GM IFS 4wd issues

[SCK5Blazer]

So the 4wd doesn't work in my 96 Tahoe, which I knew when I got it, but didn't really care since the trade involved my ragged out Civic. I'm just trying to figure out if it's going to be an easy fix or not....to be honest it will probably get the 10 bolts from the k5 when I get the tons for it so if it's costly I 'll just drive it as is for now. It's push button, sooo np243? Well it engages 4hi and 4lo, but all I get is a loud clunk and it doesn't even have the gov-lock so that combined with the bald 22" street tires can't even get it up a grassy hill...22's should be replaced with my 17's and Nito M/T's this week. There are no leaks around the cv's so is it a front diff issue? I don't see what else it could be if the tcase is engaging...and if that's the case is a swap to my Blazers np208 and 10 bolts a easy swap aside from the hole in the floor and ORD SAS kit wit X-over? Any available adapters for the 208 to 4l60e or is it going to be the same as a 700r4? I'm not a push button fan anyways so I'd prefer to swap it all in one go...granted this wiill not be right now. I'm just planning ahead and this is a daily so no massive downtime is a good thing and if swapping it all over will take too much work and just rebuilding the front diff is my best route I'll take it, I'd just like to SAS it eventually since I will have the spare parts...

 

[Fordum]

Its almost certainly the front axle shifter.
The driver side axle is engaged to the hub all the time, but the passenger side has a two piece axle with a shift collar inbetween.
Not sure on your model, but I bet it still got the heater driven shifter. Look under the front end, and you should see a cylinder with a couple of wires going into it mounted on the axle tube.

There is a fluid inside, and a heater. When you shift into 4wd, it turns on the heater, which boils the fluid.
That produces a pressure that forces that rod you see out and engages the front axle.
Usually either the wires get broken, the heater burns out, or the fluid leaks out.

Usually a new activator fixes it for a while.
Warn makes a replacement kit that removes the cylinder and puts on a cable operated shifter that you work from inside the cab like a choke cable.

Just move the knob, and it engages the front axle.

But, if the axle bushings are really worn, there can be enough misalignment of the axle ends to prevent it from engaging, but that is rare.

 

[SCK5Blazer]

I will crawl under and look tomorrow, I looked into the cable system when I had my zr2 so if that's all it is I may go that route for now...that way if we actually get the rare SC snow again this year I'll at least have a easier time getting around. I'm fairly new to 4wd all around...but is it similar to the vacuum operated system in the s10's or is what you are talking about totally different and a fullsize only thing...I actually understand the SFA better than IFS so I'm still trying to learn both, but sfa seems alot less complicated.

 

[Fordum]

Basically its the same thing as the vacuum system. They just do it electrically instead off with a vacuum actuator.

I have helped put two of the cable systems on, and they seem to work good. I don't think that I have ridden in one with it on yet, but the folks whose trucks we put them on all liked them.

Its 1:30, so don't depend on everything I say after midnight, but it seems to me that one thing I did not like about it was that it worked backward from the way I would have wanted.
You pushed in the knob to actuate it, and pulled it out to disengage it.

But, if so, that was just a minor quibble, and it might not even be the way it works. I have had a really rough past couple of days, and Saturday was a particularly stressful one, so I am headed to bed.......

 

[SCK5Blazer]

well I've had a drunken past couple nights so if my typing is ledgible I'm suprised I don't really care if it's push, pull, or coined fed at this point if it works more reliable than stock. I never had issues with the vacuum system in my zr2, but after all I heard it was on the to do list, I just got rid of it before getting to it So if it's the same genreal idea it seems like it's pretty easy solution....I'm guessing if the front diff was shot it'd be noticable so it sounds like this may be the problem...I will know more after getting under it tomorrow.

 

[owenst7]

The front diff spins in 2x4 (theres no hub disconnect), so you'd know if there was a problem there.

It's going to be either the shift motor on the side of the tcase or on the front of the diff. check for current on the harness whem shifting. Honestly, the actuators are not that expensive. My DD is a 96 with the exact same system. Had it since 96 and it has 191k on it, the first 165k was in alaska where it got shifted a lot. I had it fixed under warranty at around 20k and our friend that was the shop manager said they changed the design after almost recalling it. I just now starting to have issues with that one after 170k miles.

I'm all for simple, mechanical connections, but I honestly can't complain about the reliability here, nor can I justify the effort in changing to a different setup. I would probably do it if I were hard on it our in a lot more water (it has forded quite a few rivers in ak though). I just don't see the point on a street rig.

It's right on the front, couldn't be any easier to get to. Very easy to mess with or replace.

 

[AJMBLAZER]

With the loud clunk...does the truck move fine? I'd check and see if the t-case is sending power to the front axle.

If it is then like everyone has said my money is on the front actuator.

I had a 4x4PosiLOk on my '92 and it did work great after a bunch of fiddling to get it set right. More my fault than anything else.
However if it's just a DD I'd say just hit up GM for the newer design electric actuator. If your truck has the older vacuum setup they have a little setup that replaces it entirely with the electric version.

 

[89k5350]

the 4wd actuator is the most common thing to go on those things