Nope, not a typo, that is .046, not .0046. That was the backlash that my original G80 w/factory 3.42s and 63,000 miles was set at when I measured it before removing the carrier to be replaced with an Eaton unit (and 4.10s, of course ). Mechanic buddy of mine with 25 years experience had never seen that much EVER and was truly surprised that I hadn't snapped the U-joint. Wear pattern on the ring was textbook perfect. In our infinite wisdom, we decided to add a .020 pinion shim in addition to the shims that were on the 3.42 pinion to the 4.10 pinion. Installed the carrier and ended up with .006 backlash. I'm just curious to know if anyone has ever seen that big an amount of backlash in an otherwise quiet, undamaged R&P setup?

 

I've seen similar amounts in higher mileage rearends than yours. Usually wear due to towing. Never seen that much in a low mileage unit and still looks and sounded good. Hmmmmmm.

 

Well, I have towed my boat(s) with it from day one. Maybe extra wear attributed to the extra HP from the Whipple also had a hand in it. Just weird, that's all.

 

That is a lot of shim to have too add for the new gear, how was the pattern on that? I have seen that much before, but rarely. And even more rare that it ran quietly. But it has happened.

 

Yep, turns out it was WAY too much shim for the pinion, so much so that we are taking everything back out and using the old shims from the 3.42 pinion to ensure we have the exact same pinion spacing. I am new to differential installs and my mechanic friend may have left out a few details...like measuring pinion bearing load (25"/lbs for new bearings, right?). We may have to reshim the carrier as well to seat the ring gear closer than .046, or whatever it may turn out to be. The pattern was good, nonetheless. I now understand the comments about installing diffs being a learned art...I will gladly pay the price for an expert to do it next time. Besides that, who the hell decided gear oil needed to smell that friggin' nasty?!?

 

You think gear oil smells bad, wait until you smell the friction modifier for posi diffs.

The 25 in/lbs is correct for new bearings, 10-15 for used bearings.

 

Hell yeah it stinks. Noting stinks like Ford's friction modifier! It will ruin your shop for months! Make sure you keep up with all the rags you use and dispose of them. If not there will be one hiding in the corner that will drive you nuts until you find it.