4x4 working?

In the past, I've tested 4x4s by locking in, then turning lock to lock while slowly moving forward on loose ground. Then I could feel the front tires
grabbing as they turned on different radius.
I test drove a 90 GMC today, but didn't feel any grabbing when I used the above approach. So I tried goosing it in loose gravel while in reverse / 4 low. Didn't see or feel any signs that either front tire had spun even though the back did.
Sound like it's not working?
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wrote:

isn't engaging because most likely the actuator crapped out.
-Bret
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Yep, the light came on. Any idea what else could it be?
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One more bit of info... automatic hubs.
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The light coming on doesn't mean a damn thing when trying to diagnose things like that. That I know for sure, but not anymore to help with your situation. I am sure someone else here with even more knowledge of 4X4's will step in and help. Hope so anyways. Good luck.

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wrote:

Actually it means alot. on an 88-97 IFS truck, 99% of the time the actuator fails, which prevents the 4wd from operating. the switch that turns the light on is in the axle and only lights if the CAD splines are fully engaged, it's NOT actuated by the shifter.
-Bret

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Okay, I don't even recall a light. Didn't bother telling before because it sounded like it didn't matter.
What I remember was a drivetrain diagram next to the shifter that had clear plastic in it... and when you moved the shifter orange plastic underneath moved over the front wheels indicating that all four were engaged. Could be wrong, but does that type of indicator sound familiar to anyone?
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wrote:

what you're looking for is a "4X4" and the front axle/ driveshaft to light up... if they light up, the axle is engaged. my bud's got a '90 k1500 and his floor console is exactly the same as mine. if it lights up and there's no horrific metallic banging, grinding, etc noises, you *should* have 4wd, the NP241 is a pretty strong box. I have only heard of one xfer case failure (in my experience, and I deal with alot of trucks) due to the guy yanking the lever when the rears were spinning at about 30mph... sent the chain out through the side of the case.
hth, Bret
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Well, I've got a 95 Blazer FWD where the lights work fine, and so does the actuator, but the front wheel drive is NOT engaging....so something in your explanation is wrong.
Jack up the front right wheel; put on parking brake; spin wheel while you have someone press 4 hi button (engine running, of course). If wheel locks up and you cant spin it by hand, 4wd is engaged...otherwise, it's not.

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The S series vehicle are different in how 4x4 is engaged

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wrote:

so the truck is a 90 3500 crew cab? if it's not, it has a central axle disconnect system, not hubs. the IFS CAD setup has an extremely failure prone thermolinear actuator in the front axle.
-Bret
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Sorry, didn't realize that. It's just a 1500.
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Something that I noticed when I bought my 91 Silverado is that (and someone mentioned it another reply) the actuator is thermal. Meaning if you don't give it a few seconds (much longer in cold weather) to heat up it will not engage. You were in 4 Low, and that should have spun all the tires if the actuator had heated up and engaged. At least it does for me.
Every once in awhile it seems to take a little bit to heat up even on a warm day. In 4 High, I sometimes have to ride the brakes a little to trick the front wheels into locking in if I need them...

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If you have a 1990 F/S Jimmy then your test should have done it. Either the hubs aren't working or the front drive shaft isn't there would be my guess. Allot of people believe that you need to pull the shaft to get good gas mileage (left over from the NP203, a full-time transfer case). You have an NP241 transfer case BTW. I have some stock manual hubs and a stock front drive shaft if you find either of these components lacking. I'm in NH btw.
~KJ/TLGM

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