99 suburban front diff diagram spring came off plunger front end stays locked in in less i take accuator out and put magnet in and pull plunger back out

the out action will be spring loaded and the in action may be vacuum operation. Run the engine and see it the pressure changes.

either front diff or transfercase

drain the oil from the front diff and check for metal flakes
If you have flakes --diff problems
if the oil is clean then look else where --like cv joints or "U" joints in drive shafts

is i lockingt after you start it... and does it relese when turn off

if it has a spring between the side gears , it may be a limited slip diff center and the noise may have been the limited slip action coming off or engaging when one front wheel lost traction
if there is no metal bits in the diff then it may be nothing as long as both wheels turn the diff center , then the axle will still be intact

there is an aluminum shift fork behind the actuator that has a knurled end on it.that end breaks off and will not allow the diff to lock in.you will need to remove the passenger side axle and the actuator to access.also check the transfer case shift module.also common on that vehicle.

a common problem with Chrysler/Dodge minivans .. when you open the sliding door you will see two flat brass contacts on the door frame and two spring loaded plungers that connect to the flat brass contacts when the door is closed .. this provides power to the rear door locks when the lock is accuated.. .. i thought the contacts would surely be plated with something but they are not ... if they were plated then you would have to be careful how you clean them . but as it is you can use steel wool or sand paper and a cleaning solvent like alcohol .. clean both contacts and plunger tips .. for reliable operation you have to keep those clean ... in later years they started putting a rolling loop of wire connecting the doors electronics to the cars lock control .. thats probably more reliable .. the danger in the dirty contacts is that you might not know your back doors are unlocked unless you look every time .. and i bet the theves know that also .. ..

there is a thermal accuator that is mounted on your front differental it ingages your front diff and is acctivated by heat.basicaly it throws out a little rod that pushes a little plate to lock your front diff,it could be that when it's in four high that accuator is faulty and is disingaging the front diff.there was some issues with this and people where going and buying new transfer cases when it was that part

if you crawl under the vehicle, trace vacuum lines to transfer case they terinate in a group of 3 (vent, vacuum from engine, line to actuator diaphram under battery) . Mark lines (bundle should have a pin to prevent bad replacement, but be safe) pop 3 hose unit , unscrew switch (count the turns to return it to same position). Transfer case side has a ball that should detent fairly easily. If stuck, work it loose or replace the switch. This manual detented switchsimply routes vacuum to diaphram which pulls cable to front axle, or vents it to atmosphere when in 2wd.

You should be able to feel if diaphram is pulling in when in 4wd and is relaxed when in 2wd mode to troubleshoot. Direct vaccum to diaphram line to test. I have used aquarium airline tubing and airstone manifold to provide quick fix when a garage and/or access to parts was not available. You want to be able to direct vent to diaphram for 2wd and engine vacuum to diaphram for 4wd.

when the transfer case shifts into 4wd it activates a vaccum switch on the transfer case which sends vaccum to the accuator for the front axle. the accuator pulls a cable that locks in the axle. the switch on the transfer case is a well known problem. check for vaccum in and out of this switch in 4wd. if you have vaccum out then check the accuator under the battery. If the vaccum switch on the transfer case is bad you can find one at most parts store in the HELP section #49315. please rate if this helps