spec'ing a shed hauler - axle ratio etc

[DVT873]

JMartin, get the close ratio. You won't be happy with the wide ratio. They will likely recommend wide ratio for your application because it has a deeper 1st gear. They don't tell you that you get a wide gap between 3rd and 4th or 4th and 5th. It will fall on its nose. Because of the torque converter effect the gradability while less with the close ratio is still beyond what the tires could manage on dry pavement let alone dirt.

[Btech]

Just gonna through my 2 cents in here, I do work for a guy that has a site prep business for storage sheds and he has 3 Peterbilt 348 dump trucks and they always pull a trailer with a skid loader on it.
All have the cummins L9 paired with a 6 speed Allison, not sure what ratio rears they have as I've never had a reason to check, but I would say with a 0.65:1 top overdrive ratio 3.90 would probably be ideal (1500RPM with 4.11 is 68MPH; with 3.90 is 72MPH; and with 3.70 is 76MPH)
Other than having to do manifold gaskets and the coolant line that goes to the compressor leaking that the L9 is notorious for, they have been great trucks for him.
And from doing road tests, the engine brake on them is no joke. it will almost throw you out of the seat when it kicks in if you don't realize its on. Only time we've had to do brakes on the trucks is because of age and cracking, they haven't come close to wearing the lining out.

[jmartin]

(03-14-2025 )DVT873 Wrote:  JMartin, get the close ratio. You won't be happy with the wide ratio. They will likely recommend wide ratio for your application because it has a deeper 1st gear. They don't tell you that you get a wide gap between 3rd and 4th or 4th and 5th. It will fall on its nose. Because of the torque converter effect the gradability while less with the close ratio is still beyond what the tires could manage on dry pavement let alone dirt.

Thanks for all your info, looks like we need to dig into the Allison options. The close ratio does sound like a better fit. Will see if I can find the ratio chart for both and compare. What you said about durability is consistent with what we've been hearing from others, including a shop owner who told us it is rare that he sees any problems with them. I also found mention of a 7 speed Allison but haven't dug into into it to see which series and specs it's available in. Interesting that the exhaust brake is more effective with the Allison, but it makes sense. Regardless, I think he plans to add the jake as the cost isn't significant. We noticed that it really doesn't cost much more to add options to a medium duty, like better cluster, more gauges, better seat, sound deadening and corrosion resistant cab etc. Unlike pickup trucks, where base model to fully loaded can be a near 50k price difference and many of those options aren't even valuable from a business perspective.

[tree98]

(03-14-2025 )Btech Wrote:  the engine brake on them is no joke. it will almost throw you out of the seat

Either it's mostly the auto trans causing the braking effect or it's because the trucks you are referring to are very light. As I mentioned my L9 exhaust brake is absolutely a joke and doesn't do anything except make a tiny bit of noise. I bought the truck new and it's always been this way.