Does any one know how to modify the vacuum controls on my transfer case to allow for 2wd low range. I have heard it can be done but looking at the service manual it seems like the best you could do is 3wd. I see how to turn off the front passenger wheel power but it seems to me the front drivers side would still get power. Any ideas would be appreciated.
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2nd Gen Non-Engine/Transmission 2 wheel drive low range
- Thread starter Berrigan
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bighammer
Super Moderator
You will not have power to the left front wheel unless you have a locking differential. (with the right side disconnected, the power to the left is lost in the diff gears) If you get the transfer case in low range and keep the right side disconnected, you will have 2 low.
An electric/pneumatic switch (like used with an exhaust brake)can be used with a switch on the dash or shift knob. I used a manual pneumatic switch (same thing, but with a push pull knob) and got the same effect for about 25 bucks.
Instead of vacuum going to the transfer case, it goes to the switch, and then to the axle. Shifter for transfer case only does the gears.
An electric/pneumatic switch (like used with an exhaust brake)can be used with a switch on the dash or shift knob. I used a manual pneumatic switch (same thing, but with a push pull knob) and got the same effect for about 25 bucks.
Instead of vacuum going to the transfer case, it goes to the switch, and then to the axle. Shifter for transfer case only does the gears.
Last edited:
Hammer,
Does the transfer case continue to send power to the front drive shaft in this 2 low situation?
A few weeks ago I unplugged the Vac line under the hood going down to the trans case. I assumed that would unlock the front right wheel. I then put truck in 4 low and drove it. I still felt the hop and woble that you feel when turning corners in 4wd on paved surfaces. Not good.
Then I looked at the service manual and it seemed to indicate that the vacuum actuator on the front right axle needed to have vacuum reversed to unlock (not just removed).
Does this sound right?
Also you said the diff would remove power from front left.
Then the diff in this situation would see the same thing as the front right wheel with no traction and an open diff would let that wheel spin up. If thats the case then this 2wd low should not be used for any length of time. Maybe just backing up trailers or parking at low speeds.
What do you think?
Thanks for your help,
Does the transfer case continue to send power to the front drive shaft in this 2 low situation?
A few weeks ago I unplugged the Vac line under the hood going down to the trans case. I assumed that would unlock the front right wheel. I then put truck in 4 low and drove it. I still felt the hop and woble that you feel when turning corners in 4wd on paved surfaces. Not good.
Then I looked at the service manual and it seemed to indicate that the vacuum actuator on the front right axle needed to have vacuum reversed to unlock (not just removed).
Does this sound right?
Also you said the diff would remove power from front left.
Then the diff in this situation would see the same thing as the front right wheel with no traction and an open diff would let that wheel spin up. If thats the case then this 2wd low should not be used for any length of time. Maybe just backing up trailers or parking at low speeds.
What do you think?
Thanks for your help,
bighammer
Super Moderator
Front driveshaft still turns, but w/o the right side connected, the "stub" axle shaft between the diff and the rt axle disconnect will just spin free.
For a while I would just disconnect the vaccuum line under the hood when I wanted the 2 lo. Are you sure you did the correct one? The one for the heater controls looks about the same. Did the 4wd light come on? (It shouldn't)
The way it is set up, it does use vaccuum to disengage it. If you are in 2wd and take away the vaccuum source it shouldn't connect. With the switch I have, it has vaccuum for either way and vents off the inactive side.
Maybe with it set in 4wd and the vac disconnected, jack the right wheel and spin it by hand. Maybe your axle is not disengaging?
For a while I would just disconnect the vaccuum line under the hood when I wanted the 2 lo. Are you sure you did the correct one? The one for the heater controls looks about the same. Did the 4wd light come on? (It shouldn't)
The way it is set up, it does use vaccuum to disengage it. If you are in 2wd and take away the vaccuum source it shouldn't connect. With the switch I have, it has vaccuum for either way and vents off the inactive side.
Maybe with it set in 4wd and the vac disconnected, jack the right wheel and spin it by hand. Maybe your axle is not disengaging?
I started down the road you're on but bought a kit instead, one of the best, no, the only "store bought" mod on my truck. If you want details look for a link in my profile. Easy install and simple.
I think that if the axle was engaged all the time (failing to disconnect) that you would get the crab walk full time.
Try the test mentioned above or unplug the vacuum brake on the front axle (plug the hose) and try that.
I think that if the axle was engaged all the time (failing to disconnect) that you would get the crab walk full time.
Try the test mentioned above or unplug the vacuum brake on the front axle (plug the hose) and try that.
BD made a kit that works very well. It applies vacuum to the unlocked side of the right axle lockup actuator for a positive disconnect same as when it is in 2 wheel high.
Jay
Jay
I purchased the solenoid from www.eaglecontrols.com it is a Numatics L01SA459B. This is a very small 12v solenoid that is used with a lot of the exhaust brakes.
To install, find the vacuum line header along the top of the fire wall just above the fuel filter. You will find a vacuum line going down to the transfer case. All you have to do is place the solenoid in this line, which when activated will block the vacuum from going to another solenoid that is activated when you pull the transfer case shifter in.
So when you have it installed, you turn the solenoid on, and then pull the shifter in, and walla!!
It works very well when backing a heavy load, or when you want to creep over rough terrain, and don't need 4x4.
I hope this is at least clear as mud! It's really pretty simple.
Stick
To install, find the vacuum line header along the top of the fire wall just above the fuel filter. You will find a vacuum line going down to the transfer case. All you have to do is place the solenoid in this line, which when activated will block the vacuum from going to another solenoid that is activated when you pull the transfer case shifter in.
So when you have it installed, you turn the solenoid on, and then pull the shifter in, and walla!!
It works very well when backing a heavy load, or when you want to creep over rough terrain, and don't need 4x4.
I hope this is at least clear as mud! It's really pretty simple.
Stick
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