Vibration while accelerating at higher speeds?

[LJH]

Hello All,
I seem to have a vibration that is getting worse. The vibration only happens when accelerating at or above 60MPH or so, back out of the throttle and the vibration goes away. I am thinking drive shaft carrier bearing but wondering if any of you have experienced this and what it was.

I have not had a look under the car as of yet.

Cheers,
Jim

[cheetah993]

Where on the car is the vibration originating from? The front or the rear?

The Carrier bearing is a very good guess to be the problem, they are known for vibrating when they go bad, but there are many other things it could be.

[0000 V8]

I have this problem on allroad sometimes. When I researched it I discovered its most likely a bad cv joint. It's best to just replace the whole axel rather than re build the problem area. Not too expensive if you do it yourself.

[LJH]

I really do not think it is a CV axle joint, the vibration feels like it is coming from the back of the car and feels to be centered. I did a little research and looks like what I described is moderately common.

Now I just have to figure out what is needed to get it fixed without having to buy a whole new driveshaft.

Cheers,
Jim

[cheetah993]

Well if it is just the carrier bearing you for sure do not need to buy a whole new shaft, the drive shaft separates and the carrier bearing can be replaced separately. It is a common part to go bad, and can cause vibrations. If you take off the heat shield under the car, you will expose the carrier bearing and then you can see how much movement is in it to tell if it is bad.

[drew]

Hey Jim. My issue was with the CV joint that connects the front of the shaft to the transmission. The little boot was torn and all the grease was gone. It would start to vibrate after the car heated up. Mostly noticeable under de-acceleration but at all speeds. You can purchase those CV joints and boots separately thankfully from a few vendors. You can also purchase just the carrier bearing from 034 if it's bad. The Audi dealer will only sell you a new driveshaft.

[JimmyBones]

Jim, do you still have the stock flywheel and clutch? Hopefully it is just the driveshaft center bearing.

I have this problem on allroad sometimes. When I researched it I discovered its most likely a bad cv joint. It's best to just replace the whole axel rather than re build the problem area. Not too expensive if you do it yourself.

The allroads and C5 A6s were notorious for the CV boots tearing every 30-40K miles. It is not that big of a deal with these S4s.

[rave]

Had the same issue, had a look under the car and spotted the cv boot. Might as well not have even been on the axle anymore because both clips holding it on were gone and it was just flopping around

[LJH]

Jim, do you still have the stock flywheel and clutch? Hopefully it is just the driveshaft center bearing.



The allroads and C5 A6s were notorious for the CV boots tearing every 30-40K miles. It is not that big of a deal with these S4s.

The clutch was replaced by the previous (enthusiast) owner before we took possession of the car, not sure if the flywheel was replaced. I do get a very slight flywheel vibration at exactly 2K RPM but when I was test driving cars this seemed to be common.

While I have not gotten under the car yet but I really think it is driveshaft related. There is no vibration at steady speed or decelerating or speeds below 60'ish MPH, only above 60 MPH and when I get into the throttle.

This weekend I will dig a bit more into the issue and let you know what I find.

Cheers,
Jim

[dante18]

Manual transmission?

I had very similar vibrations last year, thought it was drive shaft related as it was only happening during acceleration at highway speeds. It degraded very quickly soon making the car undrivable. It turned out to be the "dual mass" flywheel. After I started doing a little research it became apparent that this seems to effect quite a few 6MT cars. Just a heads up.

Good luck...

dante

[LJH]

Just an update here, I finally got to look under the car a few weeks ago and did not find anything that looked to be an issue so I was a bit perplexed. I was getting a vibration through the steering wheel so I decided to try and get the wheels/tires balanced. Low and behold that was the issue....all the tires were out of balance, needing as much as .5oz in places. What I do not understand is how accelerating made the imbalance feel worse?

After getting all four wheels balanced I took the car from 40MPH to warp speed and it is smooth as can be......it is nice to have the old girl back.

Cheers,
Jim

[Mr.Wrong]

Glad to see it was just a balancing issue and an easy fix.

[Slow4]

What I do not understand is how accelerating made the imbalance feel worse?

Just a thought but if one "side" of a wheel is heavier than the other, the momentum of rotation would amplify that heaviness and throw it out rotation.

There's a scientific term for this but I can't remember what it's called.

[IslandHydro]

Just a thought but if one "side" of a wheel is heavier than the other, the momentum of rotation would amplify that heaviness and throw it out rotation.

There's a scientific term for this but I can't remember what it's called.

Centrifugal force? but I think that would be a function of wheel rpm, and not acceleration.

[Omerta]

As you accelerate your adding energy to the system as the moving the wheel moves through various natural frequencies significantly faster than the RPM's are climbing. That adds to the increases in intensity of the vibration / instability.

[LJH]

As you accelerate your adding energy to the system as the moving the wheel moves through various natural frequencies significantly faster than the RPM's are climbing. That adds to the increases in intensity of the vibration / instability.

Curious to read about this as I am havering a hard time getting my head around that. What "law" is this called.

Thanks.

Cheers,
Jim

[noob5]

You guys are referring to resonance...if I remember my physics classes correctly.
Something about being in phase and constructive interference or something. LOL

[Slow4]

^^ see, I knew I was on the right path....

[Guitarmageddon]

I wonder if you put the car on a lift and got the wheels moving at speed if that would help isolate the problem area?