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MG MGB Technical - Gearbox noise/crunch in 2nd
|My MGB gearbox was noisy so took the opportunity of overhauling it while doing the same with the engine.|
One area to improve was the sloppy gear-stick. Found out that the nylon bush for location on the ball end of the stick to selector rod was totally missing! This was replaced as well as all the bearings, bushes and gaskets. The gears, syncro's selectors all looked fine so just re-assembled with new oil.
Only managed a quick run up the road due to smoke problem, but pleased that the gear change had lost its sloppy-ness, but when changing from 1st to 2nd which worked OK, if the gear-stick was slightly pulled back by resting your hand on it there was a whirring noise as if selector fork was catching a rotating gear. If you removed your hand the noise stopped and car run OK in 2nd. It was a similar noise to crunching gears without clutch.
Do you think that this was the reason for the nylon bush being missing or is there another reason anyone can advise?
I have to take the engine out again so do I take the gearbox out at the same time and strip again, if so what should I look for?
Many thanks for your thoughts.
|but when changing from 1st to 2nd which worked OK" ???? Does it "crunch or not"?|
The selector fork "floats" when not selecting a gear, putting pressure on the lever will bring it into hard contact with "rotating parts.
The nylon bush is often missing. The PO may have lost it when removing the stick.
|Hi Allan, it does not crunch from 1st to 2nd and drives alright in 2nd. But with slight touch on the stick backwards you can feel and hear something rubbing against a gear.|
I think I need to remove box and access cover to see function of 2nd gear and where it is rubbing on.
The engine compartment, engine and gearbox were painted when out of the car and it all looked the 'dogs' now assembled, got to take it all out again! (bugger!!!)
|'Whirring' to me is a very different noise to 'crunching' from trying top engage reverse without a clutch.|
Pulling a gear lever in any direction will often result in a whirring (to me) noise, from things rubbing against each other which they otherwise wouldn't do if the lever was allowed to take up a 'natural' position. That's why we were always told not to drive with a hand resting on the lever.
Similar to the doctor saying "If it only hurts when you do that, don't do that" if it only makes a noise when pulling it back when in 2nd, then don't pull it back when in 2nd! :o)
Whirring and missing bush are completely unconnected. My V8 had the bush missing when it came to me, only realised because I already had a roadster without any slop when in a gear. The PO had replaced the first-motion shaft, so quite probably lost then as Allan says, as I found when fitting a new bush to the selector rod first, then fitting the lever, pushed it straight out again. I had to fit to the lever first, but that expanded it so it then wouldn't go into the selector rod until I chamfered the bottom edge.
|Thanks for your comments and I have now removed gearbox from car, drained the oil and removed the access cover - as per attached photo, which shows 2nd gear selected. All is fine in this position, but the gearstick can be moved slightly further past the spring indent on the shaft so that the side of syncro gear outer edge catches on layshaft gear. You can see it out of line by about 2.5mm. Also you should just be able to see the chatter marks on syncro edge.|
As the layshaft is a good fit in casting with bearing/washers, the problem seems to be the position of the 2nd gear on main shaft. Guess I need to strip it down and understand why the error - unless members have encountered this problem before?
Funny that the next gear is in line so it must be the positioning of the gears on the main shaft as the layshaft gears are all in one.
|Found out the problem. The large nut on the third motion shaft was not tightened enough to ensure the large rear bearing was seated against the step on the shaft. Less than a turn to tighten the bearing against the step/shoulder lined up the gears and all is well now! Doh!|
This thread was discussed between 22/02/2016 and 06/04/2016
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