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8.15 - Differential ( )


8.15.1 - Changing Bearings without removing Diff. ( )


Unbolt the halfshaft and reposition for clearance. Undo the four or five fixing bolts and pull the output shaft out of the diff.

Small loss of oil is possible.

Don't lose the very thin shims behind the shaft. You will need a new collar, seal and bearing. You have to drill the collar and then split it or drive it off with an air chisel, then press off the old bearing and tap out the seal from the housing.

Install new seal, install housing on shaft, press on new bearing and collar at the same time.

Reinstall in diff.


8.15.2 - Changing the Differential Oil ( )


Drain the gear oil out the plug on the bottom of the differential. Use a socket that fits the square plug snugly.

Then to get the new oil in, take the spare tyre out, remove the carpet liner on the back of the boot.

You can then see 2 metal plugs in the boot. Pry out the one that lines up with the differential.

Use a half inch drive extension to remove the plug in the diff.

WARM UP THE GEAR OIL in hot water and use a tube on the end of the squeeze bottles the oil comes in to fill the diff until the oil pours all over the garage floor, scream, and jam the plug back in while getting the oil all over the trunk.

Put some silicone on the boot plugs and put them back in.


8.15.3 - Replacing the Differential ( Brett Gadzinsky,  December 5, 2001 )

Before jumping in and assuming your differential is reaching the end of its life, there are other components which could increase noise and there could be ways to try to solve the problem, at least to bring it down to an acceptable level.

The output bearings, sub frame mounts, and maybe thicker lube can make a worn differential quiet sometimes.... From inspecting some worn and noisy units, it seems only the output bearings wear, and maybe the pinion bearings slightly. The actual gears don't wear out much if you keep lube in the thing, and after all, a rebuilt differential will have used gears in it as well. The ring gear bearings are huge and don't seem to wear much at all.

It seems that 80% of the differentials just need output bearings, thicker lube, and new sub frame bushings.

If you do need to replace your differential, Coventry West is a good way to go when ordering a rebuilt differential.

There are a few other parts around the differential which could be changed at the same time if they show signs of wear but it is hard to say what's needed without inspecting all the bits : differential, drive shaft, axles, etc. No point in going through all this work without tending to other things, so, depending on the state of your car....

To replace the differential, you need a clean garage, the bigger the better, a bigish floor jack (two helps), high jack stands, and a good selection of metric and standard tools. Please check the appropriate manuals before starting !

* Jack the rear of the car up and remove the rear wheels.
* Jack the back of the car up as high as you can, and place.
* Jack stands under the jacking points and chock the front wheels.
* From the wheel well, cut all cable ties to the rear sub frame, and the brakes/abs systems.
* Remove the brake calipers and tie then up high with wire.
* Remove the lower shock mounting bolts.
* Remove the nuts securing the axles to the differential. I found a standard size slightly loose fitting 6 point deep socket got on the nuts better around the U joints, and used a 2 foot extension, and a ratchet with a pipe on it to break the nuts free while working in the wheel well, not under the car. Use the emergency brake to hold the axles from rotating.
* Remove the rear hub pivot bolt, and remove the axle/disk/hub assembly and set it aside.
* Now is a good time to grease the U joints, and clean and grease the pivot bearings.
* Remove all the fuel pump stuff, clamp hoses so fuel does not run out (this is the worst part)
* Be sure all the cable ties on the suction hose are cut...it runs along the front of the sub frame.
* Remove the speedometer sensor from the differential.
* Remove the exhaust mounts above the differential (10mm). A small 1/4 inch drive works well here.
* Slacken the emergency brake cable at the adjustment under the car.
* Remove the center pin in the Y of the emergency brake cable, then split the cables that run to each wheel...needle nose vice grips work well here.
* Remove the center section of the exhaust if you suspect the drive shaft U joints, and it makes the job easier, although you can do it without removing it. New hardened bolts and all metal lock nuts are available at Sears hardware.
* Note the exact location of the drive shaft center bearing. Don't count on marking the bolts, it mounts on a sliding plate, and the entire mount has a lot of slop in the mounting points.
* Remove the center bearing mounting bolts, and look for a shim under the bearing.
* Remove the center bearing crossmember.
* Remove the jerid bolts to differential flange, not drive shaft to jerid bolts !
* Place a jack under the differential and take up the weight with it.
* Remove the lower shock mounting bolts.

Now, the only thing holding the sub frame in is the rear dog bones, and the big front mounts. Make sure this is so...so when you lower the assembly, nothing hangs up or gets broken.

* Remove the rear mounts.
* Remove the front sub frame mounts..the plates to the body and the large center bolt.

