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MG MGB Technical - Gear box whine

Hi,
My 1972 MGB gear box whines when in neutral and engine idling, the noise goes away if I press the clutch in or roll the car back or forwards about 1 foot. clean castrol GTX 20w50 in it & up to the high mark.
What could it be?
Thank you,
Barry
Barry 72B

Barry. Most common cause of this is the bearing on the input or 1st motion shaft. It is the big baby at front of the box. When the clutch is engaged the input shaft stops rotating and so the bearing makes no noise.

Sorry to say that if this is the case then out comes the engine/gearbox.

Tony
Tony Oliver

Barry,

Unfortunately Tony's comments are right on the money.
It is a complete 'box out job to fix.

The good news (if you can call it that !) is the box will probably go for a long time as it is now so this may help in your planning.

Perhaps when a new clutch is due may be the best time for a pull down and repair?

Pete.
Peter Thomas

Yep. You'll have to pull the whole thing then anyway, and it'll be a lot cheaper and easier to do it all at once.

Rick Stevens

As an example of just how long you can get away with this, on my ZA Magnette the bearing was so noisy it drowned out the sound of the engine and still drove around alright until I could get around to the job.

By the way, I certain it is impossible to replace the bearing without removing the input shaft so be prepared to dismantle the gearbox. "May as well" do the synchro cones, rear bearing and layshaft bearings whilst your in there.

Starting to sound expensive but it's better than doing what I just did. Put everything back together after 16 month restoration, engine back in, test drive, find leaky crankshaft rear seal, engine back out...........(b*gger)

Tony
Tony Oliver

Thank you all for the helpfull replies. Tony why dose the noise go away when I roll the car?
Will it damage other parts ?
Cheers,
Barry
Barry 72B

Thanks a lot Barry, I was hoping you would forget about that bit!

I basically have no idea. The only thing I can think of is that the position of the third motion shaft is having some effect on the whine. When the clutch is engaged in neutral the gears on the third motion are in motion but the shaft is not turning. It only turns when the gears and the shaft are locked together which only happens when you are in gear, or if you roll the car.

The forward end of the third motion is held in position by a set of needle bearings that are in the back end of the first motion. If you roll the car the third motion shaft moves with respect to the first motion. That is the only difference I can see. It is possible that the because the third motion moved a little bit it is sitting differently in the first motion shaft but how this would stop the whine is, quite frankly, well beyond my expertise.

Will it cause any damage? Hard to say. In my case all the bearings were worn out and the layshaft needed replacing as well. The gears themselves were still serviceable, but that is not to say that in any other case damage would not occur. I have had many many cars over the last 40 years. Many of them had noisy gearboxes and I have never had one fall apart on me yet, but others would tell you differently. It's really not possible to say unless we can be sure what the whine is caused by.

In any event, what I and others have previously said remains true, the most common cause of this problem is the first motion bearing. If you replace that and all the other bearings, in other word a complete overhaul of the gearbox, and the whine is still there, sell the car!

Tony
Tony Oliver

Thanks Tony, I'll be searching for a "good" used gear box if I could find it, best regards,
Barry
Barry 72B

This thread was discussed between 17/11/2007 and 20/11/2007

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