I know how much work it is to drop the rear end on these cars (did it on an XJ6 last fall) but I was thinking that changing the rear end gearing would be a step in the direction of bringing some of that torque and horsepower closer to a usable level. I mean lets face it, here in my part of the country all the fun is 0-60 and powering through the mountain curves.

If I'm not mistaken, the gearing in these are Dana posi 2:88's? Great for gas mileage but it costs in low end power. I was thinking of maybe 3:11's. Any thoughts on this? Is there anything different about these rear ends or can I get a set of gears for a Dana and pop them in?

 

you can get some 3.01 out of a flathead.

your in town mileage will improve but your highway economy will suffer with no overdrive.

 

True, but if I was looking for mileage I probably wouldn't be driving a V12...lol

 

You can't replace the gears in the 2.88 rear. The carrier is unique to that gear set. You need a carrier from a 3 series ratio. The bolts on the Jag are larger than stock Dana 44 gears so you need sleeve for the bolt holes. The pinion has a different driveshaft flange so you need to modify your driveshaft too.

 

Later cars with OD had a 3.54 rear end, and outboard brakes. I would swap the entire unit out.

Dave
Atlanta

 

Ahhh...I wondered if there were issues like thisN great info guys! Sounds like ATL has the right idea on switching the whole unit. Does the newer units mount up the same? I suspect brakelines and parking brake cable are different. Are they still posi's?

 

Oh...and what years had the OD with 3:54's?

 

AFAIK the later (93? 94?) face lift cars with the 4.0 six cyinder/ZF trans and the 6.0 V12/4L80E trans used the 3.54 gears...and would be the outboard brakes IRSs. I'm not sure if limited slip was still standard issue on those cars

I've heard of guys swapping in the entire outboard brake IRS. Can't remember every detail but apparently it's almost a drop-in....except for pipes and cables, as you mention.

Cheers
DD

 

The XJ6 1968-1987 ratios and diffs will work. Some of the Sedans had limited slip diffs.
3.54:1
3.31:1
3.07:1
3.05:1 (Swiss or Belgian market)
2.88:1

There were more sedans than XJ-S made so there is more to pick from.

The 3.6 XJ-S used the 3.54:1

bob gauff

 

I have 3.58 in mine from a V12 XJ40 I swapped the whole hemisphere all that was needed is a spacer between the pinon yoke and universal.

Next option is a spacer between the 3.54 etc crown wheel and hemisphere, there are a couple of XJS race cars here in Aus that run this setup.

Last is a complete Dana 44 center you will need the pinion yoke from a Jeep and Jaguar bearings.

 

warron, for my 78 XJS DANA 44, i brought my gears(ring&pinion) to a local rear end shop.

the guy just looked at them went in back room came out with set of gears,3.73 ratio, said they ordinary JEEP gears, $150. bucks, handed me a pinion yoke from a chevy rear, all went together perfect, been ok for 16yrs, no sounds,or whines.

i use a single piece ALUMINUM drivshaft, with HD joints.

of interest,when i had the Powerlok apart, i restaggered the plates, and it has much more BIAS in it now, can drift it just touching the throttle. and GM posi oil.

 

So was there a significant change with the gearing?

 

YES much better acceleration, the 700 over drive gives me a final ratio of 2.60, for good mpg crusing.

my factory gears where 3.07, and i went to 3.73, much more responsive, along with the more usable ratios in the 700R4 trans.

it is actually a good combination of the whole drive train package, the single piece aluminum drivshaft reduces rotational weight, and lighter overall weight of vehicle.

Thx for your interest.

Ron

 

Ron, so I can keep the original case and switch to Jeep gears?

 

Yes, with caveat

Jeep crownwheel uses 3/8 bolts Jag hemisphere has 7/16 bolt holes, holes can be bushed or use a Dana 44 hemisphere.

Easiest way I found was to source a set of Jag gears and make a spacer I have a spare set of 4.09’s including spacer if you are interested. The spacer is universal Jag and will need final machining for the 4.09’s

 

Hmmm...I'll have to think on that. I wasn't thinking of going that low of a gear. I'm still using the original TH400 which only has 29,000 miles on it, so I don't really have any reason to change it yet.

If mine are 2:88 (I think?) and yours was 3:07 and switching to 3:73 made it more responsive, then the 4:09 should be neck-snapping! Do I need to call my chiropractor?

 

You could keep the th400 and install a gear vendors. The 2 targa cars I mentioned before (the ones with the spaces ) one runs 4.09 and the other 4.27 the acceleration is very brisk. I decided against the 4.09 because of my forced induction plan.

 

Most off the shelf Dana 44 gears sets will work on the 2.88 carrier with a couple of issues:

The first is the bolt size previously mentioned. Second, the pinion has 10 spline on the Jag and 23 on the Dana gears. You'll need a new driveshaft flange to match. Finally, there is some variation on the bearing sizes between Jag and Dana. All the bearings are available and your shop should be able to provide what you need.

Beware any reverse rotation or custom high pinion sets designed for the off road crowd.

Too much to list here, but if you google jag rear ends and cobra kit cars there are a number of good write-ups.