Learn me Jaguar rear ends... Where’s Frenchy??

Ransom said:

I just opted out of going to look at a cheap V8-swapped XJ6 because I (temporarily) don't have enough garage to deal with the fact that a simple brake job on one of these is best started by dropping the subframe. Onboard brakes are neat, but they come at a price...

That sounds like such an intimidating job but it’s not. I’ll bet you can drop the rear end out of a Jaguar in less time than a Chevy pickup ( selected because I think that’s the fastest and easiest rear end to pull. 

I’m old and fat, but in my 30’s that was less than 30 minutes work.  

Once out rear brakes ( including new rotors) could be done faster than most. Rebuilding the caliper if called for was very straight forward too. Brakes is brakes.  Pop off the brake line. A couple of 3/4 inch bolts and the caliper is sitting in your hand.  Pull the old pads slide in new and Bob’s you Uncle. 

( last is a bit of Limey slang , don’t forget to call the customer Gov-nor  in your best cockney accent)

In reply to SVreX : I think it helps that Minneapolis used to have two Jag dealers who would gladly get into bidding wars and as a result a lot of Jaguars got sold.  Now with only one dealer but Porsche, Audi next door, Mercedes Cadillac nearby not to mention Lexus Bentley, Aston Martin.  Etc right on the same road a lot of deals get done.  

And we have rust!  Natures way of providing racers with good mechanicals.  

SVreX said:

Ransom said:

I just opted out of going to look at a cheap V8-swapped XJ6 because I (temporarily) don't have enough garage to deal with the fact that a simple brake job on one of these is best started by dropping the subframe. Onboard brakes are neat, but they come at a price...

That’s a good point, but I have a feeling it is dependent on the application. 

This one sure looks easy to access the calipers!

If you like the rear end visible like that  you will have to delete the steel cage. Then mounting gets a lot trickier. Trickier but not impossible.  

You wont notice it but that whole rear end assembly is too high. Probably because the same springs used in a 4600 pound sedan are used on an 1600  pound car.  

The axles should be level.  

For those who don't want the inboard brakes, an IRS from an 88+ XJ6 (the XJ40 generation or later) or a late (91+ I think) XJS is the version 2 with outboard brakes. 

Other than that, they're pretty strong and simple.  Keep in mind for high power applications, if you break an axle shaft, you're going to have an issue, as the axle shaft is a suspension locating link. 

SVreX said:

In reply to frenchyd :

Thank you. Good info. 

(I wish I was better at calculating rear end ratios) 

It sounds like you are saying most Jaguar models shared rear end overall design- packaging, subframe, integrated suspension, onboard brakes, etc. True?

In general tire height will tell you what the top speed of a given rear end is.  27 inch tall tire with a 2:88 means the top speed is 150+ mph but acceleration will suffer.  It’s also best for fuel mileage Taller tire will give more top speed but slower acceleration. 

3:54 will give you 120MPH top speed but much quicker acceleration.  Fuel mileage suffers compared to a 2:88 A shorter tire will give even quicker acceleration. 

Outboard brakes came towards the end of production. 1988 was the earliest   Better for racing  but both worked well under street driving.  Heat dissipation was the primary weakness of inboard brakes. If you could get the rotors red hot the heat would cook the seals.   

In reply to rslifkin :

In decades of racing I’ve never seen a rear axle on the XKE break.  They  are really serious big diameter forgings compared to the axles on most cars. 

What about the outer hubs? Since the driveshafts are also the top a arm (a arm length has to be reasonably fixed), how do you check that the play in the bearings at the diff and at the hub is within spec?

I'd be worried to pull a diff and then have to immediately redo all of the thrust bearings...

In reply to Robbie :

I’m not smart enough to worry about E36 M3 like that!

I’ve got a lead on a 1978 unit from an XJS. 

I am assuming posi traction with 3.07 gearing. Correct?

This stuff Is Simple and Strong, Maybe Over enginered.But you look at it and say Oh! That makes Sense.

They might Have rethought the Shiming  deal a bit but Otherwise Easy, The cobra kits I see do not use the Top Cradle but A plate on the rear Housing Connecting to a cross bar to the frame rails with Spring mounts on the Out board side of the Rails.then some ford truck radius arms to locate the Hub Fore and Aft, Easy Peasy

Just saw that last post..... That seems Ideal 3.07/Posi

There are companies in the street rod industry that sell installation kits for Jaguar IRS rear ends, Snow White is one:  http://www.snowwhiteltd.com/products.html  They aren't necessarily better than the stock mounting cage but do clean up the looks quite a bit.

GTXVette said:

Just saw that last post..... That seems Ideal 3.07/Posi

But it could be a 2.88, right?

rslifkin said:

For those who don't want the inboard brakes, an IRS from an 88+ XJ6 (the XJ40 generation or later) or a late (91+ I think) XJS is the version 2 with outboard brakes. 

Other than that, they're pretty strong and simple.  Keep in mind for high power applications, if you break an axle shaft, you're going to have an issue, as the axle shaft is a suspension locating link. 

I’m pretty sure they also went from 4 shocks to two shocks with that change. 

In reply to SVreX :

Yes, but the difference between a 2:88 & a 3:07 is pretty trivial.  

