Limited slip differential REVISITED
 

So while waiting for my timing parts to arrive I found some money to be burning a hole in my pocket, and some time waiting to be killed and i began moving onto project two, the LSD.

Which of course led me to the search function of our fine forum, yielding these results.

https://www.jaguarforums.com/forum/s...ighlight=lsd--

https://www.jaguarforums.com/forum/s...ighlight=lsd--

https://www.jaguarforums.com/forum/s...ighlight=lsd--

https://www.jaguarforums.com/forum/s...t=lsd--&page=2

https://www.jaguarforums.com/forum/s...p+differential

https://www.jaguarforums.com/forum/s...ighlight=lsd--

https://www.jaguarforums.com/forum/s...ighlight=lsd--

Here's what I found.

A bunch of conjecture, and really expensive aftermarket options.


Questions to answer:

SO have we yet established that the rear end is in fact ford?

If so, what parts can we swap?

Is it the 8.8 or 8.0?

What's the cheapest route to an LSD?

what's the easiest route to an LSD?

Has anyone actually done this with ford parts yet?

Before this thread dies and becomes one of the numerous dead threads above, can we at least put all the info together into one spot so the next time someone searches they get a nice easy answer?

No! That is not the way things work.

:icon_doh:I set myself up for that one didn't I. :icon_slap2:

I have rebuilt my diff and wanted to go to a lsd. As much as I could find out was it is a salsbury and it does have dana stamped on the ring gear oddly enough. When I went to order the parts from Jag the xk8 and xkr had the same parts and gear ratio. It does not look like any ford diff I have seen, on the outside at least. I bought my 2002xkr used with 50k on it and the diff started making noise with in 2k from purchase. It seams that the ring gear will warp if you are hard on it. Something I have never seen before. This is the weak spot on our cars. I am still looking for a viable option for a limited slip, but the soft gears should be addressed as well.

When I bought my car with 15k mi, it had a noisy differential. It was replaced under the original new car warranty. Apparently, this differential is not up to the task :icon_no:, especially on the XKR.

There are a couple of options for LSD on our cars, none of which are cheap. I will try to do this least expensive to most. The first would be to stay with the ratio you have & install a 6 cyl XJR diff this involves also replacing the front mounting plate for the diff & making sure you get the correct flange. The second would be to purchase the Quaife unit from one of the three sources in the UK, ( Paramount Performance, Racing Green Cars or TL Jaguar). This involves buying the unit then having it installed in your diff & also has no warranty in the US. The third which can only be done on cars with the Mercedes trans invloves fitting the 6cyl XJR diff & using whatever ratio you prefer, however it also requires you to reprogram your TCM at a cost of close to $2000.00. I have done this to my car with a 3.58 ratio along with many other engine upgrades, the difference is amazing. I would recomend this to anyone looking for LSD & an increase in performance. My next project may very well be to go to a 4.09 LSD which should make the acceleration neck snapping.

So you are suggesting that I can go find an year xj6, pop off the diff, and fab up a mounting plate. So it's almost a drop in replacement for the xk8 diff except it's limited slip with the same gearing and everything? What kind of power can that old diff take?

What year and model Jags have the Benz trans?

Who is reprogramming the TCM, aftermarket or dealer?

As far as the labor, I do all my own work so that's a non issue. I just hate going in blind.

What you need is an XJR 6 diff & front mounting plate & it is a straight drop in. You will need to modify the exhaust mounts for the overaxle pipes. The Mercedes trans is fitted to supercharged cars from 1998-2002. If your car is not supercharged you don't need to program the TCM. You can fit 3.07 3.27 3.58 3.77 or 4.09 ratios.

Mine is 1998 Xk8 (no supercharger for me :( )

So I'm going to go dig up an xjr 6 rear and some 3.77's whoo hoo!

Any Ideas where I might be able to find such a part... I just ran a quick search and it seems to be a hard part to find...

Here is a link to Coventry West http://www.coventrywest.com/ ask for Pete Bond xt 120. He is well aware of what I have done, they can supply the diff as well as a used mounting plate. Just make sure you tell him which flange you need on ther diff. You may want to go 4.09 as you car revs to 6500 rpm & that should put you pretty close to 150 mph & the speed limiter is @ 155. Good luck on your new car

I think I tried that LSD, but that was back in the 60's!! :icon_pala:

There has to be a way to get some LSD and better gear ratio's in these cars.....

I think the Ford theory is for the S-type since so many parts are interchangeable with Lincoln LS. The diff does look much like a Ford 8.8. The Lincoln LS guys have swap there diff for Ford LSD, which makes is believe it can be done. I had some guy look at mine and said the only thing that he saw was the cover plate might have be changed and it might not fit with all the stuff under there.

Hmmm I might have to find a 03 Cobra rear dif and see......3:55 gears would be NICE........

What would be needed to change the speedo gear?

What spline are the axles?

dont know Ill i know is ther was a company KBX Perfromance that swapped lsd from a mustang into a 2000 Lincoln LS.

What is the stock diff. gear ratio? ('05)

You don't say what Jaguar you have. I believe Dana diffs were fitted on the XJs up to the XJ8 of 1998. S-Types will probably be some Ford part, and the X-types used Jatco, I think.

What is the stock differential gear ratio is on an 05 XKR (or any XK) is?

This is all i have found on gear ratios for S-type R

Gear Type 6 Speed ZF Automatic
Final Drive Not Available
1st Gear Ratio 4.17:1
2nd Gear Ratio 2.34:1
3rd Gear Ratio 1.52:1
4th Gear Ratio 1.14:1
5th Gear Ratio 0.87:1
6th Gear Ratio 0.69:1

I has 2.87 gear on rear here is pic

Our STR's have a LOW 2.87 gear ratio.......Now if we could do a 3.55 or 3.73 that would be OUT FLIPPING STANDING!

