4x4 not engaging on 2002 Trailblazer

[eman]

I'm hoping some people could help me diagnose an intermittent working 4x4 issue. Sometimes it works and sometimes it doesn't.
Everything appears fine (no codes or service lights and the switch lights appear to be operating normally) but am not getting either 4AWD, 4Hi or 4lo to engage as of right now.
Currently, I have all 4's up on jack stands while I'm trying to diagnose the problem and I just replaced the transfer case encoder motor at the diagnosis of the mechanic (did by myself to save $ from their non-certain root cause of the issue). However, that did not resolve my issue as i was hoping and 4x4 decides on it's own when it wants to work which it isn't now.

I've gone through the diagnosis walkthrough (http://gmtnation.com/f79/4wd-not-working-step-inside-107/) but still have questions/thoughts:
When I got it back from the mechanic last week the 4x4 was working again and I noticed they disconnected the battery for some other work. Could the battery disconnect possibly be a clue that the TCCM is the issue which seems to be a problem in the 2002's? I've tried the fuse pulling in the walk through to no avail. I would think that if it was the TCCM it would be throwing a code, is my thinking correct before I eliminate the TCCM as the root cause?

With all 4 wheels in the air and switch in 4Hi, I cannot get the front drive shaft to turn with either front wheel. Does the opposite wheel have to be on the ground for this test?
In 4Hi each front wheel moves freely but does not move the opposite wheel, which I'm not really sure if is supposed to or not?

I want to be more certain if my root problem is the TCCM, Transfer case or the front axle disconnect or something else before I start taking things appear.
Any help would be greatly appreciated.
Thanks...

 

[GCTB1289]

how many miles are on your truck? what were you doing when it stopped working? while you have it up check the motor while you are changing it from 2HI - 4AWD - 4HI - 4LO
the fact that the front drive shaft won't turn means it is most likely either the switch, motor, or TCCM.
luckily mine has not crapped out on me yet. but i did have to replace the whole front differential.

 

[eman]

Thanks for the reply. It's been acting like this for a while, nothing specific that lead to the issues I'm having
145,000 miles on truck, the switch was replaced about 3 or 4 years ago as it shorted out on me. I don't recall the TCCM ever being replaced.
I just replaced the encoder motor and it appears to be functioning correctly as I can hear it switching between 2wd and 4wd, yet still no spinning wheels in 4x4 mode.
I was thinking if it was the TCCM then I wouldn't even hear the encoder motor switching over or the switch would be malfunctioning.

Is there a way of manually testing the T-case by leaving the encoder motor plugged in but handing in the air and then manually spinning the spined piston (that goes into the encoder motor)? Following the walkthrough is leading me to think it's a Front Axle Disconnect failure but I don't seem to have too much play in the front right (passenger) axle so maybe an internal failure of the fork? I just want to be more certain before I take on this project...

 

[linneje]

Thanks for the reply. It's been acting like this for a while, nothing specific that lead to the issues I'm having
145,000 miles on truck, the switch was replaced about 3 or 4 years ago as it shorted out on me. I don't recall the TCCM ever being replaced.
I just replaced the encoder motor and it appears to be functioning correctly as I can hear it switching between 2wd and 4wd, yet still no spinning wheels in 4x4 mode.
I was thinking if it was the TCCM then I wouldn't even hear the encoder motor switching over or the switch would be malfunctioning.

Is there a way of manually testing the T-case by leaving the encoder motor plugged in but handing in the air and then manually spinning the spined piston (that goes into the encoder motor)? Following the walkthrough is leading me to think it's a Front Axle Disconnect failure but I don't seem to have too much play in the front right (passenger) axle so maybe an internal failure of the fork? I just want to be more certain before I take on this project...

Now that I have read your post, it is your splined disconnect. If you ar in 4wd and you can't get the opposite front wheel to turn when you spin the front wheel, your two front half axles are not joined. This is the job of that gear case (called the splined disconnect on these forums). Get that right tire and axle out and then take the gear box off and check inside. Must be one or more parts broken there.

 

[eman]

Ok, thanks for your help, time to start dismantling. How often do the actuators go bad, I'm wondering if I should replace or dismantle and clean while I have it off. I saw roadie's archived post on the OS about how to open and clean it so that may come jn handy.. Thanks

 

[eman]

Wow, bearings are absolutely shot!! The edge of the bearing house was sheered off lying on a part of the frame of the truck with some of the bearing
Thanks for the help in the diagnosis, now to order the parts and tear apart the disconnect for the new parts. I'm guessing the gears are fine but the washers, seals, bearings and fork should be replaced while I have it open? Don't really want to have to do this anytime soon again...

So as I was trying to remove the CV Axle but it's stuck on the disconnect. So I tried to remove them together but the disconnect is also stuck to the intermediate shaft going through the oil pan? I can pull out the disconnect but it's stuck with both shafts on it and I can't seem to get the angle to get all 3 pieces off as one unit, though it was late so i gave up for the night.
Is that supposed to happen or does this mean I have some other issue going on over on the other side of the intermediate shaft (on the differential side of the truck)?
Sorry for the noob questions as this is my first 4x4 diy job.

thanks for all the help!

 

[The_Roadie]

Not much time for a longer reply now, but do you have the disconnect article from Offroadtb.com?

If you need too many parts, you might as well buy an entire new aftermarket ATP assembly off Amazon for $500.

