Thoughts on rattling - trans?? - PeachParts Mercedes-Benz Forum

tbomachines · #1 06-13-2010, 08:21 PM

Best way I can describe the noise is if you put two ping pong balls into a coffee can and shook vigorously.

I was heading down the highway today in my 300SD doing about 75-80 (highest this car has seen in a while) and all of a sudden, described noise begins at an alarmingly loud volume. It came from right underneath the center console around where my arm was. My first thought was that the flex disc had shredded...I immediately pulled over and checked it out, flex disc was fine. In fact, nothing seemed out of place. I crawled to the nearest rest area and noticed that the noise only starts at about 40mph. At the rest area I do my best to peer underneath the car and nothing seems out of the ordinary...no leaks, nothing hanging, no smoke, no smells. ATF looked and smelled fine. I went down the highway a couple more miles before getting concerned enough to pull over again and check it once more. At this point I was convinced I had spun the driveshaft support bearing somehow. But another check, nothing. I figured a spun bearing would be making quite a bit of heat, but there was nothing besides exhaust. I decided to call off my mission and turn around, and about 75-80 miles later (under 50mph the whole way) the noise dissipates and eventually completely disappears. During this whole time, there were no changes to the way the car felt or drove, just me sweating buckets in the drivers seat and nervous that the bearing is going to seize up. I made it home (150-200 miles) eventually, but have not had a chance to look under it (had to turn around and take my other car down the same route, only 8 hours later...). I came to a couple guesses:

1. I ran over something without knowing it, but I do pay pretty close attention while driving and I know I didn't hit anything at the moment it began making the noise. The object then gets stuck in between the output shaft/driveshaft and the transmission tunnel until it breaks apart. So my question is this - has this ever happened to anybody and is it even possible?? AFAIK, there is not much room above the driveshaft and even less chance of something getting stuck there.

2. A piece of underbody came off in the wind since I was going so fast. Part of it was still stuck on, part of it was hitting the driveshaft. I find this to be the most plausible explanation - no questions here. I didn't see any underbody damage however...

3. Something internal slipped out in the transmission and was bouncing around. This would describe the sound to a T, but my question now for the trans experts - would something that catastrophic even be possible without any drivability issues? I am less familiar with the trans on the car (though I've been in it) and its inner workings than the engine.

4. Would the symptoms described be consistent with driveshaft bearing failure?

I'm really just trying to get an idea where to start before tearing the thing apart...and/or if I should even worry about it vs. tearing the tranny to pieces.

tbomachines · #2 06-13-2010, 08:25 PM

Also I should add, this was on the way to pick up an engine lift to begin the swap out of that car. My gf is convinced it was just the car trying to save itself from an inevitable fate

I guess it bought itself another week. The planned trip would have totaled about 700 miles today if this pleasant surprise had not made itself known.

Volvo Diesel · #3 06-13-2010, 08:54 PM

Well, I hope you get another answer that's actually informative, BUT, just so you know you didn't imagine it, the exact same thing happened to me in November 2009 between San Antonio and Austin. I pretty much did the same things (pulled over/checked fluids/pulled over/looked under car, etc.), and had the exact same thoughts, that you did. During the time the car was making the (quite alarming) sound, the way the car drove did not change at all. Here's the good (I guess...) part: after it stopped making the sound it never made it again.

The car had about 236,700 miles on it when it happened. I had recently had the shift linkage bushings and transmission mount replaced. My mechanic in San Antonio went back over the work he did and said he could find nothing that would have caused such a noise. The car now has 257,453 miles (I work in San Antonio but live in Austin). At 249,259 miles (April 1, 2010), I had the differential and drive shaft completely rebuilt to take car of a rather annoying whine upon acceleration and while cruising at 80+ mph. My mechanic showed me the wear on the bearings that caused the sound. But, he also stated that there was no way that the wear could have caused the sound I heard last November.

So, I just keep driving....

-Chris

rhodes2010 · #4 06-14-2010, 12:22 AM

I'll share my rattle story. See if it applies.

For months I had a rattle but the car drove just fine.
One common rattle point for me is the air cleaner (rubber bushings). But not this time.

I checked the transmission bracket to exhaust pipe by wiggling. It seemed tight.
After a few more weeks I removed it to inspect.
It was the transmission to exhaust bracket.

There are two bolts that hold this to the trans, one of them wore through.
So the bracket was pivoting on the remaining bolt and rattling.

This bracket has rubber bushings to absorb vibration. But the sheared bolt
allowed movement.

tbomachines · #5 06-14-2010, 04:02 PM

(bump) I'm going to get the thing up on ramps tomorrow and do a thorough visual of the trans tunnel...I'm still pretty mystified though.

jt20 · #6 06-14-2010, 06:32 PM

do you have a cap on your upper oil pan where the view window is for the Torque converter bolts?

you haven't really described the sound either

tbomachines · #7 06-15-2010, 01:21 AM

Quote:

Originally Posted by jt20

do you have a cap on your upper oil pan where the view window is for the Torque converter bolts?

you haven't really described the sound either

Honestly I can't get much more specific than describing the rattling as putting a ping pong ball in a coffee can and shaking - that is exactly what it sounded like, maybe with a little less resonance (so maybe like ice in a drink shaker?). It increased with vehicle speed rather than engine speed. I'll check tomorrow... off the top of my head I do know there are spaces for both the torque converter drain plug and flex plate inspection with no cap on it. I inspected the flex plate not too long ago...I suppose that would be an area where some road debris could get caught.

jt20 · #8 06-15-2010, 02:00 AM

that sounds alot like my bad axle.

until I checked them for looseness, I thought the sound was coming from the midsection.

I would wiggle the driveshaft in all directions and the same with the axle shafts. Its really the only thing that makes sense for 'vehicle speed'.

84_300SD · #9 07-06-2010, 10:54 AM

This sounds slightly different than your rattle but I have a serious thud-ing that is coming form the underside of the car, I got her up on blocks yesterday and crawled under for a look, I followed the driveshaft from fron to back and I noticed a shredded rubber disk of sorts that the driveshaft is connected to right off the transmissiont. The car is bucking allot under regular accelleration fom about 10mph to 30 mph but then it goes away as I get faster. Obviously I need a new one. BUt my question is what would cause that to get shredded? IS something else wrong that causes this?

I inserted a bad pic where you can see the shredded bits around the disk.

Regards,
Aaron

jt20 · #10 07-06-2010, 11:23 AM

they dry out with age and can no longer handle the regular loads they encounter.

inspection of the driveshaft bearing would be prudent

Other than that, replacement of the flex-disk should solve the issue.

flex disk

Driveshaft support

84_300SD · #11 07-06-2010, 11:47 AM

58 bucks (shipping included) from a u t o h a u s A Z (dot) com