selec-trac vs. command trac

[JeepcoMJ]

alright, so maybe this has been covered before...

 

selec-trac is?

 

and command trac is?

 

 

i'm under the impression that selec-trac has the little vacuum switch to flip into 4 wheel...but that it's not as strong of a system. what is the vacuum switch for seeing as they are non CAD axles with this system?

 

and then command trac is a simple tcase that operates the driveshafts with a simple shift of 1 lever while sending vacuum to the CAD?

 

what are the advantages and disadvantages of these systems?

[Burls]

select trac = Is the full-time t-case (242)

Command trac = is the part-time t -case (231,207)

 

As far as i know the 242 did not use any form of vacuum at all.

[Pete M]

Select-trac (242) lets you use 4wd on dry pavement because it allows some differential between the front and rear axles when in full-time 4wd. Locks them together when you shift into 4-hi or 4-low. No CAD was ever used.

 

Command-trac (231) would eventually blow up if used on dry pavement because it only locks the front and rear together. Came with the CAD in the early years.

[JeepcoMJ]

i don't see why command trac wouldn't work on dry pavement...that makes no sense to me. is it cause the tires have no slip-ability? personally i think 4wd is about NOT slipping.

[Pete M]

It is exactly because the tires won't slip on dry pavement. There needs to be some slip in the Command-trac system. Just a little bit to prevent binding and keep the t-case from exploding. If the truck is running puny little car tires you may be able to get away with it, but as the tires get bigger and stickier or the vehicle weight goes up, the chance of damaging the system goes up.

 

Think of it as if you spooled an axle and then turned a sharp corner. Either a tire will slip, or the axle will break. Something has to give. A 242 is sorta like a posi in that it will allow for some differential when in full-time 4wd but still put power to everything. I think it has a maximum split of like 48/52%. It's not huge, and you can still get some binding when turning in a parking lot, but that's plenty to account for slight differences in tire height or when turning on the street.

[Eagle]

select trac = Is the full-time t-case (242)

Command trac = is the part-time t -case (231,207)

 

As far as i know the 242 did not use any form of vacuum at all.

But he has an '86, and the '86 Selec-Trac used an NP228 or 229 transfer case that did, indeed, use vacuum to accomplish the shift.

 

It's also a big, heavy case that's massively over-sized for an XJ or MJ. And I don't think it had a locked 4WD-Hi range, I think high range was always fully differentiated, and you could only lock in in low range.

[JeepcoMJ]

ah. but if you were driving straight then on dry pavement with command trac, binding on turns wouldn't be a problem would it?

 

i have command trac but i will be using a selec-trac vacuum switch to actuate my CAD, as I have one that fits in my center console.

 

I would like a selec-trac model in my dd but i'm not gonna spend the $$ on it...i only use my 4wd when driving in extremely slippery conditions like ice, snow, rain, and mud. it doesn't see use when dry cause i don't need it :D

[Pete M]

But there will always be a slight difference between the front and rear (even if going in a perfectly straight line the whole way), no matter how close you keep the air pressures or balance the tire wear. And that slight difference will build up over time.

[87manche]

if you only use your cammand trac in very slippery conditions then it's fine.

Pavement that's not snow covered just doesn't allow enough slip.

I once forgot to take mine out of 4wd (part time light doesn't work) got onto pavement, drove a little ways, took a turn, the front tire hopped pretty violently, I thought for sure that I had just broken something.

[Oizarod115]

also the 231 is rated slightly higher than the 242 for strength, don't remember the numbers but its higher.

 

my brother had a 242 XJ and it was pretty amazing in the ice/snow... he literally stomped it in the ice (open front/rear stock height/walmart tires) and our moms friend barely hit the gas in his GT stang with a locked rear and we took off, he stayed put. (ice, not snow.)

 

same story in the rain, the difference from fulltime to 2wd was AMAZING, it felt almost irresponsible to leave it in 2wd in the rain.

 

(that case failed from being rebuilt and filled with gear oil (they take ATF) at a NAPA repair shop.)

[carnuck]

The suspension will wind up with Command trac due to the differences in tire heights and turning radius. Eventually the leafsprings in rear will twist enough to shatter the chain or something else in the case.

 

Command trac

NP207, NP231 (NP208 from full size '80 to '88, and Dana 20 '79 and older)

 

Selectrac

NP242, NP228, NP229

 

(New Process version of Quadratrac is NP219 in FSJs and NV249 in ZJs and the '73 to '79 Quadratrac is BW 1339)