Transfer case questions (not Scrambler specific)


Legacy Registered User
My wife's old Grand Cherokee has a SelecTrac NP-242 (can select between full or part time). My Grand Wagoneer has an NP-229 (full time) case.

My Scrambler has a Dana 300 (part time only), My '05 Unlimited has a CommandTrac NV 231 (part time only) case, and my wife's new JK Unlimited has a CommandTrac NV-241 (part time only) case.

What I guess I am noticing is that the CJ/YJ/TJ/LJ/JK line appears to be part time only cases. I would have thought this to be a "strength" thing; but, the case on that SJ has to deal with a huge heavy body and a fairly big V-8... So, what's the point of a part time case design? It seems the full time designs are easier to deal with on-road during winter (no need to shift in / out for patchy slick pavement).


Blown Budget
SOA Member
Both of the full time cases use a "viscous coupler" to provide 4wd in full time. Sort of a mini torque converter on steroids. Very expensive and it will wear out in time.

The D300 is a gear driven case- I'd have to say the only difference in operation between it and the chain driven 231 and 241 is the chain driven cases are much easier to shift. Hence today's consumers like them more.

The 242 case is a great case and was available in the Grand Cherokee and in the XJ Cherokee. It's like a 241 with a full time option. The great thing about the 242 is that it offers both Full time and 4HI lock. I have no idea why it hasn't made it's way into the JK. I like to believe it's because jeep consciously is intending the JK to be more utilitarian.

The 229 in the SJ is a different bird. In 4HI it uses the viscous coupler, and in 4LO it is locked in. With a worn viscous coupler, you not have full 4WD even though the dash light is on. Even with a good coupler, there is some front/rear slip allowed. The SJ was intended as a country club/ski slope four wheeler, and the 229 is far from robust. However, it is up to the task of the vehicle in stock form as designed.

Personally- I prefer the part time only cases. Very simple and trouble free inside. The 242 viscous coupler is a $500 part!

In the NV/NP numbering scheme, the second digit denotes strength. A 229 is weaker than a 231 and a 241 is stronger than a 231.