Hello, I'm a long time lurker and 1st time poster. I have an 03 Avalanche that I am installing a set of 4.10 AAM ring and pinion gears into. I replaced all bearings and races with new Timkens and made inner and outer pinion setup bearings to ease the pattern checking. I even ordered a correct pitch nylon stop nut for the pinion to keep from damaging the threads with the actual pinion nut during setup. I had already installed an Eaton truetrac differential with a set of 4.56 USA Standard gears but I found them to be a little much because I didn't like the 20% RPM increase on the highway coming from 3.73s. Hoping for a good balance with the 4.10s. I went AAM because I found the USA Standards to be a little noisy (or maybe it was partially my setup since I am somewhat new to doing ring and pinion replacements but I have done many bearing and seal stock rebuilds in the past with re-usable gear sets). I set the pinion preload at about 20 in. lbs. each time and the carrier seems to add about 9 in. lbs of rotating resistance when installed. I have a yukon solid spacer kit to replace the crush sleeve (BTW, what does everyone torque the pinion nut to with a solid spacer? There were no instructions with the kit). I was planning on RFT torque setting with loctite if I couldn't find an answer.

The problem I am having are:

1) There seems to be 2 - 2.5 thousandths variation in backlash around the ring gear. I measured at every tooth on two different occasions when the pattern looked close. What is the limit on backlash variation? AAM specifies 0.003 to 0.006 BL with 0.004 being ideal and from my research I have come up with anywhere from 002 to .005 of variation being acceptable. .005 seems ridiculous.

2) I noticed that the number string that is laser etched into the gears matches between the ring and pinion but the numbers that are stamped into the gears are 1 digit off (something like 17B25 on ring and 17B26 on pinion). I just want to make sure that I don't have a mismatched set.

3) The drive pattern seems to look pretty good (to my somewhat inexperienced eye with 2 cut patterns) but the coast pattern looks very Toe-strong and a little odd no matter the pinion depth (tried from 31 to 44 thousandths) or backlash (can't move much here due to the backlash variation but I tried a range of about 3-5 thousandths on one setup and 4-6 thousandths on another for each pinion shim I tried.

Here are a few patterns, the first two are my current pattern which I think looks the most balanced out of all of them and the backlash is perfectly withing the specification even with the variation:

38 pinion shim with .0035 to .0055 backlash drive side

38 pinion shim with .0035 to .0055 backlash coast side

38 thousandths pinion shim and 0.004 to 0.0065 backlash drive side

38 thousandths pinion shim and 0.004 to 0.0065 backlash coast side

38 pinion shim with 0.003 to 0.0055 backlash drive side

38 pinion shim with 0.003 to 0.0055 backlash coast side

40 pinion shim with 0.004 to 0.006 backlash drive side

40 pinion shim with 0.004 to 0.006 backlash coast side

40 pinion shim with 0.003 to 0.005 backlash drive side

40 pinion shim with 0.003 to 0.005 backlash coast side


36 pinion shim with .004 to .006 backlash drive side

36 pinion shim with .004 to .006 backlash coast side
I ran patterns at .031" pinion shim and .044" pinion shim and they both looked extreme particularly on the coast side. Any and all input is greatly appreciated. I just don't want to have any noise when I set this thing up this time around. The last setup was quiet except for maintaining speed between 45 and 60mph where there was a little whine/howl. Again, it could have been the installer. Thanks!

 

I would say you are spot on with the 0.035" shim judging by the coast pattern. You want to pay attention to where the pattern is root to crown. As for the variation in backlash, it seems you have some runout issues. I would mark the ring gear and differential and then remove the ring gear to check and make sure threadlocker didn't work its way between the back of the ring gear and the diff flange. I have had that happen to me. If there is not indication from the thread locker, rotate the ring gear 180 degrees and re-install.

Look in Will's gear pattern thread for instructions I put in there on the solid preload spacer.

 

Thank you AxisT6 for your response! Do you mean the 0.038 pinion shim with .0035 to .0055 backlash pictures? I didn't use a .035 pinion shim on any of my patterns yet. I did mark with a sharpie on the ring gear every backlash reading from a couple of patterns ago. The odd thing is that it doesn't seem to be only half of the ring gear that is high and half that is low, it is somewhat random. Here is the sequence of backlash readings (in thousandths and written on the teeth that I was checking against so obviously the varying teeth were on the other side of the gear where it is meshing with the pinion).

6.5 - 6 - 6 - 5.5 - 5 - 5.5 - 4.5 - 5 - 5 - 5 - 5 - 5 - 5 - 5 - 4.5 - 4.5 - 4.5 - 5 - 5.5 - 5.5 - 5.5 - 6 - 6 - 5 - 4.5 - 4.5 - 5 - 4.5 - 5 - 5 - 5 - 5.5 - 6 - 5 - 5 - 5 - 5 - 5 - 5 - 5 - 6

I did press the ring gear onto the carrier, ran the bolts in with my electric impact quickly to try to minimize loctite seepage and then torqued to 65 ft. lbs. I think I will try to pull the gear back off of the carrier and inspect it though. I'm wondering if it is my carrier since I did have some backlash variation on the last gear set as well, although I don't remember if it was that much or not. Could backlash variation itself cause a whine while maintaining speed even if the variation was within the spec range? I would assume that it could.

 

Sorry, I misread. The pictures with the 0.038" shim looked good. I have normally had great results installing 4.10 gears into 8.5/8.6 rear ends using 0.035" - 0.037" pinion shims granted, those were 5 cut gears, but the pattern says everything.

As for backlash variation, if all measurements are within spec, I would not worry about noise.

 

Thank you Axis for your quick response! I really appreciate your expert advice! Do you think that it is worth my time to look into the backlash variation any more since it is all within spec? I don't want to take any shortcuts but I also don't want to create any more work since the truck has been tying up my lift and I have other vehicles waiting to be worked on. I just don't want this thing coming apart again any time soon. Have you run gears with that much backlash variation before with good results? I'm just trying to make up my mind whether to just button this thing up now or not. Thanks again!

 

Hey you're welcome. I would stress inspecting/rotating the ring gear. The issue I have is that the lash spec is already tight and narrow (3-6 thou.) and you seem to be all over that range. I have run gears with as much 0.002" runout, but that was a 5 cut gear with a spec of 6-10 thou. and IIRC the lash oscillated between 7-9 thou.

If you button it up and there is an issue later, it will take a whole bunch of extra time to correct it.