AG380 & 400 Suspensions

Yes they're quite a bit different. The AG-380 is the pete suspension, I forget which one. A more traditional suspension with trailing arms and four air bags.

The AG400 is the latest version of the 8 bag suspension.

What application?

 

Also, 38k rating vs. 40k rating

 

Peterbilt Flex Air & Kenworth AG380 are one & the same. The advantage is a lighter weight set up that requires little to no maintenance. Have not heard much of people having to replace bushings etc.

This is from when it was released.
http://www.peterbilt.com/newsdetails.aspx?id=164

[FONT=Verdana, Geneva, Lucida, sans-serif]FLEX[FONT=Verdana, Geneva, Lucida, sans-serif] Air, rated at 38,000 pounds, features a revolutionary new design that provides Best in Class ride and handling while maintaining superior roll stiffness and articulation.[/FONT][/FONT]
[FONT=Verdana, Geneva, Lucida, sans-serif]"The FLEX Air suspension has an installed weight that is 400 pounds lighter than the Peterbilt Low Air Leaf, resulting in more payload and potential profit for our customers. We are targeting U.S. and Canadian on-highway customers who require low weight combined with low chassis height and superior ride in applications such as tankers, flatbeds, refeers, vans and car carriers," says PACCAR Vice President and Peterbilt General Manager Nick Panza.[/FONT]

 

Think that 380 is more for on-road use only (like anyone pays attention to that) and 400 is OK for some off-road; notice the quote "on-highway customers".