What does a bad flex plate sound like?
 

Good morning! As I was driving into work this morning I noticed a sound that seemed to come from the middle of the car. I have the back seats out so there isn't too much sound dampening back there, and I have been listening for any odd noises over the past few weeks. Now, this noise. I noticed it intermittently some time ago (say, 2 weeks?)--it sounds like a tapping that increases as the engine RPMs increase. Again, it sounds almost like it is coming from the middle or rear end of the car. I was baffled until I remember seeing a thread a month ago or so of a flex plate that was near destroyed. It involved removing the tranny, torque converter and flywheel :eek: not a job I want to do in my garage. I have an injector nailing so I know what that sounds like, that was NOT what this was, though the actual noise was a similar clack-clack-clack. It produced the noise in park, drive, and reverse.

Does this sound like a flex plate problem? I would have gotten on the ground and checked in the lot but that wouldn't have faired well for my work attire. How common is flex plate failure? Difficulty rating 1-10? Anything other possible sources for this sound? I'll be checking everything out down there once we get a day without rain, but right now paranoia has the best of me. Thank you for any possible info!! --TC

First check your flywheel bolts,as the noise can be transferred.Yes the flex platte can sound like a rod knock.I would assume it would envolve unbolting trans and moving it back.

Any other ideas? I'm keeping my fingers crossed its nothing serious--anything else that could possibly make a ticking that increases as a function of RPMs?

I'm REALLY hoping my flex plate isn't on its way out...I'll be driving this for quite a bit before I get to replacing that, probably about 1000 miles.

Sure you don't mean " FLEX DISC " ? One on each end of driveshaft. Also, driveshaft center bearing and mount.
http://www.peachparts.com/shopforum/diesel-discussion/250486-how-replace-driveshaft-support-carrier-bearing-step-step-guide.html
Some pics on this forum show trashed cars when front disc let go.:eek:

---------------------
1984 MB 300SD Turbo

I would not rule out flex disc's, center carrier bearing and rear axle shafts. Especially since you say it is near or sounds like it it coming from the center of the car. Remember that sounds in the rear are transmitted through the driveshaft.

Maybe have some one drive the car for you and move around the car (including the trunk) to isolate it?

Half shaft / Axle shaft
 

Hello-

I am far from an expert, but your symptoms sound like failing rear axle shafts, a/k/a half shafts. I cannot tell for sure reading your post whether you indicate the car makes the noise when it isn't moving, but if so, disregard my suggestion, as you would only hear these if the car was moving.

I replaced mine when my car started making a sound that was (scarily) like a knock I could usually hear after letting up on the accelerator.

Advice I received on this board led me to believe that people have had pretty poor luck with the rebuilt shafts from places like AutoZone. I wasn't going to do the job myself anyway, so my indy ordered them from MB and installed. I think the total cost for the 2 shafts plus labor for install was ~$850.

Hope this is helpful!

-Chris

All you have to do is raise the car and inspect the flex discs to rule that out.

If they show ANY cracks or threads showing you should replace them.

It's not that hard as long as you remember to mark the shaft coming from the transmission and the drive shaft so you will know how to put them back together exactly.

You loosen the nut on the drive shaft and slide it off the tranny.

You may have to loosen the rear flex disc from the rear end and loosen the bolts on the carrier bearing to give you enough room to slide it off the tranny.

I also remember having to detach the muffler hangers to give me more room to work.

I loosened them and then placed an old gas can under it to support the exhaust since I didn't need the room created when the whole thing sagged to the ground.

I also had the car up on jack stands all the way around at this time.

It's not really a hard job if you do find that they are the problem.

Hey guys his noise is in park too.

Thank you for all your responses, however this noise occurs in park (as oldsinner noted) and as a function of engine RPMs rather than the speed of the vehicle--or rotation of driveshaft/rear wheels. Checking it out in a few minutes, hopefully beating the thunderstorms...

Thunderstorms all day here.Check that pulley.Then you can remove flywheel plug,a shine a light at the flex plate holes.Theres one used with flywheel on ebay.

If it does it in park- increases with RPM and you're SURE this is the case, and that it comes from the "middle" of the car- check exhaust- a small leak might create a ticking sound. If it is the flex disc though- change the d@mned thing- mine "went" all of a sudden when I slammed on the brakes to avoid hitting some a-hole that turned in front of me- and all of a sudden I had only 1st and 2nd gear. The disc/ring (or what was left of it) slid forward and was interfering with my gear change- so I couldn't get it into 3rd or 4th. Made for a miserable drive to the shop in Chicago.

dude, flex disks are cheap, just replace it if a visual inspection yields visible damage. Easy to do at that.

Once a month I do a "once over" on my SL-C. Granted I dont drive but mabye 250-500 miles on her a month I look at my flex disks, oil seepage, coolant, oil, and ATF levels, and undercarraige bolts, on my creeper.

My flex discs may have been changed in the early 90's but still thats 20 years ago (nearly) and deteroriation and wear occour.

Welcome to the world of "Classic Car" ownership, it does have its price.

