HELP front hubs wont engage!

[RM27]

1999 4runner limited 4wd 3.4l v6

So I had my transfer case brake on me a few months ago, it was rebuild (not at the dealer) gears change I hear the clunk and also the engine acts as if it was in 4lo but the front wheels won't spin and the 4x4 light is always flashing we ther it's on 2x4 or 4x4.

 

[TheDurk]

It could be the T-case, but I bet they screwed up the connections to the ADD system, so first thing is to see if TC is not engaging or ADD is not engaging.

Do you have J-shift or pushbutton? (My '99 is a 5-speed.) In any case, put it in 2wd with engine running. Turn off engine but leave it in ignition power on. Try to engage 4wd. Get underneath and see if front shaft is locked. If it won't turn by hand TC is good ADD is bad. If it freewheels, problem is in TC. (The ADD runs on vacuum so engine must be running for it to work.The TC will engage with electric if pushbutton and the J-shift needs neither.)

If it is ADD, here is my diagnostic routine:

VSV’s/ADD
Don't guess at it, troubleshoot! Start at the twin VSV's (Vacuum Switching Valves) on the driver fender wall. There are two long vacuum hoses that come up from the diff, one goes to each VSV. Check to see that one of the two hose nipples on the VSV’s has vacuum (engine running, 4WD NOT engaged. If no vacuum either side, check the check valve going to the intake manifold and look for loose hoses or a hole in the reservoir. If there is vacuum going to one hose, then put it in 4WD. See if the vacuum switches to the other hose. If it does, and no 4WD, problem is the diff actuator or the line to the diff. If it does not, then just switch the hoses and you should go into 4WD. This confirms diff is okay. (Mark the hoses first so you know which belongs where!)

OK, switch them back. Then use a test light to see if electrical signal from the TC also switches sides of the VSV. If it does not, problem is the TC, the switch on the TC, or the TC actuator, or its wiring back to the button (last two for non-J shift only). If it does, but the vacuum does not, the problem is the VSV itself.

I start troubleshooting at the VSV's because you can figure out where the trouble is without having to climb under the truck. [None of this applies to '01-'02 which have an electric actuator.]

If it turn out to be that the VSV works but the electric does not switch sides, check the sending switches on the TC. The connectors can get crushed when the TC/trans is installed carelessly. A dealer did it to me on a clutch job.

 

[csp]

The "hubs" are always engaged on one of these unless you swap in manual lockouts.