Intermittent vibration under acceleration.
 

I've owned my 2009 cobalt ss LNF since Aug. 2020. Bought the car and it drove smooth for couple months but had clicking axles when turning and steering wheel shake, while accelerating. I knew this when buying it and figured a few axles, no big deal. Well, I replaced both axles with O'Reilly "Precision" axles. They are designed for the car and when compared with the old ones they lined up. Only reason I got those is at the time they're the only place that had them. After that the car would vibrate rather roughly when accelerating between 40-80, never below or above those numbers. Sometimes it doesn't do it at all, driving smooth as when I bought it. Since then I have done both control arms and 2/3 trans mounts as they were the only parts that were at least somewhat worn. This did not fix the issue. Also, after replacing the axles, i warrantied them out thinking they were faulty, only for it to remain the same, maybe a little better. This was before the control arm and mount replacements. I've aligned it multiple times myself and that is spot on. Before I go replacing them with as close to original axles as I can get I need any information I can get. Thanks

Check your sway bar end links and sway bar bushings?

Cars been away for winter here in MN, front end is completely tight including bushings and links.

I know I had some of the same issues and I to had to replace everything on the front including tie rod ends and ball joints. Are you making sure everything is trq to spec?

All the front end work I mentioned in the original post I did myself and all of those bolts were torqued properly. New moog oem control arms for the proper fe5 or whatever suspension code we have came with new ball joints. My plan is to buy Napa or zzp or Ottp axels and using those. Like I said, only started after new axles. Previous ones were clicking but no vibration. Although before and after the steering wheel had some clunk in it. Most likely intermittent shaft but I don’t see how that would cause the issue, especially since it didn’t vibrate before.

ok yeah I got some napa aka stage 1 axles i have to install in the spring time. Hopefully the new axles fixes your problem.

Honestly, I've been having the same issue... and I'm scratching my head over it.

When I accelerate, the front end shakes like a wheel is out of balance. As soon as I release the throttle or push in the clutch, it disappears.

Wheel bearings are tight. NAPA axles are less than a year old and still tight. TCAB's are spherical bearings and tight. 3 of my 4 engine/trans mounts are brand new upgraded mounts.

If I figure it out, I'll let you know. :lol:

Did you do the upper tranny mount yet? It actually does make a difference.

F23 Upper Transmission Mount (overthetopperformance.com)

Yes, I had to do that one when converting from F35 to F23. Front trans is also OTTP; rear trans is an OG Powell mount and I replaced the bushing in it less than 10,000 miles ago. The only OEM mount that I still have is the upper engine mount and that's a ~50k mile LNF unit.

Sweet, i replaced all mine as well including the main engine mount from TTR, upper tranny mount from ottp as mentioned before and the tranny inserts are from TTR. My car is extremely stiff now lol but I'm getting use to the vibes it gives off. Car just feels more connected as others have stated before. Thankfully I have a daily or it might be a bit much to handle all the time.

Again what confuses me the most is the day before replacing them the first time, car had no issues with vibration on accel. then the day I do the axels, right away it starts. I did no other work besides the axels and I get the vibration. I'm kicking myself for not saving the oem ones and having them rebuilt. There has to be someone whos solved this issue. I can't imagine that I damaged anything putting them in as it went smoothly. I am on coilovers but maybe 1-2 inch lower than stock and like I said ONLY the axels were changed out, and ONLY after that did the vibration start. The ride height, and suspension parts were the exact same before and after so it has to be axel related. Another thing I forgot to mention that might help us solve the issue is, when I hit maybe 15-25 mph I can feel a shimmy in the front end and then it'll vibrate at 40-80. However, if I do not feel that shimmy between 15-25, then it will not vibrate at 40-80. It always smooths out at 80 everytime, go bellow 80 and it starts up again. Completely baffling. Cars away for winter and the only things I have left to check are the Strut mounts, which im starting to suspect more and more, and even possibly the intermittent shaft. To give even more mystery to the problem, there's times were I go days without any vibration. That's what's so messed up about it, its never a constant issue, it comes and goes.

EDIT: Tires are not the issue, this happened with my old tires and the new. Balance is good.

Same. I was out for a drive. Did multiple full boost pulls and they were all fine. Did another getting onto the interstate and there it was. I thought for sure it was lug nuts or a wheel bearing at first... but after those checked out fine, I feared it might have been engine related.

If yours started after installing axles, then yours is a different story. I hadn't done any work under my car in months. :lol:

I don't think it's strut mounts; those are fairly solid connections on our cars. If yours happened after changing axles... I would definitely be giving them the stink eye. Definitely sucks that you didn't keep your OE axles, because at least then you could do an A-B-A test. I hadn't thought about it until now, but I might try pulling some junk yard axles to try before buying new ones.

I've also thought of grabbing junk yard axles. Although in MN most junkyards only have LT cobalt's. You mentioned you swapped your f35 with an f23. I've read a few things that its actually stronger. Is your f35 built? How much power are you making?

Yeah funny thing is i did this also swapped to another oem axle after my passenger side one blew up on me. Then I got the vibration issues once past a certain speed when i hit close to wot. This is why now i decided to buy those stage 1 napa axles and give them a try. I'm installing them over the spring along with upgrading my brakes so i'll let you both know how i make out once weather gets better after the winter. No way i'm doing anything right now because my roads out here in Canada are pot hole city right now lol and car is in winter hibernation lol. You guys ever think about doing the trans spacer and or rotated mounts? I'm auto so I'm kind of limited which is why i didn't want to lower my car to the extreme and went with v7 yyz's instead of say sportlines or BC Coilovers.

So one potential things I can think of for both Loading__ and USMC

When you guys replaced the mounts did you have the trans/engine supported during removal, install, and torque? There was a Powell thread around somewhere talking about needing to support the engine in a specific manner and proper torque procedure to prevent vibrations after mount replacement.

Can either of you guys have a friend load/engage the drivetrain while you looking under hood? Just to see if the axles are loading weird or if the motor is moving significantly when loaded.

Typing this on my phone so I can’t remember who asked. I did the zzp rotated trans mount with the zzp front trans mount(not the upper trans mount under the fuse box. I’ve checked this out and it’s not torn but I will be replacing it regardless this spring). However the rotated trans mount did not fix the issue, although it did lessen it to an extent.

ecualk: I when installing the motor mounts, and you should do this on any car, I supported the engine with an engine stand while on the lift at my shop, just enough that it wouldn’t move when I undid the mounts, replacing them one at a time. However with the rotated mount, I loosened the upper, passenger side motor mount just a few turns, put the rotated mount in, raised the engine so the holes lined up, and bolted her up torquing every bolt to spec.
I should definitely try that load test with a buddy your talking abt. Also, a issue with these cars can also be in the Carrier bearing, but I’ve check this and mine is tight with no play so it might be something for you guys to check.

For sure; SS's are almost never in junk yards around me. The F23 is better for high power because of its 3-shaft design. The F35's problem is the 2-shaft design, along with 3rd gear not being supported as well as it should be, which allows the I/O shafts to deflect (bend) when high torque flows through third. Almost all power-related failures are third gear.

I know there's a tightening order. I did my best to do that properly.

I just need to do anything to it. I keep pulling it up to my shop door to work on it... but never get around to it.

Sounds like the mounts were done right, if USMC has the tightening order handy it might worth a quick loosen everything 1/2 turn and then torque in the order. Not sure it would fix the issue but its a thought.

I know the feeling of not wanting to work on it, not to mention you have the Viper as your racecar

Crawled under my car not too long ago and started grabbing things and shaking. The passenger side inner CV joint has a good amount of play inside the transmission... so I assume that my differential is about to go.

No biggie. I was kind of planning to move to a shorter ratio transmission anyway. Helps that F23's are like $200, as well. :lol: Still a PITA to R&R though.

You'll get better at it the more often you do it :lol:

I installed them on a rack used for alignments. Our other lifts are in ground and the cars too low to drove over them, wouldn't want to rip my nice zzp intercooler off!. Anyways, when I did the mounts, the car was resting on the wheels. Is it possible this could've prevented the rotated mount from solving the issue? I had to lift the motor up to get the "taller" mount to line up so is it possible I did this installation improper? Just curious for your opinion on this.

Where or how the car is resting isn't as important. What is important is the sequence/methodology used for tightening all the mounts. If you do them in the wrong order, there will be binding which leads to elevated NVH levels and shorter lifespan of the mount(s).

I don't have the correct procedure handy, but I know it has been discussed and posted on this forum a lot.

https://www.cobaltss.net/forums/driv...sj-lnf-253153/