Tractor First, Right?

If you pull heavy is the only tranny to have.

 

18918b is pretty common. 20918b is prefered in mid heavy haul (80000 to about 150000) 22918b is the top of the line. But has more splines on input shaft so you have to use clutch to match splines.

 

@HandLogger , you mentioned hauling up to 108,000 lbs. Maybe a 349 size hoe?
If you intend to haul that kind of weight in and out of logging sites I would recommend that you spec your truck for that and eat the inneficeintcy of hauling an occasional load over the road to Florida, or hire out that part. That will put you in the neighborhood of 160K gross, and that will demand the correct specs in order to live trying to start that kind of weight in soft footing. As others have indicated, 46K rears, 4:10 gears, and probably 18918 transmission would be as light as I would feel comfortable with in your scenario.
Spyder has a valid point in regard to hiring the hauling done. However, as a contractor myself I understand that the value of having your own outfit to be able to move your equipment on your schedule. It is hard to pencil out until you begin to calculate the cost of having your job shut down waiting for a transport.

Good luck to you!

 

Well, other HH guys can probably answer the frame size better than I, and it probably has a lot to do with the laws in your state and your trailer. If you are going to have a long neck and be able to put 20k on the steering you may need double or heavy frame, but if you will run a tag axle and only get 12-14 on the steering it may not be necessary.
My old truck has 3/8 frame with 2 speed rears (4:11/5:60), 240 wheel base, and over a million miles with no frame problems yet. As others have suggested if you find a tractor with the correct running gear, the frame that it has will probably be correct as well.

 

It's like the transfer case on a 4x4 pickup. LOW gear tops out at 45 mph, but you can change the rotation of earth. The 2 speed rears is like a transfer case built into the drives. Theres also an auxiliary transmission that fits on the back with 3 speeds. That allows you to have your heavy pulling 15 percent and a quarter million lbs, your regular ratio, if you chose something in the 4.30 range, and a highway gear when you're not heavy and bouncing.

 

The rear ends have two gear ratios, which can be shifted while rolling. The shift mechanism is air operated via a switch on the dash. They are very nice to use for starting out in soft conditions or hauling on Forest Service mountain roads, etc. Once you get on a hard flat surface and are rolling easy, you can shift into the 4.11 ratio by hitting the dash switch and letting off the throttle. Shifts as smooth as the splitter on an 18 or 13, just make DANG sure the power divider is not locked in when you shift.
They are probably very expensive to replace, but I have had no problems with mine.

 

Six types faster!