S-10 Front Diff & Posi-lok Operation Explained Options

[Miles]

I posted this write-up on ZR2.com many moons back, and would like to share it with the members here, whom might not have seen it since the mothership passed away. It answers many questions regarding the S-10 front diff & Posi-Lok cable operation.

This post will completely address (with pics) the problems associated with the factory S-10 front axle vacuum engagement system, as well as the problems associated with Posi-Lok's old kit & their newly designed kit.

If one were to use the 4WD in their S-10 frequently, sooner or later the factory vacuum actuator (located under the battery box) is going to fail. Why? It functions by engine vacuum, and is completely reliant on the vacuum lines connected to it! These lines always seem to fail at the least in-opportune time.....typically when you need it the most. Here is a pic of the factory S-10 vacuum actuator:

http://i20.photobucket.com/albums/b240/Mus...uumActuator.jpg

Posi-Lok's previous kit simply replaces the vacuum lines & actuator, with yet another cable & problematic pivoting mechanism. This old design connected to the factory diff cable. Here is a pic of how their old "2 piece" design connected to the factory diff cable, in place of where the factory vacuum actuator used to sit:

http://i20.photobucket.com/albums/b240/Mus...cs/4Posilok.jpg

The problem with this kit is that it is difficult to install, and only addresses part of the S-10 front axle engagement problem. The problem most people are experiencing is that after the old Posi-Lok kit is installed, there is a tremendous bind when trying to engage the front axle, via pulling the Posi-Lok cable in the cab. Why? Doesn't really make sense, since the Posi-Lok cable itself moved in & out perfectly fine PRIOR to connecting it to the front diff cable! But.....the problem is actually still in 2 completely different places. The 1st is in the problematic pivoting mechanism pictured above, and the 2nd problem lies in the factory diff cable itself, that is still attached to the front diff. Why is the factory diff cable a problem? Because with non-use, or by living in a colder climate, these cables will simply rust or freeze up…..meaning that the cable won’t move! Here is a pic of the front diff cable that is often completely overlooked:

http://i20.photobucket.com/albums/b240/Mus...ryDiffCable.jpg

As stated before, with this cable frozen or rusted up, it does not matter what you connect to it.....it's simply not gonna work! That is where a liberal dose of your favorite lubricant comes into play:

http://i20.photobucket.com/albums/b240/Mus...rydiffcable.jpg

Getting this cable to freely move can be a major challenge, pending on just how bad your specific cable is frozen up. If you cannot get this factory cable to move freely, you will need to disconnect it from the front diff, and try to get it to move freely then. If the cable is still frozen up while unattached from the truck, you will need to replace it. If that does not work, then the problem would have to lie in what this factory diff cable attaches to.....but that's very rarely the problem. Here's how it's all connected. The diff side of the factory diff cable...

http://i20.photobucket.com/albums/b240/Mus...tofrontDiff.jpg

...is inserted into this factory plastic housing...

http://i20.photobucket.com/albums/b240/Mus...ableHousing.jpg

...like this....

http://i20.photobucket.com/albums/b240/Mus...intohousing.jpg

...and attaches to the front diff right here:

http://i20.photobucket.com/albums/b240/Mus...esfrontdiff.jpg

When the front diff is not engaged, this mechanism on the diff looks like this:

http://i20.photobucket.com/albums/b240/Mus...fNOTengaged.jpg

When the front diff IS engaged, this mechanism looks like this:

http://i20.photobucket.com/albums/b240/Mus...DiffENGAGED.jpg

See, the cable simply pulls this mechanism out to engage the front diff, and pushes it back in to disengage it. What does this “mechanism” actually do inside the diff? Well, it slides a collar over towards the passenger side, and simply locks the passenger side axle shaft to the diff itself. Now ya know!!!

Enter the new Posi-Lok design:

http://i20.photobucket.com/albums/b240/Mus...siLokDesign.jpg

It is a simple one-piece design that eliminates their previous problematic pivoting mechanism in their old kit, and replaces the factory diff cable with their new one piece cable. I will say that their new kit does function perfectly fine.....but, once again, the installation was IMO simply ridiculous. How a company that is solely devoted to the R&D of these kits, could overlook these very obvious areas, is completely beyond me.

