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MG MGB Technical - Clutch Release/Throwout Bearing

Just over four years ago, following the break up of a couple of carbon clutch release bearings in quick succession in my '72 Roadster, I decided to go for a roller release bearing instead. I bought a three piece clutch kit off eBay. Interestingly, in the centre of the clutch cover it ended in the fingers of the diaphragm, like many modern cars, rather than the usual arrangement of the flat plate the crb pushes against. The crb housing was made of plastic and had a curious arrangement at the pivots in that there was no room for the clips and the pivots were flat at the front so the bearing couldn't pivot. I took this up with the vendor who assured me that was how it was supposed to be. One just pushed the bearing pivots into the release arm. I wasn't convinced, so filed the pivots round and removed sufficient plastic at the sides of the bearing to take the standard clips. Everything re-installed and all good, if with a slight whirring noise in background.

About 10 -15,000 miles later and an unconnected engine malady means engine out. Despite lack of miles, my thinking is replace clutch again on the price v potential future hassle argument. Bought HK9679 Borg & Beck clutch kit from a different supplier. Whilst clutch cover looks like standard MG arrangement this time, the crb looks like the same arrangement as in my previous kit. The fitting instructions point out that there have been a number of queries from customers on this arrangement, but that the bearing just push fits into the release arm, rather than use clips. The front of the pivot is squared off again. Maybe with this one the bearing can pivot slightly, but I'm still a bit wary.

Has anybody had any experience of the these bearings or would like to comment?
Peter Allen

Not that style of fitting, both graphite and roller have been able to pivot.

But I have had both graphite and roller fail. Carbon broke up as the casting had worn right through, and the roller started making noises soon after fitting. They changed from time, then suddenly got much worse so the engine had to come out.

Really annoying as the friction plate wasn't even half worn, whereas the roller bearing had completely broken up as below. I started looking at the release arm and it was off being concentric with the first-motion shaft by about 3/16" http://www.mgbimages.uk.gridhosted.co.uk/images/clutchr305.jpg

Now a graphite bearing is supposed to be able to cope with some misalignment, but it seems not this much. And although roller bearings are used as original equipment on cars like the 1500 midget and the V8, they have a completely different mounting arrangement that involves a guide tube which keeps the bearing concentric with the shaft at all times - 'D' in http://www.mgbimages.uk.gridhosted.co.uk/images/v8rb5.jpg
and are less able to take the continual sliding across the cover plate that misalignment results in.

So a roller bearing in an MGB is not the be-all and end-all it is made out to be.



paulh4

Thanks, Paul. In the end I spoke to the Borg & Beck technical service department and they confirmed that this was how the new roller bearing was supposed to be fitted and operate ie a press fit, rather than clipped, into the release arm and that there would still be a small amount of movement at the pivot. Still not sure why the design had to change, but hey-ho.
Peter Allen

Peter,
you could ask them why it's changed, I found Borg & Beck and parent company First Line to be very responsive and helpful when I was enquiring about their oil filter for a mate.

As the MGA has a different clip and Spridgets two different clips perhaps it's a manufacturing rationalisation(?).
Nigel Atkins

Peter,
a mate has recommended for peace of mind that you also fit the spring clips, part number 7H3048, 95p each.

Photo below shows the clip and roller bearing that are supplied with a genuine AP HDR (GCK109HDR) MGB clutch kit.



Nigel Atkins

In use the pivoting action is very little as the release bearing doesn't move very far from its 'at rest' position to where the clutch is fully disengaged. But you have to be sure that it can pivot freely at both positions or one side will be pressing on the cover plate more than the other and I can't see that doing any good. You can't tell where that is until the engine and gearbox are back together, by which time it is too late to see.
paulh4

Nigel - Thanks for the tip on the spring clips, which are of course different to the standard MGB ones. The AP bearing in your photo appears to be the same as the B&B one (even including the holes for the clips) - you can see my point about the bearing not being able to move very far, because of the flattened bit on the pivot. However, as Paul says it doesn't need to move that much as fully released to fully engaged is only a few millimetres.
Peter Allen

“In use the pivoting action is very little as the release bearing doesn't move very far from its 'at rest' position to where the clutch is fully disengaged. But you have to be sure that it can pivot freely at both positions or one side will be pressing on the cover plate more than the other and I can't see that doing any good. You can't tell where that is until the engine and gearbox are back together, by which time it is too late to see.”

Not forgetting that the position of the pad and, therefore, the angle of the release arm will change as the friction plate wears.
Dave O'Neill 2

Peter,
I noticed it showed the wire type spring clip which I think of as a MGA type clip but it was also fitted on Spridgets.

As the press would say, I got the tip "from a reliable source" (and not anyone associated with The White House).

Your fork arm may well have the grooves for the wire springs or you can careful add grooves.

Unfortunately I know that clip quite well and at one of my far too frequent clutch changes I think only one was found fitted so I'd suggest you use the belt, braces, bit of string and chewing gum approach.

I know too about the variability of the quality of parts and have had a release fork crack making the clutch inoperative as well as the three parts of the clutch fail. So I'd suggest you cover whatever might be necessary but don't replace any good quality parts already fitted that have a good length, of good functioning, serviceable life left in them.

The photo reminds me - check the bush in the fork arm for wear.

Good luck.

Nigel Atkins

Thanks, Nigel. Yes, I got a replacement release arm bush, having forgotten to do it at the last clutch change. The arm does wobble, which maybe what did for one of the failed carbon bearings in times gone. This whole fitting issue is maybe something to do with the switch to a plastic housing ie if plastic it can't pivot too much otherwise it'd wear out toute suite.
Peter Allen

Peter, I see your point, perhaps you should go with the fitting instructions to the letter as no one, including me, has replied specifically with experience of the plastic housing. IRCC from looking recently Borg & Beck offer a 2 year warranty(?) and
. Original Equipment pedigree
. Technical test facility for quality control, product development and technical support

Scroll down to Classic Clutch on this page - http://www.borgandbeck.com/Products.aspx#ClutchComponents
Nigel Atkins

The real issue with clutch parts these days is the poorly made fork pivot bolts and bushings, which are all made to the wrong dimensions and allow the fork to slop around radially instead of just moving back and forward. This causes significant extra wear on both carbon faces and roller bearings

On my next engine out I plan to move to a concentric hydraulic system

Dominic Clancy

I found you can take that slop out by tightening the bolt. In fact you can go too far and cause it to bind.
paulh4

Binding can only be caused by distorting the aluminium casting and pinching the fork. Using a correctly made bolt should make that impossible as the bolt is stepped.

The problem is that on new ones the bolt shank is fractionally undersized, and the bronze bushes are not only a loose fit in the fork, but have too large an ID for the undersized bolt, so the fork is not held correctly and is drooping slightly from its correct location, so is off centre on the pressure plate. This is with brand new parts.

I have a gearbox refurb lined up for a friend in a couple of weeks, and am waiting on a specially made set of bolts and bushes to avoid this issue with these parts.
Dominic Clancy

This thread was discussed between 03/09/2018 and 16/09/2018

MG MGB Technical index

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