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2000 ZR2 4x4 issue

4K views 21 replies 7 participants last post by  hobbyjeep 
#1 ·
4x4 was not engaging. I found the vacuum actuator boot was torn, so I replaced it. 4x4 worked fine for about a month.

Hit switch to engage 4x4 high. Hear the transfer case motor engage. Accelerate the truck and hear click click click (not quite grinding) that increases or decreases with speed. Replaced vacuum switch on tcase and then replaced all fluids (front dif, t case, transmission) That seemed to fix it for a week. Back to making noise click click clck again when in 4x4 high. making noise but not actually engaging front axles. Ideas?
 
#2 ·
heres an easy test to see where the problem lies. start it up, put it in 4x4 and jack up a front wheel and give it a spin. does it spin freely? if it spins freely look to see if the front driveshaft spins with the wheel or if it does nothing. if the driveshaft doesn't spin then the problem is in the front axle. remove the battery tray to gain access to the vacuum actuator and make sure it is pulling the cable all the way. 2 common problems i have found on these trucks is either the actuator takes a dump, or the cable gets stiff and either won't engage, or disengage the diff.
 
#4 ·
also check all the vacuum lines between the actuator and t-case, and up to the engine. the hoses are fairly shitty rubber and can degrade over time causing a leak. my 95 had a similar issue so i had to replace all the vacuum lines for the 4x4. they crumbled apart in my hands when i took them out.
 
#6 ·
well if it had a pin hole it may not be strong enough to engage fully. without seeing the vehicle in person i can only guess at the problem. as far as replacement lines i went to AZ and bought a roll of vacuum hose and used it. 5/32 i think was the size.
 
#8 ·
I was having an issue with my blazer. when I bought it the guy said the 4wd was messed up and that it had 4low but nothing else. Well, It had 2 low not 4low :teehee: Took it to a buddies shop, and checked into it, actuator looked fine and was engaging properly, lines were good. We replaced the switch in the t case (the one that the lines hook up to) and I was able to have 4low but no 4 high. the push buttons would flash and act weird. Bought a transfercase control module (TCCM) and an encoder motor from a member on here. Had a fun time finding the TCCM on my 1995 blazer (behind the dash under the radio) replaced that, and seemed fine in the shop, Took it out to the snow, and would not work (still had 4 low and 2wd) replaced the encoder motor and my 4wd works great now.
 
#9 ·
A little further diagnostc info. Will not engage when going over 10MPH. I hitht e swthch, hear the transfer case engage and then a grinding noise starts.
Under 10MPH in neutral or reverse, 4 wheel engages just fine with no issues.

No light's blinking no 4x4 code thrown.

This leads me to believe that there just might be a small vacuum leak somewhere. It might not have the power to engage the coupler at higher speeds, but lower speeds it can slide over.

What do you guys think?
 
#10 ·
Whole system/slide collor setup is junk!.

Best best which many have done is to replace it with a like year s-series bravada shaft/tube.

This replaces the two piece spilined slide collor setup with a once piece axle shaft.

You will need the shaft/tube from a 98-01 bravada. Some RTV, and time.

Once done your front end will be enguaged all the time. You will NOT need to be rolling forward at all to get it to work. So thats a big plus.

Only mod needed for this is to remove the outter snap ring where your CV would slide onto. And you can either use a cap packed with whatever to tell the sensor shit its in 4x4. Or just remove the sensor and splice the wires together.

Other options are a popnlock manual pull line, or just pull and secure with vise grips if the slide collor is still good that is.

Also make sure you get the updated TC vac switch. When the older ones fail they will suck fluid into the hvac system that leads to the controls hiss of death. You DONT want to have this happen.
 
#12 ·
The vac lines come out of the tcase , go under the pass side body . Then one up by the manfold . I had one get a hole there . When you put the lines back on the switch . you got a good seat and back on the right line . Also at the actuator , a good seat . The way I teasted the actuator . Push it in cover each hole with you fingers , it won't inflate . Go to the car wash , wash the underside (if there's dirt or put glass on) Start at the tcase and follow each line . Its a pin hole in the line or a bad seat at the end .

