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I am setting up a new set of gears in my 2003 GM 8.6 10 bolt. I ran the pattern once and I think I am in the ballpark. This was with a 0.037 pinion shim, and 0.010 of backlash. I know I need to thin the compound out with some more gear oil. Any thoughts or recommendations? Thanks in advance for any advice!
Is this an OEM gear set or aftermarket? And 0.010" backlash is a little loose to start checking pattern so try to tighten it some.
This is an aftermarket gear set. I was going by the 0.006-0.010 backlash recommendation that I got with the gears. Should I use a different range? I will try adding a shim to tighten up the backlash a little. Thanks!
The pattern looks a little shallow however with the backlash loose it should show better with tighter backlash. When I build I always chamfer all of the teeth edges for a smoother transition and pattern.
I always check backlash in a few spots, maybe 4 spots 90 degrees apart. It's an assumption that the carrier is running absolutely 'true', not always happens. I always 'stone' the ring gear mounting flange and the ring gear's surface the sits to the flange, A .001" flaw will produce a varying lash.
I always shoot for the tighter of the lash range. Let's say .006" as example, when the gearset is broken in properly and some decent non-abusive miles are put on it, that .006 will probably open up to .008 since the machined surfaces of the teeth are wearing together to eliminate all those imperceptable machining marks made during manufacture.
The times when a tighter setting shows a unacceptable pattern, then I will setup up for the middle range.
Last edited by FirstYrLS1Z; Jun 10, 2025 at 10:00 AM.
Ok, I tightened up the backlash from 0.010 to 0.0065. I think maybe this marking compound or brush just sucks. I added a few drops of oil and it spreads about the same. Any thoughts?
The top pic is the 'coast' side, bottom pic is the 'drive' side. No need/reason to put marking compound deep down between the teeth. How does the 'ghost' pattern of the compound on the teeth that weren't painted.
The amount of compound for the ghosts is the small amount that would normally be put on the teeth for initial evaluation, everybody always applies too much, but anyway.
The true pattern showing of the ghosts looks really good., nice wide center contact. What was the lash for that ?
If I was setting that up and those were the patterns, I'd be running it.
The backlash was at 0.0065 for this pattern. Thanks! Now I just need to set the pinion preload with the crush sleeve eliminator and put the new bearings on and I'll be set. Thanks again for your help!
Good luck with the spacer; they can be pretty time consuming, at least for me. I tried one a couple of builds ago, lost patience (I needed to finish that day/ night), and just ended up throwing a crush sleeve in it.
^^^ I agree about the crush sleeve eliminator spacer. Although once set properly they're OK, it's just the hassle to get to that 'OK'.
A spacer has no 'spring' to it, A .0005' wear in of the bearings and preload is gone. a crush sleeve has some 'spring' in the area being crushed.
The coast is a little shallow however once break-in is performed it will show centered. Be sure to run dino oil for break in and if you have carbon fiber clutches in the Eaton posi do not run synthetic oil!
The bonding agent will be softened and the carbon fiber will fall off the clutches.
Also, if you have time chamfer all of the teeth on ring and pinion to deburr and sharp spots.
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Pattern check on 8.6 10 bolt 
