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TR6 TR6 "J" over drive install

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Airfix

Airfix

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Thinking of doing an overdrive conversion to my TR6, anybody out there done this? any suggestions? It's a 1976 and the unit available to me is the complete gearbox with the J type fitted. I will need to buy the column switch, wiring harness etc. Does anybody know if the relay was installed on all cars even if they weren't original OD?
I have a relay on the left aft side under the hood which doesn't seem to do anything, it has an white with orange stripe wire to it which when connected causes the relay to operate. Wondered if this might be the OD one.
Appreciate all comments and suggestions. /ubbthreads/images/graemlins/confused.gif
 
This is a no brainer if you have a complete gearbox with j-type OD all set to install. My understanding the J-type did not have a seperate relay as did the A-type. But check your TR6 wiring diagram resources just to confirm this. The J unit you have is all set to mount on your existing gearbox mounts so you'll have no issues there. As you mention you only need the upper and lower wiring harnesses and the steering column mounted estucheon and switch. All these parts are available from the usual providers.
 
I agree that given what you have available, it is a no brainer. This past summer I did an A-type conversion on my TR4A, but I had to fix and mount the O/D unit to a non O/D tranny. With what you have you could do the swap all in a Sunday afternoon. you will be most happy with the results.
 
I'm not sure if you'll need a longer speedo cable and angle-drive for this unit also. I had to get those for my A-type conversion. It was also a straight swap since I have an early car ('71). You'll probably want to do some clutch work while you're in there too?
 
I wrote an article detailing the retrofit I did with my 70 TR-6; it's still on the VTR website under maintenance pages. It's an A type, but most of the steps would be the same.

Good luck,
 
I just had mine done in CT by Quantum Mechanics and couldn't be happier that I finally made the move. It's been great on the highways and it really cuts down on the noise in the car. Shifting in and out is easy as flip up or down and feather the throttle.

I would make sure that the unit is flushed clean and new oil and filter are installed prior to putting it in.
 
Adding overdrive is definitely an improvement. I am in the process of converting my non-OD '71 TR6 to a j-type. In fact the donor OD unit is from a Volvo which creates a couple of extra issues. Generally; teardown the tranny so that the mainshaft can be replaced with the j-type main. Then add the rear housing adapter and the new OD unit. The volvo OD has a different speedo gear and pinion which must be replaced to accomodate TR speedo plus the rear flange must be changed to match up with existing driveshaft. Then drill the gearbox top cover for an additional interruptor switch for the OD, add the various wires and switches and then fabricate a gearbox mount system to accomodate the j-type unit to the early TR6 frame. Seemed like a lot of work when I started but its all just methodical.
 
Hi,

I agree with all the others, an OD is great in today's driving environments. Go for it! I don't think you will ever regret it.

I also don't know if TR6/J-type used the relay, better check a proper wiring diagram. However, I can tell you on the earlier cars with A-type, the relay is mounted inside the passenger compartment, in the passenger (LHD/US spec) side footwell, near where the wiring comes out of the gearbox cover. It's the same type of rectangular silver "tin can" Lucas relay used in a number of other applications on LBCs.

Other things you might want to consider...

Most J-type are set up to work on 3rd & 4th gears. It's possible to set up to use on 2nd, as well, if you wish. This just requires another isolator switch fitted to the gearbox top cover (which needs to be drilled and tapped in the right place, as shown in factory service manuals). It also uses a slightly different wiring harness, as was used on TR3/4/4A/250/5 with A-type.

However, hard use of 2nd gear OD is not recommended. It should be used with care, especially with stonger pulling, upgraded engines. Probably the J-type is more tolerant than the A-type, and particularly the earlier A-type, which shift into OD much more firmly.

So, it's just a matter of whether you want OD for better cruising, or 6 or 7 speed capability for "ideal rpm" shifting to get the best out of the engine in a wide variety of driving situations.

Another cool option is to add a "logic box" (aka, "black box") offered by Revington TR. Their clever OD controller makes shifting more progressive, since the box takes over turning off the overdrive with each shift, by sensing when you move the gearbox lever. This means less reaching for the OD switch lever by the steering wheel and is especially nice if using the OD for "ideal rpm" driving, more like a true 6- or 7-speed.

In conjunction with the "black box", I am setting up a button on the shift knob itself, to actuate the OD. It just feels more natural to me.

Do you know the history of the OD/gearbox you're looking at? If not, it might be a good idea to have it looked over by a good shop, such as Quantum Mechanics, before installing.
However, if you are fairly sure it's in good condition, but it has some miles on it, I'd suggest refilling it with 40W non-detergent (racing) motor oil. If it's a recent rebuild, with no or few miles, 30W might be more appropriate. Run for a 100 miles or so, then change the oil, just to get it flushed out.

If not doing a rebuild, you might be able to tell what reduction ratio the OD is, based upon the serial number. The first two digits should be 25 or 28, which would indicate either 25% or 28% reduction. Most TR6 were set up with 25% originally. However, some might have 28%. Also, if the unit has ever been rebuilt, it could have been changed to a different reduction than indicated by the serial number.