 

[linneje]

Wow, bearings are absolutely shot!! The edge of the bearing house was sheered off lying on a part of the frame of the truck with some of the bearing
Thanks for the help in the diagnosis, now to order the parts and tear apart the disconnect for the new parts. I'm guessing the gears are fine but the washers, seals, bearings and fork should be replaced while I have it open? Don't really want to have to do this anytime soon again...

So as I was trying to remove the CV Axle but it's stuck on the disconnect. So I tried to remove them together but the disconnect is also stuck to the intermediate shaft going through the oil pan? I can pull out the disconnect but it's stuck with both shafts on it and I can't seem to get the angle to get all 3 pieces off as one unit, though it was late so i gave up for the night.
Is that supposed to happen or does this mean I have some other issue going on over on the other side of the intermediate shaft (on the differential side of the truck)?
Sorry for the noob questions as this is my first 4x4 diy job.

thanks for all the help!

When you open it up, if it doesn't look worn it should be OK. Sorry that it is stuck, that can happen especially if you have a lot of corrosion or are in places where they use a lot of salt on the roads in winter. Yes, some people have removed the disconnect and axle as a whole. I used a slide hammer to get it off.
Some have left the axle connected to the tripod arm (put the nut back on to hold it in place) and then give the tripod arm a firm rap or two at the bottom with a rubber mallet (or block of wood and a sledge). I think you may have to get creative here. Let us know how it goes.

 

[eman]

Thanks for all of the replies. Yep, I have the article of how to rebuild (Offroadtb.com Front Axle 4WD Disconnect) which is well written and a god-send in this situation.
I just wasn't sure if that is common that the intermediate shaft comes out with the disconnect assembly, glad to hear that it's not unusual as I don't want to get into fixing a diff issue too!
Thanks for all the help and input!
Time to get creative tonight to get them disconnected from each other!

 

[eman]

Here's and update for anyone that's interested:
So this last Saturday I spent most of the day messing around trying to fix this dang thing. I first rebuild the disconnect assembly adding new bearings, seals and washers (minus one washer closest to the oil pan that has two tabs on it). When I opened up the assembly I noticed there were significant stress cracking around the assembly, the 4 pins on one side of the case were sheered off and the new washers looked significantly different than the new ones. The old center washer had a large center diameter that essentially appears to allowed the axle and intermediate shaft to make contact with each other. The old large washer (with the odd sides) was not straight (in a slight v shape) and the outer sides of the washer were closer to the inside gears. The other washer with the two tabs was very thin and worn oddly.

Somewhere I messed up in ordering the washers and ordered two new large washers (ordered parts from multiple places) and didn't get a new washers with the small tabs. Once I got the new bearings, seals and washers installed (except for the old one with two tabs) tested the assembly in my hands and it worked fine each time. However, once I got it installed onto the truck and the CV axle installed I would test it again by using the actuator and hand and it would always fail to engage. After many attempts of uninstalling, opening up and reinstalling, I installed the second new large washer over the old washer with two tabs on it. Essentially, this pushed the two gears a little closer together so the gears would have less play in the assembly.

With this other washer installed it worked once I tested one the truck by hand and actuator and while going for a short test drive around town. However, when I tested my 4x4 in the snow at the mt it engaged once or twice at the beginning and then would not engage again (yea I was switching in and out to see if it was truly fixed). I'm thinking that the assembly housing is allowing the axles to flex a little in the housing, which is causing the gears to not align perfectly for the collar to slide over both gears and engage the 4x4. As I mentioned before there was significant stress cracks in the housing and around the lip that goes into the oil pan. Either way, at this point I ordered a whole new disconnect assembly so I can either finally get the 4x4 running on demand or rule out the disconnect assembly as the culprit and start looking elsewhere.

I'm hoping iit's not the anything to do wtih the front differential or something else. TCase fluid looks good/clean and was just changed about 15K miles ago. I thought I had the mechanic change the font diff fluid last year but couldn't find my records of it. I couldn't even get the differential fill plug out to check the fluid level and cleanliness of it. Nothing will budge it, not even a 2.5 ft pipe over my breaker bar or my air gun after using PB Blaster for a few days on it. How the heck to people get this plugs out without rounding the bolt head?

I'll update on if the new disconnect assembly solves the issue or not once I get it installed.

 

[Matt]

How the heck to people get this plugs out without rounding the bolt head?

One word...heat. Try heating the plug up with a hand torch first.

 

[eman]

So the new disconnect assembly works great and 4x4 is engaging on demand again. I'm still thinking that the old assembly case was allowing a slight flex that was causing gears to not line up so the collar could not engage both gears.
I got the differential plug off by torching it for 5 minutes or so and changed fluid. It was a little dirty and had some metal tinting (no shavings though). I'm thinking it had around 30k miles on it. I can't believe that they recommend changing the diff fluid after 100k miles. I wouldn't want to leave the diff fluid in for nearly that long...

 

[Wooluf1952]

So the new disconnect assembly works great and 4x4 is engaging on demand again. I'm still thinking that the old assembly case was allowing a slight flex that was causing gears to not line up so the collar could not engage both gears.
I got the differential plug off by torching it for 5 minutes or so and changed fluid. It was a little dirty and had some metal tinting (no shavings though). I'm thinking it had around 30k miles on it. I can't believe that they recommend changing the diff fluid after 100k miles. I wouldn't want to leave the diff fluid in for nearly that long...

What's even stranger is they don't call for a fluid change, just to check the fluid level and add more if it's low.

 

[The_Roadie]

I wouldn't want to leave the diff fluid in for nearly that long...

Yet some numbnuts drive 250K miles without touching the transfer case or the diff fluids and live to tell about it.