I had a bit of fun assembling an overdrive.  It took a few attempts to get it right, so I hope this is of help to others - it may save you a bit of time!u

Note:  This is a record of what I did.  It's not a recommendation from me as to the best/correct/method. I'm sorry if your overdrive doesn't work after following this, but it's up to you to check that this is method is worth using.  I take no responsibility for any damage or other losses you may suffer if you do what I did. 

If you have any comments, please contact me at mike@coppicegreenbuss.co.uk

Mike Buss

1) Cleaned up casting..  I put a couple of dings in the bearing locations removing them. I cleaned up with a file.


One Thrust bearing assembly, and rollers for the lay shaft.

Rollers and sleeve in the layshaft

Three parts of a thrust bearing.

Insert the layshaft with roller bearings into the casing.  Insert a thrust washer stack at the far end of the layshaft.  Insert the second thrust washer stack at the open end of the layshaft. 

Downward view- use a screwdriver or something to line all the bits up.

Insert the bearing rod. 

Check the endfloat.  if it's outside tolerance - 2-4 thou, I think, add shims here to suit.

When all is sorted, remove the bearing rod, and insert a thinner object.  Something between 6-12 mm thick is about right.  You need the slack to get the other items back in place.

Insert the seal.  I filled the seal with grease, old habits die hard. 

I located the seal by inserting the input shaft, without thrust bearing - into the output shaft.  This pushes the seal into about the right place - I hope!

I then located the main bearing in the housing.


I checked visually that the bearing is right in place all the way round.  The race is a little flexible, but if it's in place but twisted, it will jam up.

A view of the casing showing a rod in place of the lashaft bearing pin.

Output shaft seal installed.

Ball, spring, and packing piece.  The packing piece has a curve on one face - this should follow the curve of the drive gear.

Three balls, etc assembled with the selector ring.  The ring holds all the balls, springs, etc in place.

Input shaft with thrust bearing, roller bearing, sleeve, and next roller bearing.

Input shaft installed in the output shaft.

Input/Output shaft assembly sat on a socket, to keep the input shaft in place.

Drop the body over the input/output shaft assembly. The hammer is useful to keep the whole upright.

Thrust bearing for the selector assembly in place.

Add the synchro ring.

And the selector assembly.

And the second selector ring

Next bearing assembly parts

Drop on the washer, then the sleeve for the roller bearing.  I tapped it gently into place.  Not too hard, or it will cause the shafts to drag one to the other.

Add the roller bearing.

And the thrust bearing.

Then the idler gear & bearing circlipped together.

Drop the two collars and the roller bearing into the top

The thrust bearing, shim, and circlips ( only 2 required, not the three shown!)

Shim, then thrust bearing, then thick circlip.

Circlip cover.  A circlip holds this in place.

A few views of the whole when in place.

Tap the idler shaft bearing into place.  I put the assembly over a vice, and tapped it into place with a drift.

Refit the layshaft bearing rod.

O ring and cover.  The cover locates the bearing.  Fit the cover to the assembly.

I greased the slides, and inserted them into the selector arm.

Selector arm in place.  the bolt goes through from the top - the threaded part therefore is below.

I inserted the rod, and bolted through. It has to be in the right orientation to get the bolt through.

I then fitted the plug with a bit of blue hylomar on the thread.  It may have been better to use Torqseal.

Plug, spring, and ball.

Inserted, with a little more blue Hylomar.

At this point, it's a good idea to ensure that the selector will locate nicely in all three locations.  if you can't get to one end location, slacken the pinch bolt in the selector fork,and move the selector rod until it reaches the detent.  retighten the pinch bolt, and recheck that all detents can be reached.

End plate - the O ring is behind this to seal it.

Refit the drain plug.  Note the oil on the bench. I'd squirted a load of oil into the assembly through the large aperture, and turned the input and output shafts to get oil onto all the major surfaces.

Refit the filler plug, and the cover.  I greased the gasket before installation.