What kinds of issues, you ask? Well, let's start with the very first step. First, their instructions tell you to drill an 11/16ths hole in a specific spot on the firewall (try not to cut any “under dash” wiring harnesses during this!), remove the mounting bracket washer & nut from their supplied cable, slide the mounting bracket onto the cable, and then re-install the big washer & nut back onto the Posi-lok cable, before siding the cable through your newly drilled firewall hole. This is where I question whether or not Posi-Lok ever even installed this newly re-designed S-10 cable…..onto an S-10!!! Why? The big nut on the cable cannot just slide right off of the new cable, because its’ inside diameter is smaller than the differential bolt head, that it has to slide OVER to be removed!!! I had to use my Dremel to shave down the corners of the brass bolt head, just to be able to remove the freakin nut. Unfortunately, you cannot install this mounting bracket, without first removing the nut….which REQUIRES you to shave down the corners of the bolt head! How was this overlooked??? Hmmmmm… Here’s a pic:

http://i20.photobucket.com/albums/b240/Mus...91stproblem.jpg

Here’s a pic of the nut & washer finally removed after grinding down the corners of the head of the bolt:

http://i20.photobucket.com/albums/b240/Mus...hedproblem1.jpg

And here’s a pic of the mounting bracket installed on the cable after putting it all back together:

http://i20.photobucket.com/albums/b240/Mus...Whyproblem1.jpg

Next problem. When I attempted to slide the cable through the 11/16ths hole they outlined for me to drill in my firewall, I quickly realized that the head of the diff bolt was STILL too big to fit through my perfectly round 11/16ths hole!!!! (It’s kinda hard to tell from the pic, but you get the idea.) Here’s a pic:

http://i20.photobucket.com/albums/b240/Mus.../13Problem2.jpg

Sooooo, I got to dremel the brass head of the bolt down even more, so the diff bolt could slide through my hole in the firewall. Drilling out the firewall hole even larger was not an option, since it is obviously pretty important for the supplied cable grommet to fit very tightly in the hole. Here’s a pic of just how “round” I had to make the head of the diff bolt:

http://i20.photobucket.com/albums/b240/Mus...xedproblem1.jpg

After routing the cable through the new hole in the firewall, I was next faced with the routing of the cable down to the front diff. The instructions are incredibly vague here, so you just have to have plenty of patience & common sense to route it correctly. There is a huge amount of excess cable left over…even while installing it on an S-10 with the 5” BDS suspension lift kit! In fact, I had soooo much excess cable, I had to route it inside the back of the front bumper for it to fit correctly, with no binding!!! Here’s a pic:

http://i20.photobucket.com/albums/b240/Mus...outingcable.jpg

The last problem I encountered is the length of the actual cable itself. With the Posi-lok cable disengaged (meaning that the red button is completely pressed in), the amount of cable sticking out of the diff side of the sheath, was less than the factory amount of cable that extended past the end of its’ sheath. (Kinda hard to understand that, but maybe this pic will help draw the mental picture:

http://i20.photobucket.com/albums/b240/Mus.../14Problem3.jpg

In this pic, the factory diff cable (the one on the bottom) is completely disengaged….meaning that the cable is depressed as far toward the diff as it can possibly be. The cable on the top is the Posi-lok cable, and it too is completely depressed. While this little issue does not really affect the installation, it is a MAJOR issue if you ever need to remove this cable from your front diff. In fact, because of their shorter cable, Posi-lok explains in their instructions, a special & complicated procedure for removal of their cable from the front diff!!! Now, I didn’t have to go through this “special procedure” when removing the factory cable from the front diff….simply because it had adequate length! Apparently Posi-lok realized their mistake after designing it…and instead of just re-designing the cable to be the same length….they just made the removal process what I would consider a massive headache instead. They even included a “special tool” to aid in the cable removal. Because their cable is shorter, the engagement “stroke” (meaning the distance you pull out the cable from inside the cab) is pretty short. It’s actually a shorter stroke from their first design.

