Over Drive And Under Drive

[chris401]

Wanting some input with actual experience or knowlage. I have a build up plan for the 65 F250 2wd. Im looking to add a 27% od. This will be either the Warn 2sp avaliable from advanced adapters or the NV4500. I like the idea of using my original NP435 with the Warn but the NV4500 offers less rotating mass. Dana 60 3.54:1 will give me 1890 rpm at 70 mph. On the tail of my tranny will be the Doug Nash 120% Under Drive. This will give me a 4.24:1 axel when employed. The 352 is getting a 4.375 stroke crank, so lugging a smaller FE rod journals wont be an issue. Anyone running the Warn vs the nv4500? Any experience with a similar set up would be appreciated.
Thanks

[jecsd1]

I have the NV4500 in my highboy in place of the original NP435 and I love it. Pretty easy swap. Still have the low first gear and with OD Im turning about 2300 rpm at 75 mph all with 4.10:1 axles. I recommend it.

[Indy63]

What is the reason or goal for adding overdrive/ underdrive?

If you just don't like the wide ratio splits of the NP435 you might be happier with another 4 speed, maybe even a fully synchronized one. If you don't like the splits, want a synchronized transmission, and want an overdrive along with a more usable low gear, you'd want a NV4500. If you're just trying to improve your mileage, it will take a LONG time and a ton of miles to become cost effective IF you get better mileage at all.

I prefer simple solutions, so if you're just not happy with the gearing of the NP435 I would swap the transmission rather than adding two separate systems to the driveline with an overdrive and underdrive. Plus all the additional shifting to use both in addition to a manual transmission would get old fast.

[banjopicker66]

Couple of thoughts, I went through this process myself.
1. Doug Nash OD - I installed one on the rear of a C-6, and had to cut out the reinforcement brace running left to right under the cab to make it fit. It is rather bulky. This may not be a problem on a NP-435 (or T-18) as it will probably sit further forward under the cab, but I cannot speak confidently to this.
2. Do you use your truck as a workhorse, and need the lower rear end gears or heavier GVW? If not, you may want to consider a rear axle swap to a Ford 9" with a much higher ratio. It would be a much cheaper and easier swap, and you have a wider choice of gear ratios. If you need the pulling power, you could go with a 3.50 rear for better mileage and still have the granny gear capability for first. If you want even lower RPMs, go with a 2.75 or even a 2.50 - but you would always have to start out in 1st with that low of a ratio. The maximum GVW on a Ford 9" is 5000, I think.
Hope this helps.

[chris401]

Yeah I like the .73 OD and after the update to the OD gear I didn't see gears come back off.

I have the NV4500 in my highboy in place of the original NP435 and I love it. Pretty easy swap. Still have the low first gear and with OD Im turning about 2300 rpm at 75 mph all with 4.10:1 axles. I recommend it.

[chris401]

Drive with 3.54, tow with 4.24. Spitting gears wont be necessary with a 453 ci.

What is the reason or goal for adding overdrive/ underdrive?

If you just don't like the wide ratio splits of the NP435 you might be happier with another 4 speed, maybe even a fully synchronized one. If you don't like the splits, want a synchronized transmission, and want an overdrive along with a more usable low gear, you'd want a NV4500. If you're just trying to improve your mileage, it will take a LONG time and a ton of miles to become cost effective IF you get better mileage at all.

I prefer simple solutions, so if you're just not happy with the gearing of the NP435 I would swap the transmission rather than adding two separate systems to the driveline with an overdrive and underdrive. Plus all the additional shifting to use both in addition to a manual transmission would get old fast.

[chris401]

Thanks for that info. I considered putting UD on the back of C6 with 2.75 in an F100. Employed it would give a 3.30 +/- with a 2.75. I decided to use it on the F250. If I ever do a axle swap it will be to a Ford 10.25 3.55:1 with rabs.

Couple of thoughts, I went through this process myself.
1. Doug Nash OD - I installed one on the rear of a C-6, and had to cut out the reinforcement brace running left to right under the cab to make it fit. It is rather bulky. This may not be a problem on a NP-435 (or T-18) as it will probably sit further forward under the cab, but I cannot speak confidently to this.
2. Do you use your truck as a workhorse, and need the lower rear end gears or heavier GVW? If not, you may want to consider a rear axle swap to a Ford 9" with a much higher ratio. It would be a much cheaper and easier swap, and you have a wider choice of gear ratios. If you need the pulling power, you could go with a 3.50 rear for better mileage and still have the granny gear capability for first. If you want even lower RPMs, go with a 2.75 or even a 2.50 - but you would always have to start out in 1st with that low of a ratio. The maximum GVW on a Ford 9" is 5000, I think.
Hope this helps.