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MG MGB Technical - over drive stuck on

A good fiend has had his '78 UK B back and foreward to specialist repairer to sort the o/d sticking on when hot. The car shudders coming to a stop and has lockup in reverse. They say bring it back again and again !!. I feel that the valve controling the clutch application is hanging, for what ever reason. As an ex auto trans specialist that would be my first port of call. May be it's the internal clutch, hope not.
Any suggestion would be appreciated Thanks Sean
S Sherry

Sean,

First - make sure your friend does not attempt to back the car up until this is resolved! As a matter of course, replace all the "O" rings, clean or replace the filter, and verify how much and what kind of oil is in the transmission. If there is any doubt, we all know that 20-50 oil works and that should be used until the fault is found. I cannot remember exactly, but there are 3-4 "O" rings used on the solenoid and on the pump non-return valve.

I suppose it might be worthwhile also to see if the O/D switch is working. Check the yellow wire downstream from the switch with a test light or voltmeter to make sure it goes dead with the switch in the "off" position.

FWIW,
Allen
Allen Bachelder

Does this happen with the OD manual switch turned off as well as on? If so then it is definitely a problem inside the OD, possibly debris in the high pressure line acting as a one-way valve.

If it only happens when the manual switch is on, i.e. OD can be manually switched in and out as normal when driving forwards, then it is simply the gearbox lockout switch bypassed (either deliberately or shorted wires) or a faulty switch (rare). Some people have bypassed this in order to get OD in 1st and 2nd as well, thinking they will always remember to turn it off manually in reverse. They may, but others probably won't, it's a mad, bad and dangerous thing to do. Easily detected by driving along in 2nd gear and switching OD in and out manually. But that does assume the manual switch isn't faulty or has been bypassed as well!
Paul Hunt 2

I had the same problem a few years ago. The car would engage overdrive fine, but would not disengage.
I asked for help on this site and was told to drain the trans and fill it with auto trans fluid. I did this and it was fixed in less than 10 mile. I then changed back to 20/50. Had no more trouble. sold the car a few months later.

Steve
Steve

This thread was discussed on 03/03/2008

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