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MG MGB Technical - overdrive reassembly problem

I have been working on a Laycock Black label LH-type overdrive transmission, and I am having trouble getting it back together. I removed the overdrive unit and am now trying to put it back on. This is the overdrive unit that came off of this transmission, not a replacement.
The overdrive unit slips smoothly over the rear shaft, which I rotate a little to engage the splines. The unit slides forward to the point shown in the attached picture. There it stops solidly and I can�t push or tap it any farther.
This is not caused by the pump plunger hitting the eccentric cam, as I�ve removed the plunger. I can�t see anything else that is preventing the unit from moving the last inch or so, and I don�t want to force it.
Can anyone suggest what my problem is?
Thanks in advance for your help!
Mike Whalen


M.E. Whalen

Mike, I think the internal splines are not aligned. I've copied here some reassembly instructions from one of our UK gearbox companies. I'm afraid I can't remember the name of the company so apologies to them if they read this. However, it says the following:

119.�������� Place new gasket on gearbox adapter housing
120.������� Fit the circlip, locating ball and pump drive cam to the gearbox mainshaft
121.�������� Rotate the mainshaft so that the cam lobe is uppermost
122.������� Slide the OD unit onto the mainshaft
123.������� If it fails to reach the studs � the internal splines are not aligned � remove OD and using two spanners to lift the operating bars, use a long screwdriver to rotate the cone clutch until the splines are aligned
124.������� If it fails to mate within � - 3/8 inch then the pump operating roller is caught on the cam � use a thin long screwdriver to depress the pump plunger
125.������� Fit the retaining nuts � note that some must be fitted with the OD unit slightly raised from the adapter housing
126.������� Fit a new gasket to the remote tower housing and fit the housing � locating the plastic bush into its hole in the selector arm
127.������� Finally - check the gearlever anti rattle spring & plunger in the tower for presence and free operation

From your photograph it looks as if the studs are short of the holes so para 123 may be the clue. I had the same problem and their answer sorted it.

If you want the full file (gearbox & o/d disassembly & reassembly) post your email address and I'll send you a copy.

I rebuilt both units and used these instructions. The main box works but I've yet to do a road test with the o/d, though it works in the garage so I'm hopeful.
Richard Coombs

Mike, wouldn't you know it. As soon as I sent the above I remembered where I got the file. It's on www.octarine-services.co.uk. Click on 'Guides' under 'Information' and go for the obvious. Good luck.
Richard Coombs

Make sure that the o/d pump roller is the right way around. If it isn't the cam/pump roller issue then it could that the splines are not aligned.
Rich Boris

This thread was discussed between 05/07/2012 and 16/07/2012

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