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Carrier Installation and Setting Backlash
Backlash is a measurement of how tight the ring and pinion gears are together. A measurement of zero backlash would indicate the the teeth on the ring gear and those on the pinion gear are as tight as possible. Our goal is to obtain a backlash measurement of .008" to .014" as measured by the travel of a dial indicator. We want the carrier to sit inside the bearing bores so that it does not move side to side. Shims are used on both sides of the carrier to ensure that it is tight inside the housing. To get to our target backlash reading we will take some of these shims and move them over to the other side. If you are working on your rear end upside down (with the rear end off the vehicle) adding more shim thickness to the left side while taking shim thickness away from the left side will increase the back lash, with the opposite decreasing backlash. If you are working on your rear end either while it is still on the vehicle or off the vehicle but not upside down, adding shim thickness to the right side while reducing shim thickness on the left side will increase backlash, with the opposite decreasing backlash. You can think this through for your self by realizing that the closer you bring the ring gear to the pinion gear the tighter they will fit together (and thus the less backlash.)
In the picture notice that just outside of the carrier bearing races there are two metal shims which keep the carrier snug in the bearing bores and sets the proper backlash.
  1. Measure the thicknesses of the carrier shims which were originally installed from the factory. Mine measured .270" and .260". Added together that gives a total shim thickness of .530. Record this measurement as we will want to install the exact same total thickness of shims in our installation.
  1. Start out by sliding the differential with carrier races attached into the bearing bores. Then, insert the factory installed shims behind the carrier bearing races by tapping them in lightly with a hammer. Install the bearing caps on the same sides that they were removed from, tightening the bolts down to 85 ft./lbs.
  1. Set the dial indicator and magnetic stand up so that the tip of the dial indicator rests on one of the teeth of the ring gear. Wiggle the ring gear up and down and read the travel on the dial indicator. If the travel is between .008" and .014" you do not have to mess with adding and subtracting shims because you already have the correct backlash. However, this is highly unlikely unless you have installed gears which are numerically the same as those already installed beforehand because as gears get steeper (numerically higher) the ring gear thickness increases. With my 3.73 gears and the factory shims my backlash measured out to be .024", which is outside of specifications. If you are not within specs. with the new gears and old shims you will need to continue through these steps.
  1. My approach to finding the correct shim thickness is fairly simple. I first took out the carrier shims on the right (your left if you have the rear end still in the car.) The carrier now moves side to side very easily. Since my backlash was too great with the factory shims I knew I would have to decrease the shims on the left side to move the ring gear closer to the pinion gear. The factory shim was .260" on that side so I used a combination of shims that were .250" to start. The shims in the Ratech kit are of different thicknesses from .1" to .010" so I used a combination to reach my starting point. With the sims in place I forced the carrier as far to the left as possible (simulating how tight it would be after installing the shims on the right side) and measured the backlash. The needle traveled .180". I then reduced the total shim thickness on that side by .010" and took another dial inicator reading. This time I got .010" which is within specifications.
  1. Next I figured out what shim thickness needed to go on the other side. To figure this I took the total shim thickness installed in the rear end from the factory (.530".) I subtracted the shim thickness which I had calculated for the left side (.240") which left me with .290" for the right side. I grabbed a combination of shims (the .270" factory shim with two .010" shims from the Ratech kit.) Since the carrier must sit in the bearing bores tight do not expect the shims to slide right into place as you will have to tap the shims into place. If you try to tap in the .010" shim you will bend it right in half because it is very flimsy, so first install the smallest shims. You should be left with a thicker shim that you can tap into place.
  1. Take one more measurement of backlash after you have all of the shims installed on the right and left side just to make sure you haven't thrown anything off. If you have, take a little bit of shim from one side and install it on the other. My backlash actually decreased to .060" and I noticed that the carrier was so tight that it wouldn't easily pull out of the bearing bores so I reduced the shim thickness on the right side by .010" and all was well. The carrier sat in the bores tight (no side to side play) and the backlash measured .080".
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Determining Wear Pattern