TJim <jim@ranlet.nospam.com> wrote:

> My "new" Grand Wagoneer (1990) has the "Selectrac" xfer case. According to
> the owners manual, you can use 4hi on pavement. Is there some reason why
> you shouldn't use 4hi all the time or, at least, for extended periods of
> time? I'm used to Command Trac, so I'm still learning about Selectrac.
> Thanx
> TJim
> 98TJ SE
> 90 SJ Grand Wagoneer

I've been running my '96 ZJ with Selectrac in "full time" 4WD mode for 5
years now, with no apparent problems. I think the difference in gas
mileage would be negligible and the only additional wear and tear would
be on the transfer case, since the front axles and drive shaft are
turning all the time anyway. The overhead display says I've averaged
17.7 mpg over the last 8000 or so miles (since I last zeroed it out).
I've averages 22mpg on long trips and I've always been in 4WD full time.
My ZJ has the I6 engine.

I'm no expert, though. This has just been my experience with Selectrac.

 

"Keith Rogers" <keith_rogers@chartermi.net> wrote in message
news:1fxj9m3.1c0omjh1azfus2N@66.188.59.12.bay.mi.c hartermi.net...

> I've been running my '96 ZJ with Selectrac in "full time" 4WD mode for 5
> years now, with no apparent problems. I think the difference in gas
> mileage would be negligible and the only additional wear and tear would
> be on the transfer case, since the front axles and drive shaft are
> turning all the time anyway.

With it in full time 4WD small differences in wheel size will mean the
viscous coupling will be slipping a little all the time. That is what it is
designed for, though. (Keeps the stress from breaking drivetrain parts)

A possible drawback (if you don't really need AWD) would be in a really hot
climate. The viscous coupling heats up due to friction (For the same reason
the torque converter does in the auto tranny).

It would seem that this would be considered in the design. I've never heard
of a x-fer case overheating, just a thought.

It's not like the differences in axle traction are great enough to cause a
lot of slipping. It probably heats up more when it's being used for what
it's designed for (in traction reducing weather) and the wheels are starting
to loose traction during acceleration.