Copy Original Pattern On Used Ring & Pinion Even If Not Ideal?

[pjmoreland]

I am installing a used 3.73 gearset in my 12-bolt rear end. I have been given the advice to reproduce the original pattern it had from the original rear end. That original pattern, however, was not ideal. 72again4x4, who gave me the gearset (thanks again, Roger!!) had them in his truck and they ran smooth and quiet. Would I be asking for trouble by messing with the pattern? It appears to me that the pinion shim was too thick, and the backlash might have been too large.

[mongocanfly]

I've always heard that used gears are a crap shoot for patterns..we've used them but it's been a very long time ago..so I dont remember any issues we might have had..
That last pattern pic looks pretty good
What's the coast side look like?

[Dave]

PJ,
Used gears can be difficult to set up in another housing but the fact the wear pattern is good and was manufactured by GM is very good. The reason imo is because even if your on the high or low side of the spec, the GM gears are so hard compared to the aftermarket gears, your unlikely to have a problem. I would try to get it close to where it was or closer to the center. You can buy a shim pack at napa with different thicknesses. GM used to sell the shim packs a number of years ago, not sure if those are still available.
I'm sure you'll get it figured out.

[pjmoreland]

Thank you. I have a shim pack. Getting it closer to what it was would mean aligning it somewhat poorly, as shown in the photo I posted below labeled "Original." When I set it with .013" backlash, it got pretty close to the original alignment, but it is out of spec this way. I don't particularly like the idea of aiming for poor alignment like that, but I also don't like the idea of optimizing the alignment if it is going to result in noisy gears.

[pjmoreland]

I ran patterns with the following Pinion Shims:

.023
.026
.027
.0285
.031
.034

[pjmoreland]

.023 Pinion Shim, .007 Backlash

[pjmoreland]

.026 Pinion Shim, .0085 Backlash

[pjmoreland]

.027 Pinion Shim, .009 Backlash

[pjmoreland]

.0285 Pinion Shim, .008 Backlash

[pjmoreland]

.0285 Pinion Shim, .009 Backlash

[pjmoreland]

.0285 Pinion Shim, .013 Backlash

[pjmoreland]

.031 Pinion Shim, .010 Backlash

[pjmoreland]

.034 Pinion Shim, .010 Backlash

[pjmoreland]

This pattern was taken when the gears were still in the original donor rear end.

[Wrenchbender Ret]

I like the .0258 PS & .008 BV.
George

[pjmoreland]

Originally Posted by Wrenchbender Ret

I like the .0258 PS & .008 BV.
George

I like that one, too. The drive side contact area seems bigger on that one, and the coast side is centered better than the others.

[MySons68C20]

Originally Posted by pjmoreland

I like that one, too. The drive side contact area seems bigger on that one, and the coast side is centered better than the others.

Agree with this....Either one would probably be fine but .008 is my fav.

[pjmoreland]

Thanks, guys. I reassembled it last night with the .0285PS/.008BL shims. The backlash actually varies between .008 and .009 depending on where I measure it in the rotation. I will reinstall the rear end in my truck this evening after work.

[pjmoreland]

The rear end is installed, but I'll have to wait until tomorrow to get my daughter to help me bleed the brakes.

[pjmoreland]

My daughter helped me bleed the brakes this evening, and then I filled the rear end with gear oil and went for a test drive. It is smooth and quiet! What a relief! The gears that were in my truck when I bought it had several chipped teeth and they howled at 35-45mph. The new Yukon gearset I replaced them with howled even worse and whined when coasting. It's so satisfying to have a quiet rear end!

[mongocanfly]

Congrats!!!!!
Never had issues with Yukon, did you see if they would replace them?

[pjmoreland]

Originally Posted by mongocanfly

Congrats!!!!!
Never had issues with Yukon, did you see if they would replace them?

That's a good idea, because now I'm stuck with a gear set with just a couple hundred miles on it that nobody would want to buy. I'll contact them.

[MySons68C20]

Great news, congrats on getting it done!

[pjmoreland]

Thanks! This noisy gear situation was stressing me out, so it is a relief to have it resolved

[72again4x4]

Congrats again PJ, so glad they’re working out for you.
Roger