More of a medium duty issue...

Hi folks,
First post here. My name is Pete, and I hang out in Denver, CO. I'm looking for a little guidance from people who know how to drive heavy things. I run a service truck it's a 1985 International S-1954 with a mechanical DT466 and an Allison automatic trans. I'm running at right about 20K lbs, almost all the time. My load rarely varies like most yours do (I assume). Anyway, my issue is the transmission, I hate it, and I want a manual. I have a chance to pick up an Eaton Super 10 real cheap. My rig doesn't have air, but I can add it, so that won't be a problem. I'll have to change lots of stuff like the driveshaft, install driveline brakes, install manual clutch stuff etc etc. No problems there. My concern is, that trans is supposed to be behind a much bigger motor, and wants to be shifted at 1200-1400 rpm. I think I can get an SAE2 housing for it, but my main concern is that shifting rpm. The DT466 runs up to 2700 rpm, and doesn't even wake up until about 2000 rpm. If the trans wants to be shifted at 1400 rpm max, won't that pose a problem, especially during upshifting in the mountains? I would have to shift the trans below the point the engine is making any power; I won't even be able to get out of my own way, I'm thinking. Thoughts?

 

Thanks guys, I'll try to answer everything in order:

I'm hanging up on the 1400 thing, because in the book for this trans, it says not to downshift above 1400, and in the "engine speed vs vehicle speed" graph, it shows all upshifts happening below 1400, so I'm assuming it doesn't like going into gear if the input shaft is over 1400. Is that not accurate?

Sheet, I'm nowhere near 230HP. Maybe 180 - 190. It's a mechanical DT466 that's had some upgrades, but not alot. The AT545 that's in there now has 4 ratios, ranging from 3.45 to 1.00. The super 10 goes from 9.9 to .76. I'm hopeful It'll work ok. A 6610 would be a better choice, but that's not in the cards at the moment.

I drove a spicer 5+2 and I was always so #### clumsy trying to knock it into gear, I wouldn't go Spicer again. That was just frustrating.

 

This certainly isn't going to be real cheap. I have to add a clutch, bellhousing, flywheel, air, and possibly do some fancy footwork to get a driveline brake installed. The AT545 has a drum brake on the output flange that's the parking brake for the truck. The Eaton doesn't, so I'll have to figure out how to install / fabricate one. This is starting to sound like a giant PITA.

 

What's the specific drawback to using a trans that's too big? I'm assuming you mean torque - wise.