I’ve been doing a lot of reading on rear diff ratios and rebuilds/swaps but I’m finding some of this confusing so hoping to get some clear answers to my below questions. Thanks!

1. How feasible is it to put 3.54 gears in the 2.88 Salisbury diff? If a shop does this work, is it likely to be cost-prohibitive?

2. Can the 95-96 XJS 3.54 diff (the entire diff case, not the internals) be swapped into a 2.88 IRS without any modifications?

3. How easy is it to rebuild a 3.54 diff, leaving the ratio as-is? I’ve done engine and trans swaps - short of welding or needing a machine press, I can do pretty much anything in my garage. I’d have to buy a used diff so I assume a rebuild is possible or even likely.

4. Can a 3.54 from a different model (xj6 or e-type) be installed in the XJS without modifications? Again, talking about the entire diff unit, not swapping the internals. If this is the case, are the 3.54 diffs from other models equipped with posi-lock, or are they hit & miss in this regard? And how important is posi-lock?

5. Finally, is there a mechanical preference between the 3.31 Dana and 95-96 3.54 diff? Meaning, are there any glaring weaknesses to either?

Thanks

-Anderson

 

There is nothing special/unique to the jag diffs.

you can use standard dana44 gear set, all you need is the correct splined pinion flange.

i have a brand new flange if you need it.

 

My ideas in RED
I’ve been doing a lot of reading on rear diff ratios and rebuilds/swaps but I’m finding some of this confusing so hoping to get some clear answers to my below questions. Thanks!

1. How feasible is it to put 3.54 gears in the 2.88 Salisbury diff? If a shop does this work, is it likely to be cost-prohibitive? The carrier (the real heart of the diff) is I think different in depth, so you might have to swap the pinion gear, ring gear and the carrier. This is all doable the case will be the same

2. Can the 95-96 XJS 3.54 diff (the entire diff case, not the internals) be swapped into a 2.88 IRS without any modifications? YES

3. How easy is it to rebuild a 3.54 diff, leaving the ratio as-is? I’ve done engine and trans swaps - short of welding or needing a machine press, I can do pretty much anything in my garage. I’d have to buy a used diff so I assume a rebuild is possible or even likely. New bearings etc quite doable. I did it and I had never done a diff before.

4. Can a 3.54 from a different model (xj6 or e-type) be installed in the XJS without modifications? Yes, but most if not all are not LSD diffs. Again, talking about the entire diff unit, not swapping the internals. If this is the case, are the 3.54 diffs from other models equipped with posi-lock, or are they hit & miss in this regard? And how important is posi-lock? Most non-V12 XJ saloons are NOT limited slip. ALL XJSs are. LSD VERY important in the V12 XJS in my opinion, assuming you use the power now and again.

5. Finally, is there a mechanical preference between the 3.31 Dana and 95-96 3.54 diff? Meaning, are there any glaring weaknesses to either? I think that only 2.88:1 DANA diffs were used by Jaguar and these only went into a few mid-1980s years XJSs. Most Jaguar diffs are Salisbury ones, and these are the ones to go for as they have better output shaft rebuildability. I would go for a Salisbury type diff for any swap or rebuild, even though my rebuild was a DANA! Rebulding DANA output shafts is very hard to do and the parts are almost unavailable. I needed specialist help to do my output shafts, while the internals are far easier whether DANA or Salisbury. In a rebuild, if you need it, a new carrier is the most expensive bit. The guys at DRIVE TRAIN SPECIALISTS, 26400 Groesbeck Hwy. Warren, MI 48089,
https://www.drivetrainspecialists.com/
were very good and had everything, if you do need a new Carrier, the an Eaton TrueTrac is a very good option indeed.

 

But the flange would only need to be changed if I swapped out the internals, right? Based on Greg’s response, if I swapped the entire diff unit, I wouldn’t need to change anything.

Also - you say any Dana 44 set will work, but I have found threads with mentions of modifications needed, something regarding bolt sizes but I’d have to find those threads. If it really is as simple as grabbing some Dana 44 gears and swapping them in, are any special tools needed for that?

 

Very helpful as always Greg, thanks.

