I have a 2006 XJR. I want to put a rear diff from a 2008 XKR in with a Quaife. 2.87 to 3.31. Is it possible without any problems such as shifting issues and/or restricted performance?

 

I have not heard from anyone that has tried this, but I have read many times on here that it wouldn't work without a complicated reprogram, otherwise you get the issues you mentioned. I would have love to have done this mod myself, but I guess its not worth the headache.

The cars are programmed to run a certain way and there's cross checks to verify that. My guess is as soon as it recognizes you're at a different RPM per wheel speed it will act up. I had a similar issue installing my larger TB. The car recognized more air was coming in for certain throttle valve positions and it didn't like it. Was a real pain to get it dialed in.

 

no, not yet.

get another 2.87 diff and swap the ring and pinion

 

My first thought is speedometer/odometer correction. If that comes from the transmission, it's going to be wildly incorrect with a lower final drive. The speedometer will read low, and the odometer will read high, as the wheels aren't turning as fast as the speedometer thinks they are, and the car's not going as far as the odometer thinks it is.

If the car's electronics does compare engine speed to wheel speed, then you're truly screwed...

 

It does

 

Bummer. There’s gotta be a way. The XJ6 sold outside of the U.S. had a 3.31 rear axle. So the trans software does exist. But I’m sure the line pressure and shift algorithm won’t be suited for a supercharged V8.

 

https://www.jaguarforums.com/forum/g...ids-sdd-77299/

refer to this