Higher gear swap?

[Walt]

Howdy guys,

I've got a 1995 Ford F-800 with a 24' box I've converted into a motorhome. I'm not sure what this truck was in it's former life, but it's geared pretty low. It has a Cummins 5.9L and 6-speed transmission with a 2-speed rear end, for a total of 12 gears. The thing is, I've never had a need to use the low gear, and even in high gear, 1st gear is pretty much unnecessary -- I almost always start in 2nd / high gear with no problem. Unfortunately, to cruise at 65 MPH, the engine is pretty close to topped out at 2500 RPM, and top speed on level ground is about 70 with the pedal on the floor.

So, here's my question -- how feasible would it be to swap out the low gear in the rear end for a "really high" gear? Maybe something a half-gear higher than the current high, so 1st wouldn't be quite so low, and 6th would be a little higher? Any ideas how much something like that might cost? It seems like if it wasn't too outrageously expensive, the swap might be cost-effective in terms of reducing engine wear and reducing fuel costs, no? Any ideas?

Thanks,
Walter

[Marc]

Hi Walt,

Are you the same person that had "Rear Air Ride" problems?? A while back,Did you get that fixed??


As for TALLER gearing,The transmisson does not have 12 gears,only Six it is just a 12 volt splitter. There are a couple ways to make that dog hunt. My opinion is just that an opinion and we all know what that means. If your truck was mine,
I would do two(2)things.But I'm a little off center in my approach on things.

First find out the rear gear ratio,It should be on a Metal Tag riveted to the Axle housing.I would not have a tendecy to trust Line Tickets,Build Sheets,SerialNumbers or the Stickers on the Drivers Side Door. Depending on Road Grime you may
want to use a putty knife or scraper along with some Aerosol Grease Cutter/Remover. I use CRC Carb. or Brake cleaner its
only helping cut the grease to find the Axle Ratio Tag,Could be attached to one of the bolts that holds the pumpkin in to
The tag gives you info: Manufacture,Ratio etc. then you could find a taller gear set at a Truck Salvage/Junk Yard or a
complete rear Housing & all. Like I stated above "MY OPINION" That Tranny would become a "Friggin Boat Anchor" real quick.
If you like or don't mind shifting, There are Hundreds of Rebuilt 6,8,10,12,13 & 18 spd.O.D. Real Trannys around "Cheap"
Depending the word Cheap??? From $800.00-$2,500.00 With a Warranty. There are Allison Automatic's Rebuilt out there also.
Not so Cheap. Well opinions are cheap too.

Good Luck,
Marc

[Walt]

Hey Marc,

Yeah, that was me with the rear air ride issues. I ended up taking the truck into a shop for some other issues, and they had their spring shop take a look at it. They ended up adjusting the height on the air ride and replacing the shocks, which were very worn. I haven't even been in the back of the truck while it's been moving yet to tell if it's made any difference.

As far as the transmission goes -- I do realize there are only six actual gears with a splitter; I guess I should have said there are a total of 12 speeds, not gears. But anyway, I'm once again away from the truck right now, but as soon as I get back, I'll inspect that rear end and see if I can find the gear ratio. Forgive my ignorance, but how complicated of a job do you think it would be to swap those things out? I.E. how many hours at a shop, approximately? What should I expect to pay for a used gear set or rear housing?

Also, how would I determine if another gear set or rear housing would be compatible with my truck? For what it's worth, I know the current 2-speed rear end is a bit odd -- you're only supposed to switch from high to low gear with the truck stopped, so you really only have access to six speeds at any given time.

One more thing -- I'm not exactly sure what you mean by that transmission becoming a "friggin boat anchor" . . . could you explain? What would I gain by replacing the transmission? And what do you mean by "real trannys"?

Thanks so much,
Walter