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What gear ratio is used when the towing package is factory installed? I'm thinking they lower the gearing a bit. I have a Sport package 4x4 without the tow package and need to tow. I can add the hitch, electric wiring and transmission cooler, but was wondering about the rear. The build sheet says I have a 3.55 rear axle ratio, but then it also says I have a Corporate 8.25 rear axle. If the truck had the tow package, what would be different?
 

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first off, Welcome to the Z!!!

secondly - that's a good question. i dont have my build sheet in front of me, but on my r/t i have the 3.92 gears, no towing package, but i also have the corporate axle, but i cant remember if it is 8.25 or 9.25 (i think it is 8.25)

but i think the gear ratio is stamped on the diff somewhere. i also think you can have the same size rear axle with different gear ratios

hope that helps!

 

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i just checked my build sheet, i have the 9.25 corporate rear diff with the 3.92 gears, limited slip (or anti-spin like dodge calls it)
 

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Which axle is better, the 8.25 or 9.25? I do know that the higher the gear ratio, the better the towing and acceleration but lower mpg due to higher rpms.
 

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not sure which one is better, it would depend on what you need to do with your truck. the bigger rear end would be more of a heavy duty type
and yeah the higher the ratio number, the better the acceleration and towing but less fuel mileage
 

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The build sheet for my 2000 QC 4.7 list 45RFE auto,trailer tow group,anti-spin, 3.55:1,and 9.25 LD corporate axle.
 

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Does anyone on here know what I have to do to switch my 3.55 rear end to a 3.92? I'm not even sure where to go to buy parts. I never dove into rear end components other than changing the fluid. Any secrets that are good to know or land mines to watch out for? Thanks.
 

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you can just buy new ring and pinion to the ratio you want. and replace it. bot the eaistest if you have never been in a rear befor. easiest would be looking in a junk yard for a 9.25" with 3.92 ratio in it. itll have a tag on the diff cover that says 3.9 but you will have to do both the front and rear or you'll rip your tcase up.
 

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Ring and pinion swaps require a press. You pull the axels, remove the bearing caps, pull your planetary, pull your drive shaft, remove nut from pinion, pinion comes out from inside diff. Knock out old races and replace. Press new bearing onto new pinion, reinstall(I use an impact to set the new crush washer, if you do this take it easy using short blasts not continuous pressure, you will know when the crush washer sets) . Take planetary and remove 8? bolts from ring, install new ring(set should come with torque specs). Reinstall planetary with new races and bearings, install axels. Use marking compound to check for any misalignment.
 

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gears

I had 4.56 yukon gears installed. I had a shop do it, I just had a feeling. My '03 has the HD towing package, with the 9.25. The carrier did not need to be changed. The first set of gears would not pattern, the shop sent a video to Yukon and Yukon finally agreed to replace the gears. The way the gears are cut, (I checked with other gear manufacturers) they whine, really whine between 45 and 55 mph. It sounds like a rear off a big rig. I complained so much that Yukon now has now placed a note on the boxes stating : "Gears may make noise"

Also, everyone who has the LSD rear should take the differential cover off and look for parts, mainly the clips from the limited slip unit. They are known to fall off and grind up in the gears causing the rear to fail. Some units fail as early as 50K miles.

The 4.56 gears along with the 545RFE make it a great towing rig. And the transmission does not hunt for gears below 50 mph
 
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