hi, new member here so sorry if this has been answered before, I cannot find a link. when I try to engage 4hi/lo there is a knocking/banging and some lurching as though the gearing is slipping or not engaging fully. I have had the car off the ground and pulled out the battery tray to access the vacuum line/ actuator and cable. the vacuum line has good vacuum, the actuator works with the cable detached (doesn't seem to move with cable attached)and the cable moves freely when manually pulled. when I manually pulled the cable and 4wd activated there was no banging etc with all 4 wheels off the ground (the wife was in the car operating everything). once put back together and on the ground, its back to square one!!?? when it was in there air and 4wd engaged manually, only the driver side front wheel was turning. is this normal? any answers or ideas would be great. with winter coming, the wife needs 4wd where we live. ohhh, and the motor on the transfer case seems to work and activate as it should.

 

Does the dash switch have 3 buttons, or 4 button Auto 4WD?

 

hey, it has the 3 button panel. not auto 4wd. everything on the panel works and the 'brain' does its thing. im thinking this isn't an easy fix and hoping someone knows better!

 

When you select 4WD HI, some noise, (usually just one clunk) is normal from the transfer case as it performs the mode shift. Here's how to check if the front differential is locking in:

Raise only the right front wheel off the ground:
Transmission in park.
Start the engine.
Select 2WD HI.
The right front wheel should rotate freely by hand.

Next, select 4WD HI:
The right front wheel should not rotate.

Post your results.

 

when you say right front wheel, which perspective are you looking from? driver or passenger front wheel?
I had both sides off the ground and in 2hi both rotated freely, in 4hi both were locked.
I know what you mean about the single clunk going into 4wd... that's what it used to do, now its as if its missing the gearing or not engaging fully making a clunking and lurching every couple of seconds as it drives. so I stop and put it back into 2hi and all is fine once its disengaged, maybe a clunk or 2 dropping out of 4wd but 2hi is flawless and quiet.






IF IN DOUBT, GIVE IT A CLOUT!!

 

Blazers were built both LHD, (left hand drive) and RHD, (right hand drive). Standing at the rear of a LHD vehicle, facing the rear bumper, the right side is the passenger side.

In the test described in post #4, the only wheel off the ground needs to be the right front.

"clunking and lurching every couple of seconds as it drives": What you're describing could be what is referred to as "crow hop". It is caused by not using all 4 tires exactly the same size, or one or more tires low on air pressure. All 4 tires on 4WD vehicles must be the same size, (same manufacturer is preferred) have equal wear on them, and all 4 must be evenly inflated. If not, the driveline will bind and cause crow hop. If it is severe enough, it will destroy driveline components, (transfer case, differentials, etc). 4WD, (HI or LO) in these vehicles, should never be used on dry pavement.

 

hi, I hear what you're saying... all tires are the same size on original and straight chevy alloy wheels, both front tires are nearly new goodyear trackers and all pressures are good. 4wd has only ever been used by us in snow/ice conditions. we don't go off road. so I don't get why it would be 'crow hopping'.

 

Are the rear tires "nearly new" like the fronts are? If not, the two differentials will not rotate at the same exact speed.

If any one or more of the tires have a different circumference, the differentials will not rotate at the same exact speed, and cause crow hop.

Crow hop in the front end is more noticeable when the two front tires are not the same size, (circumference). Usually driving straight is fine, but when you turn, the inside tire rotates slower than the outside tire, which causes the front differential to bind up. The tighter turn you make, the more noticeable the crow hop.

 

hi again. ive double checked all tire pressures and measured all tire tread depths. all pressures are the same and the fr tires are 5mm and the rr are 4mm depth. after checking the pressures and adjusting, I still have the same issue so this 'crow hopping' cant be the reason. I noticed that the actuator under the battery doesn't activate when its all hooked up but works fine with the cable unattached. could that be the transfer case vacuum switch affecting vacuum to the actuator? the cable moves freely when not attached and the are 2 definite clunks when engaging 4hi/lo manually. im getting damn frustrated now as nothing seems to make sense.
also... I have 2 pipes that run along the left (driver side) frame rail. 1 goes to the charcoal canister but where does the other go? I noticed this last weekend. its corroded away at a frame mount and goes nowhere!! thx.