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Got them vibes

clydefrog

NAXJA Forum User
At what driveline RPM's do vibrations become difficult to completey eliminate?

What I want to know is if I am chasing something that is at it's designed limit. I get driveline vibrations at ~2,500 to 2,600 DRIVELINE RPM's. This is at about 77 to 80mph. I didn't have an issue before but now since I regeared (4.56 with 33" tires) it's annoying. I usually cruise at 65-70mph so it's not really an issue then but I regularly use the rig for trans-State trips. Going through Nevada desert I regularly see 80mph for hours on end. If I go slower then the semi trucks will be passing me. I am at 4.5 inches of lift, the vibrations are coming from the rear shaft which is a custom built double carden unit with a slip yoke eliminator on the NP231 running an 8.8 with perfect rear u joint angle (perfectly straight pinion angle in relation to the driveline). The engine and trans is angled down quite drastically similar to a t-case lowering kit. Should I send the driveline in for rebalance or is that pretty much as fast as it will spin before vibrating? If I could get a shaft that does 3,000 RPM's smoothly I would be in great shape, is that even possible? I guess I should post up some pics of the angles I'm dealing with.

Any ideas would be much appreciated, I couldn't find anything on driveline designed limits for a double carden unit. Thanks.
 
I should certainly think you could get a driveshaft balanced for 3K+ RPMs. Just think of some of the racing vehicles that have to sustain that sort of treatment for hours on end.

How many miles are on the build of that driveshaft?

Have you taken it out and run it through a range of motion such that you can feel each U-joint and the centering ball?
 
To answer your question, I'd say 5000-10k. Whenever I get a hint of vibes it's a sign my "centering" ball wants lubed!
 
To answer your question, I'd say 5000-10k. Whenever I get a hint of vibes it's a sign my "centering" ball wants lubed!

was going to mention centering yoke. easy to tell if its messed up while on the vehicle. push up on it. any play and it needs a rebuild
 
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I kinda thought that harmonic loud noises associated with vibrations were a normal thing in Jeeps. I had to avoid speeds between 62-69. Got my rear driveshaft rebalanced and the majority of them seemed to disappear.

I still don't know how few vibes are possible, never been in a lifted XJ with fewer vibrations than mine, but lots here seem to claim quiet smooth rides at 80. I have my doubts about that.



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I will pull the shaft and check it. Thanks for the tips on the centering yoke. The shaft has about 20k on it. I recently had to remove it to tighten my slip yoke flange and do my rear re gear and the u-joints felt normal but I never really inspected the double Carden centering yoke.

Like stated above, from sinat01, it's actually more of a noise than a felt vibration.

I am going to measure the angle of the driveshaft as well and report what I find.
 
With an SYE and double-cardon driveshaft, I like the rear axle's nose to be pointed downward a degree or two, to allow for the pinion's swing upward, when under power.
Leaf springs are flexible.
http://www.fourwheeler.com/how-to/t...ry-understanding-pinion-and-driveshaft-angle/
I prefer using an electronic angle finder for a more accurate reading .

The front driveshaft can have vibs too, becoming a problem if the front pinion is more than a degree or two out of alignment. The vibs can be felt in your feet.
A transferase drop will also increase the front shaft's u-joint angles, since the transfer case is being tilted rearward.
Both front and rear driveshaft vibs increase when regearing, due to the greater driveshaft speed. I had issues after installing 4.56 gears that needed attention.
Any noticeable vibs need to attended to, vibs can wear faster or damage u-joints and pinion bearings.
 
With an SYE and double-cardon driveshaft, I like the rear axle's nose to be pointed downward a degree or two, to allow for the pinion's swing upward, when under power.
Leaf springs are flexible.
http://www.fourwheeler.com/how-to/t...ry-understanding-pinion-and-driveshaft-angle/
I prefer using an electronic angle finder for a more accurate reading .

The front driveshaft can have vibs too, becoming a problem if the front pinion is more than a degree or two out of alignment. The vibs can be felt in your feet.
A transferase drop will also increase the front shaft's u-joint angles, since the transfer case is being tilted rearward.
Both front and rear driveshaft vibs increase when regearing, due to the greater driveshaft speed. I had issues after installing 4.56 gears that needed attention.
Any noticeable vibs need to attended to, vibs can wear faster or damage u-joints and pinion bearings.
I removed the front drive shaft and then the rear (and reinstalled the front) to test. Its def the rear. And I am more worried about the longevity as well, i don't want to severely wear something out when i am several states away from home.

I will post back when I have time to remove the rear shaft again and check the centering ball, i don't think I have ever lubed it.
 
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