Buzz through interior

OK, so I got my jeep back from the shop 2 days ago, had 4.88's and rear locker installed.

Did the R & P break-in (15-20 miles then let cool down) and then drove it on the highway the next day.

When I get to 65 MPH, their is a buzz that goes through the interior/cabin and a vibration on the floor board and rear view mirror (sounds like its coming from the front end). Its not a constant buzz/vibe but a fading and reoccurring buzz/vibe within seconds of each other. If I go faster it is still their and a little louder. Its not transmission related, I don't think, cause when I down shift on the highway it doesn't get worse or better. It just happens when I get to 65 and above.

Before the jeep went into the shop, it never had this buzzing or vibrations. It's not a tire hum, cause I can still hear the tires too.

I was thinking of taking off the front DS and see if that helps.

Any ideas?????

Most likely driveshaft vibes do to the increase in RPM's.

Take it back to the shop. How do you know they didn't leave something loose, like your front driveshaft bolts? I'd be backing away from the keyboard and crawling under that Jeep and having a gander before I even considered driving it back to the shop. Have you any idea what damage can be done to you, your Jeep, and others should the front driveline drop out at speed?

Ok, goin to call the shop and let them know. In the mean time I took off the front DS and 99% of the noise is gone, and no vibes through floor board. could that mean that I have bad U-joints? The rear DS U-joints were all replaced with the lift, while the fronts weren't.

This is a resonant vibration caused by the increased RPM of the drive shaft. The vibes caused by the drive shaft are interacting with other parts of the drive train causing resonant frequencies that show up as a buzzing. The fix, better balancing of the drive shaft. Sometimes a little more vibration of the drive shaft shifts the resonant frequency to where you can't feel it or where it only occurs at a much higher shaft RPM.

RCP Phx said:

Most likely driveshaft vibes do to the increase in RPM's.

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Agree.

jeeperjohn said:

This is a resonant vibration caused by the increased RPM of the drive shaft. The vibes caused by the drive shaft are interacting with other parts of the drive train causing resonant frequencies that show up as a buzzing. The fix, better balancing of the drive shaft. Sometimes a little more vibration of the drive shaft shifts the resonant frequency to where you can't feel it or where it only occurs at a much higher shaft RPM.

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Agree.

cruiser54 said:

Take it back to the shop. How do you know they didn't leave something loose, like your front driveshaft bolts? I'd be backing away from the keyboard and crawling under that Jeep and having a gander before I even considered driving it back to the shop. Have you any idea what damage can be done to you, your Jeep, and others should the front driveline drop out at speed?

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And definitely agree. While the first two posts are correct, so is Cruiser54--you should go back to the shop that did the work, take them for a test ride, and get their on-site opinion.

When in doubt you should always give the shop that did the work an opportunity to check/mitigate any issues.

Good luck.

OK, took it to the shop that did the work, went on a test drive. At first he said it feels like a tire thats out of round, then nothing else. Told me to drive the 500 or so miles, the break in period, and change the oil in the diff and see if it gets better. Got back to the shop and he said he'll check the preload and backlash, I thought it was going to to take a couple of hours, but all he did was got under the jeep and felt the front DS. I dunno....

Called a driveline shop here in Vegas, and told him that I wanted the front DS rebalanced. He told me to bring it down to him (the jeep) and he'll look at the front end, to make sure that it was the DS causing the vibes and nothing else. He didn't want me to pay for the balancing and have it still vibrate/buzz, so that it wasn't a waste of money. Thats a good guy/shop to me. Looked at it and everything seemed ok to him, other than the fact that the DS's wouldn't spin freely when the TC was in "N" and tranny "N" at the same time (was still on ground). So imma take it to him next week sometime to have it rebalanced (less than $40).

Meanwhile I rotated the pinion more towards the front output shaft in the TC and took it for a drive and same thing. So it wasn't the pinion angle of the D30. So hopefully the balance will take care of the vibes, and if it does or doesn't imma order a new front DS from TW and go from there.

$40 is a damn good price for rebalancing if it is done right.

Got the OE front DS balanced and installed, and still the same thing.

So then I put the front DS on the rear by itself, without a front DS. With this setup their is a hum. The more load on the motor the louder the hum gets at only above 65 mph. When coasting the hum is almost gone.

So then I put the old rear DS (tom woods) on the front and drove with both shafts connected and the hum is still their, but the old oscillating vibe/hum is gone.

Got to head to work now so tomorrow imma disconnect the rear DS and drive on the front only and see what happens.

Any ideas for now???

Just installed new tom woods front DS and 50% of the vibe hum is gone. What else can i check from here on?

4LVLFWD said:

...Looked at it and everything seemed ok to him, other than the fact that the DS's wouldn't spin freely when the TC was in "N" and tranny "N" at the same time (was still on ground)...

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This is somewhat concerning... If the vehicle is still on the ground, the driveshafts shouldn't spin freely. The differentials are still engaged, so to speak. Once off the ground and in neutral (in the transmission and TC), the shafts should spin freely.

If the shaft is balanced properly, yet you've identified it as the source of the vibration (which appears to be the case), you may need new U-joints. I had a similar resonant vibration at highway speeds with my 2001 when I first got it... Replaced the rear DS U-joints and it all went away (didn't re-balance the shaft).

4LVLFWD said:

Just installed new tom woods front DS and 50% of the vibe hum is gone. What else can i check from here on?

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Now that I read this (my apologies for the oversight), it sounds like it could be an issue with the front differential (pinion most likely)... Then again, how many miles have you driven with the new Tom Woods front shaft? After replacing my rear DS U-joints, it took about 100 miles to smooth out (but this is also because I warped the ears a bit while pressing the new ones in... apparently they needed to settle).

tom woods shaft has been on for only about 100 miles or so. would bad or going bad axle u joints cause this?

You know, I don't want to rain on the parade, but you might never get rid of the vibe/hum 100 percent.

You regeared and now all of those components are spinning at different rates from stock form. The unibody transmits a lot of vibrations. Are you running poly engine/trans mounts? You might have more luck putting some kind of closed cell foam material around the unibody to dampen the vibes/hum.

Good luck.

joe_peters said:

You know, I don't want to rain on the parade, but you might never get rid of the vibe/hum 100 percent.

The unibody transmits a lot of vibrations. Are you running poly engine/trans mounts? You might have more luck putting some kind of closed cell foam material around the unibody to dampen the vibes/hum.

Good luck.

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Would stiffer motor/trans mounts help in this situation?

Where would one get some of these closed cell foam at?

4LVLFWD said:

Would stiffer motor/trans mounts help in this situation?

Where would one get some of these closed cell foam at?

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stiffer (poly) mounts would make it worse. Stick with stock or MORE/Brown Dog rubber mounts.

anthrax323 said:

This is somewhat concerning... If the vehicle is still on the ground, the driveshafts shouldn't spin freely. The differentials are still engaged, so to speak. Once off the ground and in neutral (in the transmission and TC), the shafts should spin freely.

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Since I regeared, I've found it necessary to often "back up" to get the t-case to change gears, especially out of 4hi, which he would have went through to get to neutral.

4LVLFWD said:

Would stiffer motor/trans mounts help in this situation?

Where would one get some of these closed cell foam at?

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IslanderOffRoad said:

stiffer (poly) mounts would make it worse. Stick with stock or MORE/Brown Dog rubber mounts.

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Stiffer = worse.

Brown Dog has the natural rubber mounts that work very well, great people to do business with.

Should be someone around your area selling foam. You want closed cell so it doesn't absorb moisture.