Changing gears
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New User
Joined: Jul 2015
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Changing gears
Soo. im new to this page. i have a 89 f250 3/4 tone 4x4. 7.3 idi with the c6 transmission. i kinda wanna put 3:73 gears in my truck to help lower rpms at 60 im turning 2800 on the tack. ny question is. how difficult will thw proses be? thanks
Postmaster
Joined: Feb 2003
Posts: 3,441
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From: Muskegon, MI (home)
It's not necessarily a difficult job, but I don't recommend it to the novice mechanic; unless you have someone experienced around who can walk you through it. It does require a few specialty tools, dial indicator, calipers, press, pullers, etc. It's not a cheap deal either, obviously the cost of new gear sets but also it would be wise to get the master overhaul kits (bearings, seals, shims, etc)
Laughing Gas
Joined: Mar 2016
Posts: 1,105
Likes: 78
2x 3.55
mine likes that gearing .. but if i were on the highway alot i would likely consider even 3.08 .. though these are not a stock gear that i'm aware of .. i like fuel economy
also big tires are a must ..
also i would think it would be easier and cheaper to just drop and swap an axle than a chunk .. imo
mine keeps up with 3.55 and 35's but i still only go 70 - 75 ish max - though i could push it if i wanted to wind the motor up .. and most people hate me .. but &$#* them .. i don't know why people don't just drive a safe speed - but almost all cars / even big rigs today go 85 90 down the freeway ..
mine likes that gearing .. but if i were on the highway alot i would likely consider even 3.08 .. though these are not a stock gear that i'm aware of .. i like fuel economy
also big tires are a must ..
also i would think it would be easier and cheaper to just drop and swap an axle than a chunk .. imo
mine keeps up with 3.55 and 35's but i still only go 70 - 75 ish max - though i could push it if i wanted to wind the motor up .. and most people hate me .. but &$#* them .. i don't know why people don't just drive a safe speed - but almost all cars / even big rigs today go 85 90 down the freeway ..
i ain't rite
Joined: Mar 2005
Posts: 65,561
Likes: 5,599
From: Marlboro Mental Hospital.
check the calibration of the speedometer too. you may be going faster than it reads.
my 88 read 11 mph low for 13 years before i realized the difference.
my 88 read 11 mph low for 13 years before i realized the difference.
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Fleet Mechanic
Joined: Oct 2012
Posts: 1,943
Likes: 21
I have 3.54's in my van with a c6. It does fine at 65.
If you want to lower RPM's you can:
1. Change rear gearing
2. Change trans to one with an OD
3. Add an OD to your c6
4. Bigger tires
I put the tallest tires that would fit on my van and added an O/D to my c6.
If you want to lower RPM's you can:
1. Change rear gearing
2. Change trans to one with an OD
3. Add an OD to your c6
4. Bigger tires
I put the tallest tires that would fit on my van and added an O/D to my c6.
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Postmaster
Joined: Feb 2003
Posts: 3,441
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From: Muskegon, MI (home)
I thought about changing my gearing to 3.55 in my IDI truck. I'm concerned if I did, how much would it hurt the towing? I pull 7-12k with it fairly regularly. As much as I hate the 4.10s on the highway, I'm glad I have them when I'm hauling heavy.
Laughing Gas
Joined: Mar 2016
Posts: 1,105
Likes: 78
i hear this that 4.10 are good for towing ..
i have pulled some heavy loads and i never have had any problem at all ..
the motor has tonnes of torque so .. it's not an issue . for me anyways .. though i haven't pulled 12k i have pulled 8kish and no problems at all .. like it weren't even back there .. but maybe others have some other experience .. my motor runs good .
if it weren't for the 60' ttb case being unable to handle the ring of 3.08 to match 4x4 in my otherwise capable d70U rear .. i would be thinking of 3.08 if it were 2wd .. it does fine and could go even lower .. i would think ..
i have pulled some heavy loads and i never have had any problem at all ..
the motor has tonnes of torque so .. it's not an issue . for me anyways .. though i haven't pulled 12k i have pulled 8kish and no problems at all .. like it weren't even back there .. but maybe others have some other experience .. my motor runs good .
if it weren't for the 60' ttb case being unable to handle the ring of 3.08 to match 4x4 in my otherwise capable d70U rear .. i would be thinking of 3.08 if it were 2wd .. it does fine and could go even lower .. i would think ..
Lead Driver
Joined: Apr 2008
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Much to what leroy said, this is why there is no exact answer for gearing, everyone has a different level of expectation.
The old adage is 3.55 for mileage, 4.11 for towing. 3.73 is a good middle ground. Granted, not having overdrive really cripples your towing vs. economy.
My personal expectation is this, i want to be able to maintain direct, when towing the load i want to tow (within reason) on the hills, around here specifically, a 6 mile 6-6.5% grade, and be able to maintain OD when empty.
Given that basis, my 79 will tow 5k (pulls a car on a trailer fine, but more and it struggles). NA 7.3, 3.55 gears, 35" tires, ZF5, weighs 6250. My 92 will tow 11k, 7.3 up 2 flats, wore out ATS 088 making 8psi, 3.73 gears, 34" tires weighs 6700. Have i pulled more than that, absolutely, and with both, but it just seems hard on the vehicle. 32k gross, is waaaaaaaaayyyyyyy more than my poor 92 wanted to play with, but the tellehandler isnt suited to 20 miles trips.
