High speed vibration at 75 mph

starkey480

starkey480

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Hey guys,
I bought my Jeep used with 67k miles on it with no lift and 30 inch tires. It had a vibration starting at 60 mph like a harmonic pulsing vibration. The rear view mirror gets blurred and can feel it in whole Jeep not just one place. Decided to put a 2 inch lift, 1.25 body lift and 33s on and the vibration reduced a little bit and didn’t start until 65mph but still very noticeable. My shop said my front driveshaft needed to be rebuilt and balanced so I got that done and now I have no vibes until after 70 mph and they are drastically reduced but still there. Where should I check next? I need it perfect. Thanks!
 
Yes sir I tried balancing the old tires and didn’t help and the new tires were balanced by a shop I trust and same issue
 
I'm having the same thing going on. I check my rear driveshaft angle and it’s at 1.8-1.4 degrees difference and still doing it. I just got brand new driveshafts from Tom woods and an sye. Jeep 4.0 on 4inch lift with 33s. Got tires balanced and everything. Idk what else to look at. It only happens around 74+ mph
 
Thiessen952 said:
I'm having the same thing going on. I check my rear driveshaft angle and it’s at 1.8-1.4 degrees difference and still doing it. I just got brand new driveshafts from Tom woods and an sye. Jeep 4.0 on 4inch lift with 33s. Got tires balanced and everything. Idk what else to look at. It only happens around 74+ mph
Click to expand...

Is it a constant vibration, or a cyclical vibration (almost like a sine wave with an up-and-down pulse to it)?
 
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Chris said:
Is it a constant vibration, or a cyclical vibration (almost like a sine wave with an up-and-down pulse to it)?
Click to expand...
It’s a pulse but almost feels like rotation. The front driveshaft is at 2.3 degrees from pinion and I don’t wanna mess that up cause of caster. Idk if this is possible but could it be the driveshafts not balancing correctly? Only other thing I could think of is the duratracs I have are extremely loud on the road causing this.
 
Thiessen952 said:
It’s a pulse but almost feels like rotation. The front driveshaft is at 2.3 degrees from pinion and I don’t wanna mess that up cause of caster. Idk if this is possible but could it be the driveshafts not balancing correctly? Only other thing I could think of is the duratracs I have are extremely loud on the road causing this.
Click to expand...

Only way DS would be out of balance would be if you dented it or something on a rock. Found out mine were dented, replaced with a used $90 DS and vibes were gone
 
They’re not stock driveshafts and I have a couple scrapes from rocks but I wouldn’t think that would cause it. Btw those scrapes just happened in the past week or so. This vibration has been going on for 4 months. It’s significantly gotten better than when it started tho.
 
Could it possibly be my rear upper CA? The holes on my frame cap looks slightly bigger than the bolts going through so there isn’t that snug-ness like I have with the other CA. Would that cause the pinion alignment under torque to go a little wack?
 
I know you don't want to change the front pinion angle, but that is the next thing to look at. Pinion angle takes priority over caster as long as the steering still returns to center. Also, you can get away with a bit less caster with 33's than with your prior 30's.
 
The factory service manual has a procedure whereby you add a worm-gear clamp onto the driveshaft tube about 6" from the forward yoke. The screw of the clamp is the weight. The procedure is made to solve driveline vibration complaints when all else fails. Think of it as fine-tuning. Don't for a second think that D/L shops get anything exact and things are different when it's bolted into the vehicle. Rear axle I/P yoke for instance.

I put the Jeep up on stands (frame supported) and left the jack on the pumpkin to position the axle where it would normally be (some weight on the stands). Then I used a free vibration analysis on my iphone and had the wife ref up to 55mph where my vibration started. I had marked the driveshaft with a felt pen in 45 deg increments and I was able to find a spot where the vibration was at a minimum and left the clamp.

On the road, it made a huge difference. Barely any vibrations. As per the service procedure, I have now added a second clamp and will move this either side of the original clamp to fine tune it further - see if it improves.

