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More Aggressive XK8 Diff???

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Old 01-07-2019, 11:51 PM
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Default More Aggressive XK8 Diff???

Hello all, this is Andrew from Jaguar Specialties and I hope all of you had a good New Year.

Recently we came into a somewhat sorry 97 XK8 coupe and have been tinkering with it a bit here and there. Just so you know, this car is no gem- 155k miles, ridden hard and put away wet (often), if you know what I mean. Anyway, the high miles engine finally gave out which is how we ended up with it. Since then the engine and trans are gone and the car is waiting patiently to become a project That will come eventually.

In the meantime, this will be a great car for an XK8 mod weíve wanted to do for a while- swap the lazy 3.08 open original differential for something more aggressive (higher numeric) and hopefully with posi as well. We did something similar on my 99 LS1-powered VDP about 5 years ago, going from the stock 3.08 to a much more snappy 3.58. It made quite a difference- when was the last time you saw a 4200 lb Jaguar sedan smoke the tires?

Anyway, tucked away in the back of the shop is a 97 XJR differential assembly, 3.27 posi, complete with all of the related sheetmetal. Finally we have a home for it- the 97 coupe. So while a few other things on the car are fixed, weíll do the diff swap too. Now you may be thinking why would I care as this car will probably get an LS engine and none of whatís done here will apply to a Jag engined XK8? And thatís where you might be wrong. After working with one of our driveline specialty companies, I believe that any XK8 could go though this same swap, even with the original Jag engine and trans, and get the benefits. That could mean ratios up to 4.09 (although 3.58 is much more common) and of course posi too. And based on some preliminary number crunching, I believe the whole diff swap, top to bottom, could be done for about $1500-$2000 in parts, including a rebuilt diff as well. I wonder if any XK8 owners be interested in something like this...

Note: because of some odd drivetrain programming that I donít completely understand (Iím not a Jag engine/trans expert), this mod would not apply to the XKR. Something to do with the transmission controller orÖ

Side note- One question you might ask is why even bother with the 3.27 which really isnít that much of a numeric gain over the stock 3.08?? Well in the VDP, while the 3.58 was pretty snappy, it was a little more than we needed. The LS engines make plenty of torque and the engine in that car seemed a little busy on the freeway, even in overdrive. So something in the middle will be much better and since I anticipate that whatever engine we finally choose for this car will make more power/torque than a standard LS1ís 305-340 hp, the 3.27 should be fine. Anyway, the driveline guy is working on some parts for us now and Iíll post updates as they come. Don't worry about that Jurid style pinion flange- that will work as-is with our plan. The diff itself will remain completely stock.

Hereís a pic of the diff assembly all cleaned up and ready to go into the XK8, and the car itself.

Thanks
Andrew
WWW.JaguarSpecialties.com



 
  #2  
Old 01-08-2019, 06:36 AM
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Be interesting to see how this works out for you.

Scott
 
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Old 01-08-2019, 08:00 AM
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if it helps, in some of the South American markets a more aggressive differential is standard in the XK8 and XKR. perhaps this is for climate performance issues.
 

Last edited by WhiteHat; 01-08-2019 at 08:01 AM. Reason: typo
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Old 01-08-2019, 09:04 AM
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Hi Andrew,
I'm VERY interested in how this turns out as I've just started on my '97 XK8 coupe LS1 swap (car/kit purchased from you two years ago - better late than never! )

 
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Old 01-08-2019, 09:33 AM
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Default Very interesting.....

I had not heard this before. Where did you read that and what are the other ratios????


Originally Posted by WhiteHat View Post
if it helps, in some of the South American markets a more aggressive differential is standard in the XK8 and XKR. perhaps this is for climate performance issues.
 
  #6  
Old 01-08-2019, 10:21 AM
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The Mexico X100 3.27:1 diff is a straight-line WITHOUT limited slip. (Europe has a 3.27:1 for the X308 sedan that uses a JURID coupler)
The HU15 from the XJ40 or X300 can be had in limited slip but is slightly offset to the side.

I always wondered if the X100 had enough propshaft 'tunnel' clearance to use the HU15.

