Posi-Lok vs Vacuum

[Elwiscon]

Finally got the engine cleaned up and tuned up, now its time for the front axle, the steel s-shaped chassis vacuum harness had a clogged line,  so the front differential isn’t engaging, i put acetone, PB blaster etc and couldn’t clear it so ended up getting a used harness from Ebay. I’m about to order a new actuator, fork and vacuum lines if i can find a kit. I found information about the cable-actuated “posi-lok”, some people swear by it, others don’t recommend it. My MJ won’t be used for hardcore off-roading but i still want a reliable 4WD system, what are your opinions on the posi-lok? Should I get one? Pros/cons? The thing i don’t like about it is the cumbersome red button on the dash, I was thinking about concealing it in the center console, under the dash, etc where it isn’t as noticeable. A lot of people have it on their YJ’s and highly recommend it. Thanks

[89 MJ]

My dad had it in his YJ. It was fine. Both my MJ and Eagle have the collar slid over so the axle is never disconnected. It’s just as, if not more, reliable, cheaper, and won’t negatively effect fuel economy. 

[eaglescout526]

Or have some fun and put in an early style Selec-Trac vac switch in the console where the coin tray is. Did that on my 84. It’s actually fun, works and blends in as factory. But that’s just my 2 cents on what I did. 

[Elwiscon]

8 minutes ago, eaglescout526 said:

Or have some fun and put in an early style Selec-Trac vac switch in the console where the coin tray is. Did that on my 84. It’s actually fun, works and blends in as factory. But that’s just my 2 cents on what I did. 

Sounds interesting, I’ll look into it.

 

[eaglescout526]

5 minutes ago, Elwiscon said:

Sounds interesting, I’ll look into it.

 

One advantage to this set up I did with controlling when the axle goes into 4wd or not is that I now have access to 2Low when shifted into 4Low on the case. Not exactly why I did this, more just to have an early XJ piece that came with an advantage. I was able to eliminate the vacuum at the case and just get vacuum at the manifold to the light switch and down to the axle.

[Elwiscon]

23 minutes ago, eaglescout526 said:

 

One advantage to this set up I did with controlling when the axle goes into 4wd or not is that I now have access to 2Low when shifted into 4Low on the case. Not exactly why I did this, more just to have an early XJ piece that came with an advantage. I was able to eliminate the vacuum at the case and just get vacuum at the manifold to the light switch and down to the axle.

I’m sure it looks better than the Posi-Lok red button, and it’s OEM, may be hard to find the parts though. I’m having a hard time finding the plastic 3-line harness from the actuator to the chassis lines, but at the end performance and reliability is more important than aesthetics, just trying to get opinions from actual users. As I mentioned my MJ will be mostly used around town, very light off roading and maybe some winter driving on occasion. Haven;t seen pictures of your mod but it seems to be a great solution.

 

[Eagle_SX4]

I found a posi lock in a junkyard once and started to pull it out. However I ended up leaving it at the junkyard because the person that installed it routed the cable to close to the exhaust and it melted the cable housing making the posi lock useless. 

 

If you do get a posi lock don't route the cable by the exhaust.

[Pete M]

or for free you can lock it permanently and it'll be like any XJ after the early 90s when Jeep did away with the silly CAD thing.  

[AZJeff]

1 hour ago, Pete M said:

or for free you can lock it permanently and it'll be like any XJ after the early 90s when Jeep did away with the silly CAD thing.  

Pete is on to the best, most reliable solution.  Unless you are trying to restore your MJ to “as built” condition, keeping that sliding axle lock claptrap is a PITA.  
 

Bypassing (overriding) that mechanism makes the axle behave like all the later XJs (and the TJs) which were problem free in this aspect, and the fuel economy losses were insignificant.

[eaglescout526]

9 hours ago, Elwiscon said:

Haven;t seen pictures of your mod but it seems to be a great solution.

I…really didn’t take pics but I easily can. It was simple to do. But I forgot about the option above which is better, I just likes the idea of having some extra functions at my disposal. 

[75sv1]

I thought they went with a higher grade of bearings to help with MPG when going from the CAD. ???

[Elwiscon]

15 hours ago, Eagle_SX4 said:

I found a posi lock in a junkyard once and started to pull it out. However I ended up leaving it at the junkyard because the person that installed it routed the cable to close to the exhaust and it melted the cable housing making the posi lock useless. 

