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Discussion Starter · #1 · (Edited)
I have a question regarding the 4x4 function on a 2002 trailblazer. The problem I am having is that it is extremely hard to get my trailblazer in four wheel drive. When I am stopped, I turn the knob to 4hi, and I can hear something making noise near the transmission, then the light switches to 4hi, but the vehilce does not actually go in 4hi. But here is the catch, after about 20 times of switching from 4hi to 2wd, then 2wd to 4hi, the 4hi feature finally engages and works fine. I got stuck in a field today and it took me about 20 minutes to get out because I could not get 4hi or 4lo to engage...after 20 minutes, it finally engaged and I got out of the field. Why does it take several times switching from 4hi to 2wd / 2wd to 4hi before the 4hi feature actually engages itself?

The service 4x4 light has never came on

When switching from 2wd to a4wd, I hear the two different noises under the vehicle.
 

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Well, if it eventually goes into gear, that is the good news.

I would change the fluid in the transfer case, to start.

If your still having problems, it could be the motor in the transfer case that performs the shifting function.

There is a 3rd possibility, there is an axle disconnect motor in the right front axle, your problem could be here.

Numerous threads, about the topic, on the site. A little search is a good thing.
 

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you didn't mention it but are you switching 4WD with the gear select in neutral?
 

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:iagree: We only need neutral for in/out of 4LO.
 

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Speaking of only needing neutral for 4LOW, does anyone know what the top speed is for shifting in / out of 4wd? For instance im sure you cant be cruising down the highway going 85mph in 2wd and just click it into 4wd High and things will be fine, isnt it something like 35mph or less is a safe bet for switching in and out of true 4wd modes?
 

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Discussion Starter · #7 ·
ok, so heres what ive done so far. Ive disconnected the battery and took the #8 fuse out. Ive also changed the tranfer case fluid using the gm recommended auto-trak 2 fluid. Still no 4wd. I have put the trailblazer up on jack stands and tried to get the vehicle into four wheel drive several times, but nothing. I guess I was lucky to get out of the field the other day. Anyway, so where do I go from this point? When I switch from 2wd to 4wd, I can hear the tranfer case shift motor making noise, the light switches to 4wd, but the vehicle remains in 2wd. My question...Can the transfer case shift motor be bad even if it is making noise or would it not make any noise if it were faulty? Im thinking about changing the motor, but I would like to make sure that this is where the problem is coming from. any thoughts...thanks
 

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Discussion Starter · #8 ·
ok, after reading a few more posts, It is most certain my problem is either the shift motor or the front axle acuator...But how do I know which one is faulty? I will have to double check, but I believe both are making noise when I engage 4wd. please help
 

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ok, after reading a few more posts, It is most certain my problem is either the shift motor or the front axle acuator...But how do I know which one is faulty? I will have to double check, but I believe both are making noise when I engage 4wd. please help
The front axle actuator should be easy to test if your up in the air.
Have someone hold the left front wheel and you turn the right wheel in 2wd, get a feel for the turning resistance and look at what is turning.
Shift to 4hi. Turn the wheel, as before, and compare the feel and what is turning.
If things are the same, the actuator is not engaging.
 

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Discussion Starter · #10 ·
Can the actuator not be engaging the front axle, even if it is making noise when I shift in and out of 4wd? How hard is it to replace the actuator?
 

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Discussion Starter · #12 ·
so I took the actuator off today after reading Rodies post on the actuator repair. after i unbolted it, I tested it to make sure it was doing what it was supposed to...it was. I then took it apart and cleaned the grease off of the fingers and the metal strips. put everthing back together (tested it before i bolted it back on) and still NO 4WD! Can someone please point me in the right direction? WHERES RODIE AT?:hissy:
 

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Discussion Starter · #13 ·
I also did that test that you mentioned RayVoy. The resistance felt the same in both 2wd and 4hi. Since I have already cleaned the actuator, and I know it is working properly, do I most certain have a problem with the internal parts of the front differential? How would I check or is there any test I can do to know for sure? Any thoughts?
 

