XJ6 Series 1: Conversion To GM T700 4 Speed Auto
 

Hi, I am a new member from Australia. I have previously owned a 1985 XJ6 Series 3 however I am currently looking for a good XJ6 Series 1. Originally I was looking for a manual however as we all know they are very scarce and the ones that I did look at required a lot of TLC. It appears that that I will have more luck with an auto and I am considering the option of replacing the 3 speed auto with a Holden/GM T700 4 speed auto. If anyone has done this modification or knows of someone who has done the modification, or has any comments to make I would be very interested. I know it can be done and I am curious to find out what is involved and any good/bad outcomes. Cheers, Brendan

Why not just convert to a 5-Speed

remember that the jag is a lot heavier car than a duunydoor, i understand your reasoning as plentiful supply and cheap, but they arent that strong, personally if i was going down that road i would look for a zf out of an xj40 or a zf4hp22 out of a v8 landrover discovery 1[v8 not tdi]as they are plentiful/cheap and reasonably strong and non electronic[no computer needed-just a kick down cable], either way you will have to make an adapter plate and create a speedo sender

At least here in the 'States the TH700 conversion is very popular with Jag owners. There's an outfit in Texas (Johns Cars) selling a kit with needed conversion parts.

I've never heard any complaints. Everyone seems happy with the result. The 700 is amply robust for the weight and power of a Ser I-II-III XJ6. The lower-ratio first gear gives better off-the-line acceleration and the o'drive fourth gives relaxed highway speed RPM.

Except for the cost there really doesn't seem to be a down side.

Cheers
DD

Have both 700R and 200R in Series 1's
 

The 700R works fine in a Sereies 1 Jaguar - the stock shifter works it properly. Just install, line it up and pull to the first forward gear from Neutral... that is OD.

I have a 200R and 700R (but both are behind V8's) and they stand up to the V8 HP/torque well so the meager Jag power should be easy.

Setting up the TV cable has to be done properly or the trans will be quickly ruined due to the incorrect pressures. There are many good sites with instructions and a pressure gauge should be used. A good trans cooler is helpful.

I've had a ser3 xj6 with 700r4 behind it and now run a ser3 xj12 with the same transmission. Both made a nice improvement to the OEm Borg Warner or GM 400 three speeds. The six can lug a bit in overdrive at lower speeds. I got used to it and would sometimes shift it out of overdrive when running around town or on steep grades just to keep it from hunting between 3rd and 4th. A series one's lower final drive would be better. The v12 pulls the overdrive with no trouble and the 700 seems like the perfect auto box for it.
I used the Johns Cars kit for both cars. It's a fairly easy job as far as non-stock tranny conversions go. I'd give it a three on a scale of 1 to 5 in difficulty. As Roger said, the TV cable adjustment is important but there is a lot of information available on that.
One point: don't pull the cable out unless the engine is running and pressurizing the trans pump. The throttle valve will stick in full open if you pull it without hydraulic pressure to push it back in. Un-sticking it requires removing the valve body.

XJ6 Series 1: Conversion To GM T700 4 Speed Auto
 

Thanks for the replies, especially Rodger Mabry & Jtestrake. I am aware of Johns Cars and the 'quarterbreed' conversions and unless there is an equivalent supplier in Australia, I will probably purchase from him. I am not 100% certain however I believe that the rear axle ratio might be 3.31, perhaps 3.07 (manuals are 3.54) and I understand that at times the .70 overdrive ratio might be a bit high.... I have driven a Series 2 and 3 manual and it was the higher gearing of these vehicles that really impressed me. Thanks again for the comments and I will post again as the project moves forward.

I have heard of a conversion here in Australia using a Ford 4 speed automatic. Namely the BTR trans. They are made in Wagga. Detachable housing. Used in everything front Falcon to Diesel 4WD. Ssangyong use them in their later Musso diesel .

Mike

Gday Brendan,
Just wondering which road you are looking at going down???
I have a series 1 with 350 th400. not sure on the diff ratio but I want to change the diff or the box to help her become an open road cruiser.
At the moment she just revs too high for my liking.

XJ6 Series 1: Conversion To GM T700 4 Speed Auto
 

Hi dcburton78,
It has been quieter than I would like regarding finding a Series 1 to convert to a 4 speed auto. I am located in Victoria and there are very few Series 1's for sale. Regarding which gearbox to fit, the T700 is still an option however as hooter suggested the ZF4HP22 could well be an option too. A couple of specialist Jaguar outlets (in Melbourne) preferred the ZF as it was actually easier to fit and connect to the speedo and other accessories etc. The ratios are similar to the GM - perhaps 1st not quite as low or overdrive not quite as high however still a major step up from the old 3 speed. Whilst I wasn't too concerned, if I went down the ZF path at least I am fitting a box out of a later model Jag etc.
For yourself, I assume that the T700 would be more suitable for the 350. It is my understanding that there are some differences between the Commodore V6 & V8 boxes and the V8 box is the one to go for? I am not sure what your highway revs are at the moment however around 2500rpm at 100km/h has been my experience and this should drop to under 2000rpm. You would have the power & torque to drive the gearing so it should be a good match with benefits of less wear and tear, more relaxed cruising and better fuel economy.


Perhaps others on the forum with more knowledge can make comment as well, my experience is very limited. Also if anyone is reading this post and may know of a XJ6 Series 1 for sale perhaps they could contact myself? Brendan

personally if I was to replace the original BW66 I would go for the XJ-40 ZF as hooter reccomends;

I've heard a few negatives about the GM 700 as John Testrake explains from his experience. I have heard this same concern from other XJ-6 Series 3 owners too.

Hi John,

I saw your thoughts on the GM transmission conversion for XJ cars you posted in 2014. . I have a coupe which I am considering this for, even though the BW 65 seems to be running OK. Have you had any difficulty aligning the driveshaft to reduce vibration after the conversion? The rear mount as supplied by John's cars does not isolate the tranny as well as the BW mount, and I don't want to ruin the vibration-free feel the car has now.

Thanks, Brad

I got the driveshaft from Johns Cars also, no vibration. The lugging problem some talk about is mostly due to the TV cable geometry which the kit really doesn't take into account. It does have a bracket to relocate the cable clamp but the cable merely connects to the old kickdown pin on the throttle lever. According to the GM TV cable geometry info, it puts the cable attachment point over a quarter inch off of correct placement in just one plane, and this is a point that gm specs that location is important to 1/64 inch.
So I mounted a spare throttle body on a board in order to find the correct measurements and make an adapter to go on the throttle lever and it works like it's supposed to. I also would not use the high stall speed converter as it's not needed when the engine is no longer lugging because it's shifting like it's supposed to. I also use a vacuum switch on the converter lock-up. And I did fine tune the shift points on my transmission via the modulator springs with a spring kit from Jegs I think. The TV cable is NOT a simple kickdown cable, and there's more to adjustment than squeezing the cable clamp at wot.

BTW... the kit from Johns was a pleasure to install! Easy follow instructions and all parts included. Much fun to me.

And the 700r4 with a 3:31 or higher numerical would be a blast. Mine is a 2:88, wish it was 3:54.

My coupe started with a 350/350, yep revs too high on the freeway. 700r4 fixed that nicely.