# Toyota t100 4 wheel drive not engaging

**URL:** <https://community.cartalk.com/t/toyota-t100-4-wheel-drive-not-engaging/11598>\
**Category:** Maintenance/Repairs\
**Tags:** t100, toyota\
**Created:** [March 8, 2008, 9:49pm UTC](https://community.cartalk.com/t/toyota-t100-4-wheel-drive-not-engaging/11598 "2008-03-08T21:49:30Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jandjleavell](https://avatars.discourse-cdn.com/v4/letter/j/db5fbb/32.png) [@jandjleavell](https://community.cartalk.com/u/jandjleavell)\
**Post date:** [March 8, 2008, 9:49pm UTC](https://community.cartalk.com/t/toyota-t100-4-wheel-drive-not-engaging/11598/1 "2008-03-08T21:49:30Z")

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I have a 97 toyota t100 with ADD (automatic disengaging differential. I am able to move the 4wd shifter through both low and high positions but 4wd is not engaging. the vehicle sat for a few months and I think that may be part of the problem. any ideas how to get 4wd to engage

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**Author:** ![Beefy\_Norm](https://avatars.discourse-cdn.com/v4/letter/b/a4c791/32.png) [@Beefy\_Norm](https://community.cartalk.com/u/Beefy_Norm)\
**Post date:** [March 8, 2008, 10:03pm UTC](https://community.cartalk.com/t/toyota-t100-4-wheel-drive-not-engaging/11598/2 "2008-03-08T22:03:01Z")

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The biggest problem here is that you actually bought a Toyota. The only thing more reliable then a Toyota is the reputation.

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**Author:** ![rripstop](https://avatars.discourse-cdn.com/v4/letter/r/65b543/32.png) [@rripstop](https://community.cartalk.com/u/rripstop)\
**Post date:** [March 8, 2008, 10:17pm UTC](https://community.cartalk.com/t/toyota-t100-4-wheel-drive-not-engaging/11598/3 "2008-03-08T22:17:23Z")

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ADD uses a vacuum actuator to engage the front differential. The vacuum slides a coupler connecting the front axle which activates the diff and the front drive. There are hoses that connect from the vacuum actuator to a switch then to the manifold. Sometimes the diaphram(s) in the actuator will get torn or develop a hole. Age will certainly contribute that happening. The actuator is up by the front axle likely next the diff. Haven’t looked in a T100 before but logically that’s were is should be.