using 4wd switch in glovebox all the time?

[ctjeepman]

My buddy is picking up a 79 j20 and the guy said that he always uses the 4wd switch in the glove compartment. Is this truck full-time 4wd? it is an automatic. The Po said not to try to put it in low range....I thought that the switch in the golve box is a vacuum switch and if you needed to put it into low range you are actually doing it trough the transfer..is this correct? If that is the case then maybe something is wrong with the transfer? ANy help will be appreciated. Thanks guys

[joe]

It's a full-time x-case. The vacuum E-drive switch in the glove box locks out the clutch cones(keeps them from turning) in the x-case. When the cones are locked out you can't drive it on a dry non-slick roads anymore or you'll cause damage to the drivetrain. A u-joint is usually the first to go but the x-case can also and will eventually. HI/LO range(if it has this option) is controled by a mechanical(non-vacuum) lever on the left side of the tunnel.
I don't know why he'd want to be in E-drive all the time unless the clutch cones are shot or maybe he isn't using the "special QT juice" which is a must on this x-case. I'd drive the rig in all modes and also do a torque bias test on the clutch cones. Put the x-case in normal mode(not in E-drive), drop the front end of the rear drive shaft, have someone sitting in it applying the brakes, put a socket and torque wrench on the yoke nut. You should be able to apply somewhere between 80-170 ft-lbs to the nut before the x-case turns. If less the cones are worn. If it'll take more torque than 170 it prolly has the wrong lubricant in it.

[Bob Barry]

I use the e-drive switch all the time to put it in part-time mode (E-drive) for off-road. Easier than waiting to get stuck and need to do it. Basically, any time a part-time 4wd truck would use 4wd is the time that a QT driver should engage E-drive.

[bvibert]

It could have been converted to part time in which case the vacum switch would engage it into 4 wheel drive. Either way you don't want to drive around with the switch set to e-drive on dry roads. Like Bob said I set mine to e-drive only when someone would use regular 4wd. If the owner said not to try and switch it into low range (small lever on tranny tunnel) then I would suspect that there is something wrong with the low range unit, if its there.