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I posted last week about some problems I was having with a front diff noise when I shift into 4h or 4l in my 98 5.4. I put it up on jack stands to look around and I've noticed a few more things.
Here's what I'm dealing with: 1) When I shift on the fly I hear a loud groan as if the gears are trying to mesh but can't. While this noise is taking place the front wheels are not spinning, but within a few moments the truck jerks and the front wheels turn. 2) While this noise is taking place (and the front wheels are not turning) the front drive shaft is spinning. 3) If I shift into 4h while stopped (in drive or in park) there is no noise or jerking. 4) While driving in 4h a loud groan comes from the differential but there is no noise when in 2wd. 5) I replaced the gear lube today and all symptoms are still there. 6) I've owned the truck for the last 7 years and the 4x4 has always worked fine. More importantly, it hasn't been abused during that time either.
I've read some previous posts regarding shift fork problems that some guys have been having. Where specifically is this located and what am I supposed to be checking? Vacuum? Movement?
As you can tell I don't have much experience with 4wd systems and I'm a complete loss. However, I refuse to admit defeat and take it into the shop. I figure if could handle the blend door myself last summer I can handle this with no problem.
1) When I shift on the fly I hear a loud groan as if the gears are trying to mesh but can't. While this noise is taking place the front wheels are not spinning, but within a few moments the truck jerks and the front wheels turn.
Are you trying to shift on the fly while the truck is on jackstands?! If so, then STOP! You are asking for very expensive damage! Your front and rear tires must be traveling the same speed for 4WD to engauge....IE: Traveling in a straight line without spinning or skidding.
The front-end noise might be a bearing going bad...
I 2nd that, engaging 4 wheel drive on jack stands while the rear tires are rotating is VERY bad. The transfer case can handle it because it’s got a clutch to bring the front driveshaft up to speed first, however you front dif relies on the moving road to keep things synced up, that grinding is your shift fork trying to engage out of sync gears. What prompted this little venture to begin with?
Anyways, the only real problem I see is a bearing like ATC said.