Diagnosing aggressive vibration/rattle under load

[plush]

2 years ago I replaced the driveshaft in my wife's allroad with a good condition, used driveshaft. The car would vibrate under load and replacing the driveshaft fixed it instantly.

Now, 2 years later, very similar symptoms are back: the car vibrates aggressively under load over 60mph, and lately has been vibrating at lower speeds. It ONLY vibrates under load.

I inspected the driveshaft flange by removing the exhaust heat shield and it seems fine--no chunks of rubber missing, though I can move the driveshaft around a bit by hand within the flange.



Could it be the flange again? Or should I look elsewhere?

[rollerton]

Personally I always suspect the driveshaft CV joints before the center joint or bearing. #1 because they're easily serviceable and #2 I don't think the U-joint transmits the vibrations to the cabin as well as the CV's . #3 The U-joint and hanger are really very durable. #4 In order to even really test the bad center joint /hanger you have to basically rebuild the driveshaft.
The CV's at the end are the same for all C5 models as far as I know, so also very easy to get a pair, rebuild and install. But, at the same time I think that the CV's typically show symptoms at lower speeds also.
If you put a good load on it at low speeds- like in 4/5th and lugging it while trying to accelerate- then I think that's where the most driveshaft angle deflection occurs at the ends and that's when the CV's act up if their going bad.

[Scotty@Advanced]

The u joint in the middle of the shaft moves very little the rollers on the joint tend to wear a groove in the cups and or shaft. Over time this causes the rollers to jump in and out of the worn groove when under load.

[plush]

Thank you for the help.

I replaced the alternator because that conked out, and the problem went away for 2 days (coincidence?). The car was SO smooth... for a while.

I then accelerated quickly on the freeway to get up to speed and the strong rattling/vibration came back. NOW, it vibrates at any speed over 10-20mph, about 75% of the time. It's getting worse. Does this change your impression of what it might be?

[forcefed7]

Personally I always suspect the driveshaft CV joints before the center joint or bearing. #1 because they're easily serviceable and #2 I don't think the U-joint transmits the vibrations to the cabin as well as the CV's . #3 The U-joint and hanger are really very durable. #4 In order to even really test the bad center joint /hanger you have to basically rebuild the driveshaft.
The CV's at the end are the same for all C5 models as far as I know, so also very easy to get a pair, rebuild and install. But, at the same time I think that the CV's typically show symptoms at lower speeds also.
If you put a good load on it at low speeds- like in 4/5th and lugging it while trying to accelerate- then I think that's where the most driveshaft angle deflection occurs at the ends and that's when the CV's act up if their going bad.

Good info Rollerton. Do you know where I can find info on servicing the driveshaft CV joints? I googled using the terms "C5 A6 driveshaft CV Joint" and the search results keep referencing the axle CVs.

[plush]

Good info Rollerton. Do you know where I can find info on servicing the driveshaft CV joints? I googled using the terms "C5 A6 driveshaft CV Joint" and the search results keep referencing the axle CVs.

Agreed, this info would be great to have if you have it!

Does my problem sound like driveshaft CV(s) going out?

[forcefed7]

Bump for Rollerton.

[plush]

Bump for OP

[ECS Tuning-Audi]

If the CV's check out may want to look in to outer tie rod ends.

My B5 would shake the wheel under load mostly at highway speeds and it turned out both my outer tie rod ends were toast. Installed new ones and it drove perfect.

Might be worth a look.

Jason

[plush]

If the CV's check out may want to look in to outer tie rod ends.

My B5 would shake the wheel under load mostly at highway speeds and it turned out both my outer tie rod ends were toast. Installed new ones and it drove perfect.

Might be worth a look.

Jason

Thanks Jason. I will check them. I just replaced the driveshaft since both CVs had shot grease out everywhere and had destroyed gaskets. New driveshaft with heavily greased CVs and the problem still exists. I will look at the tie rod ends. Will the damage be visible if they're in bad shape, or is it one of those "replace it and see if it fixes the problem" situations?

Also, one of the front tires is wearing unevenly. I am not sure if this is due to my DIY air suspension fix (Fix-a-flat tutorial I found on Audizine) or an alignment issue. Could this be the problem, potentially?

[plush]

to the top

[plush]

bump for question:

Will the damage be visible on Tie Rod Ends if they're in bad shape, or is it one of those "replace it and see if it fixes the problem" situations?

[plush]

triple bump. Help!

[glennda5id]

If the tierod boot is intack they are most likely fine. You can check by jacking up the car and checking for play.

[AllroadMass]

triple bump. Help!

If your tire is wearing unevenly then check your control arms. Just did my passat b5.5 and my wife's allroad uppers and quick and easy as long as the pinch bolt wants to play nice. I had torn bushings on both cars and outter and inner edges of my tires were gone.

In my experience the outter tie rod end vibrates (pretty violently if you're at highway speed) under braking if they're gone. I usually change about 6 tie rod ends a year and all of the boots on my tie rod have never been ripped. An easy assessment is to jack the car up like Glennda5id said and grab the wheel and try to move it left and right then up and down. You'll be able to feel and see the play in the outter tie rod right away.

My left outter cv joint on the passat is going and that causes a click when we're letting off the gas and then getting back on the gas pedal. It's my student driver car so the kids are pretty hard on gas/brake control. Rather than just replacing the outter cv joint with a kit, I got a quote from Raxles for $220 per axle and plan on replacing the entire axle.

Like Rollerton said, your problem definitely sounds like an inner cv joint. inners vibrates when load is applied to them. Have you done one before? They're not bad at all. I put a refurbished Chinese crap on my rear axle about 1.5 years ago and it's already vibrating again.

[Scotty@Advanced]

Are tires all the same diameter?