Return to 3.73:1 AAM Gear Pattern Setting
I yanked out the 373s and started again. Pressing the pinion bearings on and off was ridiculously hard on the AAM gears. They clearly blew the machining of the bearing sections. So after 6000 km the rear (smaller) pinion bearing was frozen on. It took a lot of pounding to get the damn thing out at all. As a result of hitting it so many times I decided to again replace the pinion bearings and use new ones.
I felt I had a good pattern after 4 tries on the 373s. My goal this time was to do it the first try with the 4.10s. In all of the photos below, the pinion depth is compared to what the Ratech tool says the depth should be. If the tool was accurate, the best pattern should have been where the depth was 0.000". The tool is not accurate enough to trust so I used it to check movement of the pinion in or out only. Looking below according to the Ratech tool the pinon was .0011" too far out meaning the stock shim is really to thin. I had already figured that out so the tool is not too far out to lunch.
I have arranged them in order of pinion depth. The name of the trial tells you what order I actually did them in.
This pattern is too shallow.
Should be perfect according to the Ratech tool but still too shallow.
Getting better.
Getting deeper each time.
This is the one I chose as the best of the bunch. The ones below with deeper pinion positions look too deep. If I believed the Ratech tool the pinion is in too far by quite a bit.
Same pinion position as above. This time I tightened up the back lash to see what the pattern would do. It seemed a little tight so I tried one last time.
Same pinion position as above. This is the final setting. This pattern includes a total of .006" of extra pre-load shims on the carrier meaning the full carrier preload is in place now.
This and the following pattern are too deep. The cut off at the base of the tooth gets more and more abrupt.
This setting is getting to be too deep. I suspect it would have worked okay but I was paranoid about not having any substantial cut off at the bottom of the tooth the way I did with the 373s.
When you are all done setting the pattern you have to install the pinion properly. Pull it all apart one last time. You need to install a crush sleeve to maintain proper preload once assembled and of course the pinion seal is now needed. This must be done accurately. You will tighten everything up until the crush sleeve bottoms out. The sleeve has to be crushed about 1 mm before the slack is taken up on the bearings, which is nearly 1 turn on the nut. Once the bearings bottom out the preload builds very quickly from there, I know some people use impact wrenches but I preferred manual tightening.
You need to use some pretty long wrenches to do this part. You also have to have some way of holding the yoke in place. The tightening torque is brutally high until the sleeve starts to collapse.
This is my yoke holding tool for setting pinion preload. I made it from a scrap piece of steel. It was only wide enough to use 3 of the bolts. I used a 1.5" hole saw to cut the large opening to clear the large socket used to tighten the pinion nut.
If you are not familiar with setting preload then think of it like this. If you just tighten up the bearings until the clearance is taken up, the bearings will roll very smoothly and everything will be nicely aligned. If you then accelerate the car the pinion tries to push forward in the car and upward (climbing up the ring gear), and outward away from the ring gear all at once. The compliance in the many differential parts causes the bearings to allow the pinion to shift. As soon as the pinion moves forward, the front bearing goes loose and doesn't hold its end in place. The gear is allowed to move and the tooth mesh is messed up. If there is some preload due to over-tightening the nut to some degree it will hold itself in place even with a load in place.
On top of this there is the crush sleeve, the crush sleeve provides some stretch in the actual pinion shaft. This prevents the pinion nut from backing off as the loads on the axle fluctuate over years of use. As you push the pinion forward the bearing preload drops down, it will reach zero occasionally. The pinion will take up the load by relaxing some of its stretch. As long you stay within limits, this will work every time you drive. Over do a hard launch and the sleeve can collapse a little and give up some of its preload, this will usually cause gear whining.
This in.lb torque wrench is probably the best kind to use. The dial moves easily and clearly, a digital gauge is great for tightening bolts but due to its slow update speed much harder to read or believe when viewing running torque. In this case the wrench was 1/4" drive, so I needed an adapter to take it up to 3/8" then another to 1/2" and another to 3/4" and finally the large socket.
I carefully cinched up the nut until I reached just over 30 lb.in of drag torque.
Replace the carrier and re-establish the backlash that gave a good pattern. Pull your shim packs out and add .003"-.004" to each one and re-insert. You will have to use a hammer to get them in the last time since you are stretching the case now. The kit only comes with a certain number of carrier shims to make up the two packs. I found I had to compromise quite a bit. Ideally I would have added exactly .004" to each pack and assembled it for the final time. Instead I had to fiddle a bit and therefore the final backlash had to be slightly different from the pattern I wanted.
Once I had done that, measure the total preload at the pinion nut with the carrier in place. It should be higher than with the pinion alone due to the drag of the carrier bearings. I wound up with a total of ~45 lb.in which is within specification.