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Lmackattack

Rear Ends

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i would like a little less RPM out on the big roads. Currently i have 4.17 rears and i have the engine wound pretty hard to get to 60MPH i know its not bad for the engine to turn 2000-2100 but its getting old and times have changed. i have access to some 3.87 rears for cheep and they should get my RPM down or my road speeds up. i have driven a few 6 wheelers with 3.87s and i liked how top gear just cruised along at 55-60 MPH. i do get in the mud and rock pits and like to use the low hole to run the truck over soft grounds, saves on the clutch too! i never have been in a bind where the 4.17s and low low could not pull me out .the truck came with 3.87s as it was a road tractor when new. the last owner put the slowerrears in.. i need to reseal the rear rear diff as she leaks... now is the time to replace the rears

whats good or bad between the 2

should i stay with the 4.17s or swap in the 3.87s?

Thanks

Trent

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I have had one of each. Only thing you really noticed was the road speed. Brad

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i would like a little less RPM out on the big roads. Currently i have 4.17 rears and i have the engine wound pretty hard to get to 60MPH i know its not bad for the engine to turn 2000-2100 but its getting old and times have changed. i have access to some 3.87 rears for cheep and they should get my RPM down or my road speeds up. i have driven a few 6 wheelers with 3.87s and i liked how top gear just cruised along at 55-60 MPH. i do get in the mud and rock pits and like to use the low hole to run the truck over soft grounds, saves on the clutch too! i never have been in a bind where the 4.17s and low low could not pull me out .the truck came with 3.87s as it was a road tractor when new. the last owner put the slowerrears in.. i need to reseal the rear rear diff as she leaks... now is the time to replace the rears

whats good or bad between the 2

should i stay with the 4.17s or swap in the 3.87s?

Thanks

Trent

If you are looking to drop in the carriers complete, it is not that big of a job. The switch of ring and pinions is quite a bit more work and a lot of dollars for very little gain. That close of gear ratio change would probably not be the best payback in my opinion.

Rob

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Ok the rear rear diff is out. not a big job at all (the bolts were easy to remove B) ). hardest part was the U joint? anyways one thing that bothered me was the milky oil that came out. Just last year i flushed the diffs and last week topped it off with 1 gallon as it has been leaky. where does water get in from?? tomorrow i pick up the faster diffs and remove them from the axel housings..if they look good inside i think i will swap them in and see how the truck runs with them..

Trent

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Now if it was me i would keep the 4:17's and put a overdrive transmission in if you don't already have one its hard to say since you never said what type of gear box you are running currently. If you do alot of off roading with this truck i would not gear up the rears. It is best to always gear the rears down and the gearbox up. I have a 79 R-600 that came out with a 6 speed maxidyne with 4:17 rears. I hauled coal out of the strip pits and then trucked it over the open road. So what i done was swapped the 4:17's for 4:50's and then i put a eaton RTO 15 speed in and am well satisfied with it. The rears gets weaker the higher geared they are so if you do alot of off roading in the muddy pits its always best to keep them low as possible and run an overdrive tranny.

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