drcomanche Posted September 16, 2019 Share Posted September 16, 2019 When I was leaving Ocean City Jeep Week a few weeks ago, I made it about 30 miles out and then felt something change. I could feel a very slight vibration suddenly in the pedals at certain rpms and when I accelerated with enough force I could feel it get a bit more noticeable and start creating a humming noise. It only occurred when I accelerated or, to a lesser degree, when I reached highway speeds and the rpms settled at around 2300 to 2500. It made the trip all the way back, granted i was babying it a bit, and then it sat until yesterday, when I drove it for about 30 minutes. The sound is far more pronounced now, at some points managing to compete with the engine noise, and began doing it when at low speeds in higher gears as well. The sound seems to be dependent on rpms and gears, as lower gears (1 and 2) don't make the noise at all, that I've noticed. The hum doesn't change pitch, but that may be because its only rpm related, not speed, and my rpms stay at 2 to 2.5k at all times. It does get louder and more pronounced the faster I go(since its raising the rpms). It's a 93 cherokee 4.0l, ax15. I've dug through a ton of the engine over the past 6 months, so I'm hesitant to say its engine related. Maybe worth noting is that the clutch seems to be getting more obstinate, so maybe throw out bearing? Link to comment Share on other sites More sharing options...
eaglescout526 Posted September 16, 2019 Share Posted September 16, 2019 How’s the harmonic balancer? Engine mounts? Link to comment Share on other sites More sharing options...
AZJeff Posted September 16, 2019 Share Posted September 16, 2019 What happens if you shift to neutral and let the engine drop to idle while it's making the noise at highway speeds? Does it go away, or stay the same? That test will tell you if it's driveline or engine related. Link to comment Share on other sites More sharing options...
drcomanche Posted September 16, 2019 Author Share Posted September 16, 2019 1 hour ago, eaglescout526 said: How’s the harmonic balancer? Engine mounts? Engine mounts seem fine with cursory inspection, no crack or failures and no dry rot or wallowing on the rubber. Harmonic balancer seems sound looking at it while it's running. A little dry rot, but not too bad. 1 hour ago, AZJeff said: What happens if you shift to neutral and let the engine drop to idle while it's making the noise at highway speeds? Does it go away, or stay the same? That test will tell you if it's driveline or engine related. I'll test it out when I get the chance. I did it yesterday but can't remember if it did. Link to comment Share on other sites More sharing options...
yxmj Posted September 17, 2019 Share Posted September 17, 2019 Check your u-joints on the front drive shaft.....especially the one coming off the trans case..... Link to comment Share on other sites More sharing options...
drcomanche Posted September 23, 2019 Author Share Posted September 23, 2019 On 9/16/2019 at 2:05 PM, AZJeff said: What happens if you shift to neutral and let the engine drop to idle while it's making the noise at highway speeds? Does it go away, or stay the same? That test will tell you if it's driveline or engine related. When I take it out of gear, the noise ceases. On 9/17/2019 at 4:46 PM, yxmj said: Check your u-joints on the front drive shaft.....especially the one coming off the trans case..... All the u joints across the entire vehicle have been replaced withing 1000 miles. I rebuilt both driveshaft before I went on the trip. Link to comment Share on other sites More sharing options...
AZJeff Posted September 23, 2019 Share Posted September 23, 2019 5 minutes ago, drcomanche said: When I take it out of gear, the noise ceases. More questions/suggestions to help narrow it down: 1. you say "take it out of gear." Does this mean just push the clutch in, or actually shift to neutral and release clutch? Do this both ways and report results. 2. additionally, when you push clutch in (and leave it in gear), rev the engine to the "magic" 2K to 2.5K range, and see what happens. They do the same with the trans in neutral, and the clutch engaged. Link to comment Share on other sites More sharing options...
Jeep Driver Posted September 23, 2019 Share Posted September 23, 2019 3 hours ago, drcomanche said: When I take it out of gear, the noise ceases. That's your answer. You unload the trans and noise stops......it's in the trans. Link to comment Share on other sites More sharing options...
drcomanche Posted September 30, 2019 Author Share Posted September 30, 2019 On 9/23/2019 at 3:21 PM, AZJeff said: More questions/suggestions to help narrow it down: 1. you say "take it out of gear." Does this mean just push the clutch in, or actually shift to neutral and release clutch? Do this both ways and report results. 2. additionally, when you push clutch in (and leave it in gear), rev the engine to the "magic" 2K to 2.5K range, and see what happens. They do the same with the trans in neutral, and the clutch engaged. Sorry for the late responses. I don't take it out much right now, so I don't get to test very many things. In all cases stated above, the noise stops. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now