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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 ¼ - 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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