Fitting overdrive on to gearbox for GT6

[Bob Horner]

On another thread I raised the issue of a slipping overdrive and as a result it required a rebuild.  I assumed refitting it would be a simple job but Googled to see what advice was out there in forums and YouTube.  A lot of  this a MG based and there are various posts about how difficult it is and one YouTube vid from US showing a bit of force used to bang it on to the back of the gearbox and stories of hours of trying etc etc.  After finding it very difficult to mate the two myself was beginning to believe them.  However, went back the the internet and found a couple of posts in agreement that it is a simple job if you do it properly.  
 

There are 2 main issues - Lining up the 2 sets of splines inside the overdrive and then getting the spring loaded pump plunger that operates on a cam on the gearbox output shaft over said cam.  The most important thing I learnt was that the splines inside the overdrive may look aligned and some are, but not all are.  You have to get a screwdriver to turn the rearmost set of splines anti clockwise until they ALL line up perfectly - not just some of them.  The next tip is to use something to pull back the spring loaded plunger.  I used a plastic cable tie wound around two of the overdrive units studs and tightened to pull it back.  Having done all that it slid straight on apart from the width of the cable tie (1/4 inch). All I then needed to do was remove the cable tie - it slips off the spring and you can then cut and remove it. 

Other points;

It’s recommended to use some gasket sealant and also I found it better to put the gasket on the overdrive rather than the adapter plate. That was because, having at last got it on the splines but not got the pump plunger over the cam, wiggling it made the studs on the overdrive damage the gasket on the adaptor plate (it’s only 1/2 inch away from mating at that point and the studs are just touching the adaptor plate).  Once I used the cable tie method it wouldn’t have made much difference.  Also, a couple of nuts need to you lift the overdrive unit away from the adaptor plate slightly to get them on - careful not to slip it up too far.

I presume it can take a while if you don’t know the above tricks but eventually it will go on once you keep moving the internal splines (only anti clockwise) so hence battling for hours.  I worked out how to get in on but had damaged the gasket for the reasons noted above.  It meant I had to take it a apart and do it again with a fresh gasket a couple of days later.  As proof it was unlikely to be a fluke, I used the same method and it took 10 mins to get it on and bolted up.

Hope that helps someone else sometime or interested to hear any other approaches or experiences.

Bob

 note above - you need to make sure the cam is at its thinnest point where the pump plunger locates so it can go over it as easily as possible.  Broadly that's aligned at the bottom of the overdrive. 

 

[Pete Lewis]

bob next time !!!!   two big screwdrivers insert under the piston plates and lever against the case to mimick operating .

  this allows the splines to self locate 

and it pops on easy  do keep fingers out the way 

simple but effective when refitting any overdive  works for D or J , not tried on A type 

Pete

[Bob Horner]

Thanks Pete for the alternative method, hopefully never need to do it again!  Your method aligns the splines but presumably doesn't help get the plunger over the cam on the output shaft?  I found that a problem until I held it back.  On Youtube it shows a guy slamming it down on the shaft-  presumably to overcome the issue of getting the plunger over the cam but if the splines aren't properly aligned that could cause a bit of damage.  He did put a chamfer on the cam to help ease the plunger over it but I don't fancy filing off bits of metal unless I really need to.  I'll amend my post above as just realised I didn't mention that you need to make sure the lowest part of the cam is at located at the point where the plunger sits.

Bob