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MG MGB Technical - Lookijng for help with transmission problems

(I started writing this post thinking I had only 1 question - but it seems to have turned into rather a lot. Any help or advice that can be offered is very much appreciated!)

I'm trying to diagnose a problem, and would appreciate if anyone can help me with this.

My B (77) has been jumping out of third gear a little recently. The clutch is very high, and I think I've heard/felt it slip a few times. This leads me to think perhaps it is worn out. Can the car jumping
out of gear (or being harder to get into gear) be caused by this, or might there be another reason?

In addition to this, I often hear a clunking noise coming from the tranmission - one way to demonstrate
it is to sit at the bottom of second gear, give it a little acceleration and then take my foot off the pedal. Thats when I hear the clunk-clunk sound. It seems to come from futher back, but it's very difficult to tell. I had a look at the prop shaft, and can't see
any obvious play anywhere. Should I be concerned about this, might it be related to a worn clutch, or is it just one of those noises that we have to learn to know and love?

If I do need to replace my clutch, how much should I expect to pay a garage? Parts I know about, but I suspect that being an engine-out job the labour could be the killer. What would the expected lifetime be
of a new clutch?

A final question - if the clutch is wearing out, what might go wrong with it if I am on a long motorway drive? Is that likely to cause problems, or is it more likely to fail driving around town?

thanks,

Alistair
Alistair McEwan

The clunk is probably a propshaft U-joint problem. With the car securely supported off the ground, grab the shaft near either end and atttempt to wiggle/ twist it. I bet you find some slack or play due to worn u-joint bearings. They are a common failure point, and I think the replacement bearings can be had with a grease fitting.

I'm not much help on gearbox internals, but I would first check that excessive play in the tranny/motor mounts are not the cause of your problem. Is it possible that the drivetrain twists under torque and bumps the stick out of gear? Unlikely, but easy to check - just feel for movement on the stick when you appply/release power.

Good luck,

Brian
72 BGT morphing into 60 degree V6 3.4 FI camaro drivetrain
Brian Corrigan

The clunk is the rear axle and is a common fault - two of the thrust washers are fibre and wear away completely, the other two are copper and wear thin.

Replacing the washers usually effects a cure. You can test for this by jacking up one rear wheel and, with the handbrake off, turn the other whell to and fro - the clunk is quite audible and you will feel it. Watch the propshaft at the same time and you will see a delay in it moving - if the clunk happens before the prop moves it is the axle - after the prop moves it is the shaft.

The clutch sounds worn out - try accelerating hard in a low gear - if the engine revs rise out of proportion to road speed then the clutch is slipping. A high engagement point also indicates a thin plate.

The gear problem is more likely to be a weak or broken detent spring or worn syncro hub.

Clutch replacement is expensive because of the labour in removing the engine. Expect to pay for 4 hours work minimum - about £200 plus parts.

I charge £150 plus £55 for a 3 part Borg & Beck clutch.

The clutch will last from 20,000 to 100,000 miles plus depending on use. Lots of motorway work means less wear - lots of town driving in traffic means more wear. The carbon thrust bearing will wear out quickly if you ride the clutch pedal or hold it depressed at traffic lights etc.

Finally the wear on the plate will mean that you will get less drive to the wheels and you won't make it up hills so whether in town or on the motorway, hills are the killer. You will also have the rivets in the clutch ( if it is taht type and not a cheap bonded sort) gouging into the pressure plate first (not to serious as this gets replaced anyway, but eventually into the flywheel which means more work and cost - another £50 for a refaced one with new ring gear.
Chris Betson

Not sure what Chris means by 'low' gear but IME clutch slip is first observed in top gear.

The first problem you mention - jumping out of gear - is something else again and could be selectors, detent springs/balls, synchro hubs, baulk rings, or the gear wheels themselves i.e. all internal to the gearbox.
Paul Hunt

Chris sounds to be 'on the money' as far as causes (and solutions) are concerned. As far as the clutch is concerned, it's very much an outsider but I wondered if there may also be a problem with the hydraulic's? Is there plenty of fluid in the reservoir, check for leaks, air etc?

Bob
Bob Everick

Paul, yes I meant a 'low' ratio - 4th or 3rd gear.

Thanks for clarifying.
Chris Betson

Alistair,
My clutch pedal is high also. In my case we discivered (whilst rebuilding the complete clutch hydrolic system) that the master cylinder push rod is overlength. It has been cut and had a short extension welded into it at some point in the past. Just why I am not sure. Certainly the hydrolics were shot so it may have been an attempt to overcome that. Also, the clevis pin is showing some slop. Additionally, the clutch pedal has sideways travel in it, about a good inch at the actual pedal. This would act to extend the length of throw required on the push rod and may have been the reason. Of course any or bits of all these factors may also have been the reason, especially because it may have been the anly way of overcoming a problem with uncertain cause.
With the hydrolics all done, the gear change not sugesting undue wear on the cutch plate,no sign of any slippage, I will have a look to try and discover the cause of the sideways movement in the early new year. I have a feeling that any attempt to return to normal push rod length will start there.
Hope this may help you identify your issues. Good luck with it all, and a very merry Aussie Christmas.
Regards
Roger
Roger

This thread was discussed between 19/12/2001 and 21/12/2001

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