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GMC K-1500 4WD FAILURE


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dinosaur
New User

Mar 18, 2007, 12:19 PM

Post #1 of 5 (2843 views)
GMC K-1500 4WD FAILURE Sign In

I need advice from anyone with 4wd experience on GMC trucks.

I own a 1990 Sierra 1500 long-bed king cab with 4-wheel drive. It's got the 5.1 litre (350CI) engine, with an automatic transmission (3-speed + OD + 'lockout').

The 4WD has always worked well, and it was working two days ago when I took the truck to the dealer to have the wiper motor changed out. Roads were dry Friday night when I drove home so I didn't use 4wd; Saturday I never left my house, but it snowed 6 inches overnight so this morning when I left to do my shopping I shifted it in 4WD (hi range) as usual (this series has a mechanical shifter on the floor; it does not have locking hubs).

When I got to the first hill, I found out the 4wd was not working at all. I spun and struggled to the top of the hill and then stopped; shifted out and back into 4wd hi, and still got nothing. I then tried 4wd LOW-range, felt the usual grind of the gears as I got it in...but still had no 4wd. And it seemed to me the low-range gearset wasn't really engaged (Low range on this series is very low; first gear is a real crawler.) I am not completely sure about the low-range not working, though.

There was no unusual noise, and no indication of problems last time I used 4wd, and there appears to be nothing hanging or disconntected under the truck (although with the slush on the roads I could not crawl completely under the truck to see everything; I don't have a garage at home, either).

The linkage for the 4wd shifter has come unattached once before (after a badly done transmission replacement), so I know where it is, how to fix that, and what it feels like when it comes loose. That is not the case this time. The shifter feels 100% normal when operated; but the front wheels just won't drive.

I never use a mix of old and new or different size/tread tires on the vehicle, either. It always runs 4 identical AT tires. And I never use 4wd on dry roads for more than a few feet. I only use it in slippery snow or mud conditions or on steep dirt roads where I need the extra traction to climb or go downhill safely under compression.

What are the likely causes of this problem?

Dinosaur


(This post was edited by dinosaur on Mar 18, 2007, 12:24 PM)


DanD
Veteran / Moderator
DanD profile image

Mar 18, 2007, 3:40 PM

Post #2 of 5 (2835 views)
Re: GMC K-1500 4WD FAILURE Sign In

There an electric actuator motor on the front differential’s right side tube that’s suppose to automatically lock the front axle to tranfer power to the wheels after shifting into 4 wheel drive.
Mechanically you shift the 4 wheel drive transfer case but electrically the axles are shifted. This actuator/solenoid is known for failing and could be why you’re having this problem?
Dan.

Canadian "EH"






dinosaur
New User

Mar 18, 2007, 8:59 PM

Post #3 of 5 (2832 views)
Re: GMC K-1500 4WD FAILURE Sign In

Thanks for that information; it makes me worry less about what this might cost. This old truck has had a long history of minor electrical glitches; maybe this will turn out to be another one of them.

I don't suppose there's any way a mechanic replacing the windshield wiper motor could have provoked this problem without realising it? Say cutting a wire or shorting something out? The truck was in the shop Friday for that, and the problem surfaced immediately afterwards.

BTW, nice flag. Me too.


dinosaur
New User

Mar 20, 2007, 6:55 PM

Post #4 of 5 (2829 views)
Re: GMC K-1500 4WD FAILURE Sign In

DanD,

Thanks again for your input. I checked the fuse panel and found the 25A fuse for the 4WD had been blown. Replacing that solved the problem, for a cost of less than a dollar and a trip to Canadian Tire to buy some 25-amp fuses (the only size I didn't have in the glove box). Man, what a relief.

I looked at the new wiper-motor install while I was at it, and found that, sure enough, they'd installed a high-end non-OEM motor and had had to splice into the wiring harness manually to hook it up, as the connectors didn't match. Betcha a big Tim Horton's double-double they shorted something while they were in there. Duh.

Ran into the owner of the dealership today while I was at my job, and teased him about it, too. Gotta get back that 72 cents somehow....

dinosaur


DanD
Veteran / Moderator
DanD profile image

Mar 21, 2007, 4:55 AM

Post #5 of 5 (2828 views)
Re: GMC K-1500 4WD FAILURE Sign In

Thanks for posting the fix.
I’ll pass on the Timmys though my shop is completely surrounded by their stores; the sad part is I don’t like coffee unless there’s a good shot of Baileys in it. LOL
Dan.

Canadian "EH"










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