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MG MGB Technical - Overdrive problems

I have a 70 MGB with overdrive. When I am driving on the interstate with the overdrive on it works fine. When I stop and have to back up the car will not move. I do have the overdrive engaged. When the trany cool down I the reverse workes.
Allen
Allen

Allen,

DON'T try to move your car in reverse again until you're sure the od is dissengaged. you will cause permenent damage to the od and have to spend big bucks to fix. sounds like the od switch on your gearbox is stuck in the closed position. Its not the cooling but likley the time to release oil pressure in the od that makes it ok later. then again, i just made that up..sounds right!
Paul Hanley

I too have an intermittant problem with my overdrive. When cold it works in 4th fine, but drops out in third.Its now started dropping out in 4th when hot. If I pull the gear lever to the right it engages again. I'm pretty sure its the switch on the gearbox. The Haynes manual isn't all that clear on which is the O/D switch and which is the reverse light switch, but I assume the O/D switch is the one thats on top of the remote housing, the one thats impossible to get to. I dropped the cross member but still couldn't get to it from underneath. Is it possibe to get to it from the top when the gearbox is resting on the fixed cross member or do I have to resort to cutting a hole in the tunnel. If so how do I decide where to drill it. I was hoping to restrict the hole to 2" diameter.
Paul
Paul Hollingworth

Paul,
I went through the same thing with mine. I was able to adjust my switch without cutting anything. Go to my web page, go to the MGB section, and scroll down to 8th Feb, 2003 for a brief description...
Rob Edwards

Thanks Rob, I'll give it a Whirl. Very interesting site by the way. My B is a 71, but I bet yours isn't as rusty as mine. I'm joking mine isn't that bad, the sills (I think you call them rockers -God knows why )have been patched extensively but its really very solid. It owns up to have done 109,000 miles, but its probably done a lot more than that. I have to put a pint of oil into it every time I fill up with petrol, but it still runs well. Compression is moderatly OK 145-155 psi as is oil pressure 15-55 psi when steaming hot (over 70 when cold). Worst aspect is that gear change mech seems knackered making selection a little difficult. My O/D problems are probably related. I'm trying to avoid pulling the power unit out until something breaks. Its too cold in the UK now to be groveling under a car and when its warmer I want to be driving around in it.
Paul
Paul Hollingworth

Allen - slip in reverse or on the overrun is a symptom of worn or glazed linings or a broken circlip. If the gearbox override switch is faulty and you have reversed with OD engaged the one-way clutch will already have been damaged, but if you can manually switch OD in and out when travelling forwards this is unlikely to be the case. But to be absolutely sure that the override switch *is* working correctly I'd use a test-lamp or voltmeter checking that you can switch the ground coming back from the OD solenoid on and off by moving the gear lever between the 1/2 plane and the 3/4 plane. Manual switch and ignition switch off, and test at the connector where the yellow in the main loom joins the yellow/red in the gearbox loom near the fusebox.

Paul Hollingworth - as well as dropping the cross-member you also have to remove the arm-rest and pull back the tunnel carpet to reveal a panel that can be unscrewed - on a 73 anyway - and it is still tight. The OD switch is the one on the left, again on a 73, it has yellow/red and yellow/purple wires, not the green and green/brown of the reverse light switch which is the identical part and close by. The switch may be loose, but if it is tight it may have worn, if so there are usually one or two washers under the switch that can be removed to compensate. Aren't Hereford and Worcester seperate counties now?
Paul Hunt

This thread was discussed between 22/11/2003 and 23/11/2003

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