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MG MGB Technical - Input Shaft Transmission

I found my source of oil leaking from bell housing after pulling engine and trans.
It's coming out past the seal on the front cover plate on the trans.
My question is, should that input shaft have a little play in it? it can be moved slightly in all directions when you grab hold of it.
Is any movement taken up when the shaft mates with engine and spigot bush?

BTW....i did find pieces of the shim in the bell housing, that I believe, was located on the input shaft between lock nut and bearing. how worried should i be about that?

Also, i was experiencing an intermittent odd 'whirring' sound when the clutch pedal was depressed. i just recently replaced the bad throw out bearing with an aftermarket one. I thought i would replace it now with a borg and beck to see if that was the culprit.
Also replacing bush in clutch lever, seems to be a bit of play in that too.
Any other thoughts on where to look for cause of sound?
Dennis Silance

Ideally there should be no play in the bearing (other that the amount necessary to allow the shaft to turn!) Whilst the two shafts are co located through the pilot bearing, there could be play in that, or the rear main allowing the crankshaft to waggle the gearbox input shaft, and stresses inside the gearbox could well be moving the shaft anyway. But bits of shim lying in the bell housing is bad news, loss of that will be allowing the shaft to move back and fore.

Are you saying you still have the whirring with the clutch depressed? Is that before and after you replaced the release bearing? I'd never put an after-market component in that position, too much trouble and strife to replace it again if it causes problems. If you are going to replace it again anyway, then look carefully at all the components and see if you can find any signs of rubbing.
PaulH Solihull

yes, i am paul. sorry for the confusion. if you refer recent previous post by 'Tore Norway' on 'squeaking noise from clutch pedal',i replaced a shattered throw out bearing(also from moss) with an after market one(vic brit) and it was then that the whirring sound started as well as the oil leak. i now have the engine and trans out again and will not use after market replacement.

FWIW....whirring noise definitely had that bad bearing related sound...just don't know which one.

wondering how much of a job it is to replace bearing on shaft.

thanx for your input
DS


Dennis Silance

It's quite a task to replace the input shaft bearing as you will have to dismantle the gearbox to the extent that you remove the mainshaft and drop the layshaft as the first motion shaft cannot be removed until the layshaft is dropped. Then it's a trip to the press to remove the existing bearing and press the new one on. Watch out as there is a procedure for determining the thickness of the front cover shim and this is datailed in the manual. Finally refit the front cover and replace the throwout bearing preferably with a Borg and Beck replacement.
Iain MacKintosh

I read up on this last year when i pulled my engine and g/box. As I understood it the front bearing was designed to have a small amount of play, presumably to help it line up with the spigot bush. The whirring is probably the front bearing spinning in the housing. You will be able to see sign of that when you take the bearing cover off. Crumpled up shim is a common occurrence. The oil seals do harden up and are worn if the spigot bush is worn, allowing the input shaft to "wobble". In fact I spoke to a gearbox "specialist' and he said he "didn't bother with the shims, just used bearing lock!!!!!! I do wonder sometimes!! Being a belt and braces man, I did both!!
Allan Reeling

Oil seal was dry and hardened, had to be removed in pieces.

Any tip on removing spigot bush. it seems to be stuck fast?
i thought i remember it just dropping out of my 1500 midget engine when i had that out and separated and rolling across the floor.
Dennis Silance

Pack the spigot bush with grease, and drive in a shaft that fits the ID of the bush. The grease under pressure will pop out the bush. Failing that, a large tap screwed in will usually extract the bush.

warmly,
dave
Dave Braun

To remove the spigot bush, fill the hole with heavy grease, then get a close-fitting plunger the ID of the bush. Whack the plunger into the grease with a 2 lb hammer and hydraulic pressure will push out the bush.
Art Pearse

Dennis,

Can I ask whether you have a standard 4 speed GB or an OD? If you have a standard 4 speed you may want to think about obtaining a better used one because it is usually much, much cheaper to buy a used one than rebuilding your present box. Do you have any idea how many miles are on this GB or anything about its history? These boxes are great but sometimes really abused!! I drained an MGB OD GB one time, in the car, and there was barely enough oil to fill the palm of my hand!!

As for too much movement on your input shaft it could be caused by several things. These could include a bad front bearing, worn case from the bearing spinning in the case (not locked in place) or the front of your output shaft/3rd motion shaft that is inserted into the rear of your 1st motions shaft. I’ve seen that once or twice while rebuilding OD boxes. I also, as indicated above, would be concerned with shim material in the bell housing. How did it get there and where else is it? it is usually on the inside of the trans behind the front cover and should be held in place by the front cover and bearing.

HTH

Fred
Fred Wright

Fred, gearbox is standard 4 speed. yes i do know about history. approx 60,000 miles before engine was removed and freshened.

as for the shim, i just assumed it was the one located behind the big nut and lock washer on the exposed end of the input shaft.
there really isn't much in and out movement to the shaft and the lock washer is of the type that is bent over one flat on the nut to secure it and appears to be in position.

i might just go ahead and replace oil seal and new throw out bearing with borg and beck type, replace spigot bush and give it a go.

if not, i'll go from there....gives me something to work on.
i'll update post later on...its off to the shore for summer vacation now

thanx for all the input
DS
Dennis Silance

There are no other shims in the area.
This shim would have a very hard time getting out of where it is supposed to be, but it would certainly kill the seal as it did so.

"located behind the big nut and lock washer on the exposed end of the input shaft."
>>The shim is NOT behind the nut and lockwasher; it is outside it, on top of the outer bearing race and in the recess in the cover.

"there really isn't much in and out movement to the shaft"
>>There shouldn't be "much", the purpose of the shim is to reduce said clearance to zero (bearing protrusion from case vs. recess in cover, allowing for gasket). Oddly, this seems not to be detailed in the WSM, but it was in some BMC WSM as I can see the pictures in my cluttered brain, and have been setting these clearances for almost 50 years.

The several bearing faults Fred mentions are all related, and any one of them will eventually cause all of them. The common "first fail" is the flywheel spigot bush.

You don't say if this is a 3 synch or 4 synch box. Front bearing failure alone is rare on the 3 and virtually unknown on the 4 synch. A 3 synch with 60,000 wants layshaft and bearings, the 4 synch probably wants nothing, other than this rather strange oil seal/shim failure.

FRM

FR Millmore

I repeat, the front bearing is designed to have a small amount of play. The shim, sometimes shims, are there behind the front cover to clamp the bearing in place. and are carefully calculated in thickness to do just that, without distorting the cover. Sometimes when boxes are rebuilt the old shims are just put back without measuring or just left out altogether.
Allan Reeling

I learned from hard experience to replace all ball bearings on a 3 synchro rebuild. It is not cost effective to reuse old bearings; and they are available from most sources.
Rich Boris

This thread was discussed between 25/06/2012 and 16/07/2012

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