View Full Version : TR6 TR6 gearbox into a TR3 - what should I know?

08-01-2009, 08:15 PM
Hi guys - through some amazing generosity a local Triumph club member gave me a TR6 gearbox in decent condition today (he pulled it for a 5 speed conversion but still....).

While the TR3 gearbox shifts OK and has a nice tight action it would seem that the TR6 box with the 1st gear syncro is a nice swap. Any issues with fit or the bits I should be aware of?

08-01-2009, 08:54 PM
Hi Tom,

I have a 6 box in my 3 as well....mated to the original A type from the car. The PO had put this in the race car....doesn't look to be modified to fit but I will let the 3 experts answer the questions.

I can post photos if you like .

M. Pied Lourd

08-01-2009, 09:17 PM

If you are staying with the 3 finger clutch setup, then I think you may need to swap that front cover that surround the input shaft inside the bell housing (the bearing carrier slides on it). On the earlier setup, I think that cover is longer than what it is on the TR6 box. If you are switching to a TR6 style clutch, though, I don't think that is necessary.


08-01-2009, 09:45 PM
I should have added that the engine is actually from a TR4.

08-01-2009, 09:53 PM
I'm not sure if what I said is a requirement - but I do know the input shaft cover matters if you use a 3 finger clutch, or the later diaphram clutch. If it was a TR4 engine, chances are it is a 3 finger clutch.

08-01-2009, 11:07 PM
Several people have reported that the later, shorter cover works OK with the early clutch. But I didn't try it, since I installed a TR4A diaphragm clutch at the same time I put in the late TR6 gearbox. It is important not to use the longer cover with the diaphragm, as the fingers will hit the cover when the clutch is released. And of course the TOB & it's carrier need to match the clutch.

The rear crossmember needs to be modified a little, as the 4-synchro box is about 3/8" longer than the 3-synchro. I found that I had to bend the lip as well as filing out the holes.

Depending on the vintage of the gearbox, you may need longer studs for the 3 studs at the top. Also longer bolts.

The thicker flange also moves the slave cylinder a little closer to the lever; I had to shorten the pushrod on mine, but you might not need to. On the 3A, I also fabricated a mount to stretch the spring tighter (make up for the relocated slave bracket where the spring normally attaches), but I'm going to try leaving it off on the '3. If it does turn out to be needed, I can always add it later.

A new pilot bearing is probably a good idea anyway; the TR6 input shaft is a bit shorter than the TR3 shaft, but it seems to work OK.

That's all I can think of, offhand.

08-02-2009, 08:52 AM
Before putting in any tr6 box replace the cross shaft bushings, the factory used some terrible rubbish on many of these and the slop just gets worse.Don't forget the fork pin too!!
MD(mad dog)

08-02-2009, 01:59 PM
:iagree: I like to use the brass bushings from the TR3, which are much wider than the narrow steel ones the TR6 used originally. Since the TR6 box doesn't have the locating pin for the shaft, you can use two of the slave side bushings.

And after suffering the dread broken taper pin myself, I wouldn't put any gearbox in without doing the reinforcement.

Geo Hahn
08-02-2009, 05:38 PM
...While the TR3 gearbox shifts OK and has a nice tight action it would seem that the TR6 box with the 1st gear syncro is a nice swap...

If it were me (and in a way it is since I have a sound TR4 box sitting in the corner) I would not bother rassling that thing in and out (plus the aforementioned adaptations) just to get a 1st gear synchro.

But then, I'm so used to slipping the stick into 2nd (to stop the first motion) before putting it in 1st that I do that on all my cars.

08-02-2009, 05:50 PM
Thanks guys, and Geo I'm starting to see wisdom in your approach. In my case the engine has to come out anyway and a new one be reinstalled so I'm thinking now is a good time to bite the bullet.