Piston Slap: Getting in the Zone, Audi A4 1.8T Edition

by Sajeev Mehta

Published: September 1st, 2009

piston slap getting in the zone audi a4 1 8t edition

C.T. from AutoZone (yes, that AutoZone) writes:

Dear Piston Slap, I drive a 2002 Audi A4 1.8T with the CVT. It has 75,000 miles on it, and has been properly maintained. I am experiencing a vibration under these conditions:’

-Only after at least 10 minutes of driving…never cold

-Only between 70-80 mph

-Only when accelerating

-The same no matter how much throttle I give it

-I cannot feel it in the steering wheel

-It feels like it is coming from the axle/drive shaft area

-Sometimes it doesn’t happen at all

I recently took it to a reputable independent shop I have used several times to perform the timing belt and drive belt swap recommended before 80,000 miles. I mentioned the vibration, but they could not replicate it (although I am sure they drove it cold). The vibration was happening maybe 1-2 days a week then. Now it is happening 9 in 10 days under the conditions above. This is probably the only place I trust with my car where I live, but they are so busy right now that I’m afraid they still won’t take the proper time to do a 20-minute highway test drive to properly diagnose the problem.

I don’t have the time, the tools, or the skill to DIY this. I have searched the Audi forums for answers and most blame their mods for their vibrations. I’d like to be able to give my shop a better idea of what it might be…they are more likely to spend the time looking at the car on a lift than test driving, so if I can get them going in the right direction, maybe they will find and fix it.

Help me Piston Slap, you’re my only hope.

Sajeev answers:

And with that: help me, Best and Brightest! This week’s Piston Slap comes from India and Internet access is, uh, somewhat limited. And intimate knowledge of CVT repair/diagnosis is quite hard to find outside of a stealership service bay. But that’s not to say that CVTs aren’t worth their weight in gold to someone.

I reckon you have a mechanical problem internal to the CVT, since you mentioned that the problem happens as the car’s fluids warms up. Failing sensors or worn CV joints need not apply, but a used CVT from car-part.com runs $800-1000 and the labor is several hundred more. That’s probably your only route, as locally rebuilding a CVT is almost entirely out of the question given the complicated nature of CVTs.

If your mechanic is still clueless after the road test, I suggest a change of plan: add a bottle Lucas (purchased with your AutoZone rewards card, wink-wink) and sell it to a faceless dealership, or Carmax. Bad Karma to the next owner be damned, I suspect far, far more terrible financial pain in your future should you not heed this advice.

And if you’re a modern hot-rodder who loves getting on the boost, I’d recommend choosing a more robust platform for your future modifications. You know, if you did that in the first place.

[Send your queries to mehta@ttac.com]

Sajeev Mehta

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2 of 22 comments

Pch101 on Sep 01, 2009

I don't know why tires and suspension wouldn't be the first things to check. These can be inspected for wear, imbalance, etc. without replicating the problem itself. I would suspect some combination of these as the culprit. Edit: I missed the above post about the problem being solved. Sorry about that.

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Psarhjinian on Sep 01, 2009
I don’t know why tires and suspension wouldn’t be the first things to check. These can be inspected for wear, imbalance, etc. without replicating the problem itself. I would suspect some combination of these as the culprit. I think it was because he noted he didn't feel it through the steering wheel. Usually you'll feel (and see) the imbalance that causes as vibration in the wheel. I kick myself for not thinking about the motor mounts. My Saab busted two over a period of six months and exhibited about the same symptoms. I think the lesson here is that we all distrusted the CVT and were too willing to find it at fault, or we didn't listen to his description of the issue.

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