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MG MGB Technical - Noisy Gearbox?

Hi, my '67 MGBGT has a engine rattle on start-up and rumbles when reving, so I need to overall and replace big-ends and mains. There is quite a bad rattle from gearbox especially at high rev's, which vary's from nearly goes away to very noticeable between 40 - 70 mph in 4th + O/D depending under load going up-hill to over-run going down-hill. Same noise occur's throughout the different gears. The O/D and gear selection are good so I assume it is gearbox bearings/layshaft or other. Holding the gearstick does not make a difference. Question: While engine is out, do I replace the gearbox with a reconditioned one, or can I attempt to overall it and replace bearings etc? If so, what would the appropriate parts to replace? I assume gears/selectors/syncro parts would be OK?
Appreciate your valued comments.
Pete Dyble

Gearbox and diff are reckoned to be the most difficult things to repair/recondition, requiring more specialist knowledge, tools and care than probably anything else on the car. If you are sure it is the gearbox and not, say, propshaft then for my part I would replace with a guaranteed reconditioned. If some parts are worn to the point of making a significant noise, then many components are likely to be equally worn.
Paul Hunt


I don't have experience rebuilding gearboxes, but would suggest when you pull the engine to pull the gearbox with it. When I heard the "death rattle" coming from the gearbox on our Midget I had it re-built by a local expert. Not sure the cost to rebuild an early O/D gearbox, but would weight hat against the cost of the modern 5-speed. In the end I think you're going to need one, or the other.

Personally, I like the flexibility of the O/D in our B/GT.


Larry C. '69 Midget & '74 B/GT
Larry C '69 Midget

"I like the flexibility of the O/D"

Me too, I could never envisage replacing my 6-speed, effectively with a 'paddle' change on two of the gears, with a 5-speed.
Paul Hunt


Yes, using third gear with overdrive on the twisty back roads is the ticket. On our '74 B/GT it's the wiper/washer stalk, and prefer that to the later location on the shift knob. Effective, and simple to use ;-)

Larry C '69 Midget

Pete - good advice about gearboxes above - have a look through the threads here about the choice of oil - you may not be able to stop a whine but you can go a long way to arresting further wear. The engine rattle on start up presumably is the result of worn valve gear and the lack of lubrication until the pump kicks in. The rumble is pretty common with these engines and I wouldn't pull yours until the oil pressure falls significantly,
Roger W

Thank you all for excellent information and advice. I think I need to start saving for a recon!
Take Care
Pete Dyble

Sounds like worn lay shaft & lay shaft needle bearings. Depending on what engine serial number you have for a 1967, 2 models of lay shafts were used with different diameters and number of bearings. There have been quality control & heat treatment issues with lay shafts & bearing recently. A great information source for 3 synchro gearbox for MGA/MGB is Barney Gaylord's MGA Guru web site:
Rich Boris

In case it helps, I just had a recon gearbox from Heathrow Transmissions and am very happy with it - they deliver nationally so worked fine for me despite the distance. If you google them they have a pretty handy website. Mine was a 3 synchro non-OD but they do any.

Piers Colver

This thread was discussed between 04/09/2014 and 30/09/2014

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