What angle does the diff sit in the IRS, is it 5 degrees up?

 

I think it is 3 degrees. There are 3 different sets of side brackets over the years that produce different pinion angles in the IRS. I believe E Types are 5 degrees and the small saloons (S Type, 420) were in between the E Type and the XJ, but I don't know the exact figure for them.

 

It has been a while since I set up the rear differential and transmission of my Camaro (yikes) but I believe the pinion angle should be whatever it needs to be to be parallel to the transmission output shaft angle. I used a digital angle finder device and shimmed my transmission tail housing mount and rear axle mounts to achieve parallelism. I am not saying the centerlines of each component should be in the same plane, just that they should be parallel. By the way, the Camaro is long gone, replaced by a 240Z and I still have my XJS!

 

I saw a video showing the XJ at 0 and the XKE at 5 degrees. Mine shows close to 0 with a magnetic angle finder.

 

This image illustrates what I was talking about. The transmission output shaft must be checked as well as the pinion.

 

Driveline angles are actually a fairly complex subject. I was recently reading a book on the at subject. It's the bible of driveline design, called Universal Joint and Driveshaft Design manual. After looking at it, I can see why it was 440 pages!
https://www.sae.org/publications/books/content/ae-07/

 

The rear isnt adjustable, when you mount it in the cage and install the IRS it is as Jaguar designed. Just wanted to know what this official spec is.

 

The side brackets on the bottom of the differential are what control the angle. As long as you have the correct parts, the angle is correct for the car.

I measured my DS420 and it is 2.3 degrees. I believe it is the same brackets as the XJS and Series III sedans.

 

Is it really the brackets or the angle machined in top of diff casing?

 

Taking the ground as the datum point, the diff pinion angle is affected by the angle of the top of the cage when fitted to the car, and the angle of the machined planes on the top of the diff which are bolted to it!
But as far as the propshaft is concerned and the angles the universal joints are resolving from a dead straight gearbox/propshaft/diff pinion line, I think, repeat think, that all that matters to the propshaft UJs is the parallelism of the gearbox output shaft and the diff input shaft and the fact that the angle at each UJ required to join them is not too great for the UJ to accomodate. As shown in Camaros's diagram in post 5 above.
On the 3.6 automatic cars a centre bearing on the propshaft is used, but I do not know if this was for reasons of vibration reduction or to do with accomodating propshaft angles, or what. As on these versions the rear axle cage and diff arrangments are identical to the V12.
I think, repeat think, that the dog bone castings do not affect pinion angle, but they do affect the caster angle of the rear wheels (or perhaps more exactly the angle from horizontal of the bottom wishbone).

 

I will take some measurements with my electronic gauge. I understand how proper alignment works, was hoping someone knew the factory spec of the pinion angle in the cage. Its upwards x.x degrees.

 

Measure your engine angle if possible. I read the v12 is set at 0 degrees as well.