Gearbox puzzler

[X-pat]

I'm refurb-ing a TR6 (late model) gearbox, converting for eventual use in a Sprint. Main difference is the input shaft: TR6 is shorter and fatter, Sprint is longer and slimmer. Both are supposed to use the same countershaft constant gear, part no. 159621 (only part ever listed for Sprint, and as found in late, post-72 TR6 units).


My problem? The countershaft gear meshes nicely with the TR6 input shaft, but not with (what I was led to believe was) a Sprint input shaft.
TR6:

?Sprint?


On close inspection it seems that the angle of cut differs on the 4th gear on these two input shafts.


My first thought was that the gearbox internals that I had weren't really from a late model 6 and that the countershaft gear must be the wrong one, even though the gearbox number is a late one. So, I ordered part number 159621 from my usual supplier - only to find out that it was the same as the one I had! My conclusion at the moment is that the "Sprint" input shaft that I have is from another model - maybe 1850?

Any thoughts?

[xvivalve]

With the lower number of splines it would have to be an early 1850 as the later ones had more (21?), if it was the early 1850 it wouldn't be long enough as they didn't have the adaptor plate!

Could it be stag, 2000 or 2500?

[zombeh]

stag, 2000 and 2.5 shafts would all be the same length as the tr one wouldn't they?

[xvivalve]

Yes

[X-pat]

Stag also had an adapter plate, so I would have thought the input shaft would have had to be longer than the TR6 - although I've never seen a Stag item. Unfortunately no part numbers anywhere to be seen.

I think the number of splines is the same between the two shafts I have (I'll have to recount), but the angle is different so the layshaft gear doesn't mesh properly. Looks like I may have to bite the bullet and get a genuine Sprint input shaft.

[SPRINTPARTS]

I have had this problem in the past when trying to make one gearbox from 3 or 4 donor boxes.

By part number, Sprint, TR6, T2500 all used the same 4th gear (159621). Early Stags had a different tooth angle on the input shaft and 4th gear (4th Gear part no 142434). However I recall that this earlier tooth angle was also used on T2000 and early TRs, the later tooth anlge was introduced to increase the gear strength. Unless you are sure about the history of the TR6 gearbox I suggest it is an early model unit.

Philip

[X-pat]

I don't know the history of the TR6 box, although the number suggests it is a post-'72 unit. The layshaft gear in it is exactly the same as the new one I bought from RB as p/n 159621, as used in late TR6 boxes - which doesn't fit with the Dolly input shaft I have. This is what makes me think the problem is with the input shaft and not the laygear. RB are checking the fit between this gear and what they have in stock as a Sprint input shaft. Will post the update once they contact me.

[george]

it could well hail from the gear box of a police interceptor as these were geared differently can't think what the difference was but i did do a few boxes from the police squad cars and there was a special suplement on the police interceptor in the parts manual

[Dolly racer 33]

IIRC early TR6s had different ratios to later ones, a CR gearbox has a different number of splines. 1850 is very different using basically a Marina/Spitfire box & Stag shaft is 1.25 " diameter & all the others are 1"

Regards.