spec'ing a shed hauler - axle ratio etc

[jmartin]

My brother is getting quotes on a new truck that will be set up for shed hauling, think moving Amish barns.... He has asked me to get feedback on the specifications we're looking at so far.

Shed hauling is a unique application, some points for consideration:

-50k miles per year driven typically
-Fuel economy is not a primary concern
-Up to 50% of miles driven are unloaded, up to 70 mph
-Most loaded miles gross around 35k, 58-65 mph
-Some loaded miles (up to 16 ft wide) require full engine power, especially on grades (high air resistance)
-Custom built trailers, Pine Hill bumper pull in our case
-No payload on truck, other than the shed Mule (google Cardinal Mule)
-Must be reliable for many years, with good upkeep

Many, probably most, shed haulers run pickup trucks, with a few using single axle semi tractors. The advantage of a medium duty is being able to spec a much heavier engine and transmission than a pickup, and still have a low-ish ground to cab floor height. The operator is jumping in and out of the the truck many times per day, which takes a greater toll on knees and back with a higher cab. Pickup trucks are pushed to the extreme in these conditions, leading to a shorter lifespan, and expensive maintenance.

After getting initial quotes from Navistar, Freightliner, and Hino, we are leaning toward the International MV607 medium duty set up with these specs:

-Cummins L9 350 with 1050 lb ft rating, with Jake brake
-Allison 3000 RDS Close Ratio, 6-speed with double overdrive, no retarder, Performance programming
-10R22.5 rear tires
-255/70R22.5 front tires
-Disc brakes
-Locking diff

Biggest concern is to make sure we are not lugging or otherwise abusing the engine, assuming the L9 can suffer from the same issues as the X15 when lugged constantly. Among the available axle ratios are 3.55, 3.70, 3.90, 4.11, and 4.33. According to what I can locate online, the Allison 3000 is 1:1 in 4th gear, 0.74:1 in 5th, and 0.65:1 in 6th. I presume Allison's "performance programming" option may help avoid lugging, but have not found any solid information on exactly what it does.

Based on given tire size, available axle ratios, Allison gearing, and typical operating conditions given in the list above, what is the best ratio to avoid lugging under any conditions, while still running efficiently at 70 or 75 mph empty? I'm leaning toward 3.90 but want to see what the experts say.

[hookliftpete]

I would go no lower than the 4:11, running a similar setup but with a tag axle to make my gross fully loaded at 44k.

[jmartin]

Thanks for the info hooklift. What is the rpm range we should stay out of with the L9? Anything above 1500 or so ok for unloaded cruising? Is 1400 rpm getting into harmful territory? Obviously we would never run that low under any loaded conditions. Maybe we are overthinking it a little, but we only have one chance to set this spec and want to get it right for long term reliability.

[Rawze]

(03-04-2025 )jmartin Wrote:  Thanks for the info hooklift. What is the rpm range we should stay out of with the L9? Anything above 1500 or so ok for unloaded cruising? Is 1400 rpm getting into harmful territory? Obviously we would never run that low under any loaded conditions. Maybe we are overthinking it a little, but we only have one chance to set this spec and want to get it right for long term reliability.

1500-1900 is the optimum range to pull hard in for an ISX. 1650-1750 rpm provides the Least amount of wear, and your not luggung to an agonizing death below 1500 or so.

[tree98]

If i was spec'ing a truck like your talking about, I would get the 4.33 rears, but I'm only familiar with manual shift transmission's maybe the ratio's can be different on an auto and achieve the same result??

I have an L9 in a truck that's always grossing about 52K, and I can tell you for certain that the jake brake does absolutely nothing but make a tiny bit of noise, it's absolutely worthless. Maybe it would work better if I was lighter?? Just thought I would mention that.

[Rawze]

(03-05-2025 )tree98 Wrote:  ...
I have an L9 in a truck that's always grossing about 52K, and I can tell you for certain that the jake brake does absolutely nothing but make a tiny bit of noise, it's absolutely worthless. Maybe it would work better if I was lighter?? Just thought I would mention that.

yeah, a lot of the smaller engines only have an engine exhaust brake (using the turbo to choke exhaust only) and not an actual jake brake with valves with solenoids. Its fairly weak.

[jmartin]

The L9 is now available with a compression release jake, since at least 2021. I agree that an exhaust brake only would barely be worth bothering with.

Based on above advice and running scenarios with a gear ratio calculator, we’re going with 4.33s. Noticing a disadvantage with the Allison is only getting 6 speeds. There are a few scenarios where it would be nice to have a few more choices between 4th and 6th.

Thanks for all the advice.

[Rawze]

(03-06-2025 )jmartin Wrote:  The L9 is now available with a compression release jake, since at least 2021. I agree that an exhaust brake only would barely be worth bothering with.

Based on above advice and running scenarios with a gear ratio calculator, we’re going with 4.33s. Noticing a disadvantage with the Allison is only getting 6 speeds. There are a few scenarios where it would be nice to have a few more choices between 4th and 6th.

Thanks for all the advice.

Unless there is a specific need for it,.. having an auto-s$itter or automatic tranny is a disadvantage in every way vs. a stick on a commercial truck. Lower fuel economy vs. someone who knows how to shift well (as much as 0.7 mpg in most cases), higher long term maintenance costs (xy shifters wearing out, etc.), major repair costs when it wears out, higher engine wear rates (lugging the engine to death in lowest rpm it can use vs. power range), etc.

[DVT873]

At the risk of getting shot, or banned I am going to mildly disagree on the Allison vs manual. First he stated fuel economy is not a major issue. The torque converter locks up in all the higher gears if not all of them. The last I looked at drive cycle data, especially urban/suburban, fuel economy difference was something like 1 or 2%. It sounds like this is going to be an urban/suburban drive cycle vs. OTR so a lot more shifting going between lights, intersections etc. His leg will like the auto at the end of the day.

I have been around medium-duty trucks for a long time. Most all of them have been Allisons since the mid-90s. Over time I have developed a lot of respect for those transmissions, especially the 2000 and 3000 series. I have seen them live in applications where I would have never speced them or would have speced heavier i.e. a 3000 vs a 2000.

When I was selling new I never had a single customer go back to manual after going auto. Virtually every garbage truck you see and a lot of smaller tandems, or tri-axles like 16 to 18 ft dump beds are automatics. Almost all Allison. I am not a fan of the automated manuals.

The electronics do an excellent job of protecting the trans without being a PIA about it. Follow the filter and lube change recommendations, use OE fluid and filters. IF he would wear it out, not likely in his application, the last 3000 series we put in was around 6K from Weller.

As far as a performance vs economy mode there will be a button that will let him choose. Default is usually for performance. All it does is change the shift points. About the only issue I've ever seen is with the right combination of grade, weight and speed the trans may "hunt" between 5th and 6th. If that happens select 5th until your over the hill or whatever.

Whoever is specing the truck SHOULD be able to provide with all the data he would ever want to see on ratio choices, gradability, etc., IF the salesperson is competent. Allison distributors used to have somebody on staff to do just that if the truck dealer wasn't providing the info.

On the exhaust brake aka potato in the tailpipe vs a tru Jake-type the exhaust brake works well when it is coupled with an automatic. Much better than with a manual. With a manual you barely feel it. The exhaust brake slows the engine's RPM quickly enough that the transmission downshifts. The downshifting is what slows the unit. It is very noticeable. Note that you have to tap the brake pedal or nothing happens.

All of the above is based on my experience with vocational equipment in the medium-duty category.