Well I got the news yesterday, my differential is shot.

Symptom:

Car moves, but every few feet, I estimate 6 to 10, there is a loud POP and the right rear wheel is violently thrust forward an inch or two for that moment.

From inside the car, the POP feels like you drove over a log. While waiting for the diagnosis I searched the web. Found another XK8 owner who had the same issue once. His mechanic described it as one of the gears lost a tooth. As it turns all is OK until you hit that missing tooth = POP/Bang!

Fix:

I suspect the only fix is to replace the rear end.

We have a 3.06 gearing in there right?

Anyone know if there are any year to year differences I should be aware of as we search for the best replacement?

How big a job am I looking at? I am clueless and just scrabling to get all the $$$ lined up. It sure sucks to be driving an rusty old Bronco.

BTW, I wonder if this is an opportunity to replace any of the rubber bushings during the job. I guess I'm thinking if it's disassembled and exposed it can't be much $$ to press out the old and insert new right? I wonder if just the act of replacing the rear is going to hand us any opportunity(s).

Guess I'm trying to get something positive out of this.

Thanks for sharing your experience, I appreciate it. This came out of nowhere. I had no signs except maybe that the rear right wheel would lose traction more easily (with trac turned off) for no reason I could see. I hope it never happens to you.

John

 

Sounds very normal with 14 HU diff. They are weak. It's mostly because of design. All the load goes just for one crownwheel tooth. They are all same - no differences between MY1998-2003 XJ/XJR/XK/XKR. 3.2 V8 has 3.27 , others 3.06. My diff broke in July, so changed to stronger older Jag diff.

 

I have a good used diff but I am about 1800 miles away. Like XJR-99 says, the diffs are the same from almost all X308 and X100 so you have plenty to choose from when looking for a good used part.

bob

 

You can do a quick fix- but if you want to upgrade, have a stronger unit with an LSD (which it should have had from the factory)- there are options- like using the older 15HU diff but going to 3.07 ratio. I'm almost finished installing mine now.

 

This is the original thread when I had the same problem.


https://www.jaguarforums.com/forum/x...ar-diff-59936/


This is what started me off on the path. Seems like it was 5 years ago now! Theres a link to Adam699s thread and similar too there

 

The problem with the X100 is the smaller propshaft tunnel and the offset pinion shaft.

I am sure that the X308 has enough clearance but I never heard if the X100 has the clearance.

bob

 

I haven't done it on an X100 in the field myself, but the XK 180 prototype was based on a short wheel base X100 and used a 450 Bhp AJV8 (infact the first prototype WAS a cut and shut X100) and the 15HU diff with the offset nose.


Would be worth checking.

 

I have done the install a few times. You have to make sure you also get the front mounting plate & also relocate the exhaust hangers.

 

What cars have a 15HU and the 3.58 gears?

That sounds like the stuff for an LS1/T56 Swap.

 

X300/XJ40 XJ6 4.0, X305/XJ81 XJ12, later DDS, Daimler 4.0. Just part of them had LSD.

 

Do you mean the wheel/tire does not remain centered in the wheel well? Something is basically not holding the wheel hub in the right position?

Or do you mean the wheel is violently _rotated_ forward? The wheel center or the brake caliper remain in place in relation to the car, but the tire spins "funny"?

I am trying to visualize what is happening.

 

Fmertz, I meant the first description. I only saw it take place from the outside, best described as: imagine a giant with a giant several hundred pound mallet pounded it at 8 o'clock on the tire. The thing went BANG and the entire wheel shifted forward and back to normal.

BTW, what's your name ? You are always so helpful, just being friendly.

John

 

If the whole thing is moving, then I would take the blown diff diagnostic with a grain of salt. It seems too "sophisticated" for such a blunt problem. I would try to keep working on the diagnostic before committing to anything. Can you "tape" a camera under the car, pointing to the general area of the subframe and drive a few feet? Maybe you have an old phone with Skype or Facetime. It might give you more of a sense of what is happening. Is the whole subframe loose, and moving as a whole? Maybe the mounting bolts are sheared, the mount is rusted, something to that effect. Also, double check the bolts on the swing arms. Maybe they are no longer keeping the hub in place.

There are lots of details here:

my-rear-subframe-refurbishment-131715/

I guess, for me, it is hard to imagine how a bad diff causing an uneven torque could translate the whole hub. From a distance, it seems like the subframe or the swing arm is loose. Of course, this is just my opinion, from a distance. I am not in the shop with the car on a lift in front of me.

Best of luck, keep us posted.

 

The "blown Differential" threads seem to be ring/pinion gear internal issues. Your's sounds more like a failed U-joint.


From what you are describing, the damage should be visible with back of the car on jackstands.

 

You know I was thinking more in the line of the universal joint or wheel hub. The lubrication of the universals have been over looked for several years. I would get a second look or opinion.

 

Fmertz, Ungn, Gus,

Thanks for the input. I'm in a trust me mode now. I've dealt with this shop before this is thier diagnosis. I suppose the reason I accepted it so fast is that it matches one of our brothers over in the XJ8 forum who ran into the exact same symptom/diagnosis/fix a few years ago.

Maybe I'll take a ride down to see if I can get a better handle on the diagnosis if there is some way to do it diplomatically. Gosh you guys are always right on the money, on the other hand I know the mechanic and do trust him - well I'll figure it out. Thank you for the input though.

He was able to find a rear end that he will warranty for $700. He is capping the hours to install at no more than 7 so it will be expensive. In my research I've seen estimates as high as 10 hours, but also as low as 2 1/2.

Wow interesting feedback though. I've been using the XK8 as my daily driver. I'll tell you, you forget how nice it is when you drive it all the time, or until you have to drive around in a rusty 1994 Ford Bronco with 259,000 miles on it .

I'll let you know how it goes. Thanks again.

John

 

I wish your mechanic luck. I'm still trying to reinstall whole subframe back under the car. I connected the prop shaft yesterday and the strut tops but now the carrier bushes and monostrut mounts aren't lining up! Taking hours! I'm using four jacks and repositioning the whole lot as needed. Much harder to put back together than take apart.

 

When you first posted in an earlier thread (11/16) I responded that a universal joint must have failed, and I still see that as the only way the wheel could jump. The axle is part of the suspension and if it and the lower link are sound the wheel has to rotate in a circle and not jump forward.

Get the car on a lift, rotate the driveshaft, and watch the halfshaft universals.

 

OK I spoke to the mechanic. Real nice guy didn't take it wrong. They first checked the U joints = all OK. Axle = all OK. They tried spining the wheels, driveshaft doesn't move. He explained it that there is planetary gears inside, something went wrong and they get "stuck" or hung up (as in binding). I suggested the stored energy of that releasing might send the down to the axle, which is what we saw? He can't say for absolutely sure but he admitted it sounded reasonable. Not much else we can do diagnostically without opening the differential.

Guys, I can't tell you how much I appreciate your attention. I now feel like they did their due dillegence. So it is in their hands to fix.

Thanks again,

John

 

I have the broken X308 diff at my garage and I can take a video tomorrow. Rotating it you can hear how it sounds when a crownwheel tooth is broken. "Glonk, glonk, glonk."