Shift on the fly switch on 81 sx4

[olymunch]

So I bought an 81 sx4 and the 4wd switch is a later model on the fly version and a different color. How can I tell if its the correct transfer case. The 4wd works but I've only shifted it while the car was stopped.

[IowaEagle]

IIRC the NP 129 cases are identical -- just that the shift motors were different as the shift on the fly models did not have the axle disconnect and called for a different, fewer port, shift motor on the transfer case.  Any NP 129 can be made to work as a shift on the fly unit.

[olymunch]

So are you saying that if the switch is shift on the fly then the motor is as well and I can shift on the fly? What are the consequences of using the shift on the fly if it's not set up for it?   This is my first eagle so I'm pretty new

[IowaEagle]

Cannot tell if the motor was changed out for the right one without seeing it.  Who knows if the if the front axle was locked in place and then the existing motor was replumbed to make it shift on the fly??  That would all take a physical inspection.

[carnuck]

You need to look and see if there is a vacuum motor on the axle. It can be best seen by looking forwards between the passenger's side of the motor and the tire by the axle mount. If it was originally a NP119, someone may have put in a NP129 and this would be shift on the fly.

[olymunch]

I'll crawl under there and take a look, also there should be a plaque with the transfer case number on it right?

[carnuck]

Transfercase should have a round tag on the back, but if swapped, who knows what's in there?

If it's a vacuum axle, one of these will be on the tube with vacuum lines attached

[olymunch]

Thanks for the pic
Let me get something straight, so a vacuum would indicate a shift on the fly. So a non shift on the fly doesn't use a vacuum?

[IowaEagle]

Shift on the fly requires vacuum but only to the transfer case shift motor as there is no axle disconnect shift motor.

[carnuck]

Vacuum axle means it's not shift on the fly unless you modify it to be permanently engaged.

[olymunch]

Ok, I think I'll have to get it up in the air and double check, not that shifting to 4wd while stopped is all that hasslesome.

[carnuck]

Essentially if your dash switc has the pull before flipping the switch button, it's not shift on the fly. After the mod, you can pull that button off.

[olymunch]

Well it's a 1981 so It didn't come with shift on the fly but it has the shift on the fly switch but of a different color. So there's two things out of place, one being the existence of a shift on the fly switch at all, and the second being the different color.
When I hit the switch I can hear the vacuum engaging. I was just wondering if the existence of the different switch meant that I had shift on the fly but also wanted to see if there was a way I could be sure, like checking the diff or tc. I just don't wanna do any damage.

[carnuck]

Yup. Definitely check the front diff. If there is no vacuum lines or a shift motor on it, you're probably good to go.

[Draekon]

Late '81s were stop and shift, so they would have originally had a shift lever.  It is possible that switch was replaced with a shift on the fly switch, but all the drivetrain components are original stop and shift parts.

[captspillane]

The plug in the back of the shift lever is interchangeable, so it could have been replaced without modifying anything else in the system. The difference between on the fly and not on the fly is the collar of the front axle. If your wheel is spinning and the driveshaft isn't, you won't be able to slide the collar over. That's the only reason you have to stop to shift. The first two pictures show the collar that has to slide over. The transfer case itself did not change at all because that has the capability of meshing and sliding into gear while its spinning. This doesn't happen immediately since it takes several revolutions to line up, but the vacuum motor puts steady pressure on the gear until it happens. The vacuum motor then continues to put a slight pressure to keep it engaged.

If you have a front axle disconnect, you can put a hose clamp on the shift fork and then eliminate the vacuum lines to it. The last picture shows the hose clamp I installed on mine. As long as the collar is in place your axle is ready to go and essentially the same as the solid axle in the "shift on the fly" models.

I also eliminate the shift function on all of my Eagles. The 119 and 129 are both capable of being true all wheel drive. Some people quote a difference in wear and tear and fuel mileage, but realistically there just isn't a noticeable difference. The whole reason I drive an Eagle instead of a Jeep Cherokee is because they are designed to stay in four wheel drive without any adverse effects on the car. It has saved me from serious injury several times. To eliminate the 2WD function remove the vaccum motor and use rope to put a constant and steady pressure on the shift lever. It will pop into neutral and the car won't move if you do not have that steady pressure.

[olymunch]

Thanks, ya that's what I was thinking. I was kinda hoping that there was no way that you could change the switch without changing everything else but whatayagonnado.

[jim]

Advantages to changing to shift on the fly:
-you don't have to stop to shift, though like you stopping doesn't bother me;
-locking in the front axle eliminates the possibility of it jumping out when you need it;
-you can eliminate several sources of vacuum leak;
-you are more assured of shifting into 4x4 when you need it because now it is just up to the transfer case.
Disadvantages:
-having gear oil run down your arm when making the change.

[carnuck]

I want to put a cable shifter on mine (since it's already a vacuum axle in it) like Posi-lok. But if it's not 3.08 (or close) ratio, then it's coming out for the non-vacuum one I have anyways.

[carnuck]

olymunch's rig

[olymunch]

Thanks man!

[carnuck]

no prob! Got sidetracked trying to upgrade my computer this week and forgot to post them. (curse my Dain Bramage!)