Vacuum disconnect front axle shifter and vac modification

[Zoro]

I've got an '84 with the vacuum disconnect front axle. I've come to the conclusion that I want the shift on the fly ability but not all the time. Has anybody played with the vacuum lines and added a secondary switch that just locks in the front axle?

This is the secondary switch I was referring to:

http://www.bjsoffroad.com/prod-1326.htm

My idea is to have the system be able to operate both in the stock configuration and shift on the fly. Basically use the secondary switch to lock the front end in, while stopped, on days that I think I may need to use the 4wd and 99% of the time it would work the stock way. Good example would be a questionable weather day then driving on the HWY and all of a sudden it's snowing but pulling to the side of the road is not an option for safety reasons.

Yeah...I could just leave it locked in 4WD all the time but I try to shoot for max MPG always.

[eaglefreek]

Could you use another stock 2wd-4wd selector? One for the front axle and one for the transfer case?

[Zoro]

Could you use another stock 2wd-4wd selector? One for the front axle and one for the transfer case?

Yeah, I could do that. I'm just trying to keep it as simple as possible if my better half needs to drive it

[BenM]

It should be possible. If you have access to some leftover emissions parts you could use a vacuum sensor on the outlet from the front axle motor though an electric switch on the dash to trigger a pair of vacuum solenoids to engage the transfer case motor.

At rest the solenoids engage 2wd mode at transfer case, and when the switch is turned on by the vacuum signal from the front & the switch is on, it energies the solenoids so that 4wd is engaged. That way the transfer case can never shift until the front axle has been engaged. You need to use two solenoids (they come as three anyway) so that the motor can vent when it moves.

It could also power a convenient front axle is engaged indicator. The 4" switch closes (connects) when vacuum is applied, and it'd be perfect for this. If you use the 10" switch on the transfer case motor front axle port it will light up when it's in 4WD mode, but without a vent in that motor I'm not 100% sure that it will always turn on. (If I'm reading the select shift digrams correctly.)

It's a lot of vacuum hose and wiring, but foolproof for the operator.

[ammachine390]

You could also just leave the front axle permanently locked with the hose clamp method to give you shift on the fly.

[carnuck]

Just a note, but if your SO ever engages 4x4 and the front axle isn't engaged, say goodbye to your tcase! That's why it's better to have the front permanently engaged.