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TR2/3/3A TR4 Gearbox in the TR3...Finally!

CJD

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The TR3 side is a bit slow...so I thought I'd report on my little side project. The kids helped me finish off the TR4 tranny and we installed it 2 days ago. What a difference having a 1st gear synchro! Now they are zipping around the neighborhood learning to drive a stick.

For those that don't remember, I bought a $100 tranny, along with a pile of odd triumph parts about 2-1/2 years ago as part of an estate sale. The pile paid for itself many times over during the TR2 rebuild...but the tranny was the reason I bought it at all in the first place.

The no-synchro first is a true PITA. Any time I let someone drive it (like during state inspections), they always ground 1st, no matter how many times I warned them about it. I even occasionally ground 1st if I got distracted and wasn't paying attention to which car I was driving. Anyway...I HIGHLY recommend the swap if you plan to actually drive your TR3!

For the technicals...the swap is straight up, no surprises. The bolts and studs have to be exactly 1/4" longer if you go with a later box, with the thicker flange. I just took the bolts to the hardware and replaced them for longer. The TR3B or early TR4 boxes have the same thin flange as the 2/3, so no new bolts if you use that one. The drive shaft has enough play to take the 3/4" longer location of the drive flange with no trouble, as the TR4 box is about 3/4" longer total than the 2/3 box.

The only real mod that is required is to the rear tranny mount, which is also 3/4" farther aft for the TR4 box. I had planned to modify the cross-member support, but when I looked at it, I chose to simply slot the tranny mount holes. That way the mod is only to the replaceable rubber mount, and not to any parts that are permanent. The slotting took all of 5 minutes.

Oh...due to the thicker flange, the clutch cylinder actuating rod was a bit too long after the swap. The flange moved the cylinder closer to the clutch lever by 1/4". I merely mounted the cylinder on the front of the mounting plate, and I then had enough adjustment so that even that worked out great.

This particular box was in very bad shape, if you have followed the pics in my tranny rebuild thread. Broken countershaft, broken gears, chipped dog clutches, starter pinion exited the bell housing through 2 holes, etc. I rebuilt it on the cheap, grooming gears and parts to see how far I could go with it. So far the results are great. No sticking going into reverse or forward gears and smooth shifts. I'll update with a long term report if any problems pop up...

But...these old TR4 boxes are available on Ebay for less than the cost of shipping. So, if you are still fighting that 3 synchro box, I highly recommend this as a relatively quick and painless upgrade!
 
Hi John,

I hope to experience driving my 60 3A soon that has a TR6 box installed with the original A type OD that came with the car.
The 59 still has the original non synchro box also with the OD So it will be an interesting comparison.

Cheers
Tush
 
Tush, you need to get all those cars on the road. I bet you are like me trying to find a place to park all the projects...!

If I like the OD box, once the TR2 is running, I may have to start looking for TR4 OD's for a later project on the TR2!
 
I fully agree with this. I rebuilt the non-synchro 4 speed (3.5 speed?) in my TR-3. I put in new a counter shaft and bearings, synchros, springs and ball bearings in the shifter hubs. It shifted great in 2nd, 3rd & 4th. Then I broke a tooth off the 1st gear / reverse cluster. It went clack-clack-clack when I drove it.

About a year later I picked up a TR-4 gear box on ebay. It was described "in need of rebuilding, you must keep your hand on the gear **** to keep the car in gear". I picked up a rebuild kit from Quantum Mechanics, along with a top hat bushing. Again I replaced the springs and the ball bearings in the shifter hubs and the shifter housing. It works great. I enjoy that the next gear shift is a click away. The fit up was easy, I filed a slot in the rear cross member for the additional transmission length.

I wish I had the money I spent on the 3.5 speed rebuild! Live and learn.

Roy
 
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