Instead of watching the local 4-by shop fumble with tools for this gear change (as I've seen before), I decided, this time, to turn to the real professionals at Randy's Ring & Pinion, in Everett, Washington. Let me tell you, these guys KNOW gears. And axles. And differentials. Better than anyone else I have ever met.

Now that I was confident that I had found a capable set of hands to work on my TJ, it was time to select a new gear ratio. As expected, Randy steered us away from the 4.88 gearset, to the stronger and more mathmatically-correct 4.56's for our 33-inch tires.

Thanks to Randy and his crew, the Jeep now has more power and better acceleration with 33-inch tires than it did with the old gearing and 31-inch tires. I must admit that Grant and Randy were right, new gears made a much bigger difference than I thought they would!

What did I learn from all of this?

1) Lower gears are the ultimate power compensation for larger tires,

2) Next time I need gears, I'm going back to Randy's Ring & Pinion!

Below are the detailed steps of a ring & pinion installation.

Tool List

When working on your differential you will need a wide variety of tools. It is always recommended that you use the right tools for the job. Using the correct tools will save you time and help prevent parts from being damaged. Here is a list of some of the tools that you may need:

· Dial indicator
· Genuine gear marking compound and a clean brush
· Calipers or a micrometer
· Bearing pullers
· Bearing press
· Misc. hand and air tools including:
· Three foot long breaker bar or strong impact gun
· Pinion nut socket
· Ring gear bolt socket
· Main cap bolt socket
· Six point cross pin bolt wrench
· Brake line wrench
· Pry bars for removing the carrier case
· 24 oz ball peen hammer
· 48 oz sledge hammer
· 48 oz plastic dead blow hammer
· Assorted brass punches
· Center punch or number stamp for marking main caps
· Oil drain pan
· Torque wrenches:
· foot pounds
· inch pounds

1. Before I start working on anything I always make certain that I have everything I need before I start. Check all of your new parts to be sure that you have everything you need and make certain that you have received all of the parts that you ordered.

2. The next step is to lift the vehicle using an appropriate lift or a jack and safe jack stands. Always make certain that the vehicle is safe to be under before starting to work on the vehicle.

3. Then drain the oil into a suitable container. We always recycle our waste oil and hope that you will be able to recycle yours too.

4. Next remove the axles shafts.

5. Mark both of the main caps so that you will be able to re-install them on the same side in the same direction as they came off.

6. Keep track of the position of all of the original shims.

7. Clean and inspect all parts

Order of Adjustments:
When assembling or setting up a differential there are four basic adjustments. In the order or importance they are:
1. Pinion Depth
2. Pinion Bearing Preload
3. Backlash
4. Carrier bearing preload

Selecting Shims
For my first assembly I usually start with the shims that were used in the differential during the previous assembly. If the original shims from the previous assembly are not available then I recommend using the thickness listed in the specifications information.
Preparing Parts
Before assembly I clean all parts, including the new ones with clean solvent. I wash out the housing with solvent and check all of the oil passages to make certain that there are no metal particles or dirt that can lead to early wear. On many housings there are oil passages to the pinion and groves just outside of the carrier bearings where metal particles hide. Be sure to check all passages and groves for metal particles and dirt!

Seal Preparation
All seal surfaces can be polished with light emery cloth or sandpaper and then wiped with a clean rag and clean oil or solvent to remove the metal particles left after sanding.

Assembly Oil
When assembling I use a moderate coat of gear oil on all of the bearings and grease or oil on all of the seals and seal surfaces. I do not use bearing grease on any pinion or carrier bearings, only clean gear oil.

Pinion Trial Assembly
I have found that it is easiest to assemble the pinion without a crush sleeve until the correct pinion depth has been established. When initially installing the pinion I slowly tighten the pinion nut until the preload is within the assembly specifications.

