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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.


 

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