OK, what's my best overdrive option....

[lenniesdad]

Got a 71 Highboy, 360 with a manual 4 speed. I'm looking to add overdrive in the most non-invasive and correct way possible without a bunch of chopping and welding and fabricating besides drilling some holes or taking a driveshaft in for a shorten/balance. I'm intrigued by the Ranger Torque splitter overdrive but have heard the (I think) NP435?? is a good tranny to find for a swap 5 speed. Whats the best course of action?

[averagef250]

The Ranger's are OK. For what you're looking for I can't think of any other option even remotely close to non-invasive.

I don't care to use the Ranger's because they force you move the shifter back 4" or so which isn't really my cup of tee. They also add another lever, or a switch for electric shift ones that I don't want. I don't like overly complicated stuff, more of the KISS mentality and the Ranger is a reasonable solution in some cases, but often it's a PITA.

Your truck has a 435 4 speed, that's what every highboy came with until the later years when the C-6 auto was an option.

I did an NV4500 5 speed swap into my '70 highboy behind a 390 quite some time ago. Before the NV4500 I put 140,000 or so miles on the truck with a 435, 4.10's and 35" tires. I liked that setup a lot, it was perfect, I just figured a cruising RPM lower than 2500 would get me better freeway mileage. I was wrong. I got maybe 1 MPG gain on the freeway with the NV4500, but absolutely hated using overdrive. Took more throttle to run the truck down the road in OD than it did in 4th gear and had to downshift to 4th up hills. OD was useless with a cold engine, etc, etc.

In the end I built another truck, a 1971 F-250 4x4 with a Cummins and 5 speed to see how I liked the diesel. I loved it and I sold it to fund some business equipment with the intention to do a similar install into my '70 highboy. Haven't got there yet, but someday I will have the time to pull it in the shop and go to town on it again.

The best thing you can do is gear the truck for 2500 RPM around 65 MPH. The engine will be happy there and live as long a life as an old carb engine can expect to live unless something is wrong with it already. If you have 4.10 gears put 35" tires on it or switch to 3.54 axle ratio with 31" tires or 33"s and 3.73- You get the idea.

You can get a bit creative with tall gears and a 5 speed NP540 5 speed transmission or the guts from a 540 in a 435, but I don't recommend this. You end up with funky, unsupported, unproven stuff that probably won't work well for you.

[jzjames]

averagef250, you know your stuff,
plus youre from Beavercreek!

[averagef250]

averagef250,
plus youre from Beavercreek!

So was Tonya Harding! You're from around here? Just moved here a bit over a year ago. Nice place, lots of great neighbors.

[68FORDJBM]

Hello Fellow Northwesters! I'd like to hear your thoughts on my transmission options but I think I might start a new post or look around first. I have a 360 with an automatic. I'm beginning to re-build the 360 and while I have the engin and access to the transmission I'm considering my options to increase fuel economy.

[HIO Silver]

Got a 71 Highboy, 360 with a manual 4 speed. I'm looking to add overdrive in the most non-invasive and correct way possible without a bunch of chopping and welding and fabricating besides drilling some holes or taking a driveshaft in for a shorten/balance. I'm intrigued by the Ranger Torque splitter overdrive but have heard the (I think) NP435?? is a good tranny to find for a swap 5 speed. Whats the best course of action?

A TKO-500, QuickTime bell housing, and a Wilwood hydraulic clutch... Aint' cheap - around $3000 when all is said and done.

[averagef250]

A TKO-500, QuickTime bell housing, and a Wilwood hydraulic clutch... Aint' cheap - around $3000 when all is said and done.

Car transmissions, regardless of ratings aren't up for continuous loading use so be careful with this option if you plan to use your truck like a truck. They can rate transmissions for whatever they want really. The bottom line is continous loading VS actual gear size/tooth contact area/bearing load capacity/lubricant capacity/ability to disapate heat.

Kind of like how a hot small block can have 400 HP, but so does a 3406 Cat. The 3406 moves 100,000 pounds up a small grade at 1700 RPM. If you put the finest 400 HP small block made in place of that engine and geared it for 7500 RPM at 45 MPH the engine wouldn't last a minute under that load.