Here are two links for you , just to have . I have crawled all over and around , For a pin hole in a dam vac line . At times I have thought about just replaceing all the lines .

http://www.s10forum.com/forum/f220/the-4x4-vacuum-thread-327817/
http://www.4x4posi-lok.com/PDFs/troubleshootguide.pdf
 
#15 ·
Your doing good .

When parked . You push the button . You hear it engage . But it is not in 4 wheel . Its a vac leak , or bad seat at the end on the line .

The shi*y part is crawling around finding it . And Fin with the cable set up at the actuator (lube) . Like an ebrake cable sticks when shi*s in it .
 
#16 ·
A lot of times when the t-case switch gets old vacume pulls atf out of the t-case and makes the lines deterierate,along with your new vacume pod.
Also check on the drivers side near the master cylinder for a plastic vacume resovoir bottle.If your truck has one,pull the line and look for signs of atf.If the lines or resovoir are full off atf it wont pull enough to fully lock the axle.
I used to pull on the cable with vise grips while someone drives the truck a few ft,or spin the front wheels if it is jacked up.You will feel the collar lock in,take the vise grips and clamp them on the cable,so it can't slide back in.I learned that trick when I had a dz302 in a s10 blazer,the motor made almost no vacume.
 
#17 ·
I replaced the t-case vacuum switch more as a precautionary measure. I am confident fluid did not get sucked into the vacuum hoses.

One other diagnostic note. The issue only seems to appear when I try to engage 4x4 at higher speeds. The light on the 4x4 switch turns on just fine(no blinking). Everything appears fine, except that I know the 4x4 is not engaged because I'm fishtailing. When I step on it, I hear the grinding noise, but only when I step on it. The grinding is directly related to the engine RPM's. The faster the RPM, the faster the grinding.
 
#18 ·
Parked it and lifted the truck. Right front spins by hand. Start and engage 4x4 Hi and I cannot spin the right front. Wonder if the cable is pulling but not all of the way. Anyone know how far that cable has to pull the rod to engage the front axle?
 
#20 ·
You could put a vacuum gauge on it and rev the motor,to see if you are pulling full vacuum.
You could put a vacuum pump on the actuater, to see if it will lock in and not slip that way.
You could lock the cable with vise grips and drive to see of it stays locked in.
Any off the above will help narrow down your problem.Your slip collar could be messed up from too much grinding,but you wont know untill you manually lock it and drive it hard.
I have blown up more s10 front driveshafts then I can count.When the cv joint goes out they make a huge grinding noise in 4x4,and can fool you by kinda putting power to the front wheels,untill it totally self destructs.check it.

I have owned close to a dozen s10/jimmies and built several with v8s.I know you dont think you have atf in your vacuum lines,but I never worked on an S10 that didn't,unless it was new.It only takes a few drops to deterierate rubber over time.
good luck.
 
#21 ·
That is great advice. I'm going to see if I can rent a vacuum gauge at AZ. In the meantime, i did some further checking. The vents are also controlled by vacuum. When I switch from defrost to foot to head on the vents, I can still feel air coming out of the center vents. It's a small amount, but still some air is making it through. I'm wondering if the vents are not closing all the way. They are also vacuum operated. That could indicate a weak vacuum.
 
#22 ·
I chased same issue on my 97 ZR2 - hoses, switches, vacuum motor. Would be good for a while then it would start giving me probems again. A good site is www.zr2.com for more information.

Mine was fixed after replacing the intake manifold gasket. 4.3L have "issues" with intake gaskets and mine lost enough vacuum at higher speeds to cause problems with the 4wd. If you truck is using coolant... it will be an intake gasket. Checking vacuum as someone has already suggested is what I would do next.
 
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