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Transmissions and Rear Ends Three on the tree or four in the floor? Shift it all here.

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Old January 24th, 2017, 01:33 PM
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Default Re: Muncie 4spd to NP440 conversion 66 GMG 3/4 ton

Hope you guys don't mind me commenting on the topic. Gearing trucks is a passion of mine. Making the proper balance of torque & HP verses rpm and speed to do work efficiently and economically is almost an art. Compromises are required and definitely effect the results. Durability can and often is sacrificed in the end.

I was not familiar with the NP 440 so had to do a bit of research. It appears to be a car trans pressed into light truck duty. Input torque rating is only 270 #/ft, so really using it behind a 292 or 305 V-6 or SBC V-8 is fine, but a 350 V-8, probably not.

I didn't compare the RPM drop between gears with the NP-435 & 440 but I bet they are almost identical. You could extract identical performance with either trans with just a change of rear axle ratio. Depending on axle ratio you can have a stump pulling low gear and 50-55 mph cruising speed or have to start out in 1st and cruise easily at 70 mph with either trans.

Sping of 1978 I priced out and almost ordered a '78 GMC heavy half ton, 292&NP-435, it's what I was driving everyday at UPS in package cars. Then one day I got a different truck, had a Ford horn button, ran up&down the hills in town like an empty V-8 pickup. I asked the night shop mechanic about that truck. He said, "Yep, it's a loaner, 300-6, runs like a 350 V-8 don't it! I thought so too when I drove it here!". Took me a year and a half to find my used '78 F-150, 300-6, Np-435, 9" rear, Dana 44 frt, NP-205 T-case. Was 2 yes old and 27,000 miles. Got about 14 mpg on highway, 11-12 in town, don't try to cruise over 70 or mpg drop to single digits! With the creeper low and 3.55 gears I could idle away with trailers twice as heavy as what Ford's towing guide recommended. My '87 F-150 had the exact same drive train except the newer Borg-Warner T-case and Ford 8.8" rear axle, and the new for '87 EFI engine, no more fussy Carter YF-1A carb.
I had to have the 3rd/4th gear synchro replaced in the '78 when I had the clutch replaced. The diaphram spring in the pressure plate broke when I had about 70,000 miles on the truck. The trans in the '87 would shift itself out of 3rd gear when you backed off the gas to coast around 80,000 miles. I HAD to find a different trans company. My '96 F-250 has 302,000 miles on it, and the ZF-5-470 has been faultless! I put a LUK clutch in it around 250,000 but did nothing to the trans & T-case. I still have a creeper low even with 3.55 gears, can idle around at walking speeds with 12,000# on my trailer, and still have the low side of my T-case if I need slower and/or more torque, and can run 65-70 mph at 2000-2200 rpm in O/D. I will say this, the best running UPS truck I drove with a 292 had a NP-542 trans behind the engine. See a pattern here?

I'd suggest a nice wide ratio 5-speed, and a splitter or O/D or U/D of some type. I've been around all sizes of trucks for over 50 years and have never seen a 2-speed axle for a light duty truck. I have heard rumors of IH offering one in a Ton and 1-1/4T truck in the 1950's. Good luck finding one!
There's other brands of truck transmissions that would work great in light trucks, Clark is a name I've heard mentioned frequently. Common in medium duty's, most often with 2-spd axles. I drove a well used and abused Ram 3500 years ago, CTD & NP-4500, the Synchro's in three of the 5 forward gears were shot, just had to shove it past the synchros. Truck had 100,000 miles. Don't know if the but on 5th gear had been fixed but suspect it had. I hear the NP-5600 is a Great trans. I test drove the first F-250 I could find with the ZF-6 speed when it came out, close ratio 6-speed, but not really close enough to skip gears. I like my 5-speed better. 6-speed would be fine if you towed heavy, really heavy 75-80% of the time. Even with my 3.55 gears, I bet I've pulled my ZF 5-speed out of 5th gear to shift into the nonexistent 6th gear several THOUSAND times. 3.25 gears would be about perfect for 99% of my use of the truck. That last 1%, the 3.55's handle really well.
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