Need 4x4 help. not fully engaging - Blazer Forum - Chevy Blazer Forums


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Old 01-10-2017, 06:48 PM
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Default Need 4x4 help. not fully engaging

Hello guys. My 2002 4 door LS blazer isn't going into 4x4. I worked on it Saturday at the shop . I put in a new actuator in under the battery, new cable and vaccum line solenoid on the transfer case. while on the lift I had my buddy start it and put it in 4x4 hi and the front driveshaft was turning. I had him shift it back into 2 hi and the driveshaft stops turning , so I know the tccm and encoder motor is working . When I had the cable off the front diff I could turn the driveshaft slightly and pull the front diff into 4x4 and watch the wheels spin as I turned the driveshaft . After doing this work, with the battery out ,I hooked up the jumpbox and started the truck and watched the actuator pull in about 3/8-1/2 inch . But I still don't have 4x4 when out driving . Please steer me in a good direction and help.

Last edited by Eric Ferguson; 01-10-2017 at 06:53 PM. Reason: miss spelling
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Old 01-10-2017, 06:52 PM
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Also guys , the switch for 2hi, 4hi and 4lo always lights up in all functions and works correctly. And as I was saying I can here the encoder motor shifting as it should and the relay or switch in the tccm functioning everytime I work the 4x4.
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Old 01-10-2017, 10:20 PM
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When I had the cable off the front diff I could turn the driveshaft slightly and pull the front diff into 4x4 and watch the wheels spin as I turned the driveshaft .

This is what you just typed. Which end of the cable was off? If it was the actuator end and you pulled on it and turned the drive shaft, it should turn the right front wheel.

The easiest way to do this to jack up the right front wheel, start the engine in PARK, shift into 4wd hi, then try to rotate the right front wheel.

It should move a little in each direction before stopping. If it does this, the 4wd is working, if the wheel does not lock, you have a problem with the actuator, or front axle disconnect system.

The following can be done without the engine running , transmission in any position and the transfer case in any position. This just checks whether the front axle locks.


You can eliminate the actuator by just disconnecting the cable from it to the front axle disconnect then pull it by hand and see if the right front wheel locks. If it does then the actuator is not getting enough vacuum to engage it or the actuator itself if defective.

If it doesn't then the front axle disconnect is at fault or cable failure.

Hope this helps...

Bill
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Old 01-10-2017, 10:59 PM
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Bill, I had the cable off the actuator end when I was able to pull the front diff in while turning the front driveshaft slightly . And yes the front wheel turned . And I had all 4 wheels off the ground about 18inches because I had it on the shop lift . I installed a new actuator under the battery , new cable , and transfer case vacuum switch . And I could watch the actuator pull the cable in 3/8 to 1/2 inch .So I see it's getting vacuum. I can put it in 4 hi and watch the front driveshaft even turn and stop with the brake pedal. But it still won't all work together . When I tighten the cable into the diff side I tightened it all the way in . Should I ran it back out so , to adjust the pull of the cable some? Does it have any adjustment this way?
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Old 01-11-2017, 08:41 AM
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There is no adjustment on the cable. When it is screwed into the housing, it is fixed. Just like when you attach it to the actuator.

All you are doing is seeing if the right front axle is locked in. You don't need to turn the front driveshaft. All you need is the right front wheel up off the ground.

When you pull on the cable to simulate the actuator you are pulling the shift fork in the front axle disconnect. This is what locks in the right front axle shaft. You should have little movement in either direction before it should stop. That proves the shift fork has slid the sleeve from the drive side to the driven side of the axle shaft.

If that works by hand, then either the actuator is bad, ie tear in diaphragm , or the actuator is not getting enough vacuum via the transfer case switch to pull the diaphragm in far enough to pull the cable far enough to lock in the right front axle shaft.

Hope this helps..

Bill
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Old 01-11-2017, 04:33 PM
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Okaussie , I do appreciate you posting trying to help me . Whats got me stumped is on Saturday I put a new actuator , cable and transfer case switch . And while I had it on the lift I hooked the battery pack to it and watched the actuator pull in around 1/2 . So I must have vacuum or it wouldn't be pulling the diaphragm in. Does anyone know about how much the shift fork needs pulled in to fully engage?
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Old 01-11-2017, 08:39 PM
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I believe it is between 12 to 15 inches of vacuum.
If you don't have enough vacuum, it will only pull the cable slightly.
Check the vacuum coming off the intake manifold at idle. That should be close as to what you need at the actuator. Then measure the vacuum at the actuator with the transfer case in 4wd. It should be pretty much the same.

If not, you have a crimp in the vacuum line or a leak.

Hope this helps..

Bill
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Old 01-12-2017, 06:50 AM
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Quote:
Originally Posted by Eric Ferguson View Post
Does anyone know about how much the shift fork needs pulled in to fully engage?
Needs at least 1/2" movement to properly engage in the front axle. Proper movement should be 1/2" to 3/4".

Check out the Tech Article (DIY) Index link in my signature and scroll until you find the thread title involving clicking in 4hi, goes away in 2hi or something like that (it's been a while). There are pictures in that thread of the engagement mechanism that will show you what's going on and what can happen if things aren't engaging properly.
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Old 01-20-2017, 11:37 AM
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Default 4x4 not engaging

Long time lurker. This may seem weird but my 4x4 lights (4hi&4lo) would only blink. Was going to start checking/changing all the usual parts & hoses when my radiator started leaking from one of the fluid lines. Of course this was top priority so I changed the radiator ($55 on line). WTH! My 4x4 started working perfectly. Been good for about 3 months now. Go figure.
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Old 01-21-2017, 01:14 PM
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Good for you. Wish you could inform us as to how the radiator fix also fixed your 4x4.

Bill
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