 

If you do get a posi lock don't route the cable by the exhaust.

Definitely not! I’m usually very careful with cables, wires, etc 

[Elwiscon]

12 hours ago, Pete M said:

or for free you can lock it permanently and it'll be like any XJ after the early 90s when Jeep did away with the silly CAD thing.  

I’ve heard it affects wear and tear on the axle, but could be wrong 

[Elwiscon]

10 hours ago, AZJeff said:

Pete is on to the best, most reliable solution.  Unless you are trying to restore your MJ to “as built” condition, keeping that sliding axle lock claptrap is a PITA.  
 

Bypassing (overriding) that mechanism makes the axle behave like all the later XJs (and the TJs) which were problem free in this aspect, and the fuel economy losses were insignificant.

 

10 hours ago, AZJeff said:

Pete is on to the best, most reliable solution.  Unless you are trying to restore your MJ to “as built” condition, keeping that sliding axle lock claptrap is a PITA.  
 

Bypassing (overriding) that mechanism makes the axle behave like all the later XJs (and the TJs) which were problem free in this aspect, and the fuel economy losses were insignificant.

Not really restoring it to factory condition, it’s mostly a restomod with improvements, I already upgraded the electrical, I installed an AC system, added an electric fan, etc. The whole concept is to have a restored Comanche i can enjoy and drive as a truck, so I don’t really care about the vacuum actuated 4x4, as long as I have 4WD when needed.

[Pete M]

wear-n-tear and mpgs were the original reasons Jeep put it in.  then after a few years they removed it because it didn't help either thing plus added necessary cost and complexity. 

 

the only real-world downside is that if your front driveshaft is worn out, it'll cause a vibration.  but honestly, if it's worn out it should be addressed anyways.  all XJs after the really early 90s, all ZJs, and all TJs were CAD free.  plus IFS Jeeps like my liberty.

[Elwiscon]

2 hours ago, Pete M said:

wear-n-tear and mpgs were the original reasons Jeep put it in.  then after a few years they removed it because it didn't help either thing plus added necessary cost and complexity. 

 

the only real-world downside is that if your front driveshaft is worn out, it'll cause a vibration.  but honestly, if it's worn out it should be addressed anyways.  all XJs after the really early 90s, all ZJs, and all TJs were CAD free.  plus IFS Jeeps like my liberty.

Didn’t know that, good to know. That’s another good option to consider, I’d have to figure out a way to wire the dash light if I go that route. I’ll look into that option, the bypass kits are way cheaper than a good quality posi-lok.

[Eagle_SX4]

You can also change to single piece axle shafts from a TJ which does 2 things. 1, deletes the CAD and 2, gets you bigger stronger u-joints. 

 

This is what I did with mine.

 

 

[Pete M]

7 hours ago, Elwiscon said:

Didn’t know that, good to know. That’s another good option to consider, I’d have to figure out a way to wire the dash light if I go that route. I’ll look into that option, the bypass kits are way cheaper than a good quality posi-lok.

 

the dash light is less important than it is on modern 4x4s since we still have an old-school lever by our knee to indicate what's happening.   

[Elwiscon]

3 hours ago, Pete M said:

 

the dash light is less important than it is on modern 4x4s since we still have an old-school lever by our knee to indicate what's happening.   

Good point, i just have OCD lol. I read on an XJ forum you can still have it activated thru the transfer case vacuum switch.

[Elwiscon]

5 hours ago, Eagle_SX4 said:

You can also change to single piece axle shafts from a TJ which does 2 things. 1, deletes the CAD and 2, gets you bigger stronger u-joints. 

 

This is what I did with mine.

That’s a good idea, but may be a lot of work, like the idea of stronger components but I’m not planning to use my Comanche for hard offroading so I’ll keep the original axle for now 

 

 

[Pete M]

3 minutes ago, Elwiscon said:

Good point, i just have OCD lol. I read on an XJ forum you can still have it activated thru the transfer case vacuum switch.

 

yup, you can do that too.

[Eagle_SX4]

3 minutes ago, Elwiscon said:

 

There might be some confusion but I only changed the inner axle shafts not the entire axle assembly.