Continuation of Installing a Zexel Torsen Differential Carrier

Here is some basic differential terminology you should learn.

Flank – the bottom area of the ring gear that the gear teeth rise from. Also called the root
Face – the top flat surface of each gear tooth also called the top land
Drive – the convex side of the ring gear teeth which the pinion contacts to drive the ring gear
Coast – the concave side of the ring gear teeth opposite the drive, also contacted by pinion gear
Heel – the outer edge of the ring gear
Toe – the inner edge of the ring gear
Pinion depth – the position at which the pinion contacts the ring gear teeth between the face and flank
Pattern – the “footprint” where the pinion gear contacts the drive and coast sides of the ring gear teeth (viewed by use of gear marking compound)
Backlash – the amount of free movement of the ring gear with the pinion held fixed in place
Pre-load – the initial amount of force applied to the races upon the bearings

When working on a differential there are four basic adjustments. In order of importance they are:

1. Pinion Depth
2. Pinion Bearing Pre-load
3. Backlash
4. Carrier Bearing Pre-load

Be aware that adjustments of pinion depth, pre-load and backlash effect each other. When you change one you must re-check the others. Therefore it’s important to understand that for a correct install you may have to remove the carrier several times to make the necessary adjustments, indicated by the pattern and backlash measurements, to achieve proper alignment.

Before you can adjust pinion dept you must set backlash. The best way to obtain backlash reading is with a dial indicator. You should be able to get a close indication of initial pinion depth if the backlash is within, or very close to the .006” - .010” specification. On most ring and pinion sets backlash will change about 0.007” for each 0.010” that the carrier is moved. Therefore if you need to decrease the backlash by 0.007”, move the carrier 0.010” closer to the pinion by shimming the left side. If you need to increase the backlash by 0.007”, move the carrier 0.010” farther away from the pinion by shimming the right side. Use a pencil and paper to keep notes of shim combinations and backlash. A calculator might also come in handy.

After setting the backlash you can check pinion depth. Do this by brushing three or four of the ring gear teeth with a moderate coat of compound in two locations on the ring gear. Rotate the ring gear past the pinion gear four or five times to print a good pattern. The gear marking compound will show a clear pattern of pinion contact on the ring.

The pattern you’re looking to achieve should be oval in shape and centered between the face and flank on the drive and coast side of the ring gear teeth. There should be an area of no contact below the face and above the heel on both sides. It would be ideal if the pattern was also centered between the heel and toe of the ring gear, but that is not necessary. The only part of the pattern that helps set the pinion depth correctly is the contact position between the face and flank of the teeth, regardless of the location concerning heel and toe. I’ll say it again; if the contact pattern is towards the heel or the toe of the ring gear teeth ignore that and look only at the position from face to flank. In most cases an ideal heel to toe pattern can not be achieved anyway. Trying to make adjustments to get a pattern that is centered from heel to toe will usually lead to frustration and a noisy gear set. The position of the pinion bearing bore in the housing and housing alignment affects the pattern from heel to toe and can not be corrected without machine work. So once again, a contact pattern that is centered from face to flank on the drive and coast side always indicates correct pinion depth even if the pattern can’t be centered from heel to toe.

If the contact pattern is towards the face of the ring gear teeth then the pinion is too far away from the ring gear. To correct it the pinion needs to be moved towards the ring gear with a thicker shim to position it closer to the ring gear centerline. If the contact pattern is towards the flank of the ring gear teeth then the pinion is too close to the ring gear. To correct it the pinion needs to be moved away from the ring gear centerline with a thinner shim. The shim is located between the gear and rear bearing.

If the backlash is within spec but the pinion depth is not correct you match-mark the driveshaft to the pinion flange and remove the driveshaft and suspend it with wire out of the way on something like the exhaust pipe. Match-mark the pinion flange, pinion shaft and nut (if you’re reusing the nut). Now check the bearing pre-load using an inch-pound torque wrench and record it before disassembly. The pre-load is the torque required to just begin turning the pinion shaft.

