Auto locking hubs not locking

[SJD83]

Can anyone direct me to a thread that covers this? The transfer case is working and engaging, but the hubs will not engage. I have a '97 SR5 3.4. Everything worked fine until I had the top end of my engine rebuilt last year. When asked about it without the vehicle there, a mechanic at another shop told me it's probably a vacuum problem, since everything else is engaging. I'm thinking something got left unhooked or was cut when the engine work was done, as the guy was really sloppy and left a lot of things unhooked or damaged.
Thank you in advance!

 

[jgue467]

This has been covered many times here. Search this site and look for posts by The Durk, he knows this stuff on your MY back and forth. :cowboy:

 

[SaulG]

97 should have ADD actuator on front axle check the connections there then at the VSV's on inner fender.

 

[phattyduck]

If they pulled the engine, they may have damaged the harness to or the ADD position switch on the front diff. This happened on my '97 parts truck before I bought it.

So, check for:
- Vacuum line off back of intake manifold to 1-way valve, to VSV's and vacuum canister in the front driver's fender well
- small wire harness that runs from around the driver's side exhaust manifold down to the back of the front diff for the ADD indicator switch.

Switch circled in blue here:

-Charlie

 

[SJD83]

Thanks for the help, guys. I'll check these things this weekend!

 

[meRockboost]

If the dash indicator comes on for 4wd then then it may be the transfer case switch that tells the vsv to actuate the front diff.