Here’s the finished product after installation:

Connected to the front diff:

http://i20.photobucket.com/albums/b240/Mus...okInstalled.jpg

Installed in the cab:

http://i20.photobucket.com/albums/b240/Mus...nteriorshot.jpg

The last thing that you will want to do to wrap up this installation, is trace the vacuum line that is attached to the vacuum actuator under the battery box, back to the firewall. I cut the vacuum line at the firewall, and just plugged the line with a screw that fit the vacuum line well. Use whatever you like to plug the line, but make sure that it is capped off well. BTW, you can remove the vacuum actuator that's under the battery box if you like, since it's no longer used.

Now for the biggest question of all. How does it work??? It works perfectly fine! Very smooth engagement, with no binding whatsoever. My overall impressions? The instructions are still incredibly lacking, and their lack of R&D caused the install process to be a major pain in the a$$......but it does work perfectly fine. It is merely a direct connection to the front diff. Pull the cable, and the front diff is engaged. Press it back in, and it is now disengaged.

I hope this write-up more thoroughly explains how your front diff operates, as well as the things you need to know about Posi-Lok’s cable. Sorry fer the book....

EDIT 7-08: Posi-Lok has long since corrected many of these install issues that I experienced. The kit I received was one of their very first of the new design. Other than the excessive length, the install should be pretty straight forward.

This post has been edited by Miles: Jul 23 2008, 11:38 PM

[ZR2STER]

Great detailed post! No time to read the entire thing atm. Is the posi-lock system the manual over ride from the stock system? I thought the stocker was electric.
Good info :)

[Miles]

The factory engagement uses engine vacuum to engage the front diff (controlled by a vacuum switch that is located on your transfer case). The Posi-Lok cable replaces the entire factory vacuum engagement system.

Thanks btw! But, I wrote that up last year I think...

I actually have more to add (with pics) as to how the internal part of the front diff actually engages the passenger side axle shaft, but I just haven't had time to write it up yet.

[Jackson]

:clap:

[MWood]

you da man :judaspriest:

[recycle127]

Does the posi-lok replace also the push button controls? Or how does that work? My actuator just went out on me and I am thinking about posi-lok.

[ArkansasBlaZeR2]

No, you still have to use the buttons on your dash to engage the T-case. All the posi loc cable does is engage the front diff.

[Griff]

How rigid is the cable inside the cab? I ask 'cause I'd like to mount it somewhere else rather than have it hanging so exposed like that.

[abright52]

Think of it as a brake cable for a bicycle. It wouldn't be too bad to mount it elsewhere as long as the cable wasn't binding.

[Griff]

[chris02zr2]

Great right up. That is the same way I set up my posi-lock, I realy like the new setup for the s10's rather than the old bracket style.

[MWood]

Do you have the part# of their new design?

[Miles]

Their new design, is their only design. They stopped making the old two piece design last year sometime. Not sure of the part number, but there is only one for the S-10.

[Newportgeek]

Summit Racing has it listed under part # POS-500. ~130 bucks. That seems like alot to me. Anyone know where to get it cheaper?

[Miles]

I bought mine from 4Wheelparts.com for around $110.

[Kristian]

diversified creations

[Kidthatsirish]

So, I if get this straight, the 4x4 system on our trucks uses an electric system to engage the transfer case with the actual transmission. At the same time, it uses a vacuums system to engage and lock the two half axles? This fix makes the locking of the two half axles more reliable?

[Miles]

[2maro'sZR2]

Can you leave the posi-lock cable engaged all the time, and not engage the transfer case (4hi/4lo) what problem(s) does that bring up?
Im starting to understand the posilock cable. Pull the cable to engage the half shafts in the front. then push the range you want to be in( 2hi, 4 hi, 4lo). To exit, press 2 hi and then push the posi-lock cable back in.

[MWood]

Push or pull the cable while you are rolling forward, then engage or disengage 4x4. I keep my front diff engaged and i dont think it will do any damage since i dont have a front locker. Just dont force the cable in or out, because you can damage it. It can be hard to engage the front axle if you are already stuck and you cant roll forward or backwards to get the gears to mesh.

This post has been edited by woodardm: Dec 18 2007, 12:11 AM