J Type Overdrive Conversion

[oxendine]

Bought a TR6 overdrive unit from a fellow member here. Can anyone tell me what all I'll need to adapt it to a TR4 gearbox to be fitted into my 1960 TR3. I realize an adapter plate is needed and I have found one. What else to do?

Thanks, Donnie

 

[tdskip]

It is usually better to buy a complete gearbox. Some of the internals are different, with the biggest difference being the mainshaft. Check out;

www.quantumechanics.com

 

[HerronScott]

Donnie,

This is definitely a J-type overdrive? If an A-type overdrive, it's relatively simple as you would just need an A-type overdrive mainshaft, A-type adapter plate and the overdrive itself. I did this installing a TR3 overdrive unit to my TR4A transmission.

Installing a J-type overdrive in an earlier transmission is more complicated as I believe it involves not only the J-type overdrive mainshaft, J-type adapter plate and overdrive but also some additional pieces due to other changes they made in transmission at the same time. Quantum Mechanics seems to indicate you would need the input shaft and matching cluster gear wheel from a later transmission as well. You will also need to deal with the different rear transmission mount as well.

You might be better off trying to trade that J-type overdrive for an A-type overdrive.

Scott

 

[TR3driver]

Are you sure you got a J-type? A J-type adapter is more of a housing than a plate; and TR6 used either A-type or J-type. The A-type conversion is much easier. Here's a shot from the Buckeye Triumphs site, with the adapter housing on the left and a J-type on the right

Assuming you do have a J-type, here is a partial list (just the major things that come to mind, I'm sure others will supply the ones I've skipped or overlooked):

Find an OD mainshaft and matching gear set. If I recall correctly, there was no factory mainshaft that would work with the J-type OD & the TR4 gearset, so you'll have to find a late TR6 gearset and either install it in your TR4 housing or just use a late TR6 housing. If you do use the late TR6 housing, there are some minor adjustments to make it fit (like longer studs in the back of the engine block and a shorter pushrod for the clutch slave). Another option might be to have Overdrive Repair Services in the UK make you a custom mainshaft.
https://www.overdrive-repairs.co.uk/

Might as well replace at least the bearings, seals, synchro rings and countershaft thrust washers, since you'll be doing a full gearbox tear-down to install the mainshaft (and gearset).

Fabricate a new rear crossmember to mate with the J-type. The J-type sits farther back than the A-type, so it passes right through where the original TR3 rear crossmember goes. Some cutting of the frame and floorboards may also be necessary.

Drill and tap the top cover for the isolator switch. The required thread is an unusual metric pitch, not found in most sets. Here again, might as well change the seals while it's apart.

The speedometer drive ratio will be wrong, so you'll need to either change the gears or get a ratio adapter made. Most likely you'll also need an angle drive to hook up the speedo cable.

Of course you'll need to wire the whole mess up. A relay is not necessary (although you can use one if you want to); but I would suggest a snubber diode across the solenoid to keep the inductive kickback from eroding the contacts in the relay or switches.

I think that's all the major items.

FWIW, I opted to install a J-type in my early Stag, and I'm rather sorry I did. I got really spoiled with the instant shifts and 2nd OD with the A-type in my TR3A. Much "sportier" than the J-type, IMO. The A-type seems to practically read my mind and shift before the switch has stopped moving, while the J-type takes a count of 3 or so (longer at low road speeds) to shift into OD. Makes it totally useless on twisty mountain roads IMO, while the A-type is a definite benefit.

 

[Brosky]

I do wish that I had a second gear option, but I do get instant shifts on my J-type. Others who have ridden with me are amazed at how fast it shifts in and out, but it's been like that since I bought it from John at Quantum. I only use 30W ND oil as he recommends.

 

[TRDejaVu]

I never quite made it to OD status this time around (I had it 30+ years ago). My freshly rebuilt TR6 A-Type OD trans is sitting on the floor next to the car instead of being installed in it. TR4 and the trans will be going up for sale soon.