I was gonna post the ebay link to that ;)
http://cgi.ebay.com/ebaymotors/Jagua...Q5fAccessories

Maybe Motive Gear or another aftermarket company might have stock or can make a gear for them

http://www.motivegear.com/images/art/chart/chart.pdf

The only one that shows 2.87 is DANA......Who makes our rear difs? Ford?

According to what I have been reading DANA Type 44 use a 3 bolt output shaft and the rest use a 5 bolt so if we look at the picture it looks like a DANA these where used in the XJ though in the 80's for Jaguar.

So then we could order the gear through lets say Motive Gear for a taller gear in the rear end.....That is if the ring dia. is the same size.....
Then the next step would be is re-calibrate the speedometer/odometer to read correctly....

have no idea, I will be going to mustang plus this weekend to see what they say

What would be the approximate cost a dealer would charge to install a Quaife unit? Would using a dealer or Eurotoys be a better choice?
Does the ECU have to be reprogrammed on an XKR (05) if a Quaife unit is installed.
Since there appear to be a few Jag. mechanics here, maybe an installation cost estimate is possible.

The rear ratio is the primary inhibitor of performance to the XKR/XK8. The newest ones (XKR) are 3.31 but all the early ones are 3.03. The Nissan GTR is so quick because it's running 3.70 rear gear.
Has anyone found a way to lower the rear differential ratio down to 3.73 or lower? Nothing would more quickly improve the XKR performance.

if it is indeed a dana 44 c4 corvettes came with that diff and if i'm not mistaken the auto's ran a 2.92 and that sticks ran a 3.07

http://www.vetteweb.com/tech/vemp_09.../photo_05.html

This is like trying to find out the answer if there is life on other planets!

LOL - VERY frustrating, isn't it?
Such a simple question for almost any other brand.

That it is......I been looking and calling all around and no luck anywhere....

You are all looking in all the wrong places, if you are looking for a diff to fit the S-Typr R it is the same as fitted to th XJ sedans. Cars fitted with supercharged engines have the 2.87, v8 normally aspirated have 3.07 & Europe only have a V6 which is 3.31 ratio. You can purchase this thru any Jag dealer or possibly Coventry West could build you one. The problem is LSD you will have to buy a Quafe thru one of the 3 suppliers who have exclusive rights to it. The problem you will have is the TCM as I have spoken to someone that did this & the transmission goes into the limp mode with the message incorrect gear ratio. I atempted this on my own XJR in 2004 & gave up after speaking to a friend who works for ZF. If you want more power you should look into a twin screw supercharger, cylinder head porting & water methanol injection.

Do I read you correctly that you trying a Quafe unit and the computer shut you down? Since mine is an 05 XKR - essentially an 04 carry over - it reads like it literally is impossible due to the computer. Very bad news indeed if so.

Since the new XKR comes with 3.31 rear this might work in earlier models? It sounds like you buy it, have it put in and then find out if the TCM will allow it.

I guess since mine has factory 20 inch wheels I could go smaller wheel/tire combination - that sucks - but then the TCM could read that as wrong gears too.

What actually is reading the speed of the car? How does the computer know how fast the car is going? OLD cars just had a cable to the transmission. Is it reading tire rotation? Disc rotation? Where, exactly, is the sensor that is reading the speed the car is going (ie the rate the wheel/tire is turning? Sometimes a sensor can be tricked in various ways. I could live with a speedo not registering correctly.)

(BTW - What is "ZF?")

Thank you (VERY MUCH) for taking time to reply. Really. I'm in the wilderness on this and it appears not the only one.

Let me narrow the relevant question...
If I put on smaller diameter wheel/tires, would the speedometer misread accordingly? Would that "upset" the TCM to going into the limp mode?

Not sure. The Mercedes Box used in the 4.0 SC cars will check if the box itself indeed in the right gear. It does this via checking the input shaft speed and the output shaft speed. It has an input shaft speed sensor, but (and there is the issue) not an output shaft sensor. It will relay on the ABS speed sensor of the rear wheels to check it. If it is not right, you go into limp mode. So when you change the rear end ratio on these cars, the TCM will not work with that.

I am not sure if this is also the case for the S-type/XJ 4.2 cars with the ZF box, as that one does have a rear output sensor to check if the box is in the right gear.

Thanks for the analysis. I suppose one way is to buy a cheap 18 inch tire/wheel combo and see what happens.

Different topic - it's been suggested your the guy to talk to about a Whipple set up. Paramount said they'd build one for me for $7000 upfront and they'd then need about 2 months. Price included the blower. (05 XKR coupe)

Did you build/fab a Whipple setup yourself? Did the ECU accept it or require some remapping? Fit under the hood? (It's TIGHT under there!)

Changing tires will not make the difference; it will be the output shaft speed ratio to the speed of the wheels. Putting on smaller wheels does not change that ratio, only the rear end ratio will create a difference here.

Best would be to contact ZF themselves, they should know where the trigger is (in %). Chances are this could be around 10%/15%, leaving not much room for a major ratio change. Another route is to search for Audi/BMW tuners, they might also know more about teh ZF box, and if it is possible to alter the software.

Please PM me for the off topic part, but in short I did make everything myself.

Everything fits under the hood, no major changes there, and surprisingly the ECU offers a tremendous range and fuel supply. So far that hasn't been the border...