Originally Posted by lewissa81

Since there's snow in the forecast, when you need 4wd, disconnect the electrical connector to the solenoid. Do not pull a vacuum line off. Pulling a vacuum line off will suck in snow, water, and moisture, and that can ruin the iwe actuators if they are good. That's if you don't get it figured out.
It sounds like the grinding you hear is the hubs partially engaging (I know you know this already). Since it doesn't start until certain speeds, I'd check (if not just replace) the two check valves first. They're cheap, easy to replace, and available at most auto parts stores. It may not be speed that's affecting them, but rpms. The higher the rpm, the less vacuum to the iwe's. The check valves are there to stop any drop of vacuum. If the lowered vacuum is sustained, then it can fall below the 7 psi (I think it's 7) threshold needed for the iwe's to disengage.
Just because you could pull the line off the driver side iwe easily doesn't necessarily mean that it's bad. You need to use a vacuum pump with a guage to verify if it's disengaging when it should. It doesn't take much to disengage them. Good luck!

Originally Posted by 6BUBBA9

all i could find was one check valve. and that one took air both ways suction and blowing. but the one i replaced it with only went one way?

Originally Posted by Rossco

The solenoid would have to allow 'Unauthorized' Vacuum to the IWE's.

Think the OP has changed that piece out.

When that goes bad the 4x4 usually does not disengage.

Originally Posted by 6BUBBA9

all i could find was one check valve. and that one took air both ways suction and blowing. but the one i replaced it with only went one way?

Originally Posted by lewissa81

They should only go one way. When they go both ways (like the old one), they are bad. There should be two, incase one fails. Did replacing it help at all?

Originally Posted by lewissa81

Nice, good to hear you got it all fixed up.