Thanks.

bob
 

Last edited by motorcarman; 01-08-2019 at 01:49 PM.
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Old 01-08-2019, 12:02 PM
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Default HU15

On the XJ40/X300 HU15 diff I think the major issue won't really be trans tunnel clearance so much as the fact that the ZF transmission output uses a Jurid style coupling. With the (not so slightly) off-center pinion of the earlier diffs, trying to use them with the ZF trans would mean that Jurid coupling would be running at an angle. Not sure that's acceptable for them- I think they're designed to work in situations where the trans output and diff input are perfectly aligned, pointing right at each other....

However, the way we do the drivelines, and anticipating the special pieces our driveline supplier is working on, I think this will be a non-issue. A different driveline will be required but is a no-brainer. This one would run U-joints and would be a smaller physical diameter (since it will be steel tube, which is more practical anyway)

Andrew
Jaguar Specialties
 

Last edited by JaguarSpecialties; 01-08-2019 at 01:06 PM.
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Old 01-08-2019, 02:04 PM
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Originally Posted by JaguarSpecialties View Post
I had not heard this before. Where did you read that and what are the other ratios????
the information is in the 09/2009 Jaguar Vehicle Specifications Book which is posted on this forum. page 132, ratio is 3.27:1
 
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Old 01-08-2019, 09:00 PM
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The JEPC for the X100 4.0 liter to VIN (A30644) ONLY list the MEXICO 3.27:1 and EXCEPT MEXICO 3.06:1
Those are the ONLY ratios fitted to the X100.

bob
 
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Old 01-12-2019, 01:13 AM
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Default OK

Good
 

Last edited by SmittyXKR; 01-12-2019 at 01:55 AM. Reason: Changed opinion
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Old 01-12-2019, 08:20 AM
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Is it possible to swap the more aggressive rear in an 2003?
I heard it’s not possible because of the computer and wheel sensors.
 
  #12  
Old 01-19-2019, 12:13 PM
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Default XK8 Aggressive Diff- Moving Right Along

Hello all

So we are continuing with our project to transplant a more aggressive differential (with posi) into a 1997 XK8 coupe. Our driveline supplier finished up a very nice (and Jaguar specific) adaptor that can be used for this "conversion". The adaptor links the 20mm pilot pin on the diff pinion shaft to a matching pilot bore for the driveshaft flange itself and the needed threaded 4 bolt pattern on front.

This car will ultimately get a GM LS engine and transmission of some sort but the approach on the differential here could be used as well with a standard engine XK8. We are using this adaptor (1 of them) on the diff such that a GM style driveshaft (most typically a slip yoke at the front and a bolt-on flat driveshaft flange at the rear (as the XK8 does from the factory) will work here. The adaptor is used to accommodate the earlier X300 (95-97 XJ6) diffs that have the better ratios and posi but comes set up for a 3 bolt rubber (Jurid) coupling and not a flat 4 bolt flange. If this were to be used with a standard engine XK8, 2 adaptors would be needed and then a new (although not particularly special or unusual) driveshaft in between. This new driveshaft would replace the Jaguar unit but would be similar as to having the slip joint somewhere in the main length of the shaft. We did something virtually identical to this on another XK8 conversion we have in process that uses a Pontiac G8 LS (Gen 4) engine and the matching GM 6L80E (6 speed automatic) transmission. That trans, like the Jag ZF unit, uses a Jurid coupling on the output. On that conversion, we used an adaptor to go from the Jurid (GM) trans output to a 4 bolt flat flange. Our driveline supplier made that unit from off the shelf parts- no drama at all.

Here are pics of the new adaptor (shown next to a standard Jag Jurid coupling) and also a pic of the driveshaft from that G8 installation. 2 of these adaptors and a drive shaft like this would be all it would take to get an XK8 up and running with hotter gears, and posi. I anticipate that total cost for a conversion like this would be well under $1000 plus the cost of the diff itself.

Thanks

Andrew
Jaguar Specialties

 

Last edited by JaguarSpecialties; Yesterday at 12:45 AM.
  #13  
Old Yesterday, 02:32 PM
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Default Diff Adaptor Installed

And here is a pic of the adaptor installed. The face of the unit has the right 4 bolt pattern and female pilot bore for a standard Spicer 1310 Ujoint flange yoke. From there making the driveline is easy- all standard parts...

Note- the center of the 4 bolt flange yoke is domed in the back so it should clear the slight protrusion of the pinion pilot shaft beyond the adaptor face..


 
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