94 Tahoe LT "W" vin.

So, I've been troubleshooting my 4 wheel drive the past few weeks. I traced the problem to the actuator cable. When replacing the cable, I found that the end of the cable was broken off in the differential. I pulled it out and installed the new cable. 4 wheel drive still didn't work. What was strange is that when I heard people talking about a bladder or a diaphragm I was baffled. Mine didn't look like it had one. I disconnected the vaccum to the actuator (vehicle parked, in 2wd, cable disconnected) and the actuator suddenly shot out about an inch. I then knew what I'd heard about the diaphragm. Being that it would engage and disengage when connecting vaccuum, I figured that the actuator was good.I heard that sometimes if the 4wd system hasn't been operated for a long time, you should try randomly switching in and out of 4 wheel drive over a day or two and try and free up all of the parts. I was driving home between 20-30 mph, and hit the 4 hi button... CRASH!! What sounded like my transfer case began to grind like crazy. I hurried and shifted into neutral to try and salvage my hardware, and it dropped into 4 lo. I stopped, put it in neutral, and switched into 4 hi. Light worked properly, still no 4 wheel drive. Then I tried to switch out of 4wd, and it blinked a few times and stayed in 4 hi, still no power to front axle. I tried it a few more times and it finally popped out of 4 hi mode. Because i'm dumb, I put it back in 4 hi and it got stuck again. I kept pushing the button and it would drop into 4 lo about 1/10 times that I pushed the button. Long story; but, the end is that, I'm curious if it could be the vaccuum switch on the t-case causing these problems? If I am in fact getting vaccuum to the actuator, could the switch still be causing my front axle to not engage? Thanks guys, your help has gotten me this far; but, search doesn't turn up alot for this specific problem.

 

There are some pretty serious problems if the 4wd system is dropping into 4LO while you are moving. There are checks and balances in the TCCM what should prevent the engagement of 4LO when not in park or neutral and the speed is not in excess of 5mph. Are you sure that it was dropping to 4LO or is it possible that the grinding noise was from the engagement of the front axle? Are you sure that you have the same gear ratio in the front and rear differentials?

 

The light for 4 lo came on, and the t-case sounded like it was grinding pretty hard. I didn't try to drive in 4 lo, so I'm not sure if it was actually in; but, Later when I was stopped and it would go into 4 lo when i pushed 4 hi, it definately engaged the 4 lo in the t-case. Still no power to my front axle though. very strange...

I'm not sure if they're the same being that Ibought it used. My impression is that the guy i bought it from didn'tmodify the truck, or fix the stuff that went out. I've got a long list of things to fix; but, winter snow presses me to fix the 4wd and the heater core first.