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96 T100 4X4 not engaging

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Old 10-12-2010, 05:22 PM   #1
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96 T100 4X4 not engaging

So I have been pretty happy with my truck and it's never let me down.. until last saturday.
I did notice that the 4x4 light sometimes didn't light up on the dash, however I always assumed it was still locking in becuse I never had any traction issues.

Anyway on saturday I did find some traction issues and found that the front isn't locking. This doesn't have locking hubs (which I am used to and I still think I prefer but that's another story for another day) and it's supposed to engage when you throw it into 4H or 4L.

Anyway I had to get pulled out and look like a moron and I'm not gonna have that happen again so I need to get this fixed. What should I start with checking and looking at?

I can see there is some deal with two vacuum lines going to the DS 1/2 shaft in the front and the vacuum lines appear to be OK, but can someone explain in laymans terms how the system works and what I need to be checking.

Is there a switch on the 4wd shifter that could be out of adjustment?

Anyway to easily test the front vacuum unit I mentioned above?

All help is greatly appreciated! I can't let this thing stay 2wd or I'll never hear the end from the Dodge diesel crews..
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Old 10-12-2010, 06:14 PM   #2
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Check all the vacuum lines running down to the differential, to make sure their still in good conditon and not broken/cracked/disconnected. Then, look in the FSM for the procedure for checking the 4wd VSS switches mounted to the fender. I'm not sure on the procedure myself, but I know it isn't that hard.

-Edit-Here's a link for a little more help.

http://www.off-road.com/trucks-4x4/t...tem-19259.html

Last edited by 250000_yota; 10-12-2010 at 06:17 PM. Reason: Found a link
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Old 10-13-2010, 09:04 PM   #3
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IIRC, the front axles are always spinning, even when in 2 wheel drive, thats why most replace the hubs with manual ones (asin or warn)
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Old 10-13-2010, 09:32 PM   #4
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yes, the front axle's are always spinning, but I believe the issue he's having is that either that the ADD system isn't working. The actuator probably isn't moving, for one reason or another. When I worked at the dealership, we recommended that people engage 4wd at least once a month, to make sure the actuator's didnt freeze up. I've replaced quite a few on newer tacoma's and tundra's because of this.
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Old 10-14-2010, 04:15 AM   #5
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Quote:
Originally Posted by 250000_yota View Post
Check all the vacuum lines running down to the differential, to make sure their still in good conditon and not broken/cracked/disconnected.
X2

My 95 T did the same thing. Remove the wrapping on the lines and check em. When it happened to me, one of the lines melted on the exhaust manifold.
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Old 10-18-2010, 02:13 PM   #6
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we recommended that people engage 4wd at least once a month, to make sure the actuator's didnt freeze up.
Interesting, my T sat for over two years (one year outside) while I put it back together after the roll over and I took it out two weeks ago, shifted into 4 wheel drive and it worked right away. Then I did some vigorous wheeling this past weekend with no problems at all!
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Old 10-19-2010, 08:43 AM   #7
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Congrat's on gettin your truck back up and movin!

Ya, I've replaced many many actuators. Mostly on Tundra's, Tacoma's and 4Runners, but I have seen them freeze on the older ADD diff's like in our T's.
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Old 11-17-2010, 12:11 PM   #8
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No 4WD

Hey, my 4wd does not engage from time to time in my 96 also. seems something heats up after a long drive, and the tranny/t-case/ whatever needs to cool down before it will. Had to pull mine off the beach once with a 4cyl nissan. embarassing. I'll leave it to better wrenches than I to decide what actually heats up, but if i let it sit for a while. or try the next day, it works fine. Good luck!
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Old 11-25-2015, 02:26 PM   #9
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4x4 Light on dash lights up but 4x4 no worky

Not to Hi-jack this thread, but I have searched everywhere on a ton of forums and haven't found anybody that is describing the issue that I'm having. The issue: Just bought a 1997 T100 4x4, and the 4x4 doesn't engage. What happens when I shift into 4hi or 4lo: Light on the dashboard immediately lights up, I hear a clicking in the dash from the relay, and I hear a sort of wirring/rubbing sound coming from the tcase/diff area. I have checked all the vacuum lines, solenoids, etc. Vacuum is applied to the right lines at the right time, so I have ruled out the solenoids and possible vacuum issues.
With the front wheels jacked up in 2wd both wheels spin freely (not moving the others, like a 2wd truck.) When I shift into 4wd the wheels slightly turn each other but not locked in like they should be. I thought the ADD in these trucks meant the front axle was always locked, even in 2wd. But obviously I'm misinformed. Plz halp.
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4wd, 4x4, 89, 96, click, coming, drive, engage, engaging, fix, hear, light, t100, toyota, wheel, working

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