What is it and do I need it?
- Thread starter Fish!
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Gennybro
Active member
That is what engages your front axles for 4 wheel drive.It is vacume operated,a lot of folks do away with that set up and get the 4x4 posilock system.The trouble with the vacume system is that the vacume lines ran behind the battery,and acid from the battery would eat up the hose,not to mention dry rot over a period of time.
The posilock system is operated by use of cable control,quadratec has it.
So, perhaps you have thought that you was in 4 wheel drive,dash light said 4x4 engaged,you probably,even checked to see if the front drive shaft was turning,which it would be.but that little unit is what engages the front axles for 4 wheel drive.
What model jeep do you have,give us some info.
The posilock system is operated by use of cable control,quadratec has it.
So, perhaps you have thought that you was in 4 wheel drive,dash light said 4x4 engaged,you probably,even checked to see if the front drive shaft was turning,which it would be.but that little unit is what engages the front axles for 4 wheel drive.
What model jeep do you have,give us some info.
That's exactly what I did. What's a 'dash light'?
It's a 1990 YJ (Sahara)
Right after I posted, I found this:
Dana 30 Vacuum Disconnect | Jp Magazine Article at Automotive.com
Do a lot of people opt for a one piece axle swap?
SteelHeadz
Super Moderator
The dash light he's implying about is the 4wd lamp that turns on when the 4wd is engaged. The wiring on the front axle actuator is for the dash lamp switch and has nothing to do with the actual 4wd engagement since it's vacuum controled.
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Saddle Tramp
New member
I may be wrong but I don’t think a solid axes swap is done that often except maybe on a hard-core machine, not a daily driver. Once the disconnect goes away lockable hubs will need to be installed too or the whole front axle will turn all of the time resulting in lower mileage and additional tire wear. Also if you have a locker in the diff that can not be completely disengaged (ARB, OX) just keeping the jeep on the asphalt will be hard to do when its dry and impossible if its icy. Granted lockable hubs are an acceptable method of disconnecting the front axle as all newer CJs have them but you must stop, get out of the jeep, and lock the hubs before you engage the 4 wheel drive. One of the perks of a Wrangler is that you can do this on the fly without getting out of the jeep. I would trash the vacuum hose and install the cable upgrade. In the long run it will be more reliable and cost about the same after you replace the vac hose a few times.
Sorry, I was being a little sarcastic when I mentioned the dashlight. Almost none of my dashlights work since the rig has been so beat up.
But while we're on the subject, if I reconnect the wiring and the dashlight does come on, does that mean the vacuum line is still working? Or will it give a 'false positive', telling me that I'm in Hi/Low 4 when the vacuum is not actually engaged?
Given that most of my dashlights are suspect, is there a some way to test to see if it's going into 4x4 mode short of lifting all four corners off the ground?
Thanks guys!
Yeah, I have to keep this as a semi-daily driver. The price for the cable actuator doesn't seem too bad compared to the vacuum actuator. That I think is what I'm going to head towards - assuming that it's not working now.
Bounty__Hunter
Super Moderator
You can put in the solid 1-piece axleshaft even on a daily driver, and it's not gonna change your mileage a bit. It will however turn your front driveshaft even when in 2wd so you will have a vibe if the front driveshaft is out of balance.
The '90 shouldn't have any wires to the front axle disconnect, only vacuum lines. The 4wd light switch on a '90 is on the firewall with a vacuum line running to it.
If your 4wd light comes on when in 4wd, chances are the disconnect is working properly.
If you want to test the disconnect, pull the double vacuum line from the axle and feel for good vacuum alternating between the two lines as somebody shifts the transfer case from 2wd to 4wd and back.
It's also a good idea to remove the 4 bolts holding the disconnect to the axle and pull the disconnect out of the housing. Then move the aluminum shift fork by hand to ensure it moves smoothly.
The '90 shouldn't have any wires to the front axle disconnect, only vacuum lines. The 4wd light switch on a '90 is on the firewall with a vacuum line running to it.
If your 4wd light comes on when in 4wd, chances are the disconnect is working properly.
If you want to test the disconnect, pull the double vacuum line from the axle and feel for good vacuum alternating between the two lines as somebody shifts the transfer case from 2wd to 4wd and back.
It's also a good idea to remove the 4 bolts holding the disconnect to the axle and pull the disconnect out of the housing. Then move the aluminum shift fork by hand to ensure it moves smoothly.
Gennybro
Active member
JUST MY OPINION,they say that ya can shift into 4wd on the go,I dont think its a good idea to do,that aluminum fork that engages your axles on the front,isnt all that stout,and the burrs that ya create on the splines is anouther maintenance issue . If its not an emergency,take your time and stop the vechicle to engage 4wd.
I have a 91 yj 4 banger, 5 speed,bought it used and it had the 4x4 posiloc on it,at first I wasnt to crazy about how it engaged but got used to it. On mine ,I have the vechicle stopped and use the control knob to engage it,you well be able to tell when you have it engaged by the feel of the knob.At times I have to move the jeep back and forth a little till you feel on the knob that it has engauged.I think its a better option then the vacume system.
I have a 91 yj 4 banger, 5 speed,bought it used and it had the 4x4 posiloc on it,at first I wasnt to crazy about how it engaged but got used to it. On mine ,I have the vechicle stopped and use the control knob to engage it,you well be able to tell when you have it engaged by the feel of the knob.At times I have to move the jeep back and forth a little till you feel on the knob that it has engauged.I think its a better option then the vacume system.
Bounty__Hunter
Super Moderator
gennybro, being stopped isn't enough for the disconnect to engage, it's highly unlikely the splines will be aligned well enough for the shift collar to move. It's not until you move with the front wheels turned slightly will the shafts rotate at a different rate & align properly.
the vacuum system is slightly better in this respect as the vacuum pressure on the fork is more forgiving until the splines are engaged.
the vacuum system is slightly better in this respect as the vacuum pressure on the fork is more forgiving until the splines are engaged.
i have a 97 tj that is my daily driver has one piece axles,i have a lockrite in the front,i notice no difference in 2 wheel drive on pavement than before i installed the locker,4 wheel drive on ice,very interesting,keeps your attention focused on driving.if it was mine and i was having problems i would put in the one piece shaftsget an axle shaft out of a junk xj,get the right size seal for the axle and be done with it
Last edited:
Gennybro
Active member
jfrabat
New member
Well, i disagree; I run a solid axle, and no manual hubs. I also run from Panama City, Panama to San José, Costa Rica a couple of times a year (about a 600 mile trip each way) with no ill effects. Keep in mind that while, yes, the front DS will rotate, so does the front DS on a TJ, and the TC is the same.
DREDnot
New member
I've had two YJs with the vacuum actuated axle.
The 87 was frozen up through non-use due to the vacuum lines being disconnected and tied up out of the way during earlier bodywork.
Sourced a used one from a junkyard($20) and reconnected the vacuum lines and it has performed flawlessly ever since.
My 90 was used offroad continuously since new and the original owner said he never had any issues with it. Neither did I.
Plug everything in, Test it to confirm proper operation, and enjoy the shift-on-the-fly goodness.
The 87 was frozen up through non-use due to the vacuum lines being disconnected and tied up out of the way during earlier bodywork.
Sourced a used one from a junkyard($20) and reconnected the vacuum lines and it has performed flawlessly ever since.
My 90 was used offroad continuously since new and the original owner said he never had any issues with it. Neither did I.
Plug everything in, Test it to confirm proper operation, and enjoy the shift-on-the-fly goodness.
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