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4WD not engaging

Hello guys, ive seen a few of these posts but no resolutions to my specific parameters. I have an 88’ suburban im rebuilding. I just took it off roading this weekend, and have many questions, but first the details. I have a manual gear shift and a lever shifter for the drive options ( 2H 4H N 4L in that order ) and manual locking front hubs. The type of environment was dirt, but due to all the rain it was extremely soft like sand, could dig a foot deep with my hands. Now as for my first question, i do not believe my 4WD is engaging, because when i would get stuck ( and it happened far more than i am happy with ) only my back tires would dig down Regardless of 4l or 4h.

  1. How can I diagnose/fix this? If done professionally is it costly?
  2. my lever for drive option goes to 4L no problem, and you hear a difference in the engine but as i mentioned the front two dont dig. However my 2H and 4H and right next to each other if i put the lever on 2H and drive, the lever moves down to the middle space between 2H & 4H same situation with if i put lever on 4H. Is it possible its not engaging or staying in gear? How can I diagnose/fix this? Is it a sever or costly problem?
  1. Given those comments above, my truck did great driving through anything i tried, but if i stopped even once, i would get stuck. how do you recommend preventing/getting out of this situation. When we set up camp ( after digging myself 4x ) i had to get towed onto a tarp because that was the only way i could get started without digging again. How would you guys recommend i get out/prevent the digging if i didnt have a nice friend to pull me out so many times.

I don’t see where you say you got out and locked the hubs.

  1. Take it to an independent mechanic, a driveline specialist would be preferred. Expect to spend $70-$100 for a diagnosis, then whatever it cost to fix the issue.

  2. It shouldn’t go into 4L unless the transmission is in neutral first, and even then it might put up a fight. If it goes into 4L easily whilst the vehicle in gear, then something is wrong and chances are that four wheel drive isn’t engaging.

  3. It sounds like you’re not getting four wheel drive to engage based on what you’re describing.

Things will make getting stuck more unlikely (assuming you have functioning 4WD)

  1. Proper driving technique
  2. Proper tires for the terrain
  3. Lockers, front and rear, but if you only have one, it should be on the rear axle
  4. Enough ground clearance

Due to it’s size, (wheelbase in particular) the Suburban isn’t an ideal off-road vehicle, it’s length can cause it to get hung up or high centered more easily than say something like a CJ or an early Bronco.

Most Chevy/GM’s had auto-locking hubs by 1988. However they could fail, and cause 4WD not to engage.

I’ve had several 4wd’s similar to yours. The most common issue is a failed actuator. The actuator is threaded in to the front differential. If you look at the front axle, you should see a large nut with electrical wires coming out of it. That’s the actuator. Google “88 suburban 4wd actuator” to see an example of what I’m referring to. You can unplug the electrical connectors, screw the actuator out, plug it back in, shift to 4wd and see if it extends. It should extend pretty quickly. That extension is what locks the hubs. If it extends very slowly or half way, it’s no good. If it doesn’t extend at all, test the wiring to the actuator with a test light. When in 4wd, power should be sent to the actuator. If no power is sent when in 4wd, it’s either the ball switch on top of the transfer case, or the 4wd fuse, or the wiring.

This all assumes there’s nothing wrong internally with the transfer case. Most likely, if you had a mechanical issue inside the transfer case, you’d have quite a bit of grinding going on so you’d already be aware if it was a mechanical problem.

Those 4wd actuators were notorious for failing, and GM later redesigned them. If you can ensure power is being sent to the actuator when you shift to 4wd, I’d bet money the actuator has failed. I’d bet 100 bucks. Cause that’s about the price of a new actuator. The ball switch doesn’t fail too often unless it gets dirt and mud in it from lots of off-road, and the wires should be easy to inspect. The older actuators are wax filled contraptions and just weren’t too reliable.

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friend bought a 88 chev 1500 around 1990 that had 60k miles. he got a low price based on miles so he was happy. he lived 1 mile from work and only used the truck for going to work. and he put 2k miles each yr and only 20k miles in 10yrs he owned it. and i think the 4wd acutator was the only thing that failed on it.

There’s also a Vacuum actuator that could be bad. It’s located in the engine bay.

To get into 4L i have to shift lever to side, past neutral and then allows me in 4L. As for the stuck response, i have a 4 in lift on it, so about 8-10in total clearance since i took off the step. I could use better off road tires thats for sure, but what is a lock? And I definitely have manual hub caps. I tried unlocked and locked ( i knew it was supposed to he locked ) but doubt lead me to try both and i saw no real difference. I will check the actuaor as someone else mentioned, but as for my drive lever is it a malfunction for 2H 4H or is that possibly a standard thing?

