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Triumph TR6 - OD transmission upgrade

Hello Gents.
I hope some were able to get to the ATDI in Steveston BC. It was a great show.
My question is directed to those who have upgraded to a J type OD and rebuilt transmission.
While I'm in there, what else should I be upgrading or replacing? My clutch seems to be working ok.
I'm going to go with the poly and fiberglass diff covers with new seals and hardware.
Ujoints? All the release hardware? Mounts?
Steve Crosby


Propshaft UJ's and balance. While you have the 'box out it is an easy time to do this, impossible at any other time.


T Sharp

Steve-I would disassemble the OD and check the clutch lining thickness remaining to the rivets. I think they are considered to be worn out at .040". New ones are $200+, but better to replace it now than having to R&R the trans/OD after installation.
Berry Price-I was at Stevenston, but my TR6 wasn't.
BTP Price

I've recently installed a J type onto my 4 speed gear box. I re-built the original box first then put the re-furbished J OD on the back. That part was easy. The rear mount for the new unit did have to be modified. I used a 3" x 9" x 1/2" steel plate and ensured the driveshaft was in line with the drive plane through the gearbox. I placed the gear box in then marked the location for the holes.

I'm now getting an extra 5MPG and the car is a lot faster. But there were issues: see my post re: OD not disegaging.

Be carefull about having the propshaft directly in line with the gearbox centerline. Your U-joints will stay in the same relative position (no oscillation) and will tend to wear out the needles/cup much quicker!

If you plan for a few degrees offset the needles are in constant motion spreading the grease and wear around.

Check on-line for the British V8 Newsleter - it had a good discussion about this several years ago.

Since the MGs and TRs use the same type of driveshaft, here's a link to an article I wrote a few years ago about 'out of phase' U-joints:

Good luck,
Tom Sotomayor

Great article Tom. A few years ago, I was experiencing a nasty vibration at the differencial. I thought at that time it was the Drive shaft alignment and attempted to true it up a bit. It seemed to work. But you're point on bearing wear is well noted. As you say, a happy middle is required (1 to 3 degrees).


Thanks for your input.
New clutch is in and I think I finally have all the bits and I'm getting ready for the final assembly. Can someone please tell me where the OD relay is normally located?
Steve Crosby

Depending on the year, there may not be a relay. My 75 doesn't have one - check your wiring diagram. You will love having an OD!


BJ Quartermaine

I don't think that the J type requires a relay as the solenoid only draws 2 amps.
Berry Price
BTP Price

Thanks for your response Barry and Berry.
Further studying of wiring diagrams shows no relay. One less worry.
How is the backup light switch wired? Do I just double up on the switch tabs? Do I use the original wiring along with the new lower harness for the OD? Anyone have a good description of the wiring or photos? I have some schematics, and itís unclear.
It won't be long now!
Steve Crosby

On the top of your tranny is one interupter switch. This one is for the prevention of having the OD on and going into reverse gear. The switch on the side of the tranny top cover at drivers side rear is the reverse light switch. It should have a green and green/brown wires to it. Does not matter which spade connector goes on either terminal of the switch. The switch can be tested by simply taking you OHM meter to the switch. OHM meter across terminals when not in reverse gear (engine does not need to be running) you should get open circuit. Put tranny in reverse and you should read below one OHM.
(If your tranny top is '74 then it will also have seat belt interlock switch on RH side).

I agree, you will wounder how you drove the car without the OD.
Rick Crawford

Hello All,
The transmission has been installed and there are issues. During the first test run I found that the fist times the switch was operated in third and forth gears, the shift to OD was delayed and very harsh. I returned to the shop and checked the transmission fluid. About a cup full drained out before it stopped level with the bottom of the filler hole. I'm using Castrol 30 weight non detergent as suggested by the rebuilder. I did another test run and got only one good shift into OD in fourth gear, smooth going in and rough shifting out. Again the shift was delayed. I suspect that the oil is too light. What do you recommend? Any other suggestions would be appreciated. I also found that the column switch was faulty. I rebuilt it and will check it out with a meter tomorrow. Iíll replace it later. I really donít want to dismantle the dash again, just yet.
Steve Crosby

So .... I drained the transmission and refilled it with 80/90 hypoid. The test drive was much better. The shifts are harsh still but more positive. I suspect the switch is still not consistent and so will replace it this weekend.
The 30 weight non-detergent was not the best idea.
I ran in OD top gear for only a mile or so and ran into rain. With the transmission tunnel cover missing, it's quite the sports car experience.
The saga continues.

Steve Crosby

This thread was discussed between 15/08/2007 and 21/09/2007

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