Quick help: Rear axle u-bolt torque spec..
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#29
08-31-2021
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One more potential issue of over-torquing the U-Bolts…CRUSHING THE AXLE TUBE! Snap a U-bolt and all that happens is you cuss for a minute or 2, yank it back off, and go get a new one. Crush the axle tube and you’re REALLY F$&%ED!!!! Then it’s off to the local junkyard to find yourself a new rear end!
In my case, my original 7.5” axle on my 00 2WD 2.5L rusted out on the passenger side under the inside U-Bolt and started leaking gear oil. NOT GOOD. Got a good 8.8” LSD 3.55 out of a 1997 4WD 4.0L. Turns out it was tagged as a 3.73 but I spun it and it’s definitely a 3.55, so someone swapped the gears. Why someone would go higher ratio, I have no idea unless they were trying to gain MPG. My truck was originally a 4.10 because I have the AT. Once I get these leaf spring bushings changed with some ES Poly bushings (going to have fun with a cut-off wheel since my bushing bolts are seized) and get rid of the previous owners RETARDED idea of leveling it by installing LOWERING shackles, I’m actually going to pop the factory 4WD lift blocks in there since I saved them and the longer U-Bolts along with swapping to the 4WD rear shocks and then lift the front with 4” spindles. I already upgraded the tire size to the 235/75-15’s because there IS a difference in the ABS speed pickup wheel on the diff between the 2WD and 4WD rear ends. Verified that with my scanner reading the VSS output and a GPS speedometer and found it to be ~6% off, exactly what the 225/70 to 235/75 difference is. Then I’m going to install 33’s and 5.13 gears. I was going to run 4.56’s with stock tires. Did some number crunching and found that 5.13’s with 33’s is slightly more RPM than 4.10’s with 225/70’s. 225/70 (736.06 rev’s per mile) with 4.10’s is 2,263.38RPM and 33’s (32.5” and 620.56 revs per mile) with 5.13’s is 2,387.6RPM at 60MPH. 225/70’s with 4.56’s is 2,517.33RPM at 60MPH. All of those are in OD with the 0.75 OD ratio. They also have 5.36’s. Those come to 2,503.96RPM. I must have been running too many numbers earlier and miscalculated something. I actually like the 5.38’s better. Figured all that while writing this post, lol. Part number is F88538 or 88F538, depending on the brand. Still have to get the speedo corrected in the PCM for the new tires though. Speedo doesn’t change with gearing on the 98-01 models because it runs off the ABS sensor in the pumpkin. But tire size will affect it.
For anyone wanting to know how to do that calculation, go to tires.com, click the menu and hit “tips and guides” and then scroll down to “tire basics”. Click that and hit the “tire size conversion calculator”. Type in your tire size in the top column and read the revs per mile in the bottom, second from left box. Multiply that by your gearing, then multiply that by 0.75 and you get the RPM at 60MPH. Then find your NEW tire size diameter (33’s are 32.5”) and multiply that by pi. Then divide 63,360 (inches per mile) by your tire circumference and you get revs per mile. Now start playing with known gear ratios. 3.55, 3.73, 3.90, 4.10, 4.56, 4.88, 5.13, and 5.38. Multiply your new revs per mile by each gear and then multiply by 0.75. Find the one closest to your original RPM or your desired RPM if you want to go up or down. To give you a cheat though, 33’s with 4.88’s is almost identical to 225/70’s with 4.10’s. 33’s with 4.88’s is 2,271.25RPM and 225/70’s is 2,263.38RPM. You’re within 8RPM. I wanted 4.56 RPM though to try to free up the kinda sluggish 2.5L and I have future cam plans. So I guess it’s actually 5.36’s for me!
EDIT: Come to find out 5.13’s are as low as they go for the 8.8”. Well, at least I get a LITTLE more RPM with them!
In my case, my original 7.5” axle on my 00 2WD 2.5L rusted out on the passenger side under the inside U-Bolt and started leaking gear oil. NOT GOOD. Got a good 8.8” LSD 3.55 out of a 1997 4WD 4.0L. Turns out it was tagged as a 3.73 but I spun it and it’s definitely a 3.55, so someone swapped the gears. Why someone would go higher ratio, I have no idea unless they were trying to gain MPG. My truck was originally a 4.10 because I have the AT. Once I get these leaf spring bushings changed with some ES Poly bushings (going to have fun with a cut-off wheel since my bushing bolts are seized) and get rid of the previous owners RETARDED idea of leveling it by installing LOWERING shackles, I’m actually going to pop the factory 4WD lift blocks in there since I saved them and the longer U-Bolts along with swapping to the 4WD rear shocks and then lift the front with 4” spindles. I already upgraded the tire size to the 235/75-15’s because there IS a difference in the ABS speed pickup wheel on the diff between the 2WD and 4WD rear ends. Verified that with my scanner reading the VSS output and a GPS speedometer and found it to be ~6% off, exactly what the 225/70 to 235/75 difference is. Then I’m going to install 33’s and 5.13 gears. I was going to run 4.56’s with stock tires. Did some number crunching and found that 5.13’s with 33’s is slightly more RPM than 4.10’s with 225/70’s. 225/70 (736.06 rev’s per mile) with 4.10’s is 2,263.38RPM and 33’s (32.5” and 620.56 revs per mile) with 5.13’s is 2,387.6RPM at 60MPH. 225/70’s with 4.56’s is 2,517.33RPM at 60MPH. All of those are in OD with the 0.75 OD ratio. They also have 5.36’s. Those come to 2,503.96RPM. I must have been running too many numbers earlier and miscalculated something. I actually like the 5.38’s better. Figured all that while writing this post, lol. Part number is F88538 or 88F538, depending on the brand. Still have to get the speedo corrected in the PCM for the new tires though. Speedo doesn’t change with gearing on the 98-01 models because it runs off the ABS sensor in the pumpkin. But tire size will affect it.
For anyone wanting to know how to do that calculation, go to tires.com, click the menu and hit “tips and guides” and then scroll down to “tire basics”. Click that and hit the “tire size conversion calculator”. Type in your tire size in the top column and read the revs per mile in the bottom, second from left box. Multiply that by your gearing, then multiply that by 0.75 and you get the RPM at 60MPH. Then find your NEW tire size diameter (33’s are 32.5”) and multiply that by pi. Then divide 63,360 (inches per mile) by your tire circumference and you get revs per mile. Now start playing with known gear ratios. 3.55, 3.73, 3.90, 4.10, 4.56, 4.88, 5.13, and 5.38. Multiply your new revs per mile by each gear and then multiply by 0.75. Find the one closest to your original RPM or your desired RPM if you want to go up or down. To give you a cheat though, 33’s with 4.88’s is almost identical to 225/70’s with 4.10’s. 33’s with 4.88’s is 2,271.25RPM and 225/70’s is 2,263.38RPM. You’re within 8RPM. I wanted 4.56 RPM though to try to free up the kinda sluggish 2.5L and I have future cam plans. So I guess it’s actually 5.36’s for me!
EDIT: Come to find out 5.13’s are as low as they go for the 8.8”. Well, at least I get a LITTLE more RPM with them!
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