My driveshafts are in top shape with all new Spicer components and I had them rebalanced by an experienced shop. It didn't help! As I pointed out, there are other components that come into play once the D/L(s) are installed.

Might be worth a try. 2 stainless worm gear clamps = $2.50
 
I’ll check the caster again but I think I’m as low as possible. Last time I checked I was around 5-5.3. I also think my lca are pretty close to maxed out. Not to the point of springs being weird that is. I’m heading out to Drummond Island tomorrow so I guess I’ll cruise around 70 and then fix it when I’m back.
 
RaymondT said:
The factory service manual has a procedure whereby you add a worm-gear clamp onto the driveshaft tube about 6" from the forward yoke. The screw of the clamp is the weight. The procedure is made to solve driveline vibration complaints when all else fails. Think of it as fine-tuning. Don't for a second think that D/L shops get anything exact and things are different when it's bolted into the vehicle. Rear axle I/P yoke for instance.

I put the Jeep up on stands (frame supported) and left the jack on the pumpkin to position the axle where it would normally be (some weight on the stands). Then I used a free vibration analysis on my iphone and had the wife ref up to 55mph where my vibration started. I had marked the driveshaft with a felt pen in 45 deg increments and I was able to find a spot where the vibration was at a minimum and left the clamp.

On the road, it made a huge difference. Barely any vibrations. As per the service procedure, I have now added a second clamp and will move this either side of the original clamp to fine tune it further - see if it improves.

My driveshafts are in top shape with all new Spicer components and I had them rebalanced by an experienced shop. It didn't help! As I pointed out, there are other components that come into play once the D/L(s) are installed.

Might be worth a try. 2 stainless worm gear clamps = $2.50
Click to expand...
I’ll try to look at that and see what I can do. Thank you!
 
Thiessen952 said:
It’s a pulse but almost feels like rotation. The front driveshaft is at 2.3 degrees from pinion and I don’t wanna mess that up cause of caster. Idk if this is possible but could it be the driveshafts not balancing correctly? Only other thing I could think of is the duratracs I have are extremely loud on the road causing this.
Click to expand...

It's either the pinion angle (some are more sensitive than others), driveshaft, wheel / tire balance (or the tires themselves), or it could be a compounded issue like @psrivats had with his, in which case it needs to be taken to a driveline speciality shop that specializes in balancing the vehicle as a whole, as oppose to just a single component.
 
Chris said:
It's either the pinion angle (some are more sensitive than others), driveshaft, wheel / tire balance (or the tires themselves), or it could be a compounded issue like @psrivats had with his, in which case it needs to be taken to a driveline speciality shop that specializes in balancing the vehicle as a whole, as oppose to just a single component.
Click to expand...

Balancing is only one part of things. Everything needs to be checked systematically till you find the issue. It takes time and effort.
 
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I have a pretty good handling TJ, but I have a hard time understanding the need for 75 miles per hour plus speeds...but I've seen enough on the roads zipping around to know there are people that drive them that fast.

I'm not trying to frown on anything it's just a little hard for me to get my mind around it... I'm all about killing vibrations and getting things smooth.

Carry on... I'm just yakking.
 
The legal speed limit is 75mph and because the Jeep can do it pretty well. :)
 
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Chris said:
It's either the pinion angle (some are more sensitive than others), driveshaft, wheel / tire balance (or the tires themselves), or it could be a compounded issue like @psrivats had with his, in which case it needs to be taken to a driveline speciality shop that specializes in balancing the vehicle as a whole, as oppose to just a single component.
Click to expand...

I agree, it is a compounded issue.
Rotation between shafts with different bending stress that are set on axial load will create a harmonic vibration due to static unequal force applied to the part.
Try to align them in one single axis and the sound disappears. The further away from the datum (straight) line will result to a radial load in which will result to greater dynamic force.
As a result, the efficiency of bearings and other mechanical rotating parts such as u-joints, related clamps, bolts, bushings, guides, etc. is being compromised.

This is why I stay OEM basic stock he-heh.
 
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