or fully releasing the clutch. Then this year I've noticed that it's started dragging the idle speed down as the pedal is depressed, something it has never done before, and neither does the V8. But note that a number of people say their does this with carbon bearings.

So even though it has only done 50k over 22 years and I've never worn any clutch out from new before (V8 100k and counting), I'm going to have to get the engine out to replace a clutch with years of life left in it, in order to go back to a carbon bearing. I'll obviously stay with the correct bearing for the V8, but would never use an after-market roller bearing in the roadster again.

Yes pinned bearings (pic attached for identification) were a problem at one time - known about 10 years ago, but they should all have been used up or discarded by now.


paulh4

I've been running a roller release bearing, in my supercharged '67 B, since '93 with no problems whatsoever. It came with the Heavy Duty Borg and Beck clutch that I installed at the same time. I'm a big fan of them and always recommend them to anyone about to replace their clutch assembly. RAY
rjm RAY

Guys,
opinion seems divided at best!
I wasn't aware of the carbon issue, my last MGB was sold over 25 years ago and only recently bought another.
If anyone is recommending a roller can they specify the particular one they recommend.
My thoughts are moving towards a borg and beck kit including a carbon bearing as unless I am sure a roller will have a longer life I am not sure I would take the chance.
One that is definitely going to last is what I am looking for.
Neckieman

I installed a heavy-duty clutch in our B/GT in 1995 (Borg & Beck) with the roller release bearing like Ray. No issues to date. I haven't seen the new arrangement, but wouldn't hesitate to install again if needed.

Regards,

Larry C.
Larry C '74 B/GT

" unless I am sure a roller will have a longer life "

Well that's the point. When I realised - when I first started getting problems with it - that when I came to change the clutch again I was hardly going to put the same roller bearing release bearing back in, so it was a complete waste of money. The only time you might need a roller bearing is if you habitually 'ride the clutch' and cause premature failure of a carbon bearing, something that I don't suffer from.
paulh4

The carbon throwout bearing was obsolete 50 years ago. It's a primitive design that causes the engine to slow down when the clutch pedal is depressed due to the friction between it and the pressure plate. Who else still uses this layout? No one. The roller release bearing has been around for decades with an excellent service record. It's your car and you have to make the final decision as to which one to use. Choose wisely. RAY
rjm RAY

I had a couple of carbon bearings break up (not the aforementioned unreliable pin type) in fairly quick succession, the last one was in France on the way back from Le Mans. However, the latter one may have started to fail after the slave cylinder seized a couple of months previously (a most strange fault, initially leaving me stranded with no drive and then slowly releasing itself back to normal). Anyway, I went for a roller bearing the next time, bought as a complete clutch kit of eBay. The assembly is a bit of a strange one to my MG orientated eyes as it follows the modern practice of having no centre to the cover plate - all the fingers of the diaphragm just kind of end in the middle. Also the roller bearing is just supposed to be a press fit into the clutch arm. I wasn't sure about this so adapted the clips from the old carbon thrust.

Only done about 10 - 15k since so a bit early to come up with findings, other that it's been noisy from day 1. A bit like the sound of a gearbox bearing on the way out. You know, that whirring sound. Other than that, fine! Of course, as Paul suggests, if you're going to replace any of the clutch assembly, you'll do the lot at the same time. Even on modern cars all three components are replaced together, the release bearing being a marginal cost compared to the labour element and the cost of the other components.
P A Allen

I pulled the engine out tonight and split the gearbox off. I found what looked like a brand new B&B clutch and cover and a completely work out carbon bearing, just about to start rubbing on the metal surround.
The car was subject to a body rebuild a couple of years ago and had only done a few hundred miles since so I expect the clutch was done then, however either the bearing has worn out in a few hundred miles or it wasn't replaced at the time.
I'll probably just leave the clutch in there but definitely need a new bearing, still making up my mind on what!
Neckieman

