[Dave in MN]

Sorry, I have not read Les Andrews section in his book about shimming the pinion. I am offering the following from a recent experience regarding the ill fit of a new 4:11 gearset.

Last year, early in the driving season, I lost a tooth on my 4:11 gearset when the double nuts on the pinion gear loosened. I ordered a replacement 4:11 set and installed it using Tom Endy's very detailed write-up. Upon completion and with the maximum number of gaskets shifted to lessen the backlash between the pinion gear and the ring gear, I still had an excessive amount of backlash in the neighborhood of .070".

Not being satisfied with this amount, I contacted Steve Becker at Bert's who gave me the name and contact info of the manufacturer of the gearset. The manufacturer coached me on the procedure of centering the pinion gear to the ring gear prior to starting the assembly procedure. I determined I needed and then machined a shim that was .067" to place between the pinion gear and the first tapered bearing. With this shim in place and again using Tom Endy's procedure, I was able to obtain about .005" backlash with adequate but not excessive gaskets to provide a good seal to the components. The assembled rear end is very quiet and took us to Loveland and back this summer.

Because of the difficulty I had with acheiving proper backlash in my own rearend assembly, I decided to put on a differential rebuilding clinic at my workshop. There were about 20 local club members in attendance for each session. I held one session where we took two assemblies apart and evaluated their condition and developed a list of repairs to complete and components to purchase for restoration. After the components were repaired and new parts purchased, I hosted two additional Saturday sessions where we assembled the differentials. One assembly needed shims at the pinion gear to get the backlash exactly where we wanted it. The other assembly did not require any shims.

It is often said or assumed you can only get the backlash as good as the shifting of gaskets will allow. This statement is true if you don't try adding shims between the pinion gear and the first or rear tapered bearing you press on to the pinion. The bearing shims sold in .005" thickness for shimming the carrier races can be used between the pinion gear and the rear bearing that is pressed on to the pinion. They fit the components perfectly. During the clinic I hosted, we did use 7 of these shims to obtain the proper pinion gear centering on one differential.

An interesting side to all of this was that when the pinion was properly centered and the backlash was correct, we had a good contact pattern when checking the assembled components with yellow bearing grease laced with yellow pigment.

The first photo (white lithium grease) shows the contact pattern before shimming the pinion gear. It has a bad pattern with the pinion gear teeth riding over the edge or crest of the ring gear teeth. This state would not last long. This contact pattern was the best I could achieve by just shifting gaskets at the pumpkin. Excessive backlash was very evident in this case. This was a new 4:11 gearset.

The next two photos show a more centered engagement on both the thrust and coast side of the 4:11 ring gear. This pattern was achieved with shims (.067") at the pinion as described above. The backlash was about .005".

Good Day!