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MG MGB Technical - Any one have an overdrive mainshaft?

So heres my story...I found a 1971 MGB convertable at the breakers yard.

The car was in terrible shape but I happened to look under the car and it had an overdrive transmission.

I new the guy at the counter and he gave me a really good low price as I explained the unit would be more or less a core in my opinion.

In other words I wouldnt bring it back if it wasnt perfect. He asks if I want to take it out or have his guys do it....

The car was so rusty I figuired they would just torch it out with the cutters. An easy job imho. Let them do it Ill go home to borrow my brothers pickup....

I get back to the breakers and my buddy at the counter tells me they had a problem.

The new guy decide to man handle the transmission out and it was leaking oil.

Some how they left the drive shaft connected and with the wieght of the car on it and they cracked the rear case.

I was a little upset because I thought I scored a nice peice but I lost out because I didnt stay and do the work.

So the price was reduced more. It was still an overdrive and the parts were worth more then I paid for it.

I got a replacement O/D case.

I got a look inside my damaged transmission.

It was one of the cleanest inside I ever saw. No wear
what so ever. Either they never knew it was overdrive or it was rebuilt.

So I need a new main shaft as the damage cracked the nub off the back of the main shaft.

Does any one out there have one in decent shape they would be willing to part with?

Or know where I could purchase one?

I asked John Esposito at quantum mechanics but he said he doesnt have any spares at the moment.

http://www.quantumechanics.com/qm-htm/home1.htm

I know its a tough part to get I just thought I would ask if any one out there new where I might get one.

If I had that part I could fix my transmission.

I think I got all the internals to fit in about 15 boxes but you know what happens when you leave something like this apart to long....

You never find all the peices! :-)

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29014#23

The part number is 462-130 #23a N/A

Thanks for reading my story.




Steven Devine

Wow..... Dont all answer at once!:-)
Steven Devine

Have they just broken the threaded part off? Could you not drill and tap the shaft and use a bolt to secure the flange. All the torque is taken on the splines further forward .
jim soutar

Hey Jim,
I thought of that...but I think the shaft is heat treated. Im not sure how it was done.

Basically it opens up a can of worms that I dont have the answer for. I really think its a needle in a hay stack to look for.....but what choice do I have?

If I thought a machine shop would tackle it I would try your idea as I have nothng to lose.

Thanx for your reply!
Steven Devine

"Wow..... Dont all answer at once!:-)"

We've all got one, but we're using them :o)

The LH OD flange nut is tightened to 55 to 60 ft lb, better than the 150 ft lb of the D-type or the non-OD 4-synch, but still quite a lot for a bolt possibly half the size of the original thread. While it's the splines that take the torque when accelerating and decelerating it's the nut that has to withstand the torque reversals, as there is always some play in the splines or you would never get the flange on or off without a press.

OD gearboxes are pretty common in the UK, and you could also try http://www.overdrive-repairs.co.uk/
Paul Hunt

Do you mean the gearbox mainshaft or the O/D annulus ?

The rear flange slides onto the shaft of the annulus and is retained on the shaft by a large washer & nut.

Don't agree with Paul - the flange is a tight fit on the shaft but no press required.

The torque on the nut pulls up the bearing centre races (2) onto the spacers, shims (if fitted) & speedo drive gear - nothing else.

The D type nut is done up to 100 - 130 ft lbs, not 150.

I have some on the shelf if you can't find them anywhere locally.

Chris at Octarine Services

Chris

Its the main shaft thats broken, The nub that fits in the annulus has been snapped off. I appreciate your responce...let me look a little longer as Ive come across a couple of leeds.

Thanks for thinking of me! :-)
Steven Devine

This thread was discussed between 28/02/2014 and 01/03/2014

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