The differential is now held up only by the jack. Lower it SLOWLY as it wants to tilt and fall off the jack, and get hung up on something.

If you had the car up high enough, you can roll the jack and assembly out from under the car.

Next, you need to disassemble the sub frame, which consists of hundreds of bolts, washers, bushings and spacers. (this thing is really complex!)

If you mark parts, differential cage for front and back, and note the order parts come off, including washers and so on, its not hard, well it is hard, the parts are heavy and hard to deal with, glad my garage has a thick rug on the floor!

The entire rear suspension comes apart, the sub frame has the big lower part, a plate that bolts on the front of it, with another
plate around the differential input shaft, bolts on the bottom of the big part that go into the differential, bolts and nuts everywhere.

With things apart, inspect the rear A arm bushings and pivot shaft, and the washers/spacers/bearings on the A arm pivot points. Also note how the rubber covered big washers go on the back differential mounts. Remove the axles from the differential, all the bolts, and the diff should be separate now.

At this point, I would strongly recommend replacing the rear sub frame mounts (big front ones).

I did it myself, it is a bit of work without the correct power tools... Paint any parts that need it, clean everything up spotless, undercoat the area above the differential, wash all the nuts and bolts and washers in solvent, one at a time as to avoid mix-up. As things come apart, I assemble them as much as possible, and lay them on the floor in the locations they cam out of.

Assembly is the reverse of the above. Grease all moving parts well. Since you cleaned the bolts and bits up, they should go back in easy...all parts should assemble easy, except for the weight of things. Needing force is a very bad sign, back up and think/inspect. The cage around the differential is offset, so you need to know how the bits point (front to back).

Check the drive shaft u joints, center bearing condition, jerid, and if you have U joint problems, I recommend a good used drive shaft off a newer car. I had no luck balancing mine after replacing the U joints, and the insert in the differential end that centers the shaft while the Jurid is fit wears out and the drive shaft to differential alignment becomes impossible to get right.

If things look ok, disturb it as little as possible !

When the job is done, you know everything is right back there, all clean and shiny...and quiet ! The first time I did it, the job took two days. The last time I did it, it took under 6 hours start to finish.


8.15.4 - Rebuilding the Differential ( Martin Violette,  February 22, 2002 )



Before I bought my í91 XJ40 a couple of years and 60,000 miles ago I was lucky enough to find Jag-Lovers and the XJ40 buyerís checklist, on which as I checked over the car I duly noted a faint whine in the differential. Well, after some procrastination (ha ha) and a whole lot of noise from the rear end, I finally got around to dealing with the problem. Here are some notes on what I did to rebuild the differential (Ď91MY GKN, non-Power-Lok). Please note, although this is a bit of a how-to, Iím not a pro, and Jag gives virtually no guidance on this procedure, so try this at your own risk. And I am assuming that you arenít a novice, so I havenít gone into detail on some standard procedures.

Removing and replacing the diff is covered in the on-line book (very well, thanks to Brett Gazdzinsky), in Haynes, and of course in the shop manual, so I am not going to describe that procedure here. But there is no info in Haynes and very little in the shop manual about the diff because Jaguarís official policy is to replace, not rebuild.

But I thought that since I had to remove it anyway, why not have a crack at rebuilding it. The shop manual gives info on tearing down and reassembling the Power-Lok version to replace bad clutch plates, and the info there is critical, so it should be referred to. After the diff is removed it should be securely anchored to a heavy work bench, the two lower wishbone studs removed (30mm box end required, and these are installed with 200ft lbs/270Nm of torque and Loctite 273 so they are difficult to remove. The shop manual states these are to be replaced but it seems you can only get them as part of the Power-Lok clutch kit, so I didnít. I am guessing that the kit has an updated version of the studs, but I donít know for sure.) Then remove the rest of the cover bolts and the cover. From now on everything should be scrupulously clean.

While the diff is bolted to the bench (use the two bottom case to subframe bolts) remove the pinion nut, washer, and drive flange. If you havenít already removed the output shafts remove them now, and keep their shims marked as to which go on which side with which bearing carrier.

At this point the case must be expanded to allow removal of the crownwheel and output bearings. There is a Jaguar special tool, but two pipe-type furniture clamps and two pieces of angle-iron served me well. Use a dial indicator as shown in the manual to be sure you arenít overdoing the case stretch. When you are ready to remove the crownwheel assembly be prepared to capture the bearing cups, which will otherwise fall off. Then remove the pinion gear shaft, and drive out the inner and outer pinion bearing cups. Be sure to keep any shims with notes, illustrations or whatever you like to use to put them back in the right places. (N.B. If you are only replacing bearings, and not shafts or gears, you will reuse the old shims- there is no need to re-shim the assembly or check teeth mesh and backlash, as none of this changes.) Mark the output flange to case and pinion shaft, and the crownwheel position relative to the case for reassembly.

