Ge-gear or install a GV overdrive? - Ford Powerstroke Diesel Forum
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Old 07-14-2014, 04:53 PM
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Ge-gear or install a GV overdrive?

I do a fair amount of highway miles in my F350 dually/zf6 truck and need to do something about the RPM the engine is turning at 65-70mph. I tossed around the idea of forking out for a Gear Vendors OD unit but the price is pretty steep along with the extra maintenance that it requires.

I'm not familiar with RPM/speed on the AT single-wheel trucks but would like to get mine back to 1800rpm at 65mph on the highway. It has 4.10 gears in it.

Have any of you guys re-geared one of these trucks for highway use? I know I'll have to do both diffs as it's a 4WD rig. The fact that it has a six speed plus has low range in the transfer available, I don't think I need the high gearing it has.

Using some engine speed calculators shows that going to 3.73 gears isn't really going to make that much difference in engine speed (less than 200rpm drop in speed).

Considering that I have a PHP chip installed, has the torque/RPM curve really changed much? If I'm unloaded or hauling maybe a ton in the bed, will the engine do fine at 1800rpm cruising on the highway? At what point is the engine running too slow?

Last edited by ttyR2; 07-14-2014 at 05:31 PM.
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Old 07-14-2014, 06:24 PM
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Unloaded or a ton in the bed 1800 rpm will do fine on the highway. My truck came with 3.73's and the only other 7.3 is our work 450 with like 4.56's or something. Kills the MPG but pulls like an ox. 1500 is to low to me unless I'm just easing my way through town. Unloaded I like 2000 rpm on the highway so about 70 mph. Depending on weight of what I'm hauling/pulling I like 22-2400 rpms even if that means leaving OD off (light on) and eating up a little extra fuel.
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Old 07-14-2014, 06:57 PM
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I talked to Gear Vendors about this same thing. The 1997 F-Superduty with a 5 speed and4.63 gears revs higher than it needs to at highway speeds. They were not too thrilled about this application. Said the jack-hammer effect at lower rpms would be too hard on it. They will take 1000 hp, but the torque pulses from a diesel are another matter altogether. Some input from others on this subject would be appreciated.
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Old 07-14-2014, 07:16 PM
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There's a member on here with one but I can't for the life of me remember who or where I saw the post. He said it pulled fine still and was up about 3 MPG I think is what he posted. I picked up an 87 FJ 60 land cruiser for my wife that has a Chevy V8 setup with the Toyota 4 speed manual. It has a ranger O/D , it is way less than the GV unit and drops hers about 500 rpm's. I usually leave it on the low side for town and under 60 mph driving and when on the highway shift to the high side. You can split every gear If you wanted , making your 6'r a 12'r. I've read lots of noise complaints but the only noise we have is throw-out bearing rattle. No slipping , still pulls fine , going back with an auto and an LS motor , so we just drive it in hopes it will die and speed up the swap. Might be another avenue to look at if twin sticks don't scare you.
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Old 07-14-2014, 07:35 PM
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Scratch that , doesn't appear AA makes one for our application.
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Old 07-14-2014, 08:12 PM
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Why not just run taller tires?
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Old 07-14-2014, 10:09 PM
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Spacers are bad news. Would have to run them to run bigger tires on a dually. If I can find anyone with real-world GV experience, I'm heading that direction I think.
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Old 07-15-2014, 01:27 PM
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I am thinking if the engine was not lugged at low rpm the "jackhammer effect" would be minimal. If I can find a used one at a reasonable price I am gonna buy it with proper driving habits in mind......

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