Finally, your car is probably fitted with a 3.45:1 crown wheel & pinion set in the differential. With the OD this will make for quite low rpms at highway cruising speeds. You might like that, but optionally could have 3.7:1 or even 4.1:1 fitted for better acceleration. I think UK-spec "PI" TR6 were usually fitted with 3.7:1, whether or not they were fitted with an OD. 4.1:1 was used in the 4-cyl. cars with OD, while 3.7:1 was fitted to non-OD cars.

Have fun!
 
Alan
What setup are you using for the shift lever mounted OD switch?
 
[ QUOTE ]
Alan
What setup are you using for the shift lever mounted OD switch?

[/ QUOTE ]

Hi,

Here's a picture of it installed but not wired. (Note: Hmmm, I guess I could have dusted it off first... at least I put a piece of white packing material behind it to help see it better in the photo).

I modified an old shift knob that was lying around gathering dust. It's one of those aftermarket leather-covered knobs. They are wood underneath the leather, so pretty easy to work with. The emblem was easy to remove from the top, just glued on. A Dremel hollowed out a space for the switch and I drilled a hole out through near the mounting hole, to route the wires out the bottom (a hollow shift lever would be even better, and I understand might have been used on GT6, Spitfire or Stag).

The button switch is a round, black plastic one from Radio Shack/ It's bezel is just slightly larger than the emblem originally on top of the knob, and is slightly curved. It's a prefect fit.

When hollowing the knob, I made it a tight fit, so the switch stays in tight without any glue.

Looks almost like a factory installation. I still might try to hide the wiring on the shift lever with some heat shrink tubing, but the car has no wiring harness at all right now, so that project might wait for a while!

Another possibility, there are a number of drag race-oriented places that sell knobs with switches built in for either nitrous or line locks. www.summitracing.com has quite a few, probably jegs.com and others, too. Many seem to have a shift pattern or logo imprint that might be a problem if engraved, but might just be printed so it could be wet-sanded off. Some are T-handles, others are round like the original TR4 knob, some in black, some white.

Another option would be a push button switch that's mounted on the shift lever itself, just below the knob. I've seen a variety of these, pretty sure something could be found to do the job.
 

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Thanks for all the great input.
I bought the trans/overdrive setup. It's a 25% unit.
The whole setup is spotlessly clean, not a speck of dirt or oil anywhere. I checked out the number on the gearbox, it's a GRXXXXX, had me worried for a few minutes as the TRF spares list calls for a CC, CF or CDXXXX gearbox. I went to the Rimmer Bros website and apparently a GR prefix means factory overhauled. The unit looks so good it may just be fresh from overhaul.
The guy I bought it from imported it from the US and was told everyting had been done, (no paperwork though)bearings, synchros etc. I can see the new gasket edges on all the cover plates, the mainshaft has no play and shifting is smooth (not that it means much when it's just laying on the floor. Checked the solenoid with 12 volts and the reverse and 3-4 switches with a meter all work fine.
I will give an update once installed, plan on doing that in late Feb, early March just before driving season, just in case I will be putting a few miles on it before reinstalling the entire interior. /ubbthreads/images/graemlins/driving.gif
 
[ QUOTE ]

Finally, your car is probably fitted with a 3.45:1 crown wheel & pinion set in the differential. With the OD this will make for quite low rpms at highway cruising speeds. You might like that, but optionally could have 3.7:1 or even 4.1:1 fitted for better acceleration. I think UK-spec "PI" TR6 were usually fitted with 3.7:1, whether or not they were fitted with an OD. 4.1:1 was used in the 4-cyl. cars with OD, while 3.7:1 was fitted to non-OD cars.


[/ QUOTE ]

I'm thinking 3.7:1 was on the carb TR6, and 3.45:1 on the PI 'home market' TR6 because there was more torque. I could certainly be wrong and I'm sure it would be easy to look up- perhaps someone wants to chime in with the authorative answer on that one. I do think the 3.45:1 with OD would be fine on a well tuned stock spec carb car and would make for even more relaxed cruising- would just lose a bit of acceleration.
 
Just installed the o/d unit, had to modify the output flange, redrilled the holes and machined about 0.100" to allow the drive shaft to fit into the relief, looks like it was a Volvo short flange.
Cars is up on ramps and blocks and it seems to work with no load on it.
Question? what about that steel bracket which bolts from the shifter housing to the aft mount on the regular 4 speed? How is it mounted on the o/drive? I can't see how it can work, no pics in any parts books either.
Any ideas welcomed.
/ubbthreads/images/graemlins/confused.gif
 
[ QUOTE ]

Question? what about that steel bracket which bolts from the shifter housing to the aft mount on the regular 4 speed? How is it mounted on the o/drive? I can't see how it can work, no pics in any parts books either.
Any ideas welcomed.
/ubbthreads/images/graemlins/confused.gif

[/ QUOTE ]

Mine doesn't have one. Leave it out.

Bill
 
Thanks Bill,
mine doesn't have it now either. Took it for a spin with the tunnel still removed, one oil leak from the rear top left stud on the OD unit, I had removed the nut and put a harness clamp there, tightened it up alright but it still poured oil, removed the clamp and the washer looks like its copper. Anyway installed the nut with no clamp underneath and no more leaks.
It all seems to work good, was surprised at the jerk on engagement though, never ridden in an OD car before.
Time to install the interior
 
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