What separates us from owners of beater cars is 2 things. 1) we fix things that break to improve longevity. 2) our cars are inherently cool, if only to us. Neither of these statements prove factual to the vast majority of owners of other makes/models.

Even if most of our cars are only worth a few grand, they are still pieces of awe to us, and a select group of others who appreicate what we have. Thoes who dont are the suckers that sell a vintage MB dirt cheap for one of us to scoop up and replace something like a flex disc for cheap and save from the scrap heap or a parts car (in the case of exorbanant rust).

In any case, inspect the flex discs, and be sure to take pictures if in doubt. Someone on the board will be sure to lend advice/assistance (if in area) and keep you'r 126 on the road.

Keep your head up, most of us were "broke college students" at some point, I know I was, any my SL-C endured.

Flex Plate are like twenty bucks. Here is my tread about a destroyed flex plate on a 300D.

http://www.peachparts.com/shopforum/diesel-discussion/237244-pics-cracked-flex-plate.html

Flex PLATE goes between flywheel & torque converter, could make noise while running, but not moving . . .

Flex DISK goes on each end of the drive shaft, could only make noise if car was moving . . . so that is not what is making the noise in this case.

seems to be some confusion here . . .

Unfortunately while I was changing my fuel filter (1st order of business) it began to rain. I packed up and headed inside without being able to crawl under and check the plate.

Lexxani, I believe you're referring to the driveshaft flex disc. The part I am referring to is between the torque converter and flywheel, which would require separation of engine and transmission.

DeliveryValve, how long did it take you to complete the job? As I read in the thread, all you had were jackstands and a HF trans hoist? I assume an added expense to the piece of sheet metal would be a front pump gasket? Still only a couple bucks.

I agree that the flex discs should be checked every chance you get, but what most here are ignoring is the fact that a bad flex disc talks to you more thu vibration than sound. It's obvious that your noise is coming from somewhere forward of the rear of the transmission. It could be flex plate or something as simple as something rattling against an exhaust pipe, or even a broken weld.

We actually dragged it out for a week. Including one day we spent 3 hours of cleaning the grime from the transmission, transmission tunnel and back of the motor. But I would say actual repair at a slow pace can be done in a full day. But probably a good weekend should be sufficient.

Front pump seal is like 5 bucks, few bucks for crush washers, and the expense of transmission fluid and filter change.

Another tip is you need to look out for the torque converter being damaged on the flex plate mounting surfaces where the bolts go in. If the flex plate is damaged enough it can rub and wear the mounting surfaces. If the flat mounting surface has been reduced in size it can cause alignment issues and strength issues. So be on a look out on that.


.

I was driving it around today and tried to pinpoint the sound some more. From beside the car it sounds like it is coming from the torque converter area. However inside the car it almost sounds like its coming from the fuel tank :confused: I was thinking maybe it has to do with the lift pump surging fuel back into the tank? I don't think it is exhaust, when I was under there today it looked ok, was pretty solid. Also, I would imagine that the turbo would muffle the sound of each cylinder a bit--this sounds almost like nailing on one. This is driving me crazy!!:dizzy2::freak::bomb:

Edit: I still haven't had the time to crawl under the car and check the flex plate, I have to clean the whole thing first, there is years of gunk on the bellhousing...seems like a weekend job.

FTW

I should add I recently checked the flex DISCs for any wear when I was servicing the transmission, and found no play in the driveshaft. My differential does have a whine however, only noticeable without the seats or rear deck in so its not too loud. A diff oil change is definitely in the short term plans. I recently changed the wheel bearings while doing the brakes, inspected everything back there. The subframe mounts are like pancakes so they need to be replaced, and the swaybar links are loose/need to be replaced. Halfshafts look okay, and the boots are still in good shape.
However I don't understand how these items would really carry a knock that is 100% correlated to engine RPMs. I do see what you are saying with vibration, but this is constant even when the engine smooths out from idle. Thank you all for the suggestions. --TC

Car is in N and making these noises when revving?

I have the same problem, I think, and I believe it to be the flex plate. I bought one on this site. Seems like an awfully small triangle and I'm worried it is not the right part. Anyway, I'm taking it back to an independent transmission shop and they are going to change it out. Anybody ever paid somebody to do this job? How much did they charge? Thanks

My transmission guy typically charges $85 an hour. R&R no including bench time averages $650 (can $ of course)

update: The noise has something to do with the fuel return line surging into the tank. I was under the car today and checked the flex plate. It looked okay to me, though there wasn't too much room to see. I ended up replacing all of my fuel lines in the "going crazy" process as a preventative measure (and maybe trying to get the power back in the engine?). I also threw some sea foam in diesel-purge style from a can and the noise stopped. However, I noticed the return line was putt-putting pretty bad, though I think the cigar hose is designed as sort of a muffler for this. I was happy to realize the noise stopped, but now I wonder if this is normal for the lift pump to be so violently pumping that it creates an audible noise in the tank?

FWIW the fuel is clear finally (after draining the tank, I have another thread on this) and replacing every little bit of fuel hose under the hood seems to have sealed things up and restored some power. I'll admit I freaked out a bit on the flex plates :(