Changes top speed from 149 mpg to 153  in an XJS ( in perfect circumstances )

positraction was on most Jaguars except occasional batch’s of XJ6’s 

In reply to stuart in mn :Actually mounting a Jag without the cage is pretty straight forward but it’s more work. The  top four bolts mount the whole assembly, so alignment gets hypercritical ( even with a kit). This isn’t something that can usually be shimmed straight. If the welded in assembly is wrong it’s cut out the old and weld in another. 

 Then mounting the shock absorbers is pretty straight forward. Next  figure out where to put the drag link mounts. ( again alignment) Finally you need to tie the front  and  rear inner pivot points together.  ( that part is easy with the kits) 

The real  trouble happens is the inherent conflict between the arc or the suspension pivots  and the arc of the drag link pivots.  

Jaguar gets away with it by putting the whole assembly on  rubber and let’s everything sort itself out.  

Street rods basically turn the whole rear axle rigid or nearly so. 

While racers are trickier.  We rigidly mount the whole rear end but instead of a forward facing drag link we bring the drag link forward at about a 45 degree angle and intersect the inner pivot point.  Thus the arcs all pivot around the rear suspension. 

One other technique is to eliminate the drag link completely by fabricating a set of front and back links Like a modern Formula one car does. You could also reduce unsparing weight by picking up suspension loads at the rear hubs through links.  

Also, I think this might be a bit later than you are planning, but I know singleslammer swapped a Jeep Dana 44 clutch type lsd and 4:1 ish ratio ring and pinion gears into his 1996 xjr differential case in preparation for the 2017 challenge (which he didn't make it to because of engine trouble).

But it sounds like Dana 44 stuff is close enough to make a lot of the stuff work internally on jag diffs.

In reply to Robbie :

Actually Jaguar bought both the Dana 44 and the Salisbury version of the Dana 44 and that’s the prime difference.   Earlier center sections are all Dana but some point in the late 1970’s early 80’s  Jaguar bought Salisbury versions.  I think when they switched to outboard brakes they again went with Dana’s  but bearings and bolts Changed too so I could have details confused.  

Ive always replaced bearings simply by going to a local bearing place with the old in hand because  it’s massively cheaper than going through either Jaguar or the Jaguar specialists. 

Bolts I tend to use up my supply of AN grade hardware.  

The Jag rear end works well on rods and such, but one should think twice before installing one in a car that will see any sort of hard braking use - cooling the rear brakes is a very difficult job even on 2500 lb. cars.  Most conversions are cars that just putter around the street as show or toy cars, in which case there should be no problem.

frenchyd said:

rslifkin said:

For those who don't want the inboard brakes, an IRS from an 88+ XJ6 (the XJ40 generation or later) or a late (91+ I think) XJS is the version 2 with outboard brakes. 

Other than that, they're pretty strong and simple.  Keep in mind for high power applications, if you break an axle shaft, you're going to have an issue, as the axle shaft is a suspension locating link. 

I’m pretty sure they also went from 4 shocks to two shocks with that change. 

Thinking about it, there's one other key difference: the Gen 2 IRS is usually (maybe always?) found with an open diff. 

In reply to rslifkin :

That must be one of those batch things Jaguar always did. Every new version I’ve seen has had positraction even the Six cylinder cars. I’m certain the V12’s had positraction.  

Easy,  sure way to check, jack up one rear tire and try to spin it. No spin, posi.  Even if one does spin the possibility exists that the diff lube had been changed without the supplement and the clutches got burnished.  

I had success a couple of times draining the lube, adding fresh with the supplement and just driving it.  But even if you need to replace the clutches and plates it’s just unbolt,  replace and bolt back together no set- up required. 

In reply to wspohn : The sedans weigh around 4600 pounds the XJS is 4200 pounds  with basically the same brakes as the XKE and testers don’t ever mention fade issues.  

You’d need to get the rear brakes really hot to have issues.  I’m talking about race track type braking. Remember most braking is done at the front.  True I’ve rarely seen a Jaguar pull a heavy trailer but maybe a heavy trailer down a fast right winding mountain road might cause issues.  

Yes the rear brakes fade on big high speed race tracks Like Elkhart Lake on track day cars  but even Indy cars  used their biggest air scoops at Elkhart Lake.  

Brainerd while a 3 mile track with one really long straight  puts all the heavy/ hard braking in a few corners with enough time for the brakes to cool. 

Blackhawk just doesn’t have the sort of speed needed. Atlanta spread the heavy braking far enough apart, same with most California tracks I’ve been at.   The old Riverside might have pushed the brakes but I only raced there in the XK150 never with anything with inboard brakes. The Bahama’s has slower speeds and time between, Watkins Glen same thing.  

I never raced Mid-Ohio so I can’t comment. 

Poorly maintained brakes with lots of water in the brake fluid could have fade issues anyplace but inboard or  outboard wouldn’t make a difference.  

In reply to frenchyd :

I'm not sure on the XJ40 V12s as far as posi.  I know most XJ40 and X300 cars were open diff and all X308s were (even the XJR).  Although I think the diff was slightly different on the X308 than the earlier cars, so it may be just the X308 that never had posi.