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MG MGB Technical - Overdrive overhaul

Hi

I have my gearbox and engine out of the car, the overdrive was working fine before i took it out.

But i want to do anything needed on the overdrive whilst i can get to it.

I am planning to change the filter element and magnets, anything else worth changing or checking?
whiskeyfrank

Other than giving a good clean and oil change, I think most of the fairly easily remedied problems can be done whilst the unit is in situ, other than the switch which is very awkward to get at. Some people even resort to cutting an access hatch in the transmission tunnel. So worth checking out latter, if all apart.
Peter Allen

Get a set of O rings and change them all.

See here also - https://octarine-services.uk/gearboxguide.htm
Chris at Octarine Services

Depending on the size of your hands the switch on the LH-type can be accessed easier if you remove the small panel on top of the tunnel, drop the cross-member and pull the gear lever across to the driver's side. Original switches have to be tapped round with a drift, but replacements have the hex as the largest diameter so it's possible to get a socket on them.
paulh4

I've had my overdrive switch out and taken a fibre washer out from underneath it. I did drop the cross member as paulh suggests. I think I was able to get pipe pliers on it. Good job it wasn't too tight.
Paul Hollingworth

If lowering on to the fixed crossmember, it pays to remove the speedo cable first as it can get a permanent kink and a waving speedo as a result.
Paul Walbran

Both mine have a notch for the cable to pass through. I've had the removable cross-member up and down loads of times while looking at problems with the V8 OD switch and OK so far.
paulh4

ive ordered a kit from MGBHive for the orings and filters and two switches for reverse and overdrive, think thats about it.

thanks
whiskeyfrank

I had my transmission and overdrive checked when the engine was out recently. The transmission guy replaced a pump cam in the overdrive the was worn and scored. The unit was working well and continues to. He also replaced a couple of synchronizers and now it is difficult to shift into 1st gear and reverse when the transmission is hot.

Let sleeping dogs lie?
Glenn Mallory

Clutch is dragging, nothing to do with the OD unit. If the biting point is low then there is air in the system. But if that's 'normal' then it's quite possibly the clutch splines dry. Did you replace the clutch at the same time?
paulh4

ETA: Paul has made a very good point too, I should have thought of this too as I have suffered more clutch problems than you'd believe with my midget, including currently, that was my thinking for trying to get another gear first.

Glenn,
you may already know or considered the following but - are you letting the revs fully die away before trying engagement of first and reverse or if running on fast idle tried engaging another gear first.

It maybe that you were used to the worn set up and now need to get used to the refreshed set up and/or allow it to bed /wear in.

Also (a pet subject of mine), even though you will have fresh oil in the box, a better quality or more appropriate oil in the gearbox might help a little with selection and overall, New Mexico sounds like the type of area where the ambient and car running temperatures might get high (and also perhaps also cold?), some oils work better, more reliably, for longer than others.
Nigel Atkins

ETA - And I'm not suggesting any oil will overcome deeper issues only that a better or more appropriate oil might help with minor issues and overall, checking the Archives will prove this is so and not just my opinion (though it is :) ).
Nigel Atkins

This thread was discussed between 03/12/2019 and 12/12/2019

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.