Initial Carrier Assembly
I have also found that it works well to assemble the carrier snug but not tight during trial assemblies so that it is easier to remove and replace during the several attempts necessary to find the shim combination for correct pinion depth and backlash.

Adjusting Backlash
After installing the pinion, the first adjustment that I make is backlash. I believe that a clear indication of pinion depth can only be obtained when the backlash is within, or very close to specifications. I have found that the backlash will change about 0.007" for each 0.010" that the carrier is moved. If I want to decrease the backlash by 0.007" I move the carrier 0.010" closer to the pinion. If I want to increase the backlash by 0.007" I move the ring gear 0.010" farther away from the pinion. This is not exact for all ring & pinion sets, but it is a good general guideline.

Checking the Pattern
After setting the backlash the next setting to check is the pinion depth. When checking the pinion depth I use only genuine gear marking compound. Gear marking compound gives a clear indication of gear contact without running or smearing. I usually mix a little oil with the marking compound so that it is smooth but not runny. I brush three or four of the ring gear teeth with a moderate coat of compound in two different places on the ring gear. Then I rotate the ring gear past the pinion gear four or five times to obtain a good pattern.

Important Pattern Information!
Reading the contact pattern is easy as long as I am not mislead or sidetracked. The only part of the pattern that helps me set the pinion depth correctly is the contact position with regards to the face and flank of the teeth. If the contact pattern appears to be towards the heel or the toe of the ring gear teeth I pay no attention and look only at the pattern position from face to flank. The pattern will also change from heel to toe but in most cases an ideal heel to toe pattern can not be achieved. Trying to obtain a pattern that is centered from heel to toe will usually lead to frustration and a noisy gear set. Even if it does not seem intuitive or reasonable, I am only concerned with the position of the pattern from face to flank. I have found that housing alignment and the position of the pinion bearing bore in the housing affects the pattern from heel to toe and can not be corrected without machine work. A contact pattern that is centered from face to flank always indicates correct pinion depth even if a pattern that is centered from heel to toe can not be obtained.

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 the pattern the pinion needs to be moved towards the ring gear so that it is positioned 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 the pattern the pinion needs to be moved away from the ring gear so that it is positioned farther away from the ring gear centerline.


Used Gear Sets
When setting up a used ring & pinion I am basically concerned with the pattern on the coast side of the ring gear teeth and I pay very little attention to the drive side of the gear teeth. This is true for most used gear sets but in some cases both the coast and drive side should be considered.

Adjusting Pinion Depth
When changing the pinion depth I always make large changes until the pattern is close. I 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. I purposely make adjustments that I know are moving the pinion too far. If I move the pinion too far and the pattern changes from one extreme to the other then I know that the correct pattern is somewhere between the two extremes. Once I get close to the correct pinion depth I 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 I remove the carrier and set the final pinion bearing preload.


Setting Pinion Bearing Preload
In differentials that use a crush sleeve this is relatively easy. I always use a new crush sleeve for final assembly. I 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.

Crush Sleeve Design
On a crush sleeve design differential it usually takes between three hundred (300) and four hundred (400) foot pounds of torque to crush the crush sleeve. Over the years I have used huge breaker bars and or very strong air operated impact wrenches to crush the crush sleeve. I also proceed very slowly so that I 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. Again, I recommend taking 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 preload I 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 I check the preload again to make certain that it is correct.

Preload Shim Design
If the differential uses shims to set the pinion bearing preload then this step may take a few times to get it right. I usually use the original shims on the first assembly or add 0.003" to the original preload shims to make up for the bearings settling into the housing. When first tightening the pinion nut I am careful to tighten it slowly so as not to damage the bearing if the preload shim stack is not thick enough.

If the preload is too loose then I remove shims so that the bearings will be tighter against the races and increase the preload.

If the preload is too tight then I add shims so that the bearings will not be as tight against the races.

