I'm new to the forum, signed up because I'm stumped with my sons 98 Blazer. Recently bought this back in Apr for his first vehicle. We knew it needed work and he's done 90% of the wrench turning at this point but we're stumped on his 4 wheel drive not working. His buttons appear to work for 2wd, 4H and 4L when pushed. The amber light comes on and stays lit, it doesn't flash and go back to 2wd for either 4H or 4L. We've changed out his transfer case vacuum switch and the front differential vacuum actuator under the battery. Prior to swapping those out, his vehicle appeared to be in 4H or 4L according to the dash switches.

After swapping out his transfer case vacuum switch today, he pulled out into the street (snow packed thanks to yesterdays storm), put it into 4H and gave it a quick hit of the throttle only to see the back tires spinning and the front tires just moving along like they're not engaged. Had him put it into 4L and while he was sitting at a stop, the back tires were spinning a little. A quick hit of the throttle and the back tires spun, no movement from the front ones of being engaged.

What else could we be missing? Possible vacuum leak somewhere? Wouldn't that cause the switch lights to blink and not engage the 4wd? With the KOEO, I can hear the actuator working like it's engaging in the transfer case, but it just doesn't seem like the front wheels are truly engaged.

Any help is greatly appreciated. I've done some searches on the web and the only other thing I have found so far in the TCCM, but it seems like people with TCCM issues also have the blinking amber light on the switch panel and then it goes back to 2wd. Thoughts?

Thanks
Chris

 

Welcome aboard. I am pretty new here myself. Someone will have the answer for this. It seems the lights are responding appropriately so the transfer case is engaging. You replaced the vacuum actuator that routes to the front gearbox - are you sure the connection to the cable was solid?

After that it sounds like it's gonna be something in the front gearbox locker - I don't know how that works yet...

We had my kids front box out for a lift kit a couple weeks ago and afterwards the front was not locking in. I suspected the vacuum switch connection to the cable. After a week of driving it magically fixed itself and is now working so we lucked out.

 

Yeah as far as I can tell the cable for the vacuum actuator is working correctly. It's just throwing me off because the indicator lights say its working, but driving it seems to say otherwise. We haven't jacked it up off all 4 tires yet to test it that way, that's next. My assumption is they're not driving but we'll see.

Chris

 

The indicator lights tell you that the transfer case is locking in. Not sure on a Blazer but if you look underneath on most 4WD the front drive shaft is not turning with the transfer case disengaged and will turn when engaged. I bet if you looked under when in 4WD the front shaft is turning. So what's going on is the front drive shafts are not locking in. The locking mechanism is in the front box, hence the vacuum actuator and cable.

 

Those front end actuators or the cables are notoriously bad. If you get all 4 wheels off of the ground and put it in 4WD and see if the front drive shaft spinning then odds are that the front diff isn't engaging. 9 out of 10 times it is the front diff not engaging.

 

(aJust jack up the right front wheel, leaving the other three on the ground. Start the engine and put into 4WD but leave trans in park. Verify 4WD indicator is lit steady. Can you turn the RF wheel (pretty easily) by hand. If so, the front axle is not locking in (RF axle is what it locks in for 4WD). If it does lock the RF axle, does it release it when you select 2WD?

 

Ok thanks will do. Son is at work today till 5 so will probably do it tomorrow before he goes to work. I'll get back to you guys with an update. Thanks!

Chris

 

Jacked up the front right side today, started the truck, put it in 4H and the front right wheel spins freely by hand. Double checked to make sure it was in 4H and spun it again, same result.

Chris

 

so problem is that front axle is not locking in. Do you have vacuum to the actuator during this test? Is the actuator pulling back when 4WD is selected?

 

As far as I know the actuator is working correctly with vacuum. If there wasnt vacuum, would the 4wd indicator light stay lit for push button? My next step was going to be looking for a vacuum leak but it seems it wouldn't go into 4H if there was a leak...?

Chris