MY buddy is looking at a new used truck and had some questions about it. This is the question that he posted on my forum (http://www.mistercmk.com/forums/show...=4638#post4638):

The gear/diff options: (with door code)
19 – 3.55 Non-LS
18 – 3.08 Non-LS
H9 – 3.55 LS
B6 – 3.73 LS

so my question is, both diffs on a 4WD system match then (obviously same gearing)? Both are either LS or Non-LS?

 

Both gear sets have to match (or be really darn close) to work properly.

The rear is the only unit that has the factory option of being an LS unit (limited slip aka traction-lok). The front uses a vacuum actuated sliding fork to engage/disengage the differential. The front diff is actually an open unit loosely based on the 8.8 Ford rear with reverse cut gearing since it is used in the front.

-Kerry