I am always very careful to clean the shims completely so that there are no particles that may cause a false preload reading or cause the shim stack to change thickness over time as the vehicle is driven. When making preload shim changes I like to remember where I started and which thickness’ I have tried. I recommend writing down the thickness and resulting preload of each shim combination tried. After reaching the correct preload I 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 I check the preload again to make certain it is correct.

After setting the pinion depth, backlash, and pinion bearing preload I set the carrier bearing preload. I like to set the carrier bearing preload fairly tight. There are three different shim or adjustment methods that cover most differentials.

Screw Adjuster Design
The first and easiest method uses screw adjusters to set the backlash and carrier bearing preload. When setting the carrier bearing preload on this type of differential I am careful to oil the adjuster threads on both the housing and on the adjusters themselves. I am also careful about the order in which I tighten the adjusters so that the backlash stays where it should even when under heavy loads.

The ring gear is always forced away from the pinion gear when ever it is transferring power and it is never forced toward the pinion gear. When setting the backlash and carrier bearing preload on a differential that uses screw adjusters I start with the backlash wider than the final setting that I am adjusting it to. I always make certain the last adjustment that I make on the left adjuster is to tighten it. If the backlash becomes too tight I start over by opening it to a position where it is too wide again by backing off pressure from the left adjuster and then I use the right adjuster to open up the backlash again. At this point I tighten the left adjuster which closes down the backlash toward the final setting. I always make certain that the last adjustment that I make on the left adjuster is to tighten it so that there is no possibility of a space between the adjuster and the bearing race. Any space or looseness on the left side can let the carrier move when under load and this can cause the backlash to open up.

After the backlash approaches the final setting I tighten both the left and right adjusters evenly so that the carrier bearing preload increases. I like to set the carrier bearing preload as tight as I can with a ten (10) or twelve (12) inch long spanner wrench. I have never encountered carrier bearing failure due to excessive carrier bearing preload on a screw adjuster type differential.

If the preload is close and the backlash is too wide I tighten the left adjuster a notch or two until the backlash is correct and the preload is tight.

If the preload is close and the backlash is too tight I tighten the right adjuster until the backlash is correct and the preload is tight.

Like I stated before, I always make certain that the last adjustment that I make on the left adjuster is to tighten it so that there is no possibility of a space between the adjuster and the bearing race.


Outside Shim Design
There are also designs that use shims between the carrier bearing races and the housing. On these types of differentials I set the carrier bearing preload as tight as I can without damaging the shims while driving them in. I have never seen carrier bearings fail in this rearend design because of excessive carrier bearing preload. During the original set-up of this design I set the backlash with very little carrier bearing preload. After I have set the backlash I add shims to both the left and the right sides until I obtain the correct preload.

If the preload is close and the backlash is wide I add shims to the left side. This increases the carrier bearing preload and tightens the backlash at the same time.

If the preload is close and the backlash is too tight I add shims to the right side. This increase both the carrier bearing preload and the backlash at the same time.


Inside Shim Design
The last design uses shims between the carrier bearing and the carrier case. On this design I also set the preload very tight but not so tight that the carrier is difficult to install or remove. I keep the preload very light while setting the backlash so that the carrier is easy to remove and install. After I have set the backlash I add shims to both the left and right sides evenly until I obtain the correct preload.

If the preload is close and the backlash is wide I add shims to the left side. This increases the carrier bearing preload and tightens the backlash at the same time.

If the preload is close and the backlash is too tight I add shims to the right side. This increases the carrier bearing preload and the backlash at the same time.

Left: New 4.56 Gears Right: Old 3.73 Gears

Left: New 4.56 Gears Right: Old 3.73 Gears

ANY OVERLOADING OR OVERHEATING WILL CAUSE THE GEAR
OIL TO BREAK DOWN AND THE RING & PINION WILL FAIL.

©2000 Randy's Ring & Pinion Service

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Why should you let Randy do YOUR rear?

Because if you don't...let's just say it's not a pretty sight!

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