Question about X305 (XJ12) differential interchange
 

Does anybody know what ratio does 1996 XJ12 rear end use? Also, is there a way to visually distinguish an LSD from an open diff? I need a diff for my X300 normally aspirated car.

The V12 used the 3.58

Not sure about external identification....unless here's a tag mentioning LSD.

Seems like I read the LSD units had a paint stripe on the side or something? Not quite sure, though.

Others will chime in.

Cheers
DD

Limited Slip Diffs have a BLACK X through the ratio color code sticker.
3.58:1 will have a red and yellow stripe sticker. If the sticker has a BLACK X across it, that will be a limited slip.

JEPC has the info

Blue=4.09
Blue Black X=LSD
Brown=3.77
Brown Black X=LSD
Orange=3.27
Orange Black X=LSD
Red/Yellow=3.58
Red/Yellow Black X=LSD

bob

My Vehicle Care manual states the diff ratio is 3.54:1 for all X300 types. ? An inconsequential difference anyhow. The limited slip (referred to as "Powr-Loc" in the manual) apparently was an option on the XJ12, but who knows if it was available for USA models?

You finally got her running smooth, and now a diff problem? What are your symptoms?

I've seen 3.54 mentioned as well but more often 3.58 is quoted

The XJR/6 came with 3.27 gears.
XJ6 4.0 and XJ12 came with 3.58
XJ6 3.2 came with 3.77 or 4.09...if my memory serves



The consensus is that it was not offered in USA V12 X300 cars, which is supported by my sales brochures.

Cheers
DD

Noise coming back from the rear end, louder at low speed. I also feel the vibration transferred onto the handbrake lever which makes me think that the rear hub bearings could be shot as well. The shop told me that the car needs a diff, and the guy at the shop knows these cars well. I'll get the car running on the lift and listen with mechanic's stethoscope, but I am very sure it's the diff. May be both, diff and bearings, though.

Was LSD offered on US models as an option?

The diff is Salisbury 14HU, right? I seem to remember reading that Ring and Pinion are the same as one of the Dana Spicer units, but I can't find that link now.

I am thinking about buying a spare diff, rebuilding it and taking it to a professional to check out that I ajdusted it right.

These cars have a bit of an appetite for diffs and wheel bearings. I had to replace the diff on my XJR/6 at just 75k miles and over the course of the years replaced rear wheel/hub bearings as well

It was standard on the XJR/6 and, AFAIK, optional on USA market XJ6 cars....though it seems very few came thru with it. It was n/a on USA X300 V12s


Can't remember the model number offhand.

The old style (inboard brake type) differentials were a kissin' cousin to the Dana 44 and some have used Dana gears. Not sure about the later differentials



Cheers
DD

Dana 44.

BUT, the pinion has a different spline count requiring
a special order companion flange, AND, the ring gear
holes are often/usually 3/8" versus 7/16".

Search for posts by ICSAmerica.

It is not likely that the gears themselves need replacement
unless they suffered from lack of lubrication. I would suspect
bearings or loss of preload first.

Loss of preload would be the cheapest to repair.

I was contemplating changing the rear end ratio a to make the car feel a little bit quicker. I am fine with losing a bit of top speed and fuel economy. I don't remember ever driving the Jag over 100 mph, so if the top speed goes from 136 mph to 120 mph I could care less.

FYI
I have a 2.88 out of an '85 xj12 and it has a green with black X

different car

Yes, that is why i included the year and model. I was just trying to add to Bobs list of color codes for anyone wondering what green w/black X meant. Sorry if my info was not appropriate for this conversation.

Thank you. All info will come in handy sometime!