If I order a used 3.54 from a 95-96, other than cracking it open to look inside, is there a reliable way to tell if it needs total rebuilding prior to installing it in my car?

 

No 100% reliable way, but turning it ans making sure it feels smooth is a reasonable guide. Any wetness round the pinion (input) shaft would indicate a new seal is needed, ditto output shafts.

As to bolt sizes, this refers to the bolts that hold the carrier to the ring gear. Jaguar ring gears are threaded for bolts sized 7/16ths, most USA ring gears are sized for 3/8ths. One advantage of using the TrueTrac is that it comes with holes for both sizes.
https://www.drivetrainspecialists.co...rac--rear.html

So if you are buying a new carrier but using your old ring gear, you need to ensure the carrier has holes for 7/16ths bolts. But there are plenty of places that will rebuild a carrier and also lots of stuff on YouTube on how to do it. On a conventional LSD carrier, the clutches that control the slip get worn out, which is why they need rebulding. But if your replavement Jaguar diff has not had a hard life the clutches will probably be OK.
Just in case you have not seen it, this is my diff thread, as you will see it is not that hard too get it apart.
https://www.jaguarforums.com/forum/x...tified-229645/

 

First the XKE has different lower suspension mounts than the sedan. ( they just unbolt and you can swap them over). There is about a 6 degree difference in the pinion angle between the XKE and the sedan.

Second pop the cover off a used one and if there isn’t metal in the oil. And the clutch plates look OK, put the cover back on ( with a new gasket ) and use it for another 50 years of so.
I’m a racer. I’m a million times harder on my differential than you’ll ever be and I’ve never had one fail on me. I have several pumpkins for different tracks. I’ll use a 2:88 if I ever go to Bonneville A3:31 for Daytona. And a 3:54 for ELKHART LAKE. Short tracks would call for a 4:11 if I ever went there.
At very worst I’ll replace a seal or two. But mind you I go screaming into the corner with my brakes glowing red hot. Lap after lap. Yes I change the diff fluid after every race, but I really cook the fluid. ( make sure the fluid you use is good for positraction ( not all fluids are, but Chevy sells a supplement).

Positraction is only important if you plan on either getting stuck in a snow bank/ heavy mud or racing the car. Ordinary driving you really don’t need it.
Later 3.54-1 diffs are out board brakes rather than inboard. The whole rear end can be adapted but the parking brake will need modification and brake lines need to be changed. Also outboard brakes use 1 shock/spring unit per side while inboards use 2 per side. Also the XKE is narrower than the sedan but yes you can change the “pumpkin” with the sedan just remember to swap the lower A Arms.

 

Mguar,

Just to clarify, outboard-braked XJS also have 2 springs / shocks per side.

Paul

 

Further to clarify, the actual diff, whether fitted on an outboard or inboard braked XJS is identical.

 

All responses have been very helpful, thanks!

 

there isn’t a market for sedan rear ends yet. So cheap me looks for those.

 

ring gear are easily sourced with 2 sets of bolt holes. Just be sure to buy the right one. The 2.88 carrier would need to be spaced to accommodate a 3.54 gear set, im not crazy about spacers under the ring gear. Id just swap the entire carrier for a correctly sized unit. An LSD unit for 3.73 and below(numerically), standard Dana44 ring/pinion set, 26 spline flange and a rebuild kit. You can have any ratio you want(LSD carrier dictates what range of ratios you can use)

 

Other thing to be aware of if you have a later XJS with the diff mounted speedometer pickup is you need the tone ring on the limited slip carrier in order for the speedometer to work. Only the XJS diffs have that.

As mentioned, the offset of the carrier is different between a 2.88 ratio and 3.07 and numerically higher. Take a look back at Warrens posts, it is possible to put in the entire center section from an XJ40 sedan, however, the guide pin on the nose of the pinion would need to be cut off, unless you can find a very early ( first 2500 cars) differential. Also non USA market, as the USA cars had a 2.88, while the rest of the world was 3.54. The early cars used the Sailsbury type ring and pinion and had a separate piece to incorporate the guide pin into the driveshaft.