04-01-2012, 12:57 AM
Car is a 99 Z28 T56 that a buddy and I had installed a set of used OEM 4:10 gears last spring. It had stock 3:42's with .0075" lash and a .032" pinion shim, we put new pinion bearings with a solid crush sleeve in with the 4:10's and ended up with .008" lash with a .023" pinion shim. It was quiet everywhere but very slight throttle between 35-50. After multiple passes at the track it slowly started having a slight wine at most all cruising speeds but quiet when coasting or into the throttle. Here's what the current pattern looks like, the backlash opened to about .009". I was thinking about adding .002-.003" to the pinion shim what do you guys think?
04-01-2012, 02:01 AM
The pattern doesn't look bad but getting a used gearset to quiet down may be next to impossible. Would likely be best to just start with a new set from scratch.
04-01-2012, 02:04 AM
What about tightening the lash to about .006"
04-01-2012, 06:40 PM
I used OEM gears (AAM) and I had to open up the ID of the pinion shims because they sat on the radius from the pinion shaft to the gear. Before I noticed this I was at about a .023 pinion shim like you. Then I noticed the shim getting bent like a countersunk washer by the pinion radius. After I opened up the shim ID I ended up with a .034 pinion shim. Also if you truely have factory GM gears they run much tighter BL when initially set up, BL spec is like .004-.006.