Need experienced 4WD advice.
 

Hi all,
Thanks for listening.
Something is wrong with my 4WD system. I can deal with the controls just fine but Im at a bit of a loss as to how the mechanical operation of the 4WD system functions. What I really need to know is if I can remove the transfer case and possibly the front differential(and then I guess I need the front axles to come out too) and still continue driving. Fabbing up something to block the TC hole in the transmission is something id have no problem with. Once I have this stuff on the bench I can investigate and research and fix it up. I just dont have time to do it all at once since it is my transportation to work everyday. Any insights or thoughts are appreciated.

Also I read somewhere that some people put in a front end from an envoy and make it it full time 4WD. I cant seem to find anything about that on the web though, anyone here seen it done and know what it entails? Thanks again for your time.

Someone will correct me if I'm mistaken but I think that the Bravada was the vehicle with a full time front differential, not a Envoy. It has a viscous coupling and no two piece axle on the passenger side like a standard differential has. All "S" series vehiles that are 4x4 equipped use a transfer case which is attached to the transmission. You can't remove the transfer case and just block a hole and continue driving it. Your best bet is to drive it in 2wd until you can take it off the road to work on it.

There is no TC hole in the transmission. To remove a transfer case, you will need a completely different transmission and driveshaft. This is not a viable path to keep something on the road as it is major work and you end up with a total piece of junk. I would urge you to at least tell us what the vehicle is and what the problem is. Maybe we can help get you to a temp solution that will allow you to drive. If it is a second gen Blazer, we will need to know 3-button or 4-button controls.

thanks for the quick replies.

It's a 98 gmc jimmy 4wd 3button. Some time ago the tccm died. I didnt worry about as I lived in flat land. Last summer though I moved to a mountainous snowy area. Then last fall I repaired I repaired a vacuum leak and drove down the mountain. Apparently the vacuum actuator was trying to pull in but i didn't notice till i was back in town. It was making a chattering noise. Im pretty sure the slip ring and gear in the TC are gone. I think the flaky controls killed the mechanical parts.

One reason I wanted the transfer case on the bench is to figure out the control of the 4wheel Low motor. I'm done with the tccm. I will either make my own electronic controls or it will be all manual. Is there a way to make the 4wheel low gear manual? Even if i have to crawl under the vehicle to actuate it

The only thing vacuum operated in your 4WD system is locking the front axle in - nothing to do with operation of the transfer case itself. On the 3-button, there is a vacuum switch on the transfer case that is opened when the transfer case goes into 4WD. Vacuum is applied to a servo mounted underneath the battery and the servo operates a cable hooked up to the front axle (on the passenger side of the diff) and pulls on a slider that locks in the right axle so power can be transmitted through the front end. This slider can be damaged and/or be out of place and make noise. So next I have to ask if you know exactly where the noise is coming from, and if you have any other evidence that the TC is bad? Apparently this noise is there in 2WD, or you would not be so intent on doing all the work at the start of the Summer.

You may want to read this one:

https://blazerforum.com/forum/tech-a...4hi-4lo-41226/

If you're bound and determined to run the TC manually, just take the encoder motor off and use a wrench on the shaft to put it in the different positions. I don't see why an otherwise functional 3-button wouldn't work this way. Of course you have to crawl under the vehicle to do this.

Well that is good news for me. Im not afraid to get under there, Ill likely be skulking about the underside anyway installing chains.

That link is perfect If I had seen that in my initial search i might not have even posted this question. The thing WAS making the noise in 2HI but i disconnected the vacuum hose as soon as i noticed it. still it was about 40 miles of mountain driving. From the link you gave I guess what happened was the vac switch was partially pulling on the slip ring. I tried working the cable by hand and it seeemed ok but after reading that link I think maybe it is binding. TC might be fine I guess, now i just need to get a look at that slider for the front axle. Well at least I no longer feel i need to have the thing on a bench to investigate it. Thank you so much for your time in all this. Ill get under it this weekend and see what I can see.