Detroit dd15 for heavy haul 3 axles RGN

Fine for a flat lander... try lifting off on a 12% grade with 80,000 on the deck and pick up gears with your 13 speed..

 

Let’s go to extremes why don’t we?

 

I’ve been in a 97 T800 the last two days, 455 Cat 13 speed 3:70 rears and it’s pulled a LOT of heavy loads in excess of 80,000 on soft jobsites for 22 years. A 13 will do it.

Upon further consideration I think we decided a while back that this is probably the only thing that can haul over 80,000.

 

Most of us pulling 140,000 lbs gross have 46,000 lb rear ends with 3.91 or 4.11 gears and an 18 speed trans. The engine size is not so important.

 

the 40-140 rears work great too and come with a 400# bonus. the 3.90 or 3.70 is good if only heavy part of the time. I have used 3.70 to haul 140,000 for years in the rocky mountains but did spec 3.90 in my own first new truck and loved the difference. I would not chose the 13 speed for mountain work but it is ok for flat work. any 13 with a pump and cooler that is. if you stay east of the Rockies and baby it in the Appalachians a 13 will work well for you but you should look to change those rears. you will be lucky to find 12th gear loaded without having to watch the trans temp very closely.

 

3.70 is a bit too tall imo esp with tall rubber. Even with 22.5 LP the 3.25s aren't ideal but running in direct you can make it work.

 

Ehh, not ideal? Whatever. This truck was a 425 Cat 3:70 40,000 rears with a 15 speed. Their whole fleet was speced that way at the time. It obviously has deep reduction but the steps between gears were similar to a 13 speed. I hauled a lot of loads with it, soft job sites are just as bad if not worse than steep grades and that truck ran 600,000 miles. A truck doesn’t have to have the heaviest everything available to do the job.

 

Sure anything will "do it".
Just an 18 speed will do it soooooo much better.
And I'd take a 15 speed over a 13 for hauling heavy in the Bush anyday. Way better trans for lifting off heavy then the 13. The splits are way closer on the low side of the trans.

 

But he doesn’t have an 18 he has a 13 and that’s what he’s asking about.

 

I agree that 3.70 and a 15 will work if it is the right one
RT14615 low ratio 15.52 high 1.00
RTO14615 low ratio 12.20 high .79
RTO14613 low ratio 12.56 high .87
RTLO 14613B low ratio 14.71 high .85
I have done much more with a lot less but it is a lot more enjoyable with a better setup, the OP is asking if he can do it with what he has.
the short answer is yes if he works within certain restrictions. if he wants to move beyond those restrictions he should be ready to change some aspects of his equipment to make what he has work better and last longer.