Input shaft problem fitting TR4A gearbox in TR4

[Steve Priest]

It looks as though my initial enthusiasm at finally getting my gearbox in was a little premature - I've hit a problem. Basically I'm replacing the original non-overdrive gearbox in my TR4 with an A-type overdrive gearbox from a TR4A. All was going well until the final tightening of the mounting bolts. It quickly became apparent that after tightening I could no longer turn the engine over. I slackened the mounting bolts and it freed up so something is amiss.

 

The gearbox is now out again. The profile of the input shaft in my new gearbox differs from my old gearbox. The problem appears to be that the splined section protrudes too far and contacts with the face of flywheel.

 

Here's the input shaft on the new gearbox:

 

 

And for comparison, my old gearbox:

 

 

And here's the flywheel:

 

 

Measuring from the engine flange, the distance to the recessed face of the flywheel is about 30mm. Measuring from the gearbox flange, the distance to the start of the splines is about 28mm and here lies the problem - it projects about 2mm too far forward. In comparison, on my old gearbox, the distance from the flange to the start of the splines is about 37mm so there's about 7mm of clearance when fitted.

 

Looking at the parts catalogue, the input shaft is the same for the 4 and 4A. My car has it's original flywheel (I think), which is fitted with a spring clutch (not a 4A clutch). I assumed a 4A gearbox would be a straight forward swap with my 4 gearbox (albeit with longer studs and bolts) however I guess I've missed something. Any suggestions gratefully received.

 

Cheers,

Steve

 

 

[graeme]

Hi Steve,

 

All the TR gearbox input shafts that I have seen are like your original type, even the saloon boxes are the same except for the spline diameter. Do you have any history on the replacement box, has it been rebuilt?

 

Cheers

 

Graeme

Edited January 10, 2015 by graeme

[Lebro]

Looks like you have an incorrect input shaft, cheapest solution would be to remove the input shaft, & grind the end of the splined section down (ideally in a lathe) to increase the clearance.

 

Bob.

[RogerH]

....or could you use the shaft from the original box.

 

Roger

[Steve Priest]

Thanks all, that's very useful. It's confirmed what I thought - the input shaft is wrong.

I been in contact with guy who supplied it. He's been very helpful and will replace it.

 

Cheers,

Steve

[Guest ntc]

Check the length of the nose cone as they differ.number 8 hold the mouse over info http://www.rimmerbros.co.uk/Item--i-GRID200088

Edited January 10, 2015 by ntc

[Chilliman]

 

 

....or could you use the shaft from the original box.

 

Not sure that's possible with that box Roger, my guess is that although the parts would be of correct physical dimensions to enable a swap the angle of the teeth on the gear of the constant pinion shaft in the new box would be different to the old box so if he tried to swap them the constant pinion shaft would fail to mesh with lay shaft gear....unless you were prepared to swap that as well but then you're into a full box rebuild and not a quick fix!

[Lebro]

+1 may be lucky, but may be A) different angle, different dia / No. of teeth

 

Bob.

[Alec Pringle]

Perhaps the later TR5/6 input shaft fitted to an earlier box ?

 

Cheers

 

Alec

[graeme]

Perhaps the later TR5/6 input shaft fitted to an earlier box ?

 

Cheers

 

Alec

 

Alec,

 

I have a selection of TR4/4a/250/6 and saloon boxes, all have the same step on the input shaft. I wonder if it could be a Dolly Sprint or Stag input shaft that has been machined down?

 

Graeme

[Steve Priest]

Thanks Neil - the new box has a 2 3/8" extension same as my old box. So I think this is correct for a 4 with a spring clutch. I know it has to be 2" for the 4A diaphragm clutch otherwise it hits the fingers.

 

I did wonder if the shaft could be from a Sprint. Anyway, looks like I now have a way forward.

 

Thanks your input all. Needless to say it's been a learning experience. Looking forward to getting my car back on the road.

 

Steve