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Ok, these things are pretty simply.
Think of it this way. Your stopped, engine running and in PARK (and in your case, up on jack stands).
When your in 2wd, the rear driveshaft will not turn because it is connected to the transmission and the tranny is in PARK. However, the front driveshaft is free to turn and it should, with a little resistance.
Now, shift to 4HI. As before, the rear driveshaft will not turn. Now, because your in 4 wd, the front driveshaft is connected to the rear driveshaft and the front will not turn.
That is a quick test for the transfer case, if things happen as described above, the transfer case seems to be working ok.
OK, front diff.
It is an "open" type of diff. This means, that only one wheel will receive power from the driveshaft. Unfortunately, it is the wheel with the least resistance (and of course, if the actuator is not working that will be the wheel with the least resistance).
So, still in 4hi (as above), one front wheel should be connected to the driveshaft and hard to turn; the other will not be connected and will be easier to turn.
Ok, now have someone hold one front wheel while you turn the other one. This should/might cause the diff to flip the power to the other wheel (no guarantee here, it is difficult to do).
 

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Discussion Starter · #15 ·
with the vehicle up on jack stands and the transmission in park, when I engage 4hi the back wheels will not spin but the front wheels spin freely (with little resistance). So is the problem definately with the transfer case? could it be the transfer case shift motor? :confused:
 

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Discussion Starter · #16 ·
does the transfer case shift motor supposed to lock the front driveshaft when engaging to 4hi? if so, is that where my problems are???...even though the shift motor is making its normal noise when shifting between 2hi, awd, 4hi, and 4lo?
 

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with the vehicle up on jack stands and the transmission in park, when I engage 4hi the back wheels will not spin but the front wheels spin freely (with little resistance). So is the problem definately with the transfer case? could it be the transfer case shift motor? :confused:
Hold on.......... it is the front driveshaft that will test the transfer case.

does the transfer case shift motor supposed to lock the front driveshaft when engaging to 4hi? if so, is that where my problems are???...even though the shift motor is making its normal noise when shifting between 2hi, awd, 4hi, and 4lo?
When you shift to 4hi, or 4 low, the encoder motor in the transfer case will operate clutches that will engage the front driveshaft. At this time, the front driveshaft is connected to the rear driveshaft.
In park, neither one will turn. Shift the tranny to neutral and then turning either shift (by hand) will cause the other one to turn with it.

Note: this is not so when in 4AWD (but that is a topic for an other day).
 

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Discussion Starter · #18 ·
With the vehicle up on jack stands and the transmission in park with engine running, the rear driveshaft will spin but the front will not. When engaging 4hi, when I spin the front driveshaft the rear driveshaft spins as well, indicating that the transfer case is operating correctly? right? When engaged in 4hi, the passengers side wheel will rotated very easilly by hand. The drivers side wheel will also rotate, but i did observe a little resistance with this wheel. What next RoyVoy? Thanks for the help.
 

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Well............. I think you are saying, that the transmission was in neutral.

If it was in park, the rear driveshaft should not turn.

The part about being in 4hi and the turning of the front shaft causing the rear shaft to turn, at least shows that the clutch is doing it's job.

This thing is designed to then signal the transfer case control module TCCM that it is in the desired gear position. The TCCM then does 2 things.
1- ooperates a lock in the transfer case to lock the shift motor into the position selected.
2- the 2nd thing the TCCM does, is to send a signal to the front axle engaging the disconnect/connect motor.

You need to ensure the signal is being sent, received and then operating the front axle motor (the one you took apart).

Can you hear the axle motor operating?

BTW, things should operate without the engine running, you only need the key turned to the "run" position.
 

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Discussion Starter · #20 ·
Right, the tranny was in nuetral when I observed both driveshafts turning in 4hi...so that means the transfer case is doing its job as well as the shift motor i am assuming. I did unbolt the actuator and switched between 4hi and 2hi several times to ensure that it was working properly...which it was. I also took it apart and cleaned the grease off the fingers as Rodie described in his post. After reassembling it, I checked it again to make sure it was working, before I bolted it back on...which it was. any other suggestions?
 
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