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Discussion Starter #1
Just finished up getting my pinion depth all dialed in on my 4.10 swap into my GM 8.5". The ring and pinion are a very slightly used G2 Performance set with minimal mileage on them.

Now my question for you rear end gurus. I'm trying to get my backlash set at around the recommended 0.008" (0.006"-0.010" is the spec). With the supplied carrier shims in my kit I am falling on either end of the spectrum. At the low end I am getting around 0.005" and if I swap out for the next thicker shim I am at around 0.010". What do you recommend I run it at? Error on the low end of backlash or the high end? It's for a mostly street but some strip Camaro that will be driven fairly hard. I'm leaning towards setting it up on the tight side as it will only increase a bit as the gears wear in if my thinking is right.

Thanks for your expertise in advance.
 

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High Performance Rear Ends
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Do you have it shimmed tight enough that you can't pull it out by hand? If not then go with the shims that give you .010 backlash and then add about .003 to .005 to the ring gear side (left).

Are you sure that the backlash is supposed to be set that loose? The newer 8.5/8.6 gears are 2 cut and are supposed to be set to about .005 backlash.
 

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Discussion Starter #4
Thanks for the info.

Off of their website for GM 8.5 & 8.6 rear ends it specifies 0.006-0.010. I think Yukon, Richmond and most other gear suppliers suggest the same.

I do have the carrier preload pretty snug right now as I had to lightly tap in the shim pack to get it in. I only have shims in 0.050 increments so it is difficult to get it right on the money. I am sure with good oil and proper break in I would be fine with the 0.005 backlash, I would prefer to go this route just wanted to see if anybody has ran backlash this tight (or tighter) before and could offer reassurance through their personal experience. I guess my fear is running it on the tight side and having it heat up and eat itself alive.
 

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in moderate HP applications the gear wear is minimal after the initial lapping done in the first few hours of operation.
I wouldn't be afraid to run it at 005 or 010 as long as it turns free and is not running the drive pattern off the toe.
 

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High Performance Rear Ends
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Do you know if you have a 2 cut or a 5 cut gear? The 2 cut gears run backlash around .004 where 5 cut gears run backlash around .008. You need to know which gear you have before setting the backlash.

If you are just tapping the shims in place but you can still pull the differential out by hand then it's not tight enough. You will have to pry the differential out when the shims are tight enough.
 

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Discussion Starter #7
As far as 2 cut or 5 cut go I really am not sure....... can not find any info regarding that online. I am assuming it is a 5 cut gear set as the ring gear teeth are tapered - they are taller at the heel than at the toe.

The shims are fairly tight in there, I have to tap them in and can't pull the carrier straight out by hand. I am going to run it the way it is, what I could really use is a 0.030 shim or so to place on the passenger side bearing but the kit doesn't come with shims that small. I feel confident it should be good with the info you guys have provided me. Thanks again!
 

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I think you are getting your decimal in the wrong place. Do you mean .003 shim? A .030 shim is pretty thick.
 

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Discussion Starter #9
Yes you are correct, I meant 0.003". Anyways it spins freely and smoothly with that minimum backlash. Going to button it up and find out for good haha
 

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I'd be happy with the .005" Backlash with good tooth pattern. Take a strip of printer paper and feed into the ring and pinion to see what your backlash really is. Printer or copy paper is .004" thick. If you still have backlash, you have more than .004" lash. You can double the paper to .008" and try that also.
 
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