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Old 04-19-2013, 10:51 AM   #1
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Slight RPM related Vibe

About this time last year I had a regear done at a very highly recommended local ring and pinion shop. Previously to that I had installed a 4" sus lift with tc drop and 33" tires. Before the regear and after the lift I had no vibrations at all. Upon getting the regear I started feeling a very slight vibration above 60mph if I layed my arm on the center console (you can also detect a change in sound .. kind of like gear mesh).

Thinking it was probably u-joints, since then I have replaced both axle u-joints, front drive shaft u-joints, installed an SYE, Tom Woods drive shaft, Currie upper and lower control arms, got rid of the tc drop, and adjusted the pinion angle. The vibe is still there.

The other day I took it back to the ring and pinion shop and they pulled the diff. covers and checked the gear wear and specs., and said everything there was good (it has about 5000 miles on it since the regear) They also drove it with the front drive shaft removed and the vibe was still there.

I'm pretty sure this vibe is related more to engine/transmission rpm than to speed. The only thing that really changed at the regear was rpm's at a given speed. I've found that I can make this happen at lower speeds by gearing down and running the rpm's up. I'm also thinking that it might be either clutch or transmission related since my engine oil pressure is running minimum 40psi at idle. I know my throw out bearing is making a slight noise and planned on doing a clutch job after the first of June (if it last that long)... I guess I'm hoping it's something like the pilot bearing.

Anyone else had this kind of vibe? I know this is a long post, but I wanted to get all the facts out there.

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Old 04-19-2013, 11:10 AM   #2
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It sounds to me like the lash isn't properly set. If it's too loose or too tight, it will whine or howl, depending on which it is. The fact that you can hear gear mesh is what's giving it away to me at least.

The only other thing I can thing of to check outside of the differential would be the transmission mount to see if it's separated. For giggles you could unbolt the u-joint caps where it's bolted up to the pinion yoke and rotate it 180 degrees and bolt it back up. You can get weird drivetrain vibration if the point where two yokes are connected aren't put back in line with how they were when taken apart, since driveshafts are balanced, but I really doubt that's the problem, it or a separated transmission mount wouldn't produce gear whine.

Can you take it to another shop for a second opinion?

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Old 04-19-2013, 12:52 PM   #3
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Originally Posted by Angus Brown View Post
It sounds to me like the lash isn't properly set. If it's too loose or too tight, it will whine or howl, depending on which it is. The fact that you can hear gear mesh is what's giving it away to me at least.

The only other thing I can thing of to check outside of the differential would be the transmission mount to see if it's separated. For giggles you could unbolt the u-joint caps where it's bolted up to the pinion yoke and rotate it 180 degrees and bolt it back up. You can get weird drivetrain vibration if the point where two yokes are connected aren't put back in line with how they were when taken apart, since driveshafts are balanced, but I really doubt that's the problem, it or a separated transmission mount wouldn't produce gear whine.

Can you take it to another shop for a second opinion?
Thanks for the response. I don't think it has anything to do with the drive shaft as this is the second shaft and u-joints with (exactly) the same issue..the first one was stock, and the one on there now is a cv shaft. Transmission/tc mount was replaced right after I did the lift due to separation so it's less than a year old and I've had the skid plate off in the last two months and it was fine. It might not be exactly gear whine that I'm hearing, but could also be bearing whine. The shop that did the work does tons of wranglers, and they were very willing to open it up again and check it, as well as pull the drive shaft and road test it a couple of times...and all for free. And because I can get it to do it at lower speeds by gearing down, I no longer think it's coming from the difs.

I've been driving it like this for almost a year, but I tend to stay below 60 on the freeway so I don'thave to deal with it, and it hasn't gotten any worse or better. I'll probably just keep using it until I pull the trans for the clutch job...who knows, maybe I'll stumble on the cause.
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