So I got my old friend out today and gave him (her?) a bath, which of course was undone a couple of hours later by getting stuck out in a rainstorm -- which reminded me, I still have a leak along the top of the windshield somewhere. Water runs down the inside of the windshield in even a modest rain event. You tend to forget things like that when the car has been in a shop garage for 16 months getting its new 4-speed automatic transmission and special shifter.

I wanted to give everyone a heads-up about some of the issues we faced while doing this. First of all, I pestered many members here for months about a new suspension and tire setup. The goal was to get away from the factory 15-inch rims, not because I didn't like them, but because tire selection is getting to be an issue. The most performance-oriented tire I could easily find for the 15-inch rims were Cooper Cobras, and of the four sets I've had for this car in the roughly 10 years I've owned it, I've had 6 out of 16 tires separate. That kind of poor quality control is ridiculous, and I was just over it. So we set out to use 17x8 rims (custom-built by CCW) and I eventually decided to follow the guide posted by Bernard Embden here: Rim and Tire upgrade Decision

The problem when you're dealing with largely handbuilt cars, though, is that no two of them are alike. Bernard seemed to get out of his conversion without having rubbing issues, but I apparently will not be as fortunate. I'm getting scrubbing of the tires -- not too bad, but it's happening -- during travel over large bumps. Cornering doesn't seem to be an issue. But either CCW (my car) and Ronal (his) build wheels differently, or you should probably not try to get as close to the limits as I did.

Another issue we found with my car was either the body had been assembled incorrectly, or my car had accident damage at one time. We found this out when we discovered I have about a half-inch extra room in my right rear than I do in my left rear fender wells. The body is either a bit off-center relative to the suspension geometry mounts, or something got bent in a previous life and I'm forced to deal with the aftermath. I would never have noticed this had it not been for the adventure of fitting new wheels and tires.

Not everything was bad news, though. Not by a long shot...

1) Do wider, more modern tires and wheels make a difference? Absolutely. I don't recognize the cornering of this car now. It's something completely different than what I had before, but we didn't lose the classic XJS ride. I truly got the best of both worlds. I ended up using Firestone's Firehawk Indy 500 tire but there are dozens of good options. The Firehawk is the "poor man's Michelin Pilot" and feels much more stable at speed than the Coopers ever did.

2) We are lucky to have so many aftermarket options for suspension components. I used Bilstein shocks in the front and KYB grays in the rear. We replaced the springs in the rear with factory-spec replacements just in case. The specific Bilstein/KYB combination we used was chosen to get the ride as firm as possible without going to custom-ratio shocks, and I'm pleased with the result. We should be thankful we have so many choices when it comes to suspension parts; other cars from this era can't say this.

3) Whoever took the Sport Pack rear anti-sway bar out of the option list for these cars was loopy. I installed a factory version on the rear end, sourced from a car in the UK. I can't tell you yet whether it's the bar, the wider tires, the firmer suspension or a combination thereof, but the car is much safer in corners and resists "crabbing." We also upgraded the front bar a bit to a slightly larger ADDCO piece, and then added poly bushings in most places. The result is a car that is still a GT, but is quicker in the corners.

4) Going to a GM 700R4 transmission fixes most issues relating to transmission and gearing. We kept the factory 2.88 rear end and swapped out the 3-speed GM400 transmission that had failed. The result is a car that now gets 32-38 MPG on the interstate and around 25 MPG in mixed driving. City driving hasn't improved much but the taller first gear makes the car more responsive off the line. It's crazy how this one change has turned an old V12 into the most fuel-efficient car in my yard.

5) I'm including a picture of the Kilduff shifter we're using, and you'll notice I'm still waiting on a custom surround to be built, as the new shifter is much larger than a factory Jag unit. I like it, but I'm not recommending you copy me because it is off-the-wall and changes the look of the interior immensely. Had my car not already been a little modified when I got it, I probably would have eschewed the change. I guess the best way to put it is that it works for me.

I've already put about 300-350 miles on her (him?) this week and the most pressing need it has now is to get the freon recharged and figure out if I have a leak in the A/C system. Once that is solved, I'll drive it anywhere. People laugh a little at the suggestion that a V-12 British car of this age can be a reliable traveling partner, but it's not a lie. I'm still astounded by the low sales values on these cars.

 

I have read your posts, great write up .. you have taken an unusual path with great results.
I am impressed with the engineering involved - seriously well done.
BUT... haa you knew that was coming.. I showed the wife and she nearly feel out of bed laughing.
I like to drive fast, corner fast... rev this motor which is hard to do in most normal circumstances and we live in the country with lots of windy 100km windy roads.
But wify, likes cruise mode at the speed limit boring as, so I am stuck with 3 speeds.
Video please... just to amuse me..

Original - functional - practical - but ... ugly as sin.. LOL
Love it!

 

I hope to get some time to shoot some video soon, especially of -- as a friend put it today -- the "forklift" shifter in action.

I can understand why that particular piece of equipment won't likely see a huge takeup rate from other Jag owners looking to do a swap. However, John's Cars sells what they call a "Quarterbreed kit" that allows a 700R4 to be practically a drop-in replacement for the GM400, and I would recommend to anyone doing that particular mod. We paid, I think, $50 for this transmission. We obviously then cracked it open, freshened it, fiddled with the valve body a bit and some other things. But pay a couple thousand or so extra for that fourth gear (via the kit) and getting quicker off the line, instead of replacing it with yet another 3-speed? Yes, please.

The best part of what we did is that it swaps back fairly easily. We kept the factory shifter and it will drop back in anytime I get tired of the Kilduff. There was very little cutting/trimming involved in this conversion. The factory ECU and electronics don't know the difference.

As for the wheels and suspension, most of those suspension upgrades can be done simply by selecting those parts the next time you need to freshen something. I'd say 95% of all of our work was bolt-on. Not nearly as much engineering as there would have been had I done the manual transmission swap I originally planned.

Jess

 

Terrific work, the car sounds marvelous.
As the one side of the car being longer than the other, this is a true story:
Jaguar sent a model to Karmann in Germany in the late 1970s with a view to their prototyping a convertible version. Being German and therefore thorough, the first thing Karmann did was to accurately measure all the vehicle's dimensions in detail. They found one side was an inch longer than the other, and rang Jaguar accordingly. They were told this is quite normal for jaguar and not to worry!

 

Whenever I see the vast garages and acres of space in photos by US and Australian members, it reminds me I definitely live in the wrong part of the World.

Last time I saw that number of levers emerging from the transmission tunnel was in my Land Rover Series III Safari!




Graham

 

Whooo I love the colours inside and out! And the wheels.

 

not a hack, pic of my CCW wheels, different car tho!

RX7 ,CCW wheels