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 Post subject: Driveshaft vibration
PostPosted: Sat Aug 12, 2017 8:39 pm 
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Joined: Tue May 16, 2017 7:39 am
Posts: 17
Okay so I have 4”jba Rear Springs, rear upper, and lower iron rock adjustable control arms. I have a rear driveshaft vibration that starts at 38mph gets worst at 45 then ends at 47mph. I’ve adjusted the pinion up and down in half turn increments to get it as good as possible. The U-joints were original so I changed them (great shape with 130k). That didn’t make a difference. So I thought maybe the lower control arm mounts are not perfectly symmetrical causing the axle to not be at a perfect right angle to the shaft. Threw it back on the alignment rack and have .17 .13 toe so almost the same. I measured the angle of the shaft and it is 14.5 degrees which seems like a lot to me. Everyone on this forum though says you shouldn’t have a vibration with a 4” lift.

Any ideas fella’s? I’m running out.

If this is the way it is I might dump the t-case for a 231 short and do a double cardan shaft.

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05 CRD Ltd new rockers, lifters, valves, arp's, weeks 1,2 Id silicone hoses full 3" exhaust, Carter intank pump, Hayden/GM fan 4”Lift Jba upper fronts, new front lowers, cut cv’s, bilsteins, 790’s, top plate, 2 conduit nuts, Iron Rock adjustable 3 link, custom diff bracket Jba 4” rear springs 16x8 rubi wheels 265/75 Yoko’s, manual tans/w231


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 Post subject: Re: Driveshaft vibration
PostPosted: Sun Aug 13, 2017 7:44 am 
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Joined: Thu Jul 07, 2005 5:49 pm
Posts: 27226
Location: NOW Southeastern Ohio/ Tanzania
I ran 4.5 inches for over 90,000 miles, never any issues with vibrations, part of that was with MOPAR tri-link and JBA extension, and then JBA bolt on. No issues at any speed
Don't know anything about your setup, never seen in person, never seen the need for replacing the lower control arms since I could completely stuff the 32s in the rear
Are you positive its the rear?

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 Post subject: Re: Driveshaft vibration
PostPosted: Mon Aug 14, 2017 7:55 pm 
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Joined: Tue May 16, 2017 7:39 am
Posts: 17
I know you don’t think these trucks need longer rear lower control arms. I’ve read your opinion on the matter a lot on this forum. I’ve read 4x4 and CRD sections back to 2014 posts but I live in south Jersey which is as flat as a pool table. All I have here are the pine barrens and the beach to drive on. I wanted my rear wheels centered at ride height. I don’t need to stuff any wheels here. The rear arms are almost an inch longer and the wheels are perfectly centered.

I have an update on my issue so I figured the alignment rack wasn’t 100% infallible so I measured the rear lower control arm mounts to the front u-joint weld seam. There was a 3/4” difference. So I adjusted the rear lower arms. I went in one turn on the driver rear and out one turn on the passenger rear then I slid the t-case Cross member to the driver side about 1/16” tops. I am within 1/2” now. The vibration is about 25% Better.

My passenger front can’t get enough negative camber. It’s at -.01 degree. I think this makes some sense now. Tomorrow I am going to see if the front subframe has dowels or not. If not I’ll move it to the passenger side helping the camber and the rear driveline side angle. Then maybe new motor mounts.

On a side note I also moved my from lower control arms forward 1/4”. I pressed the bushings on the new arms. It aided in tire clearance and caster. Was totally worth it.

_________________
05 CRD Ltd new rockers, lifters, valves, arp's, weeks 1,2 Id silicone hoses full 3" exhaust, Carter intank pump, Hayden/GM fan 4”Lift Jba upper fronts, new front lowers, cut cv’s, bilsteins, 790’s, top plate, 2 conduit nuts, Iron Rock adjustable 3 link, custom diff bracket Jba 4” rear springs 16x8 rubi wheels 265/75 Yoko’s, manual tans/w231


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 Post subject: Re: Driveshaft vibration
PostPosted: Tue Aug 15, 2017 3:39 am 
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Joined: Sat Apr 01, 2006 9:38 pm
Posts: 12988
Location: Colorado Springs
JohnnyCRDhead wrote:
I know you don’t think these trucks need longer rear lower control arms. I’ve read your opinion on the matter a lot on this forum. I’ve read 4x4 and CRD sections back to 2014 posts but I live in south Jersey which is as flat as a pool table. All I have here are the pine barrens and the beach to drive on. I wanted my rear wheels centered at ride height. I don’t need to stuff any wheels here. The rear arms are almost an inch longer and the wheels are perfectly centered.

I have an update on my issue so I figured the alignment rack wasn’t 100% infallible so I measured the rear lower control arm mounts to the front u-joint weld seam. There was a 3/4” difference. So I adjusted the rear lower arms. I went in one turn on the driver rear and out one turn on the passenger rear then I slid the t-case Cross member to the driver side about 1/16” tops. I am within 1/2” now. The vibration is about 25% Better.

My passenger front can’t get enough negative camber. It’s at -.01 degree. I think this makes some sense now. Tomorrow I am going to see if the front subframe has dowels or not. If not I’ll move it to the passenger side helping the camber and the rear driveline side angle. Then maybe new motor mounts.

On a side note I also moved my from lower control arms forward 1/4”. I pressed the bushings on the new arms. It aided in tire clearance and caster. Was totally worth it.

Yeah your angles are all wrong.

OE style driveshaft..............
Image
You will have vibs unless you achieve the above angles,not to mention the tailshaft and pinion shaft must be in perfect alignment also.

It took me 2 weeks to get my rear setup perfect,I SFA'd my KJ and have 5 link setups front and rear.

Double cardon(CV) driveshaft..............
Image
The above is a "cruise speed" not stopped static angle.


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