03 expy front end noise

[strwrsnut]

I am hearing a loud metal to metal knocking coming from the area of the front tires. It gets louder the faster I go. Only makes the noise in 2wd. In AWD it makes a grinding noise. Can someone help lead me in the right direction as to what it may be. I thought it may be the brakes, so i changed the brakes and it made no difference. I read that there is some kind of vacuum that is required to keep the expy in 2wd, is this true.
Thanks for any help

 

[AvroAero]

The vacume system is used on some F150s expys use an electric motor. Try checking the transfer case oil, unscrew the fill plug and put your finger in there. See if theres still some in there or if theres shavings.

If you have stands put the truck on them and put in in drive and listen. (ALL FOUR STANDS) Switch it to 4wd and see what happens.

BTW keep a someone at the brake at all times.

 

[strwrsnut]

Thanks .. I will give that a try and post the results.
Thanks

 

[Junkyard Monkey]

Metal to metal? Get all four in the air and check the steering: ball joints, wheel bearings, tie rods, idler arm, etc.

Then, check the cvs and rear driveshaft (sometimes it can sound like it is in the front when it is not).

Check the rear diff too!

 

[speede]

There is a vacuum line that runs to the self locking hubs. The vacuum line is charged in 2wd. If you have a leak or low vacuum, the hubs start to engage and chatter. Once they engage, they are locked until vacuum is sufficient to dissengage unit.