Converting a non-o.d. tranny to a J-type

I want to take this opportunity to say what a great website you have here. I was searching the web the other day for some information concerning an upgrade I'm considering for my transmission and came across the British Car Forum and I've got to say I'm extremely impressed, both with the quantity and the quality of questions and answers I've seen so far. I had to join to become a part of this forum and I hope to be able to contribute in some small way. But I must say, I'm not as knowledgeable as most of the people in this forum and so will only put in my two cents when I'm sure I know what I'm talking about, which isn't often...
Now, for my question: I have a TR250 that has a rebuilt TR6 transmission (#CD31144). Recently, I bought, on e-Bay, a complete, re-built J-type overdrive with the correct mainshaft which I plan to install on this existing tranny. Has anyone out there ever attempted this before? If so, could you give me pointers on what I'll need to do in order to pull this off. How much of a job is it to change out the mainshaft? I've also read somewhere that attaching the rear tranny mount can be a real pain. Any help anyone can offer will be greatly appreciated. /ubbthreads/images/graemlins/driving.gif

arbs, it's just a matter of rebuilding the tranny for the most part to get the new main shaft in, BUT!!!, now for the tricky part. Lining up the gears in the rear is a pain, if you can set in on the floor and figure out some way to keep it from flopping around, never had any luck going horizontal on a table. Any good maintenance work shop manual will tell you more than I can on the forum, as the adjustment on the solenoid is the most important. Don't put you fingers between the two cases when sliding home, it tends to go in a hurry. Wayne

Thanks for the tip, Wayne... but tell me, what do you mean by "going horizontal on the table? Dave

He means it's easier to assemble the rear section while the trans is standing up on the ground rather then laying down on the bench.

I thought that was what was meant, but wasn't sure... by the way, I found some great tips in past forum questions, i.e. Quantum Mechanics and a great article on the Buckeye Triumphs forum about attaching the rear of the tranny...Thanks for your help and will continue postings on how this turns out. Dave

Hey Dave, while you have the J-type out of the car, would it be possible for you to take some photos and measurements for me? I was at the PRI trade show last Saturday with a couple other TVR owners and we saw what appears to be an updated Laycock overdrive that they rate at 1200hp.

I don't have a J-type of my own to take measurements of, or a D-type for that matter (just in case someone wants to take D-type measurements & photos).

I'd be happy to. The only thing is that the o.d. unit is somewhere between here, central Maine, and New Zealand. (I sure hope that guy is legit...in all fairness, he was very helpful when I had some concerns about the mainshaft fitting my tranny). Anyways, I have yet to see it. So, if you are in no rush...

arbs,
Two years ago I bought an overdrive on e-bay from a guy in New Zealand. I wonder if it is the same guy? If I remember right, he owns a auto repair shop. The O/D is out of a Triumph 2000. It works great.

The gentleman's name is Ian Priestly. I don't know what he does for work, but he's knows quite a bit about overdrives. After I bought the unit, I got to thinking that maybe I should have asked a few questions as to whether or not the unit would work on my car. He said he would send the correct mainshaft if the one in this package was the wrong one, and would sell me another shaft and a gear that would be needed if I had the earlier transmission. As luck would have it, the person I bought the car from had replaced the tranny with a later TR6 tranny, which is the one I needed for the o.d. that I bought. Hope he's the same guy. Did you do the conversion, or was it a replacement? Dave

I just found the old e-mails from him. His name was Terry Cartwright, so he is not the same person. I did the conversion myself. At first I was a little apprehensive about doing a tranny job. I'm mechanically inclined and have worked on every other part of the car but for some reason I thought the tranny would be overwhelming. It turned out to be a fairly straight forward job. So much that I ended up pulling the gearbox out of my tr3a and rebuilding just for fun. Do you have a Haynes manual. I have both the Haynes and tr6 workshop manual and found Haynes to be dead on accurate. The important things is when you have the old mainshaft out with all the gears/synchros on it to remove them and keep them in the same order and direction on a dowel or rod. Don't want to get the various parts mixed up and don't rely on your memory. The only hassle was removing the main circlip off of the mainshaft. Mine did not cooperate so expect to buy a new one (cheap part). Also, now is a good time to replace the synchros. Also clean and examine closely every part for wear and consider replacing any bushing or bearing that shows any wear. The last thing you want to do is do another rebuild a couple thousand miles from now. I also replaced the throwout bearing,clutch etc.since they will eventually go. Also, make sure you replace with the correct oil. There is a lot of different opinions on that...I use GL-4 gear oil. One more thing, you will need a 90 degree angle drive for the speedo cable. Let me know if you have any other questions and I will try to help you out

