- Joined
- Mar 20, 2005
- Location
- Hendersonville, NC
Re-geared a JK yesterday evening. Nothing fancy, 4.56 Motive gears to help it push 35" BFGs down the road. But I did encounter something worth sharing (and erasing the whole "there's no tech" on here anymore).
Here is the first pattern (coast side). Centered, a little tight at 0.005" backlash, and a broad contact patch. The issue is the backlash. 5 thou is too little clearance and will generate excessive heat during break in as well as while driving. The other thing is the pattern doesn't really gradually develop. It's kinda like "Boom, in yo face" like a @McCracken wise crack on @Loganwayne.
Ideally, you want a pattern that develops gradually and rolls into a wide patch and then gradually dissipates. This will allow a smooth break in and prolong gear life. Picture a cam lobe that gradually opens and closes a valve as opposed to a squared off lobe that harshly does so. You want that smooth transition if at all possible.
Would this pattern be acceptable (assuming BL was in spec)? Yes it would. But it can be better...
I removed the carrier and mearured the shim pack. Pass side was 0.118" and driver's side was 0.137". Carrier preload was good, so i knew my overall shim thickness was dead nuts. Just need to move some from side to side. I Knew I needed more backlash, so I made a new stack and moved 0.008" from the pass side to the driver. New shim thickness turned out to be 0.110" and 0.145". This pushed the ring gear away from the pinion just a hair.
Reinstalled the carrier and measured backlash. It was now 0.008", perfect. Ran a pattern and you can see the results. It changed significantly. The pattern now rolls smoothly at the start into a broad patch that transitions to a taper at the opposite end. The depth remains unchanged, just how it actually contacts changed.
What does this mean? It means that taking the extra 10 minutes to fine tune the pattern will give longer gear life, less heat, less noise and basically erase any chance at a failure.
Here is the first pattern (coast side). Centered, a little tight at 0.005" backlash, and a broad contact patch. The issue is the backlash. 5 thou is too little clearance and will generate excessive heat during break in as well as while driving. The other thing is the pattern doesn't really gradually develop. It's kinda like "Boom, in yo face" like a @McCracken wise crack on @Loganwayne.
Ideally, you want a pattern that develops gradually and rolls into a wide patch and then gradually dissipates. This will allow a smooth break in and prolong gear life. Picture a cam lobe that gradually opens and closes a valve as opposed to a squared off lobe that harshly does so. You want that smooth transition if at all possible.
Would this pattern be acceptable (assuming BL was in spec)? Yes it would. But it can be better...
I removed the carrier and mearured the shim pack. Pass side was 0.118" and driver's side was 0.137". Carrier preload was good, so i knew my overall shim thickness was dead nuts. Just need to move some from side to side. I Knew I needed more backlash, so I made a new stack and moved 0.008" from the pass side to the driver. New shim thickness turned out to be 0.110" and 0.145". This pushed the ring gear away from the pinion just a hair.
Reinstalled the carrier and measured backlash. It was now 0.008", perfect. Ran a pattern and you can see the results. It changed significantly. The pattern now rolls smoothly at the start into a broad patch that transitions to a taper at the opposite end. The depth remains unchanged, just how it actually contacts changed.
What does this mean? It means that taking the extra 10 minutes to fine tune the pattern will give longer gear life, less heat, less noise and basically erase any chance at a failure.
Last edited:
