New question reguarding auto-locking 4x4 system

[MTMatt]

I have read a lot of the threads here relating to 4x4 problems but nothing to suggest that vacuum is part of the automatic 4x4 process on the 94 X 4.0L, 120K miles.

The problem: pushing the auto 4x4 button puts it in 4 wheel drive and a fairly high pitched, medium volume whistle begins at about 3 mph (no whistle when stopped) as speed increases, pitch decreases and volume increases. Then, when I disengage the 4x4, the whistle continues until I stop, put it in neutral and give the engine a good revving. No more whistle until I again use the auto 4x4.

Nothing new has been added recently. It's been six months since I flushed the auto trans (no slippage afterwards though it was dirty), and other boxes and several years since I replaced the auto hubs, bearings/races and brake pads. Its not brake squeal noise. I'm almost sure its air leaking somewhere from a vacuum valve, motor, or actuator involved with the 4x4 system.

Since i can't hear it until moving it's difficult to pinpoint the source.

Any ideas?

 

[Maniak]

You are correct, vacuum is not related to the 4x4 system.. Its all electric or mechanical.

The noise your hearing is problably coming from the from the the xfer case, front drive shaft, or somewhere in/around the front diff. Since it only makes the noise when in 4x4 and when moving.

The only way to really issolate it is going to be lifting the truck (all 4 tires) and putting it in drive while its in 4x4.

Do use common sense, don't hold it up with jacks.. Use a lift if possible or be very careful using Jack Stands..

~Mark

 

[MTMatt]

No resolution to high pitched noise.

I put on new brakepads and rotors in front and shoes in back, put grease in appropriate spots indicated by brake manufacturer recomendations

Totally disassembled auto hubs and wheel bearings, new rotors, cleaned and repacked bearings and hub with a good grease. Not lithium based.

The noise continues but not as I described before. the noise is always high pitched but will vary from one day to the next.

I put it up on blocks but could not recreate the noise. Only unbalance tires made a noise.

Still baffled, still looking...

 

[MTMatt]

Can someone describe in detail what happens inside the transfer case when 4x4 is engaged? Doesn't an aluminum fork position the drive gear to engage the front drive line?

 

[sumless]

I believe so, but honestly I've never broken one down to see. This link
http://www.rsgear.com/borg1354electric.htm

Might give some insite as to the inner workings of it, but you might also look thru out the forum as theres several refs to tranfer cases.
I'm not aware of any vacuum lines associated with the transfer case, but you might want to investigate changing the oil in it, perhaps its lacking lubricant? Dunno. Good luck

Cheers!
-Joe

 

[DeRocha]

...cleaned and repacked bearings and hub with a good grease. Not lithium based...

Exactly hub much grease did you pack into the HUB? The hub should only get a thin thin thin amount of grease to prevent rust... Too much grease can hydro-lock the hub preventing full engagement.

 

[gsmaclean]

I have read a lot of the threads here relating to 4x4 problems but nothing to suggest that vacuum is part of the automatic 4x4 process on the 94 X 4.0L, 120K miles.

The problem: pushing the auto 4x4 button puts it in 4 wheel drive and a fairly high pitched, medium volume whistle begins at about 3 mph (no whistle when stopped) as speed increases, pitch decreases and volume increases. Then, when I disengage the 4x4, the whistle continues until I stop, put it in neutral and give the engine a good revving. No more whistle until I again use the auto 4x4.

Nothing new has been added recently. It's been six months since I flushed the auto trans (no slippage afterwards though it was dirty), and other boxes and several years since I replaced the auto hubs, bearings/races and brake pads. Its not brake squeal noise. I'm almost sure its air leaking somewhere from a vacuum valve, motor, or actuator involved with the 4x4 system.

Since i can't hear it until moving it's difficult to pinpoint the source.

Any ideas?

No ideas, but I'll be watching closely, because my 94 Limited makes the exact same noise - but not all of the time. It seems to be more prevalent when it is cold outside and the truck is cold soaked. Once it warms up, or if it's warmer outside, the noise is not there.

 

[DeRocha]

Can someone describe in detail what happens inside the transfer case when 4x4 is engaged? Doesn't an aluminum fork position the drive gear to engage the front drive line?

Take a peek at How 4x4 works

 

[Mud Bug 94]

the noise ur hearing is the front axle,driveshaft and transfer case spinning.. its a little whiring sound correct?there is absolutly no vaccum accuation...its purely mechanical...if you put in nuetral, push the 4x4 button, the light comes on, and then put it in drive or reverse and roll alittle bit it then engages the hubs..mechanicly.while driving the hubs will be locked.when you put it in nuetral again, and hit the 4x4 button, you only disengage the t-case, the hubs will still be locked until the vehicle rolls foward or backwards to mechanicly disengage them. the main cause of this noise is the extera gears in the t-case spinning. but some is from the front axle...its perfectly normal so ur ok with the noises.