To remove the pinion nut and washer you will need to use a special flange holding tool or breaker bar to hold the flange in place while you loosen the nut. You may also want to install the cover loosely with a couple bolts so the pinion doesn't fall out. With the nut and washer off use a two-jaw puller to withdraw the flange by placing the two jaws on the backside of the flange and the puller screw on the pinion. Examine the sealing surfaces of the flange for nicks or gouges. Replace the flange if it's damaged. Use a blunt chisel to remove the pinion oil seal, being careful not to damage the carrier housing. The pinion can now be removed from inside the carrier case to replace the bearings, races, correct thickness shim and crush sleeve. It’s easiest to assemble the pinion without a crush sleeve until the correct pinion depth has been established. Install the new pinion oil seal. When initially installing the pinion slowly tighten the pinion nut until the pre-load is within the assembly specifications of 12-15 in. lbs. on a new pinion gear and 6-7 in. lbs. on a used pinion.

Understand this is the hard way to set pinion depth without the six or seven special jigs, and guage a GM tech has available. They can simple install the various jigs and get a reading on the guage that translates into the correct thickness shim required.

When changing the pinion depth always make large changes until the pattern is close. Consider 0.005” to 0.015” to be a large change and 0.002” to 0.004” to be a small change. Changes of 0.005” to 0.008” or more will lead to the correct pattern faster than small changes will. If you move the pinion too far and the pattern changes from one extreme to the other then you know that the correct pattern is somewhere between the two extremes. Once you get close to the correct pinion depth make smaller changes until the pattern is centered between the face and the flank of the ring gear teeth. After the backlash and pinion depth are set remove the carrier and set the final pinion bearing pre-load of 12-15 in. lbs. on new pinion gear and 6-7 in. lbs. on a used pinion. Use a new crush sleeve for final assembly. Use oil on the pinion nut washer surface during all assemblies and red Loctite on the pinion nut threads during the final assembly. The oil on the washer surface helps the nut turn easier while it is being tightened and the red Loctite helps keep it tight.

On a crush sleeve design differential it usually takes between 300 and 400 foot pounds of torque to crush the crush sleeve. Use a large breaker bar and or very strong air operated impact wrenches to crush the crush sleeve. Proceed very slowly so that you get it right the first time. The pinion preload will be zero until the bearings contact the races. When the bearings contact the races the preload will increase very quickly. Take plenty of time to set the preload carefully so that the bearings will have a long life. If the crush sleeve is over crushed and the pinion bearing preload exceeds the specified allowable range the only solution that I know of is to install another new crush sleeve and start over. After reaching the correct pre-load, moderately tap both ends of the pinion to seat the bearings, races and yoke. Be careful not to hit the pinion so hard that it damages the bearings. After “seating” the pinion check the pre-load again to make certain that it is correct.

After setting the pinion depth, backlash, and pinion bearing pre-load it’s time to set the carrier bearing pre-load. During the original set-up you set the backlash with very little carrier bearing pre-load. Now set correct pre-load by inserting equal thickness shims to each side. Make it fairly tight, as tight as you can without damaging the shims while driving them in. If the pre-load is close and the backlash is wide, add shims to the left side. This increases the carrier bearing pre-load and decreases the backlash at the same time. If the pre-load is close and the backlash is too tight, add shims to the right side. This increases both the carrier bearing pre-oad and the backlash at the same time.

Now that the pinion depth, pinion bearing preload, backlash, and carrier bearing preload are set recheck the pattern once more to be certain that everything is perfect before final assembly.

All new gear sets require a break-in period to prevent damage from overheating. After driving the first 15 or 20 miles it is best to let the differential cool before proceeding. 500 miles are recommended before towing. Tow for very short distances (less than 15 miles) and letting the differential cool before continuing during the first 45 towing miles. This may seem unnecessary but many differentials are damaged from being loaded before the gear set was broken-in. It's also recommended to change the gear oil after the first 500 miles. This will remove any metal particles or phosphorus coating that has come from the new gear set.

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