Hi. I'm a new guy that's having trouble with my '97 S-10 Blazer and I found this forum while searching for help.

My problem is that my front differential is not engaging when I try to go into 4WD. There are no troubles at the transfer case end, since the driveshaft spins and everything works fine there. So far I have replaced the vacuum switch on the transfer case, the vacuum switch on the front differential, the vacuum line going from the transfer case switch to the vacuum pod (for lack of better term) under the battery, the vacuum pod itself, and even the shift cable that goes from the vacuum pod to the differential. I can engage the 4WD by hand, but for some reason the vacuum pod does not seem to have enough power to engage it. The vacuum pod is working, as I started the vehicle without the battery installed and I can see it suck in when the 4WD switch is pushed. I thought that maybe the cable was just old and had too much resistance to allow the vacuum pod to engage the 4WD, but a new cable did not fix the problem either.

One other thing that I have noticed is that since I have replaced the cable, there seems to be too much cable extending out on the vacuum pod end. The pod itself is half compressed when it's hooked up, and it was not like that prior to replacing the cable. Seems like maybe something should be pushed in farther on the differential end???? It is definately connected to something inside the differential, though.


Any help greatly appreciated!

 

Did you replace the cable, or did someone else? If your cable isn;t hooked up properly, that would cause a bit of a problem. Even though you replaced the vacuum hose running to the actuator (what your calling the pod), you could have a vacuum leak elsewhere, robbing suction from the actuator. Start with the vacuum hose off the rear of the upper plenum (assuming this is where the 96 and newer are still getting their main source of vacuum, I actually don;t know th location as I have a 95 and 93). Trace all hoses, making sure they are in good shape. If the hoses turn your hand black, replace it.

Check out this link, 4x4 VAC. and this one as well, Vacuum for 4x4. This guy thought he originally had his vacuum leak fixed after discovering two loose connection, after further searching, he finally sealed up all the vacuum leaks.

 

Here is some info that may be helpfull..

PosiLock 4X4 Engaging System Install

The PosiLock 4X4 Engager replaces all the vacuum aspects of your 4X4 system, insuring rapid and reliable switching
from 4X2 to 4X4 and back. One of the most common problems with stock systems is the vacuum switch on the transfer case. Second in line is failing vacuum hoses that leak and prevent 4X4 from locking in. The PosiLock system is all mechanical. It operates on the basis of using a throttle type cable to pull or push on the CAD cable connected to the front chunk. The cost is a bit high, but the benefits are well worth it.

The system can be bought from J.C. Whitney and others.


Here is what is needed for the install:

Miscellaneous metric wrenches
9/16" drill bit
Drill
cable ties to keep cable outta way of moving parts
torx bit screw drivers to remove panels under dash
2 hours of free time, 5 hours to test the system (some people prefer more or less time) 45 minutes if ya have a buddy
difficulty 2.5-3 out of 5 wrenches
Since the introduction of the S-10 style vehicles, the front ends of these very capable vehicles have always had Independent Front Suspension with the front axle being engaged by a cable/vacuum operated control system. While
the system works flawless when the vehicles are new, with age and deterioration the vacuum side starts to fail. This can lead to various unpleasant situation, for example- bragging to buddies that you can go anyway but you can't seem to make it into your driveway but your wife's/significant other's metro does. So while, some people option to replace the defective parts, which can amount to a lot of money.

Current prices-

Vacuum Reservoir-$35-40
Vacuum switch down by 'case-$25-30
Hoses-cheap just a pain to replace/run
Vacuum Actuator-$30-35

With these prices, and coupled with the facts that I live in a state that sees a lot of different temperatures throughout the year (which leads rubber parts tend to wear out a little faster than most) and I am planning on a Solid front end swap in the near future, I just opted to install the cable operated system by Whitey inc. to end my headaches.

Note: This is the same for the '83-88 style systems with the cable actuator and vacuum reservoir is on the Passenger side fenderwell. The same kit does both types of locations including 88-00 where the actuator is located under the battery, refer to install instructions.


Locate which vacuum line is the one that feeds the switch on the transfercase off of the reservoir. It should be about 3/8" vacuum line that runs down by the tranny dipstick. Pull off all the vacuum lines that run to the 'case- less of a mess to
worry about and since they are useless after the system is installed, they would eventually rot and fall of anyway. Plug off the tee with the supplied vacuum cap.


Take off the Dash panels to gain access to the mount for the Go Pedal, and proceed to drill the 9/16" hole that is need to run the cable through the supplied rubber grommet. Run the cable through and carefully pull through into the engine compartment as to not to lose it later. Mount up the handle and make sure to make it solid (the plastic surrounding the place they have you mount it isn't that strong so use the supports included in the kit). Reinstall the dash panels.


Remove cable actuator from mount, remove cable clip, mount up the Bell crank plate per instructions.

Adjust cable so as the cable only has to be pulled about 1-1.5" out for the front end to be completely engaged.



What is wrong, How to fix, How to install

***HOW TO CHECK WHAT IS WRONG***

You will probably know when your 4x4 has failed when you needed it in the mud pit.

To read the codes for the 4x4 with electric shift transfer case, install a jumper wire from terminals "J" and "A" on the ALDL (12 pin connector under the driver's side dash)

T

 

I hooked the cable up myself. Seems like it's hooked up O.K., since I can manually engage the differential from the actuator end of the cable, but it doesn't seem to have a lot of movement before it engages. I noticed in the third post here it said that it should move 1-1.5". There is a definate click, and I assume that's when it's engaging. I'll have to look into it farther.

 

I did a home made posi-lok kit and my '87 only moves about 3/4"-1".

 

Found the trouble. While replacing the other two vacuum lines, I found a hole in the 7/32 line right by the "T" on the top of the transmission. This was completely out of sight until I pulled the old line out. Also, the short section of 5/32 line that runs to the back of the manifold was pretty dry rotted. Everything is working fine now that I replaced all the lines.