Also another comment, that sounds simple i would just like clarity. I’ve been drivinf stick shifts for about 7 years now and i am very well adapted. However this one trip alone has had more stalls then my entire drivinf career. All from trying to start rolling, from a stopped position. Is there a uniquely different style to drive stick in sand?

I’m assuming you also have larger-than-stock tires. 33’s or 35’s seem about right for that amount of lift. Did you regear it? Assuming a 3.73 stock axle ratio, with 35’s and a 350 SBC, you’d probably want 4.56’s. Also ground clearance is measured from the lowest point of the vehicle, which in your case is probably the differential on the rear axle.

It your problem is likely not the transfer case lever itself, but something that it’s connected to. a lever is a simple machine, there’s not much to it, but there are linkages/joints that the lever is connected to, it could easily be something on the the transfer case itself.

By 1988, the 1/2 ton trucks had shift on the fly / automatically locking hubs. Is this a 3/4 ton? If you have manual hubs, you don’t have the actuator, and everything I said goes out the window. In the case that you have a solid front axle and manually locking hubs, it’s either the shifter linkage, or something mechanical (hubs, axle, transfer case).

4wd engagement does not rely on vacuum, 1988 and up 1/2 ton trucks. It’s all electric (and mechanical). Pre 1988 and 3/4 ton, you may be on to something there. I do not know.

Yes its a 3/4 ton axle. Manual hubs. It was installed with the lift back in maybe 2002. Was handed down to me ( non running ) when my dad passed. Now i an rebuilding it. I believe 33’s are on it.

Hmmm…that changes it up. I thought I was going to get you 4 wheelin, but I’m more familiar with the half tons. Should be a similar setup to the old Jeep CJ’s I used to toy around with, though.

Let’s do some tests. Others can correct me if I’m wrong.

Shift to 4wd. You should not be able to turn the front driveshaft by hand if the transfer case has engaged 4wd.

Now lock the hubs, and jack up the front end, both front tires off the ground. You should not be able to rotate the right front wheel with the hubs locked in 4wd.

Let me know what you find.

As for driving in sand, if you ever start to spin, you will dig to China and be stuck. Mud tires are no good in sand. They just dig. You need wide tires in sand. And preferably a light vehicle. A 3/4 ton suburban in sand… well, they’re not really made for each other.

Also, in sand and mud, momentum is your friend. You cannot crawl through sand and mud. Crawling is for rocks. Low gears will not help, unless you don’t have enough power to keep the tires spinning.

I will have to do these tests on Saturday for im out of town until then. But i will definitely get back to you asap. 4L will work fine for 4WD I assume. I will have to check linkage in lever as a previous comment said but im not sure where to start on that

Put my trailblazer through the paces. Towing a boat to a boat launch the road was torn up to high hell for logging operations going on at the time. Saw a potential escape route, and the sand road was full of 1 foot ruts. Stopped at potential turn around walked the rest of the road to the launch and said no way. so the potential turn around was a 6 foot lane that was ok, with a 3’ drop off on the other side of the sand uphill access… Pulled in gong uphill all 4 wheels smoking sand. Then tried to maneuver a turn around backing the boat into the road. Could not do it with the skinny lane, so F it, they got big equipment if I get stuck, Boat trailer over the 3’ drop, 4 wheels smoking in the sand as the trailer frame was riding the ridge. made it down, made it out. OH THE FUN!

Maybe you could put it on a lift and see if all four wheels spin or not in 4wd mode. If they all spin, could still be something wrong as there’s no load in that test situation. But if the two front wheels don’t spin at all, definitely something wrong with the front wheel engagement.

Deep sand by the way is one of the toughest situations for a 4wd vehicle. Deep sand is the only situation I ever got partially stuck in my 4wd truck.

Yes 4 low is fine for testing. Or 4 high. I’m just trying to see if 4wd is engaging at all.

It’s entirely possible 4wd is engaging fine and you got stock in sand anyway.

i don’t think both front wheels will get powered when lifted off the ground in 4wd, unless the front differential is a limited slip or locking differential. Which is pretty uncommon for a stock rig. I think only the passenger front tire will pull.

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Sand is tough. I learned this at 17 in a 1980 CJ 5 with “buckshot” brand bias ply tires (the original “buckshots”). That Jeep was nigh unstoppable in most situations. Until I tried to pull someone else who was stuck out of sand. I instantly dug holes in the sand until the frame of the Jeep rested on the sand. In hindsight, there’s no reason my friend should’ve had his 76 Caprice down by the river anyway. Even less of a reason that I should’ve attempt pulling that big boat out with a lightweight Jeep. 4wd was useless. Live and learn!

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