Gear ratios
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Cross-Country
Joined: Aug 2019
Posts: 60
Likes: 4
Gear ratios
I have a '66 F100 with a 351 Cleveland with a M5ODR2 behind it. I will be rebuilding the motor this summer and it should make around 400 ftlbs of torque @ 2500 rpms. I do not think the tranny will hold out (it needs attention as well). So I thought about a Tremec TKO. The M5ODR2 has a 3.90 first gear and the Tremec is 3.27. My rear end is a 3.70. The question is would I need to change my rear end gear to a 4.10 to compensate? I use the truck to haul 1200 lbs of wood stove pellets over a mountain pass 5-6 times a year and tow my Fiat from time to time, but mostly he is used as a daily driver..
See A Man About A Horse
Joined: Apr 2003
Posts: 4,937
Likes: 699
From: Mariposa, Ca.
Fix It Again Tony.
Seriously, someone will be along directly with a link to one of the on-line gear ratio/rpm calculators. There will likely be members here with the combo you are thinking about. Good luck.
Fleet Mechanic
Joined: Jun 2019
Posts: 1,899
Likes: 236
From: Southern California
My T-18 has a 2.99-1 second gear, which is functionally first, since first is 6.35-1 or something like that. With a 3.70 differential I have no problems moving forward with or without a load. I would run the gears you have until they didn't get the job done, you can always swap them out later.
Fleet Mechanic
Joined: Sep 2016
Posts: 1,459
Likes: 70
From: Southern Maryland
I have a '66 F100 with a 351 Cleveland with a M5ODR2 behind it. I will be rebuilding the motor this summer and it should make around 400 ftlbs of torque @ 2500 rpms. I do not think the tranny will hold out (it needs attention as well). So I thought about a Tremec TKO. The M5ODR2 has a 3.90 first gear and the Tremec is 3.27. My rear end is a 3.70. The question is would I need to change my rear end gear to a 4.10 to compensate? I use the truck to haul 1200 lbs of wood stove pellets over a mountain pass 5-6 times a year and tow my Fiat from time to time, but mostly he is used as a daily driver..
Laughing Gas
Joined: Nov 2001
Posts: 1,062
Likes: 78
From: Edmonton, Alberta
If you want that super low first, you're probably going to have to stick to TRUCK transmissions, so the one you might want to look at is the ZF 5 speed that was used in the 90's in F250's & F350's they came behind 351W (5.8L) & 460.
A friend had a mid '90's F350 4WD Crew, 460/5 spd ZF, last report I heard a few years back was he was at 470K, still on the original untouched trans....
A friend had a mid '90's F350 4WD Crew, 460/5 spd ZF, last report I heard a few years back was he was at 470K, still on the original untouched trans....
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