2ND Gen "ADD" Newbie Question

[B.C. Hoshall]

If this question is covered in the FAQ, please direct me. I did not see it.

I just got a 93' Runner and cannot get the front axle to engage. The truck has manual locking hubs and the ADD Control System. With the front end off the ground and on stands, I lock the hubs and can see the half shafts engage. The T-Case locks in but the 4WD light DOES NOT come on. If I engage the ARB up front, the passenger wheel locks in but the driver spins free. (again, the half shafts are engaged and I can see them spin only when hubs are locked)

How does one begin to diagnose where the failure lies in the ADD system?

 

[toy4xfun]

it sounds like something is broke. the arb should lock and both wheels should spin. i would start at the hub on the wheel that is not turning and make sure your manual lock in hub is not shot.

 

[B.C. Hoshall]

Hub seems to be working fine. Once I lock it in, I can see the half shaft spin. Unlocked, no spin. It is the drivers wheel in question and the ADD seems to be the culprit. I just don't know where to start in the diagonostics.

 

[KLF]

Just making sure... is the engine running when you shift into 4WD? The ADD system needs engine vacuum to move the sleeve inside the front diff.

Otherwise, take a look at the VSVs on the passenger side inner fender.

 

[B.C. Hoshall]

Yup. Tested with engine running and no engagement. After sifting through some diagrams, I am suspect of perhaps one or both (ground?) VSV's. When I pull the T-Case shifter into 4WD, I hear a relay click under the dash (ADD Relay) but no 4WD light comes on. So I think the Transfer Indicator Switch is functioning but I cannot isolate the Transfer Position Switch or the Transfer Pressure Switch. Both which I assume control the VSV's. So unless I am off track, IT lies between the Transfer Position Switch and the VSV's. Is there a fuse for this circut? Hmmm.

Thanks for posting.

Ben

 

[2ndGenToyotaFan]

Take a vacuum pump, pull the vac lines off the front axle, hook the pump up and try both hoses till the axle is locked up. One of the lines engages the axle shaft, the other disengages... I have an ADD front axle in my truck with no Add controls, I used a vacuum pump 6 months ago to lock it up and haven't had to mess with it since...

 

[B.C. Hoshall]

You guys rock. With a little patience, I found the VSV's and tracked the vacum lines. Both lines and the "T" connector were burned from a PO's power wire which had grounded out. They were burned most of the way through. The burned wire was no longer there but the damage was done. I replaced the fitting and Vac lines, started the truck, slipped it into 4WD and the dash light came right on. I took it out into today's Northern Colorado snow storm, and the front was most certainly engaged.

Props to the IH8MUD Addiction Support Crew!

 

[KLF]

Cool, great to hear you got it fixed.

But I'm with Jerod. Put it in 4WD, then pull all that vacuum line and VSV crap outta there. Loop the vacuum lines at the dashpot on the front axle. Leave it engaged at the front diff, since now that you have manual hubs you don't need the ADD system anymore.

 

[B.C. Hoshall]

Good idea. How would I create a vacum in the diaphram and keep it there. What did you and Jerod do to maintain the "engaged" pressure of the ADD link?

 

[B.C. Hoshall]

I think I just answered my own question... There must be no return spring to slide the actuator from engaged to unlocked. So if I have the axle splines engaged and disconnect and cap the Vac lines, the ADD should not disengage. At which point, the manual hubs are all I need.

Sound about right?

Thanks,

Ben

 

[NorCalBorn]

I like threads like this, all I have to do is chime in with a reply and go about my days.

 

[toy4xfun]

hey this great now i do not have to ask the question when i put manual hubs on my 95.

 

[2ndGenToyotaFan]

Correct, I have no hoses hooked up to my ADD diff. I just locked it and left it.

 

[selk78]

thread revive...

sorry to hijack this thread but this thread is the closest thread i could find in my search. I have a question? do you need to deactivate the add system or can you just leave it as is? i'm gunna be adding manual hub locks to my 92 pickup and it has the add system on it, all the thread's on switching from add lock 4wd to manual hub lock's don't say anything about whether or not to leave it alone or deactivate it, anyone know?

 

[NorCalBorn]

*I'm pretty sure this is all in this section's FAQ's, but just in case..

... i'm gunna be adding manual hub locks to my 92 pickup and it has the add system on it, all the thread's on switching from add lock 4wd to manual hub lock's don't say anything about whether or not to leave it alone or deactivate it, anyone know?

You can..

Leave the ADD system intact and once you turn your hub locks and engage the 4wd you're good to go, just like two people above have done.

Remove the vacuum system, leaving the actuator on the front diff, but open it up and hose clamp the actuator into the active position, things will only be turning when in 4wd anyhow.

ie: Toyota Tech: Defeating the ADD System - ORN

Do like a few of us have done and get the earlier drivers side output and chuck the entire ADD system.

A big thing to note whenever people switch to the manual hubs is to be sure to use the correct splined washers under the c-clip before installing your locking hubs. This will prevent your front shafts from "clunking" around and prematurely wearing out your inner bushings.