The output bearings will need to be removed by an automotive machine shop, unless you have a large hydraulic press. Be sure to instruct them to keep the shims with the appropriate side of the crownwheel- I marked one side of mine with paint. Take the output shaft assemblies with you and have them taken apart as well, and take your new bearings to have them pressed on the shafts. Total cost for this in my case was less than $50.

Examine the old bearings for edification, even though it should go without saying that you will replace them all. In my case, the starboard output bearing was the most damaged, the inner pinion the next worse, but all were shot. Interesting wear patterns, but thatís another story. All gear teeth looked like they were brand new. A note on bearings: you can buy rebuild kits from the usual sources, or for about half the cost you can buy bearings and seals from a bearing house, which is what I did. But one warning: both the pinion shaft bearings are special. Mine were SKF, and the codes after the size and duty numbers indicated (when I finally found them on the SKF Web site) that they were produced especially for application as differential pinion shaft bearings. The other bearings are pretty standard fare. I paid about $150 for all, including seals.

While all that is going on you will have cleaned up the diff case, and all the subframe parts, so you are ready to put the diff back together. The first step is to properly install the pinion shaft and output flange assembly, which is the most difficult part of the operation. The pinion shaft nut has to be tightened to bring the bearing into a preload state, and either too little or too much preload will cause premature bearing failure. This bearing preload is achieved by tightening the nut on the pinion shaft to crush a steel sleeve until the desired preload is reached, so that the assembly is as rigid as if it were solid. This means it is a tighten and measure, tighten and measure operation. And itís one-way - the nut canít be loosened, if there is too much preload you have to start over with a new crush sleeve (I bought two in case, although I didnít need the spare). Factory assembly uses some very sophisticated computer controlled air driven machinery to do this which just canít be replicated in a shop. It is worth doing some research before attempting this job, and in particular I recommend visiting the Timken Web site for technical info on bearing preloads.

Bolt the case back to the bench, assemble the pinion shaft, including the new crush sleeve, install it and fit the output drive flange. The threaded part of the shaft must be dead clean, as well as the nut. You are going to need an inch-pound torque wrench, Loctite 273 (I couldnít find this so I used 271 which is almost identical), a clock or watch because you are going to be working against the adhesive cure time (get the data sheet from Loctite), and a torque multiplier. This last tool is expensive (around $400), so try to rent one if you can find one. I work on farm stuff, so this gave me an excuse to buy a used one on e-Bay. I used a 4-to-1 multiplier, and I still showed about 125 ft-lbs on the torque wrench I used to drive it, which means the actual torque on the nut was over 400 ft-lbs. This is the torque it took to crush the crush sleeve. You could do it with a large pipe on the end of your socket wrench, but you wonít have the necessary control over the pinion bearing preload, which is what the crush sleeve is for- the idea is to tighten the pinion shaft nut just enough so the frictional drag on the bearing is between 35 and 55 in-lbs. To achieve this requires precise control over the amount the pinion nut is tightened, and checking the turning torque after each 2-5 degrees the nut is turned, which would be very difficult with a long breaker bar. To see how much you are going to turn the nut, measure the difference between the old crush sleeve and the new, and divide this by the pitch of the shaft threads. For example, if the pitch is 13 tpi, then one turn is one-thirteenth (.077) of an inch, and if the crush sleeve difference is say .040 inches, then you will turn the nut approximately one-half a turn to get ďin the zoneĒ of the required preload. But for a number of reasons you will start measuring preload early, in fact, right after you have tightened the nut far enough to take up any slack (you will feel it when this happens). I started measuring about every 5 degrees of tightening. Tighten, remove the multiplier setup, attach the in-lb torque wrench and measure, repeat. With about 30 minutes of cure time for the Loctite, you have canít waste a lot of time. As soon as you get the preload you want, stop! If you have consulted the Timken site you will have noted that too little preload (as long as it is positive) is a whole lot better than too much.

After this things are easier. Stretch the case again and insert the crownwheel and bearing assembly, and then everything else is pretty much cut-and-dried, just reverse what you did to take it all apart. Be sure all shims are in their correct positions and that you have followed your alignment marks. And donít forget to fill the case with new lubricant!

I now have over 600 miles on the rebuild and it is still dead silent, so Iím pleased. It wasnít easy, and if I had to do it again I would seriously consider replacing it, especially since a couple of our well-known dealers have brand-new Power-Lok versions available for a great price. But it was interesting and I ultimately saved enough to do the SLS conversion at the same time and then some. And a few new tools for the box.


 

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