 

[glemon]

Good advice from all on this list already will add that if you go this route there is a good conversion instruction site, here https://www.buckeyetriumphs.org/technical/jod/AdaptingJOD/AdaptingJOD.htm

As well as lots of other good technical information, I am not sure if the this will work on the same on the earlier frame, but it may give you some ideas you can adapt if there are diffferences, I used this method on my car and it was a pretty easy deal and worked well.

Will add that I did my first gearbox rebuild mating the J-type O/D to my Tr250 box, had to take all apart, rebuild, fit new mainshaft, great help from the buckeye triumphs rebuild site plus I bought my parts from John at Quantum mechanics, and he answered rebuild questions I had via e-mail, great resource.

 

[TR3driver]

but I do get instant shifts on my J-type.

Can't be as fast (or as hard) as an early A-type. The A-type has a big accumulator that holds full pressure all the time, so when the solenoid moves that pressure is immediately dumped into the operating pistons. The J-type has no accumulator, so after the solenoid operates and the dashpot moves, that little one-lung pump has to build pressure before the clutch ring will move.

The A-type operation actually had to be slowed down for IRS cars, because the shock was tearing up the differential mounts.

 

[cheseroo]

The A-type operation actually had to be slowed down for IRS cars, because the shock was tearing up the differential mounts.

I've got a J-type in the 6 and A-type in the 250. My little driving game entails trying to be very adept at timing the engagement with the J-type (engage OD, lift off throttle, resume throttle) to where it sounds like a regular gearchange. Every time I do the harsher engagement of the A-type, I mentally cringe at the shock the diff mounts must be going through. I know they've be reinforced and all but it just *feels* like it can't be good for stuff under there. No criticism, just an observation.

As to mating a J-type to a TR4 box, it sounds to me like it would be the hardest possible permutation of an OD retrofit with modifying a 6 box to fit the 4 chassis the next easiest with just going to an A-type the ideal solution. I've rebuilt my gearbox with the buckeye instructions and it's pretty straightforward. As always, there is lots of help to be found on here.

 

[Brosky]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Can't be as fast (or as hard) as an early A-type.[/QUOTE]

I have to agree that it is not as harsh of an engagement as the "A" types that I've ridden in, but it is just as fast. Once you flip the switch, it is engaged or dis-engaged at that instant. No delay whatsoever.

 

[DNK]

Paul, did yours come from Quantum or been gone thru by them or is it stock?

 

[TR3driver]

Every time I do the harsher engagement of the A-type, I mentally cringe at the shock the diff mounts must be going through.

You could always use the clutch to soften the shift. That's what I do most of the time, for "casual" shifts into OD. But at full throttle, I get just a nice, solid kick in the pants; much like a performance automatic transmission. Of course, the alloy flywheel makes a big difference too.

 

[TR3driver]

No delay whatsoever.

Well, I've explained why that is physically not possible. So I guess you're entitled to your opinion.

 

[Brosky]

It was rebuilt and installed by Quantum. I guess I must have a defective unit because it does what is physically not possible.

 

[sail]

Must be the chrome.

 

[Brosky]

It's probably the red paint. That's what Don blames most of the time.

 

[DNK]

Paul, the reason I asked was maybe Quantum knows how to juice up the shift a bit.

 

[Brosky]

Don, you may be right. After I picked it up and drove it home, I called John to tell him that everything was fine, he did ask me if the shifts were smooth and quick. Having not experienced anything but that, I said yes.

That's why I said that others, such as Eric from Her Majesty's said that he noticed how quickly it engaged and disengaged, I assumed that was to be expected. I never questioned why he said what he said.

But if John did do something, I have no idea what it could have been as he never pointed out anything special on his bill or when I picked it up.

 

[DNK]

Think we might need to do a little water board torture to find out

 

[Brosky]

He is clever and probably knows more about these than anybody. He would be the guy to ask if there were a question.