Hi,

I know the TR6 gearbox is pretty similar to the TR4, which I'm familiar with, and would assume it's also difficult to get the retaining ring off the mainshaft to remove the gears, and equally challenging to reinstall? Seems to me I saw either Roadster Factory or Moss sells special tools for the job, but pricey at nearly $200 for the set, but nearly mandatory to rebuild the tranny. Another challenging thing is removing the large castellated nut at the rear, which is torqued to 90 ft lbs. There was a special factory tool with a long handle and pegs that fit into the 4 bolt holes on the flange, that attaches to the drive shaft, to hold the shaft from turning while loosening or tightening the large nut. It should be possible to make a tool, with a little ingenuity.

I agree that while the gearbox is apart you should definitely replace all seals, major bearings and the synchros, at a minimum. Some of the vendors sell all the commonly replaced items in a kit for a discount.

And yes, use GL-4 gear oil, again assuming the gearbox is essentially the same as the TR4. There are brass parts inside that will corrode if the newer GL-5 gear oil is used. I think it's sulfur content in the newer stuff that is the problem. It's not easy finding non-GL-5 in the local auto parts places here locally. But, I did see Redline synthetic at one shop, and that states it safe for this sort of gearbox.

I've not installed the J-type, have an A-type in my TR4 project car (not yet back on the road) and there are a number of other small items you'll need, assuming it's pretty much the same. There is a wiring harness and, probably, a couple switches that need to be installed in the top cover of the gearbox. To do this, the top cover must be drilled and tapped in the right places. A good shop manual provides all the details on where to drill. The switches operate by preventing the OD from engaging in certain gears, allowing it to engage in others.

The info about the actuating solenoid is correct, too. Proper adjustment is very important. The solenoid actually has two coils: one strong and one weak. The strong one pulls the lever to engage the overdrive, and the weak one holds it engaged until power is released. If not properly adjusted, the strong coil stays engaged and will burn out the solenoid very quickly. It's a little different arrangement on the J-type, than on the A-type I'm using. Your solenoid is horizontal, where it sits vertically on the A-type.

One other item you'll likely need is an adapter plate on the back of the gearbox, before it's possible to attach the OD. I know it's sold separately and required for the A-type. This installs first and there are instructions on safety wiring the bolts in the service manual.

Then when installing the OD you have to do a series of things, sometimes seems you don't have enought hands. There is an oil pump that builds pressure to actuate the OD, and the plunger for that needs to be retracted a little to allow it to slide into place on an eccentric lobe. At the same time, you'll likely need to have the gearbox in top gear, turning it to get the shaft to line up and engage with the OD.

It's a bit of a project, but certainly one that someone with modest mechanical skills can do. As others recommended and I've already mentioned a couple times, the service manual is very helpful. The procedure and all necessary accessory items are carefully spelled out, because ODs were fairly commonly added to cars by the dealers and their service departments needed to know how to handle it. I have Haynes and a good reprint of the factory manual. Each is useful in its own right and I often find myself double checking info from one to the other.

Good luck with your project!

Thank you, Mike and Alan, for your words of encouragement. I wondered how difficult this job would be and wondered if I would be better off in the long run to hire the work out. That's why I've been searching the internet for any information I could find, knowing that there has to be someone out there who has done this same thing and was succesful and was willing to share their experience. I'm somewhat mechanically inclined as well and thought I could do it as long as I knew what I was in for. There's nothing like the voice of experience to kind of light your way...like using dowels to keep the gears in their proper order. Brilliant! /ubbthreads/images/graemlins/cheers.gif That tidbit alone is worth the price of admission in my book. As for GL-4, Alan, I have a gallon of it in my basement...aging, like a fine wine, just waiting for the day when I crack that baby open. Dave

Hi again Dave,

I looked it up after leaving my previous post and need to correct one thing. The solenoid setup on the J-type is quite different from the A-type, so may or may not be as critical to adjust.