Gear vendors overdrive

[ttyR2]

Im looking for opinions on putting a gear vendors overdrive unit in my 2000 f350 dually 4x4 with the zf6. Does it really return the mileage they say it will? How is it for strength? Is it able to stand up to some engine mods? Ive seen 16.5mpg on the highway at 65mph with the truck. It has the stock 4.10 gears in it and stock 235-85R16 tires.

[arcticatdan]

I have one on a 2000 f250 ccsb 6sp with 3.73 gears. It works great, with my gearing it works best for towing having more gears. The 6th over work best at 75mph or more when empty. With your 4.10 and 235s it should help with mileage. If you install it your self have you driveline redone by a quality drive line shop. I had some problems with mine until I contacted Driveline specialist of Texas. They are very good, my truck is smoother than stock now.

[ttyR2]

Using the info from Speed versus RPM calculator and Gear Vendors Under/Overdrive Ford 4-Wheel Drive Manual Transmissions., I calculated that with 235/85-R16 tires, the engine would spin 2200RPM in 6th, and 1700RPM in 6 over. 1700rpm is getting a bit low to pull the truck efficiently at 70mph, isn't it? Speed limit in Oregon is 65 (tho most folks do 72 or so).

[ttyR2]

Hrm...ran into a conundrum. It looks like there are issues with the GV unit. Needs relatively frequent maintenance (frequent for drive train components), and doesn't like back-torque (especially from an exhaust brake).

The US Gear units seem to be a LOT better, and run between the transmission and transfer case, so allowing use in 4WD. Alas, they are no longer in production. So...might be one of those deals where I'll have to search for a while and find a good used one out of a wrecked truck or something.

[arcticatdan]

When you use your exhaust brake DO NOT have your overdrive engaged. I have not seen any US gear units for sale in a long time. I also do not know how hard repair parts would be to get. I change the oil in mine everytime I change engine oil, about every 5000 miles.