I've used rollers in all my cars with no noise and no problems....
I'm thinking that the throwout lever arm bolt and bushing, may be worn, leading to more contact of the bearing...
I always have replaced ALL of the mechanical parts while I'm in there...Not that much money , compared to the expense of going back and re-doing the job. (Just my 2 cents).
Edward
E B Wesson

My experience of roller release bearings was short lived, I fitted a B&B clutch kit to my B but only used the plate and cover, and a roller release bearing which I bought from the MGOC, after I had fitted it, I started the vehicle to try the clutch, and on pressing the pedal there was a very loud noise coming from the release bearing, after a road test it still the same, so I replaced it with a carbon thrust, I was not very happy with it, doing two clutches in one day was not my idea of fun, what was strange was that when I contacted the MGOC to get a refund on the bearing, the voice of the man in the stores, did not sound surprised when I told him the problem, which made me think, this was not the first one they had back faulty, A.T
andy tilney

I'm not disputing peoples experience of reliable roller (or should that be ball) release bearings but you may wish to watch John Twist’s video on the subject.

If you’ve got 6 minutes to spare click on the link below or copy the link into your browser.

www.youtube.com/watch?v=4KIdkOWVcGg

Bob
R.A Davis

Interesting, particularly saying the Midget 1500 has a component that keeps the two parts concentric. I wonder if the V8 has that as well, as it also has the roller bearing as standard. That sits in a carrier, which is maybe what keeps it concentric.

As far as wear in the release arm and pivot goes, it should be noted that the slave cylinder has a spring behind the seal, which is constantly trying to push the piston out of the cylinder, and this is constantly pressing the release bearing - lightly - against the cover plate. However wear in the release bearing and/or pivot may be causing the release bearing to bear against the cover plate unevenly when the pedal is depressed, as well as non-concentric, and that may be the cause of problems with both roller and carbon types. It's something I'll be looking at carefully when I do the roadster clutch, as it had catastrophic release bearing failure in that the casting broke up soon after it came to me.
paulh4

Mr Twist makes perfect engineering sense. The V8 release bearing carrier is a clever design in that it allows the bearing to stay square even though the fork moves through an arc. When replacing just make sure the bearing is paired with the right pressure plate.
Allan Reeling

Sorry I'm prattling on, completely forgetting both my V8's have LT77 gearboxes. Don't know how much of the above is applicable to the standard clutch.
Allan Reeling

The roller bearing I have has a carbon face to address the issue implied by John Twist.

But if PB is using them regularly without problems then I am more than willing to believe that they are fine, and will check with Peter to make sure I have the same unit before fitting with the new engine (complete with his supercharger spec head).

I have to say I have sometimes found some of John Twists videos, though backed by years of experience, are a bit shade-tree mechanic, and there are certainly areas where a more refined engineering approach that is not hamstrung by production cost constraints can (and does) offer a better solution than the traditional approach.

dominic clancy

Had a look at my new V8 roller bearing today. The bit that faces forwards is plastic, about an inch or so long, and in the shape of a cylinder with the walls only about 1/4" thick. So that's not going to stand any non-concentricity for more than five minutes.

If a roller bearing for the 4-cylinder has a carbon face, then depending on how thick it is, it is still going to wear with non-concentricity.

It takes many years of use to determine whether something is suitable or not - unless it is catastrophically bad and fails within a few miles. As far as those who say they have many years of satisfactory service from a roller bearing, going back to the JT video he does say that at one point near the middle of the travel it IS concentric, becoming more non-concentric either side of that. The release arm with no clutch in position is capable of moving both backwards and forwards a great deal further than it moves in use. If the slave push-rod moves back and fore by the typical 1/2", then the release bearing is only moving a small portion of that given the ratio of the arm. If the point of concentricity is when the clutch is near fully disengaged, then the amount of non-concentricity and hence wear will be minimal. But if the point of concentricity is nowhere near that point, then wear will be significantly more.
paulh4

Twenty three years of hard use has proven the roller release bearing in my supercharged B. I couldn't be more pleased with the performance that it has delivered. RAY
rjm RAY

This thread was discussed between 13/05/2016 and 19/05/2016

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