TR2/3/3A tr6 OD tranny on a TR3 engine

[charleyf]

I recently acquired an A type overdrive tranny for a TR6 with serial number of CD22000. I am planning on using it on a TR3 engine. With this in mind I got to thinking about what the clutch and slave cylinder configuration should be. I am guessing that I would need TR6 clutch disc and cover plate along with the throw out bearing and slave cylinder for the TR6. I also believe that I will need to use a TR4A flywheel or have the cover plate holes redrilled and tapped on a TR3 flywheel. Can anybody help me on what to use?
Thanks,
Charley

 

[TR4nut]

Charley-

You can keep the TR3 clutch and flywheel. I think the TR6 gearbox should pretty much be a bolt in operation. You will wind up with a rear gearbox mount that is maybe 0.75" further back than where you had it before so you will need to slot the mount points to fix that.

Randy

 

[TR3driver]

There is no reason you can't use the TR3 clutch if you want to. I ran that way for a lot of miles, no issues with the clutch. I only swapped clutches later because I wanted to use a flywheel that was already drilled for the later clutch.

If you do want to use the later clutch, then you will have to change all those parts, plus the TOB carrier. Be sure they add the dowel pin holes to the flywheel as well as the 6 tapped holes. Any error in the location of the pins can cause vibration later on.

There are several ways you could go on the clutch slave mounting. I still have mine mounted TR3-style, with the slave bracket on the back of the gearbox flange. Since the TR6 flange is thicker than the TR3 was, that moves the slave slightly closer to the operating lever; so I shortened the pushrod enough to allow adjustment in the usual manner. I also made a little tab to connect the spring (to keep the tension about the same).

Another option would be to beat the flange flat on the cover that goes on the front of the gearbox, and mount the bracket there. I think the brace is threaded enough to fit; and that if you then mount the slave ears on the rear of the bracket, the resulting location should be just about right (within the adjustment range of the pushrod). But I haven't tried it.

PS, the length difference is only about 3/8". I drilled new holes in the cross member that just touched the old holes and used flat washers plus lock washers on the bottom. Also had to bend down the flange on the back of the cross member; but that may vary.

PPS, the extra length also moved the speedo cable back in the hole through the floorboards. I added a piece of slit fuel hose around the cable for protection. Here's a shot where you can see the bend in the crossmember and the hose on the speedo cable housing.

 

[charleyf]

Thank you Randy and Randall. This should get me on the right track. At this point I do not have any clutch parts so will decide which is the best way to go. I lean towards the later clutch rather than the three finger one on the TR3. But I will need to come up with a TR4A flywheel or a modified TR3/4 one to be able to do that.
Charley

 

[TR3driver]

IMO the early clutch is actually more rugged, lasts longer and works better. The diaphragm clutch was mostly to reduce costs. The only advantage of the later clutch that I can see is that it is lighter, so less inertia to accelerate in every gear. Lots of TR6 folk have lots of trouble with them, especially since many of the supplied replacement clutches are not the right clutch.

BTW, I don't see a year for your TR3. If it is before TS50000, then you'll also need to modify the transmission tunnel to clear the starter bulge in the TR6 gearbox; and use a starter that matches the flywheel you wind up with. If you don't want to lose the gearbox dipstick, it is possible to move the TR6 shift components into the TR3 top housing (which is what I did). Otherwise you'll have to put the car on a lift to check or top off the tranny oil. Another option may be to drill the TR6 cover for the dipstick (but I haven't tried that).

 

[M_Pied_Lourd]

Randall, Thanks for the tip on the speedo cable. I never thought about my drive being a little further back and now that you mention it I can see what you mean. Mine has a TR6 tranny, clutch, flywheel conversion mated to the original A type that came with the car. Cheers,Tush

 

[sail]

The smallest of your issues but I had my 4A cover drilled for a dipstick with success. Nice to have. The OD is wonderful to have, a mantra for you while on your back under the car.

 

[charleyf]

This TR3 project is a compilation of parts that seem to mostly come from TS 30000. But I have found some from later and some earlier. It is interesting to note that as much as the cars did not seem to change over the years there were a number of small changes in the pre TS 60000. I have looked over the Spare Parts Catalog and viewed many of the changes over the years. But I sure have missed a lot of them like the transmission cover you mention. Thanks for the additional input. I appreciate your thoughts about the TR3 clutch being the better of the choices.
Charley:joyous: