About a week ago, I changed out the very worn passenger side CV axle on my Forte. The axle that I removed appeared to be the OEM axle but I think it was either rebuilt or it was a used axle because it had paint pen markings on the inboard joint. I replaced it with a new Trakmotive axle but it did not have the dynamic damper on the shaft like the OEM axle did. Now I have a vibration on acceleration from about 50-80mph. Its only on acceleration and only in that speed range. It feels like a buzzing sensation, kinda like hitting the drunk bumps on the fog line but not as severe. Does the dynamic damper really make that much of difference? Or is something wrong with the new axle? Or is the wheel bearing complaining because I used the impact gun set to kill to tighten the axle nut? I bought a new wheel bearing and snap ring just in case I killed the wheel bearing.
In my brief research, it is possible to get a bad CV axle out of the box. I bought Trakmotive because I used to sell them at the parts store where I worked and we had a very low rate of defective returns. Way less than the few Cardone axles we carried.
A new OEM axle is out of the question because its like $600 from the dealer 
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Thoughts?
I’ve had two new axles bad out of the box. Both had the same symptom, shaking on acceleration. Both times I took them back and swapped for another of the same brand and the problem went away. YMMV.
Ugh, I hope this doesn't turn into a massive PITA swapping axles until I find a good one. I bought this one from RockAuto because they had the best price by almost 40%, even after shipping. I threw out the box after I swapped the axle in. I can't get a time to work on the car until next weekend. How bad is RockAuto for returns?
I'm almost half tempted to buy a good used axle because it seems like nothing comes close to OEM quality on CV axles 
RA is good on returns, if you are in the short term warranty period, and I think they'll want the original box, not sure, but they will pay shipping back. You can buy another from them, swap it in, put the bad one back in the box and return it. I think they're cool with that.
The occasional bad part is what's not good about buying from RA. I got stuck with some bad fully loaded shocks (springs, top hat, etc.) for a LS400. By the time I got to putting them on, I was out of the no hassle return period and into the manufacturer's warranty where you have to pay shipping. Wasn't worth the bother. The springs were so much softer than the originals that it looked like I slammed the car. And it bottomed out everywhere.
Yeah, I'm fine with buying another axle before I get a refund on the one that is installed currently. I'll have to talk with RockAuto's customer service to see what they can do. I don't blame RockAuto on this one. I know stuff happens sometimes.
The axle looked really good. It appeared well manufactured and I could detect no issues by moving the CV joints around by hand but we all know that don't really do anything for a CV joint.
It just sucks I have to spend more time redoing something I thought would be a somewhat easy fix.
Any idea why the OEM axle comes with the dampers and the aftermarket replacements do not? Is it a cost thing? Or does it not matter that much?
Most CV axles throughout automotive history have been "undamped," and they don't normally cause vibrations at any speed...
stanger_missle said:
Any idea why the OEM axle comes with the dampers and the aftermarket replacements do not? Is it a cost thing? Or does it not matter that much?
As a former halfshaft engineer, I can actually answer this. Like anything else, the dampers are there to dampen vibrations. Specifically harmonic vibrations in the bar of the halfshaft caused by the engine/transmission. They are specified by the OEMs to the original suppliers of the halfshafts based on each vehicle's configuration. Sometimes only on one halfshaft, sometimes on both. But the aftermarket doesn't get those specs and it's an easy cost save to leave them out. Old cars make noise and the aftermarket is less likely to get returns due to vibrations and noises.
As for your vibration issue at speed, that's likely an incorrectly manufactured part combined with cheap grease in the joints. Higher specification grease can sometimes limit those vibrations, but not always.
Good luck with the next halfshaft. Silver lining: you know the process now and all of the bolts should come out easily.
In reply to ShawneeCreek :
Thank you for that AWESOME information! The GRM community is amazing. It makes sense that the OEMs would want to reduce the drivetrain NVH as much as possible (tied to ROI obviously) but the aftermarket would not. Especially on a 9 year old Kia crapbox 
I'm not thrilled I get to remove/replace the axle again but now I'm pretty convinced that something really is wrong with the replacement axle. I was pleasantly surprised on how easy the whole procedure was on this car. I have a new wheel bearing but I think I won't tempt fate by replacing it. I'll try another axle first. I'll contact RockAuto's customer service on Monday to start the process.
Thanks all!
I know with the Honda aftermarket shafts, it was very difficult to find a good rebuilt. Most of the problems with them were due to wear on the ball and socket in the housing and those got reused in most cases. So the vibrations would never go away until you put in a new shaft (be it OE or aftermarket).
