So like virtually everyone else with one of these vehicles, my vacuum actuated 4 x 4 isn't working. It's been diagnosed as a faulty transfer case encoder motor AND faulty wiring to the same (above the transmission and essentially inaccessible according to a repair estimate I found in this ZR2). If it weren't for the wiring issue, I'd just put a t-case motor in it, but don't feel like wasting $120 if it's not going to work.

I'd be more than happy to just put a push pull cable in so I have 4x4, but all of the threads say that once completed, you still need to push the various buttons on the 4 button controller on the dash. Well, that part doesn't light up or function. So what does that 4 button controller do that simply engaging with the cable doesn't accomplish?

I've heard you can do an axle swap to a Bravada RF axle and basically have a full time AWD. If that works, then I would think that the cable pull would accomplish the same thing.

PS, it's a $1000 ride that I'm not going to spend a fortune on, and the only reason I need 4WD is to get to EMT calls when it's nasty out.

Thanks in advance
ZRTwice

 

The 4wd on these Blazers is WAY over complicated...

There's 4 versions (that I'm aware of) in the 4wd in the S-chassis.

The 1st I'll mention is NOT what you have if you have a ZR2, and that's the aforementioned Bravada AWD. The front diff is always engaged, there's NO selection inside the cab to go from 2wd to 4wd or 4wd low range, and the system is completely computer controlled; when slippage is detected in the rear wheels, power is sent to the front wheels.

The 2nd I'll mention is also not what you have since you mentioned you have the push buttons, but is by far the most simple, and that's the manual transfercase. Pull a level on the floor, and bam, it puts the transfercase into 4x4 high range or low range, whichever you choose. I'm not 100%, but I believe on those there's still either an electrical connection or vacuum switch on the t-case that engages the front diff via a vacuum switch, a diaphragm, and a pull cable (more on that ingenious system in the next paragraph...)

The 3rd I'll talk about is the NOTORIOUS 3 push button electronic 4x4. These have a vacuum switch on the top of the t-case that, when you push the button in the cab to engage 4wd, pulls vacuum on a solenoid under the hood mounted to the firewall, then in conjunction with electrical power applied to that solenoid, pulls vacuum on a diaphragm under the battery tray, which THEN pulls on a cable that runs down to the front diff, pulling on a sleeve inside passenger side axle shaft tube, which locks the front diff in. This system is bad about sucking transmission fluid up into the vacuum lines through the vacuum switch on the t-case... When they do, the transmission fluid wreaks havoc on the rubber lines, gets to the actuator diaphragm under the battery tray and ruins it, and in worse case scenarios gets all the way up into the vacuum lines under the dash that control the HVAC settings...

The 4th is the auto 4x4 setup, or 4 button electronic 4wd. It can function both just like the 3 button AND the Bravada AWD setup, but is fully selectable. It does NOT have the vacuum switch on top of the t-case, so a lot of the common issues associated with the 3 button 4wd are negated, but not eliminated... They too are prone to having the actuator under the battery tray rot out and stop engaging the front diff, be it just from the rubber in them being old or a battery boiling over and rotting it out...



The t-case motor is mounted on the side of the t-case, so if I were in your position I would start by crawling underneath and checking out the wiring going to it. Someone could have just ran up onto a stick and yanked on the wires or something, no telling really under you take a look... Also check all your fuses both in the driver door jamb and under the hood, and I would even go as far as seeing if you can grab a replacement 4x4 switch from a local salvage yard and pop it in place of yours. They do loose contact internally sometimes and will stop lighting up and working all together (my 4 button will intermittently stop lighting up, although it still functions as it should; most of the time a couple well placed "taps" will make the lights come back on)

 

Blazen_red_4x4 did a great job summarizing the situation with these 4wd systems.

The only thing to add is that there is also the transfer case control module (TCCM) that can fail or the connector to the TCCM can become corroded. From what you describe it might not be the problem but I thought I'd add this just for completeness.

I'm also chiming in because I wanted to encourage you to consider Blazen_red_4x4's advice to try to look at the electrical connections to the transfer case.

You did not say how your issues were diagnosed. Did a mechanic get underneath? Was an error code read? Was it someone's best guess? Even the dealer's make mistakes in diagnosing problems on these which to me is not surprising as the last 2nd gen Blazer is at least 13 years old now.

To reiterate what Blazen_red_4x4 described, there is no reason to assume your vacuum actuation is bad. The axle and the transfer case are supposed to engage at the same time but if things are not working properly, one can engage with the other not. But, if you do decide to work on it, I'd suggest replacing out the vacuum lines since they do rot and can cause headaches later when they leak. I did this on my 4-button equipped truck. The description of what I did is at the link in my .sig file below.