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MG MGB Technical - Overdrive problem

The 71 roadster was very slow in engaging the overdrive and on checking the oil level it was quite low, after putting about a litre of oil in it cured the slow engaging, (leaking around the filter housing) .
The overdrive is now when in third gear jumping in and out of overdrive especially when excelerating hard sometimes in rapid succession. I can make this happen also by moving the gear lever from side to side. I think I can remember reading something in the past about a switch on the overdrive but cannot remember the details. Thanks for any help. Trev.
Trevor Harvey

That is the inhibitor switch, prevents engagement in gears other than 3rd, 4th.
Either it is faulty or set up wrong.
It is positioned at the top left of the gearbox, screwed into the remote. Adjustment is by adding or subtracting a fibre washer between it and where it seats on the remote.
To access, lower the gearbox onto the fixed crossmember and push to the drivers side - after first removing the speedo cable to prevent kinking it.
Paul Walbran

Could also be loose, or loose connectors. If pulling the lever towards you (on an RHD) reliably engages it but pushing it away from you disengages it then almost certainly adjustment or loose. Because OD is available in 3rd and 4th the switch operates as the lever is moved across from the 1/2 plane to the 3/4 plane and is usually reliable, V8's (and later LHD) where it only operates as you pull the lever back into 4th gear are more finicky.

You will almost certainly have to get at it from above, and unfortunately with a 71 you will have to pull the tunnel carpet back. With the centre arm-rest you can cut a piece out of the carpet (keep it to put back) to remove the small panel that is on top of the tunnel on Mk2 cars that gives slightly better access. More info here http://www.mgb-stuff.org.uk/gswitch.htm#2aa


paulh4

If it's adjustment that's needed how do you do the adjustment.
Trevor Harvey

The only adjustment is either to tighten it up if loose or remove a shim/spacer as the other Paul said. The switches and spacers are shown in that link.
paulh4

We access from below (as described) all the time. Yes, it is tight but with the right socket can be done
Paul Walbran

This thread was discussed between 06/04/2023 and 07/04/2023

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