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MG MGB Technical - Clutch problem

I am starting to get an occasional grinding, rough pedal action on my 71 roadster, suspect it is the thrust bearing, it isn’t there all the time.
I replaced the clutch with the thrust about 5 years ago when doing an engine rebuild so it has not lasted to well as I only do about 1000 miles a year. It’s also getting a bit noisy as after a run and is all warmed up on tick over it rattles but disappears when the clutch pedal is depressed. If the clutch has to be replaced is the easiest way to remove the engine or just the gearbox?
I don’t know what make of clutch I fitted but would like a recommendation for good quality replacement, if it comes to that. Trev
Trevor Harvey

Does sound like the release bearing, BT, DT. Having been involved with both ways I'd only ever take just the engine out for a clutch, and I'd do that first even if the objective was to get at the gearbox.

In any event when they are apart check the alignment of the release bearing to the first-motion shaft. Mine was way out and wrecked a graphite bearing and then the replacement roller bearing and cover plate. I spent some time altering the arm to get them aligned correctly, used a graphite bearing this time, time will tell.

I know roller bearings are used on modern cars, also the V8 and midget 1500, but they have a guide tube to keep the two aligned which the 4-cylinder MGB doesn't




paulh4

I agree with Paul - just take the engine out and leave the gearbox in its place. I don't think it is possible to remove the gearbox on its own from underneath. Even if it is possible, it is a very heavy lump and would be difficult to cope with from under the car.
Mike Howlett

Agree with above. Just take engine out. You can't take gearbox out by itself without chopping out a crossmember. I got through a couple of release bearings in quick succession, so feel your frustration. One failure, I think, was partly down to a semi-seized clutch slave cylinder that threw me as it would right itself. While engine is out, as Paul says, check alignment. Also that bushes and bolt on clutch release arm in good nick. I always replace gearbox front oil seal as well while everything's apart. Now have roller bearing - probably about 20/30,000 miles in so too early to say on reliability, but certainly better than 5000!
Peter Allen

There was a dodgey batch of thrust bearings on the market a few years ago. You might’ve got one of these or it wasn’t put in correctly. Either way it is engine out, inspect and check/replace items as suggested. Not a big job if you have the gear and do it yourself, expense if you pay someone!
Mike
Mike Ellsmore

I have seen someone take the gearbox out without chopping the crossmember. Problem is to do it he needed to remove the remote. OK on the way out but not to flash to replace onto the top of the gearbox in situ, so he ended up having to remove the engine after all.

There is another less common grinding noise that can occure with the clutch. Though isn't the clutch itself but a dry cranksft spigot bearing. It is easily differentiated, it occurs only while the clutch is being slipped (so when relative movement between 1st mo shaft and spigot bush). Not present when the car is stationary and the clutch is depressed fully.
Engine still has to come out, but it is useful to know what you are looking for/needing to check, expecially if the expected culprit looks OK.
Paul Walbran

That can apparently be done with the 4-synch without OD, but that's all. But having read the description http://www.mossmotoring.com/pull-mgb-engine-read/ I really didn't think it was worth the effort fiddling about.

I've also seen someone say theirs has the fixed crossmember converted to removable, done so neatly he thought it was factory. But he didn't post any photos.

paulh4

Re clutch changes, I remember my late Dad extolling the virtues of being able to take a box out from inside the car a la Morris 1000. However, I don't know if it's an age thing (mine!), but being able to take engine out now seems like an easier option using mechanical handling ie hoist, not that we can do it anyway with the B. Mind you, a Morris 1000 box is a fraction of the weight of an all synchro B box, so probably a lot easier to move around.
Peter Allen

So it looks like an engine out job hope it can hold out until the autumn. I would replace the whole clutch and as far as I know it would come with a release bearing so what make to go for as maybe the roller bearing might be the way to go. The one I fitted previously was a graphite if it is the problem it has not lasted long.
Trev
Trevor Harvey

HELLO,

I saw a swap replacing carbon of former bearing with
1992-07 Honda Civic throwout bearing.
It seems an easy task but I do not know reliability of it.

A WEB seach will give you full procedure.

Cheers,

J.G.C.
J. G. Catford

The problem with the graphite release bearings a few years ago was that the graphite was pinned into the casting rather than bonded as previously, and they had a reputation for breaking up quickly. They vanished fortunately, but in the last few months there has been several reports of non-pinned bearings breaking up, since I fitted one in 2016.

It's a bit of a conundrum. If your bearing is concentric with the first-motion shaft then a roller bearing should be OK, but they can't cope with misalignment as well as the graphite ones can. I've read claims that some roller type (maybe not MGB) have a graphite face to cope with that, which rather defeats spending more on a roller.

Looking at pictures it seems the Honda Civic mentioned is completely different, no pivots for our release arms, so you would have to get or fabricate a carrier from somewhere. The V8 has a carrier, although it's a bit confusing as some sources show the bearing without the carrier and some with, and the part numbers for the two types can be interchangeable.
paulh4

Now that the dreaded roll-pin type Paul refers to has been vanquished (we hope), a graphite bearing should last as long as the rest of the clutch.
In my experience the roller bearing has not had as much life as the graphite one. I suspect it is due to the fact that the clutch arm swings through an arc and so there is only a very small window where the bearing is concentric with the shaft, and in particular when fully loaded (cltuch disengaged) it is at its most off-centre.
Paul Walbran

John Twist says that - and shows the release arm moving through it's full travel without an engine and hence clutch attached to demonstrate. But with the slave push-rod only travelling 1/2" in normal use, and given the different lengths of the release arm either side of its pivot, the release bearing is only moving back and fore a small portion of that 1/2". Even if it is exactly concentric at one position, the change from that between operated and released is only going to be a fraction of that small portion. Lateral non-concentricity is a far bigger problem.
paulh4

This thread was discussed between 13/05/2019 and 14/05/2019

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