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MG MGB Technical - OD switch adjustment

I need to make an adjustment to the OD switch that is on top of the transmission. I read John Twists article on how to do this and know I have to lower the back of the transmission and take off the tunnel cover but do I need to remove the drive shaft or just undo the bolts on the crossmember and lower it?

The OD is occasionally jumping out of OD. A slight pull on the shifter and it pops back in. I am figuring it has to be the switch adjustment. This is a newly rebuilt D type OD with about 1000 miles on it. Just started doing this last summer. I assume there are shims that are used to adjust this?
Bruce-C

Bruce,
I had a same problem with my overdrive unit. I had to remove the fiber washer from under the overdrive isolation switch(Moss #140-470 page 40 mgb/c catalog) to get it to work correctly. All I had to do was remove the tunnel cover. I did not have to lower the gearbox. There was just enough room for me to undo the switch and screw it back in.
Good Luck, Tony
Tony Shoviak

May depend on the year. Earlier cars with the large tunnel cover may not need the rear of the gearbox to be dropped, i.e. 3-synch, but I found I needed to with my 4-synch.

Just remove the four bolts securing the crossmember ot the chassis rails with the tail of the box supported on a jack, and lower it. You don't need to disconnect the drive shaft.
Paul Hunt

Paul,
He said he had a "D" type overdrive which was fitted to the three synchro MK1 B's which is what I have. The later B's had a LH type which was fitted to a four synchro geaebox which would require the gearbox to be lowered.
Tony
Tony Shoviak

That is good news. Neither is a big deal as the car is currently up on jack stands, but I will start by taking the tunnel cover off and seeing if I can get to it.
Bruce-C

Try turning the gearstick through 180 degrees. A bodge, but it might get you a few more miles before having to do the job properly - in my case about 500..!
Neil
Neil

Pulled the tunnel cover this weekend and was able to get to the switch. It was a little tight, but it came out without too much issues. Found that it was actually easier to access it from under the car (on jack stands) that made putting it back in very easy.

Bruce-C

I have a 1970 roadster with the later OD on a 4 syncro gear box. I lifted the tunnel carpet and insulation and drilled a 2 inch hole with a hole saw over the OD switch. Next cut a round door a bit larger than 2 inches from a piece of scrap sheetmetal and attached it to the tunnel with several sheetmetal screws.

Jim
J Brownell

This thread was discussed between 25/01/2009 and 03/02/2009

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