Piston Slap: NVH Nightmares No More?

Sajeev Mehta
by Sajeev Mehta
piston slap nvh nightmares no more
Doug writes:I have a 2007 Mercedes-Benz S550. I accidentally bought it in 2014 off eBay (long story) for about trade-in ($13,000), with 150,000 miles on the odomater. In a twist of good luck, it turned out to be a one owner car and using CarFax I was able to see and verify that it had been maintained by the selling dealer right up to a few weeks before its eBay appearance. A call to the dealer confirmed the complete service history. Even the brake pads and rotors were new, and it had a newish and very expensive set of Michelins. Almost three years later, it has been very reliable for my teen daughter and has 180,000 miles. It had a few quirks I have fixed myself (clogged charcoal canister, minor trunk leak caused by a missing rubber plug, sticking power driver seat) and only one real repair (dead stereo amp rebuilt by Becker).Now that my daughter is off at college and content with a ZipCar, I am driving it and intend to keep doing so. I have noticed a vibration in the center console area of all places, while driving around town. You feel it through your arm resting on the console lid. It’s a deep vibration, if that makes sense — coming from under the car.You don’t feel it in the seat, nor do you feel it in the steering wheel. You do not feel it at a standstill, just at 20-30 mph. It goes away at higher speeds, and the car is rock solid and smooth as glass at 75 mph. I am stumped as to the cause, and with the age of the car, I don’t want to set a dealership or even an indy shop loose on it without more of an idea of the cause. I was thinking maybe a motor mount, but it seems like I would feel that all the time, and especially at idle, which I don’t. I was wondering about maybe some kind of driveshaft or transmission mount or connection point, but it seems like a fault that would get worse with increasing speed instead of going away. Do you have any ideas?Sajeev answers:Dumb luck or no, good on you for finding a cherry W221 S-class. These seem significantly more cost effective than the W220 ( don’t take my word for it) so, faint praise aside, fixing this NVH issue isn’t a waste of money.This problem is likely a driveline issue, either the driveshaft, the transmission and/or differential mounts. With your email’s signature file in mind, your career likely gives you neither the time nor the knowledge to make this a DIY repair. Either you pay someone to throw parts at it (good luck) or you find a shop investing the coolest NVH monitoring tools. Time to find such a shop, or even break tradition and take an out-of-warranty S-class back to the dealership.Your symptoms remind me of when I had (slightly) deformed differential mounts on my 1995 Lincoln Mark VIII, but no way in hell am I making that recommendation. NVH troubleshooting is not for the faint of heart.I am confident you’ll pay more for a proper diagnosis to pay less overall.[Image: Shutterstock user Joyseulay]Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.
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4 of 27 comments
  • Pwrwrench Pwrwrench on Mar 21, 2017

    Yep, driveshaft rubber flex damper(s) are the likely culprit. There is usually one right under the driver's right elbow if it's resting on the center console. Most Mercedes and BMW RWD/AWD have a multi piece drive shaft. There are usually needle bearings at the shaft joint(s). The car in question is at about the miles where those bearings wear out causing vibrations. Find a driveshaft shop that is experienced in Mercedes. A-number-1 No-No is to disassemble the driveshaft without marking the relationship between the parts. It's very difficult and time consuming to get them back together correctly. Most experienced techs will tell you to scrap the drive shaft and buy a new one. BIG $$$.

    • See 1 previous
    • Importamation Importamation on Mar 22, 2017

      @DenverMike I agree. I'm not willing to turn it over to anyone yet at this age and mileage. I can live with it to a degree, but I don't want some serious failure either. I have a tenant that has a two bay garage where he wrenches on Hondas, mostly. I think I'll ask to put it up on his lift and I'll inspect these rubber parts myself one Saturday and see what I find.

  • DenverMike DenverMike on Mar 21, 2017

    Sometimes you just have to put it up on the rack and give it hell. A bent wheel or flat spot on a tire wont be felt at low speeds, and at high speeds, the wheel velocity hides the defect. Ever notice on washboard roads, when going over 50 mph everything smooths out?

  • Art Vandelay Dodge should bring this back. They could sell it as the classic classic classic model
  • Surferjoe Still have a 2013 RDX, naturally aspirated V6, just can't get behind a 4 banger turbo.Also gloriously absent, ESS, lane departure warnings, etc.
  • ToolGuy Is it a genuine Top Hand? Oh, I forgot, I don't care. 🙂
  • ToolGuy I did truck things with my truck this past week, twenty-odd miles from home (farther than usual). Recall that the interior bed space of my (modified) truck is 98" x 74". On the ride home yesterday the bed carried a 20 foot extension ladder (10 feet long, flagged 14 inches past the rear bumper), two other ladders, a smallish air compressor, a largish shop vac, three large bins, some materials, some scrap, and a slew of tool cases/bags. It was pretty full, is what I'm saying.The range of the Cybertruck would have been just fine. Nothing I carried had any substantial weight to it, in truck terms. The frunk would have been extremely useful (lock the tool cases there, out of the way of the Bed Stuff, away from prying eyes and grasping fingers -- you say I can charge my cordless tools there? bonus). Stainless steel plus no paint is a plus.Apparently the Cybertruck bed will be 78" long (but over 96" with the tailgate folded down) and 60-65" wide. And then Tesla promises "100 cubic feet of exterior, lockable storage — including the under-bed, frunk and sail pillars." Underbed storage requires the bed to be clear of other stuff, but bottom line everything would have fit, especially when we consider the second row of seats (tools and some materials out of the weather).Some days I was hauling mostly air on one leg of the trip. There were several store runs involved, some for 8-foot stock. One day I bummed a ride in a Roush Mustang. Three separate times other drivers tried to run into my truck (stainless steel panels, yes please). The fuel savings would be large enough for me to notice and to care.TL;DR: This truck would work for me, as a truck. Sample size = 1.
  • Ed That has to be a joke.