View Full Version : Volvo OD Unit

08-06-2006, 08:51 AM
Hi all, Ebay occasionly has J type overdrive units for Volvo's listed. I know that the gearbox mainshaft has to be changed, and an adaptor plate and electrics added to convert a standard four speed. Has anyone done this? Thanks, Mike

63 TR4 Surrey Top ( Back from paint shop /ubbthreads/images/graemlins/laugh.gif )
71 MGB OD & Wires

08-06-2006, 10:28 AM
I used a J-Type from a 1974 142E on a late TR6 gearbox. If you can find the super-rare 164 O/D unit , it already has the correct output flange for a TR3-6. The 142 flange is for the small u-joint. You will also need the correct TR6 speedo gears and housing. The boss's were there for the rear mount but undrilled. I'm sure there is something else I left out.

Alan T

08-06-2006, 04:24 PM
Hi Mike,

I gotta ask... Why would you want a J-type? Is it for your TR4?

Heck, I'd put in an A-type! No contest. First of all, it shifts faster and is a more durable unit. Plus, TR4 came with A-type, so installing one would greatly enhance the value of your car, while a J-type might give little increase in value, or could even reduce it in the eyes of a potential buyer, if that ever becomes important.

A-type are 22% reduction ratio, but can be rebuilt to 25 or even 28% ratio, if you wish. Most J-type are 25%, but might also be a different ratio, depending upon the car it's out of, or if it's ever been modified.


08-06-2006, 04:39 PM
I must disagree with Alan on this one. I'm running this J-Type Behind a close ratio gearbox behind a full-tilt TR4 Racing engine. It is so much smoother in and out compared to the A-Type. I ran A-Type O/D's for about fifteen years (with no real problems) but do not plan to go back unless forced to.

Alan T

08-07-2006, 12:25 PM
Thanks for the replies. I have an MGB with an L type OD, and its great for freeway driving. Would like to have same option in the TR4. Looking at the J type option because it would be a less expensive way to get overdrive. I already have a spare four speed gearbox I can use. I just don't have the $2400 that someplace like Quantum wants for a rebuilt A. Thanks, Mike

63 TR4 Surrey Top
71 MGB OD & Wires

08-08-2006, 03:44 PM
Hi again Mike,

In fairness, I have to say that when it's intended primarily for highway cruising use with a moderately tuned engine the J-type will probably do fine. Some points in its favor are that in stock form it will typically have a little more reduction (25% compared to 22%), most likely you will only be using it on top gear (where it's least stressed and OD durability is less of a concern) and you won't object to a slight delay as it engages.

That's a bit different than using the OD as a sort of "7-speed" gearbox. I.e. using the OD on 2nd and 3rd, as well as top gear to get just the right rpms in fast corners. For a more "sporting" purpose like this, an A-type might be preferred.

So, if you can get a J-type cheap, it might work out really well. Just so you know, a key reason J-type takes longer to engage than an A-type is that the A-type runs at high pressure all the time, while the J-type doesn't build up to engagement pressure until the switch is turned on. The A-type uses a higher overall pressure, too. Because of this, the A-type is a little more inclined to leak oil than the J-type.

Some other things to consider. Yes, the gearbox will still need to be modified with a shorter main shaft. It should also at a very minumum be thoroughly cleaned inside. Any used OD should at least be cleaned carefully, too. This is because the two share oil and one that's in rough shape can contaminate and damage the other. You are also correct that an adapter plate is also needed, between the gearbox and the OD. I'm not sure if the one for the J-type is different from the A-type adapter plate, but would guess it is. The electrical harness, switch and relay are all pretty easy to find or make up, so really aren't an issue.

Now, Volvo has shared a lot of parts with Triumph over the years. So, by all means there is good likelihood a Volvo OD, specifically, can be made to work. Often the major difference between Laycock OD units is the tail piece, providing different mounting methods for different cars and, often, differing speedo drive fittings and gear ratios. Even so, a fabricated adapter plate might work if the rear mounting is different, instead of trying to track down a tailpiece for the OD. And, often an angle drive can be used on the speedo fitting to resolve clearance issues, but doesn't correct for any gearing differences that would make your speedometer inaccurate. However, the speedo drive in the OD might be changeable, or the speedometer itself might be re-calibrated instead.

All are certainly issues that can be resolved. It would be great, though, to work with someone who probably has some expertise on making this sort of swap, like John Esposito at Quantum Mechanics.


09-29-2006, 09:44 PM
This caught my eye, as I want the same mod.
Is it ok to mention that there is an article describing the required changes for this mod on the Quantum Mechanics website? Pretty much what's been described but good reading all the same.
My .02 worth,

09-30-2006, 09:58 AM
I've made this conversion adding a volvo j-type OD to a stock TR6 transmission. It is not a difficult project and in the end you will have a completely rebuilt tranny complete with OD unit. All the necessary hardware is readily available as are write-ups on rebuilding your transmission while its out of the car and converting the OD unit. Below is a list of parts you will need:

-new mainshaft (quantum mech)
-adapter plate (quantum mech)
-eccentric cam/key (quantum mech)
-new rear output flange (quantum mech)
-wiring harnesses (multiple providers)
-speedo pinion gear (multiple providers)
-OD isolator switch (multiple providers)
-tranny rebuild kit (multiple providers)