In the process of rebuilding a late model XJS irs( Salisbury w/inboard brakes/abs/GKN Power Lok/2:88 gears all verified) to replace the existing unit under my series 1 xj6 Looking to replace all the seals/bearings in the suspension and diff. Gearing will stay the same and the Power Lok freshened up/rebuilt. Poly bushings used where applicable. Will be doing the vented rotors upgrade. Plan on tieing the irs cradle to the unibody. This going behind a turbo'd LS1/t56(1st gear is 2:66).

I've done some searching, but can't find any specifics. What I'm wondering is what practical upgrades can I do to help durability/reliability? What vendor would you recommend for price/availability of parts? What vendor/parts would you stay away from due to personal experience? Does a yoke exist for the Salisbury that takes 1330 universal joint? Are the GKN PowerLoks durable enough to around 500rwhp? Is there a heavy duty/race clutch pack or rebuild kit for them. I know the output shafts from the diff twist if launched w/sticky wide tires.
​​ Are there some bearings/oil seals that have a better reputation than others? Is bracing the LCA's worth it? I know about the hubs having issues and will inspect them for damage. Any advice that the forum has is welcomed.
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If you want a accurate speedo when all done, changing the gears to 2:88 causes problems. There are no stock speedo heads for that ratio.. I changed mine to a Speedhut GPS speedo that works perfectly. has setup built in for testing 0-60 times and 1/4 mile.. plus altitude and other stuff.

Cannot help with that IRS..mine stock one that has worked well so far.. be sure to change the rubber brake lines and consider a S2 or S3 master cylinder.

 

I consider it must upgrade to outboard brakes and new rear hub carrier in a performance application. The later ones have reinforcement webbing, the early ones dont and crack. You may have seen the one that cracked on me in a 400 HP application.

Use XJ40 rear hubs and stub axels and it will be FAR cheaper than upgrading the inboards. The inboards suck and in a performance application they really suck. This way you can have bigger brakes and service them easier for FAR less money.

I just finished a close ratio T56 with a 3.54 rear gear. 1st is great and allows one to creep along easily in city traffic at very low speed. 6th allows for 1850 RPM at 70. Just about perfect for a stock v12. For an turbo LS I think a 3.31 or 3.06 would be great depending on the cam and expected RPM range.

I'm pushing about 450 HP through one of these upgraded Dana 44 based units. Get a fined alu diff cover to keep it cool and up to 600 HP wont be an issue. The later Diff's have a finned alu cover so you may already have one. You're not gonna get enough traction to blow up the diff with out some major wheel well cutting to fit some sticky and wide tires in any case.

The OE limited slip is friction based and will get hot and open up over 400 HP with a hard hitting turbo this is a major liability and can cause a spin. If you're serious you need an aftermarket locker. I can sell you the right piece. PM for for a phone consultation.

As for the drive shaft it's a little complicated. I can sell you the right piece. PM for for a phone consultation.

You definitely will have to brace the IRS to prevent it from twisting up and destroying your mounts in the process, Doesn't take much. Just run 2 ladder bars from bottom of the IRS forward as other have done. I did this and put rubber bushing on the body side and it's offered no harshness at all and stoped the wheel hop. I though I would have to do more but it was enough for hard launches.

 

Thanks Roger and ICS for the info.

The brakes are pretty much done(hats/wilwood disks/caliper spacers/parking brakes modified). Just had to buy materials for the machine work. Have to order rebuilt calipers to finish that off. One of the reasons I haven't jumped at the outboard set up is out of concern for limited back spacing/offset for rims. If the calipers turn into sieves the will go that route. I'm going DIY hydroboost for a master cylinder. I know some here find that offensive, but it seems cost effective/smaller footprint(?) compared to a stock rebuilt master cylinder/vacuum booster. Need all the clearance around the engine I can get.

Not that worried about the speedo. I'll use some sort of GPS for that.

Going to run the 2:88s. Seems the best/economical set up to help boost. Engine is going to be a stock shortblock w/forged pistons and rods/317 heads(large chambers)/LS6 cam and not going to spin it past 6K. Not thrilled with running this t56. Seems like no matter what gearing you use, either 1st or 6th is useless. Would love to use a 5speeed, but no real good/practical options that I could find.

ICS - I saw the pics of the t56 install and was wondering what shifter mount/position did you wind up using? Did you keep the reverse lock out solenoid? How close to factory opening did you get? What clutch master cylinder did you use?

 

Guess I do not beat on my Jag enough? Never had any traction problems or IRS part breakage. Do have the finned Dana 44 rear cover...

 

The shifter position is default rotated 180 degrees, it's perfect for driving. I loved it and I had the customer drive the car and he found it comfortable too.

The clutch master is 5/8 Wilwood. Super easy clutch with lots of resolution.

Reverse lockout is module is aftermarket.

The close ratio T56 with the .63 6th gears when using a 3.54 is nearly perfect. All gears are usable. 1st creeps along in stop an go traffic easily. 6th cruises well enough and noticeably lower revs than the OE 4 speed auto which had a .75 4th gear. If I was starting from scratch I'd use a 3:31 diff ratio. It Would offer a higher top speed and there would be almost no difference in 1st but the 3.54 is great and this project has a budget.

 

The rear dif is freshened up along with new bearings and bushing for the suspension. Had the cage and lca's powder coated. Still have to order shocks and install springs, but I'm getting there slowly but surely.

Also, are the SNG Barrett rear cage v-mounts worth the extra cost? Looking around for parts between xj6/12's and XJS's, I see two different part numbers for XJS's rear v-mounts. One is for hardtops and another for converts. Does anyone know the difference? I will be adding some sort of brace/connection between the rear cage and body. I'm just trying to give everything the best chance to survive some juvenile antics from time to time.