[grivera]

As an off-season upgrade, I'm considering replacing the OEM carrier in my 8.5 rear with an Eaton posi carrier and Moser 30 spline axles. I would also upgrade the pinion yoke to a forged 1350 size. If I retain the 3.08 gears (assuming in good condition), and change all bearings (keeping same shims), would I need to reset pinion depth? Or would it be smarter leaving the pinion bearings in place and just replace carrier and set backlash and r/r all seals? The purpose would be just a little more strength for occasional track time.

[Formulabruce]

Due to the fact you are changing carrier, even though same gears, you can sure "try" the pinion and leave it in the carrier. That said " trying" it means just getting a pattern on the gears. Typically worn gears with have a much longer contact patch. If the wear is off the end of the ring gear and you can feel a sharp edge, you better be real sure of back lash and preload. I would change gears at that point.
Re using same pinion depth is the place to start though.
Good luck.

['ol Pinion head]

Early 90's, I first learned diff builds under an older friend who was fairly smart with gear setups. Used gear sets are what was mainly used & for the most part we had good experience with building w them. For that course of several years, the two of us built a gob of 8.5's with used gear sets sourced from other rears. By the time I began building GM rears by myself, was building more & more rears with new quality R&P sets, as nice used 3.73's, 3.90's, 4.10's were not out in the yards where I was sourcing housings & posi cores. At time I would run across 3.73's in prev 1/2 ton work vans nearly every week. Very seldom did such a set appear to be in good shape/lot of wear, thus skipped pulling them.

Two things need to be done before any carrier replacement with nice used R&P set.
-first, backlash measurement should be taken with a magnetic base dial indicator. this series of backlash measurements should be in several places around the ring gear.

-second, i always take an accurate pinion depth reading. I want to know what's going on in respect to the pinion. On OEM 8.2, 12 bolt, & 8.5 gearset rears, ESP w early 8.2 gearsets, the machined face of the head of the GM pinion is nearly always machined oddly. Though the face is a flat plane, the machined face of the pinion will often be at a slight angle to the C/L of the carrier bore. As a result, pinion depth readings will change depending on where the reading is taken. Many many years ago what I learned to do is clean the face of the pinion head, then take the magnetic target plate & set it in one spot. With a yellow paint pen, I draw the outline of the domino sized target plate of my tool on the face of the pinion. Later, i will take a pinion depth reading in the exact same spot.

Initial pinion depth reading... with the carrier bearing bore & caps area spotlessly clean, will insert my pinion depth guage & carefully position the tip of the dial indicator. Then carefully fasten & torque the lightly greased carrier bearing caps to spec. With the pinion depth tool properly positioned, will carefully drag the tip over the magnetic target plate & get THE indicated number. I'll record this number as well as the backlash number as recreating the same relationship is very important to quiet opperation after a carrier has been swapped or pinion has been removed.

Upon careful removal of the pinion depth gauge will put it up away from any possibility of it being bumped into. Have found the last thing that I need is a "helper" during this process. While well meaning, no thanks!

In the above inspection, if the backlash is loose, typ have an issue. Depending on the purpose build of the rear, the backlash I'm looking for may be .007 or it may be set as wide as .012 to be acceptable w used set of gears. If the pinion nut has not backed off slightly, or pinion bearings are not tracked & severely galled & worn, the position of the pinion may be in the exact same position as when the gearset was originally assembled. Thats what i really like. It's when well intentioned folks go to replacing pinion seals, tightening pinion nuts, & not understanding what's going on in reference to the two tapered pinion bearings facing each other & the exact pinion depth, do problems often begin.

Have seen the results of the following many times. Eventually over time a pinion becomes loose & eventually gets in a bind with the ring gear. Typ see this more with really low ratio gear sets, as the pinion is relatively small, 8,9, 10 tooth pinion. Often on coast to partial acceleration,is when the ring gear & pinion have lost several teeth... loose pinion was the cause.

Upon removing the pinion from the housing to press off the large pinion bearing & remove the races from the hsg, one has to be extemely careful that the new big pinion race is installed to its full depth. Fully clean the surface in the housing & fully examine that there are no raised burrs on the edge of the seat area from errant driving out of the pinion bearing race. Another area where I don't let a well meaning visiting "helper" help.

If from the original R&P set-up, the pinion was not loose, & the measured backlash was fine, the contact pattern should be able to be recreated in a fairly straight forward manner. when an original ring & pinion setup is cked and there is considerable backlash, there are on many occasions the instance where one is not going to be able to get away with reinstalling the original pinion shim & carefully tighten, running a pinion drag measurement, getting the exact pinion depth, then installing the assembled carrier & ring gear with a recreated say .008 to .010 backlash. In those instances, where the contact pattern has changed with very minimal wear to the ring and pinion, & in order to have a quiet installation, one can't simply recreate the original pinion depth & "suck" in the backlash, run a few patterns, & deem the reinstall acceptable. On numerous occasions with original gear sets that had some wear & the backlash was wider than I have preferred, have been able to use a one thousandth thicker pinion shim, tighten up backlash some, then reach an acceptable pattern with the proper drag put on the pinion.

I've never been able to reinstall both of the original cast side spacers used with the original carrier when setting up with a new carrier. Have over a hundred lbs of organized clean used cast side spacers & a large stock of GM & aftermarket side shims.

[67Fbird]

super shims carrier shims will be on your order list!......^^^ pinion head hit it on the head...lol look feel measure...FIRST!!! then write it down and proceed. I have in the past open up the offset by .025 (remove .025 from ring gear side and install on other side...just to put new carier and gear in to see where to go. you can always move the gear in but you can chip/bind the gear if your too tight..

[grivera]

Wow - thanks for the very informative post 'ol Pinion head!! Experience is everything with this type of thing as I never considered all those variables.

['ol Pinion head]

Thanks, there are so many things to learn on setting up nice used & new R&P's for a quiet long life that I typ caution long time owners & hobbiest from attempting this theirself. This is ESP the case when one can only source the gears in used condition.

[68 Firebird]

about ten years ago I swapped my open carrier and installed an Auburn HP Posi.
I kept the original 3:08 gears since they only had 73,000 miles.
OPH is right check backlash measurement first and duplicate.
The Auburn unit came with new carrier bearings installed. The pinion received a
new bearing and reused shims to set depth. Been nice and quiet as always.
It took a few times to get shims right to duplicate backlash. Also remember checking
contact pattern to verify.

Gerry