Super 40 vs 40 rear ends.

Super 40's are definitely stronger than 40's they were made more for long distance heavy work imo. Guys in the bush with logging trucks would seem to go for the full out 46's whereas the guys hauling lumber trains from the mills to the customers would go for the super 40's. In both cases grossing out at 135-140000lbs. One bad thing is when it's time for a rebuild expect to pay some $$$$ compared to a standard 40 rear end. That being said there's a lot of 15-20 year old heavy haul trucks out there with super 40's that haven't been rebuilt yet. Your choice. Pay now or pay later lol

 

There is a misconception about what “Super 40’s” really are. Some people believe that 40 diffs in thicker housing (DS405 for example) are super 40’s.
IMO super 40’s are 46 diffs in slightly smaller housings (DT40-170 for example). Inn this case you only save about 50 pounds of weight on a set of tandems however, some OEM manufactures won’t let you spec a road truck suspension, like low air leaf for example, with full 46 diffs. Full 46 diffs are usually speced with heavy duty suspension like Neway.

 

If you can do super 40's or 46k rear ends.

With water you usually overload yourself and you don't want to blow your rear end because it couldn't handle it.

 

The safe side is to have the other parts of the drive line heavier than the rear ends so you don't have drive shafts laying in road?

 

The only real difference is a 3/8” housing vs 1/2” on most depending on which 40, and which 46 rear is specd, also the frame slipper by the 5th wheel

I do quite a bit of running 100+k on my 404s

 

I’d also like to add that Kenworth offers the 8 bag AG460. It’s a beefier version of the AG400. IMO, the AG460 is a great setup overall, even off road where you need traction.

 

Yes, there are proprietary suspensions you can spec with 46’s. Peterbilt Air Trac is another. I’ve never figured out the real difference between AG 460 and AG 400…..I do know that the last KW I speced, the salesman said you could get the AG460 on super 40’s which is weird because Peterbilt makes you spec a light duty Air Trac if you want super 40’s?

 

BTW it’s been almost a decade since I’ve speced a new truck so the nomenclature may have changed. But the Eaton/Fuller/Dana/Spicer…..or whatever Eaton calls themselves these days…..Rear ends in question were DT46-170 (46k) and DT40-170 (super 40) again the only difference between the two is the housing thickness (1/2” vs 7/16” IIRC) you can’t tell them apart at a glance and the difference is only 50 pounds for a set of tandems. I would go ahead and just get 46’s unless you absolutely want a LowAir, Flex Air, AG 400L, AG 380 or some other light duty highway suspension.

 

Aside from the rears, have you considered a 3/8” frame? If you’re considering a W900 L or B, get yourself some added hood support brackets and (depending on the year) change the rear spring hangers to the later version.