Place i used to work for has a 83 S1400 international service truck. Weighs 17000-19000 and the NA 6.9 in it moves it surprisingly well, has 4.88 gears with 9R20 tires, tachs out at 58mph, pulls a 6% grade at 35mph
The old adage is 3.55 for mileage, 4.11 for towing. 3.73 is a good middle ground. Granted, not having overdrive really cripples your towing vs. economy.
My personal expectation is this, i want to be able to maintain direct, when towing the load i want to tow (within reason) on the hills, around here specifically, a 6 mile 6-6.5% grade, and be able to maintain OD when empty.
Given that basis, my 79 will tow 5k (pulls a car on a trailer fine, but more and it struggles). NA 7.3, 3.55 gears, 35" tires, ZF5, weighs 6250. My 92 will tow 11k, 7.3 up 2 flats, wore out ATS 088 making 8psi, 3.73 gears, 34" tires weighs 6700. Have i pulled more than that, absolutely, and with both, but it just seems hard on the vehicle. 32k gross, is waaaaaaaaayyyyyyy more than my poor 92 wanted to play with, but the tellehandler isnt suited to 20 miles trips.
Place i used to work for has a 83 S1400 international service truck. Weighs 17000-19000 and the NA 6.9 in it moves it surprisingly well, has 4.88 gears with 9R20 tires, tachs out at 58mph, pulls a 6% grade at 35mph
Fleet Mechanic
Joined: Oct 2012
Posts: 1,943
Likes: 21
I have 3.54s and just towed my wifes van about a week ago. Trailer+her van was about 6500lbs. My van pulled it without any issue, but if there were any real hills etc in the area i would have eanted 4.10s or a turbo. I towed it without my DNE2 engaged. With it engaged it would have been like starting out with a 2.83 rear end. Unloaded i leave it engaged and dont have an issue, but i would not tow with it that way.
Postmaster
Joined: Feb 2003
Posts: 3,441
Likes: 5
From: Muskegon, MI (home)
Much to what leroy said, this is why there is no exact answer for gearing, everyone has a different level of expectation.
The old adage is 3.55 for mileage, 4.11 for towing. 3.73 is a good middle ground. Granted, not having overdrive really cripples your towing vs. economy.
My personal expectation is this, i want to be able to maintain direct, when towing the load i want to tow (within reason) on the hills, around here specifically, a 6 mile 6-6.5% grade, and be able to maintain OD when empty.
Given that basis, my 79 will tow 5k (pulls a car on a trailer fine, but more and it struggles). NA 7.3, 3.55 gears, 35" tires, ZF5, weighs 6250. My 92 will tow 11k, 7.3 up 2 flats, wore out ATS 088 making 8psi, 3.73 gears, 34" tires weighs 6700. Have i pulled more than that, absolutely, and with both, but it just seems hard on the vehicle. 32k gross, is waaaaaaaaayyyyyyy more than my poor 92 wanted to play with, but the tellehandler isnt suited to 20 miles trips.
Place i used to work for has a 83 S1400 international service truck. Weighs 17000-19000 and the NA 6.9 in it moves it surprisingly well, has 4.88 gears with 9R20 tires, tachs out at 58mph, pulls a 6% grade at 35mph
The old adage is 3.55 for mileage, 4.11 for towing. 3.73 is a good middle ground. Granted, not having overdrive really cripples your towing vs. economy.
My personal expectation is this, i want to be able to maintain direct, when towing the load i want to tow (within reason) on the hills, around here specifically, a 6 mile 6-6.5% grade, and be able to maintain OD when empty.
Given that basis, my 79 will tow 5k (pulls a car on a trailer fine, but more and it struggles). NA 7.3, 3.55 gears, 35" tires, ZF5, weighs 6250. My 92 will tow 11k, 7.3 up 2 flats, wore out ATS 088 making 8psi, 3.73 gears, 34" tires weighs 6700. Have i pulled more than that, absolutely, and with both, but it just seems hard on the vehicle. 32k gross, is waaaaaaaaayyyyyyy more than my poor 92 wanted to play with, but the tellehandler isnt suited to 20 miles trips.
Place i used to work for has a 83 S1400 international service truck. Weighs 17000-19000 and the NA 6.9 in it moves it surprisingly well, has 4.88 gears with 9R20 tires, tachs out at 58mph, pulls a 6% grade at 35mph
Laughing Gas
Joined: Mar 2016
Posts: 1,105
Likes: 78
does it tow poorly ? a slug off the line even empty ? did it come stock with that gear ?
not that i'd trade but for the sake of general knowlege i'd be curious to hear a report on how well/or poorly the idi handles that low a gear .. i'm guessing it must not do too good otherwise you'd keep it i suppose ..
not that i'd trade but for the sake of general knowlege i'd be curious to hear a report on how well/or poorly the idi handles that low a gear .. i'm guessing it must not do too good otherwise you'd keep it i suppose ..