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command trac vs. select trac


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Command Trac is a part time 4wd system. It locks the front and rear driveshafts together, making them turn at the same speed. With minute differences in axle gearing and tire size... this is only to be used off road or snowy conditions. If none of the tires can slip at all, breakage will ensue.

 

The NP 207 is a part time case, used from 84-86

87+ Jeeps with Command Trac got the NP 231.

 

Select Trac is a full time 4wd system. It behaves like AWD, and while still powering both axles, it allows them to turn at different speeds if necessary, so you don't break anything. Full time can be used anywhere, at any time.

 

84-86 got an NP 228 or NP 229

87+ will have an NP 242.

 

207/231: 2HI - 4HI - N - 4LO

 

242: 2HI - 4HI PT - 4HI FT - N - 4LO

 

I'm not certain on the controls of the 228/229.

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The 1986 Selec-Trac is a very different animal from the 1987 and newer Selec-Trac. The old NP 228/229 box is a very heavy, very strong transfer case. It is probably overkill for a Cherokee or Comanche. The difference between the 228 and the 229 is that one used a viscous coupling for the full-time mode and the other used a mechanical differential ... and I can never remember which was which.

 

They key part is that the 228/229 did not have a locked (part-time) mode in 4WD-High Range. When you shifted into 4WD-Hi, you had AWD -- with differentiation. IIRC, the only locked range was 4WD-Lo.

 

The controls were funky, too. There was a lever, and there was a separate vacuum switch. They had to be operated in a specific sequence. I once owned an '84 XJ Wagoneer that had that system, but I never had it registered and I don't have any recollection of exactly how the system worked.

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