1987 300TDT Transmission (?) Issue? - PeachParts Mercedes-Benz Forum

1987-300TD · #1 12-11-2014, 12:34 AM

Good Day Gurus!

I have been having a transmission shifting issue for several weeks. I checked the fluid levels and they were slightly low. I added fluid and the problem has persisted. I was planning to get to it over the next several weekends as life has been busy for the past couple weekends. :-)

Alas, my time may have run out. Today as I was driving, my car acquired a "rumble" as I was driving. The "rumble" does not occur when the transmission is not engaged. However, whenever I have my foot on the accelerator, the "rumble" happens.

The "rumble" is both a noise and a vibration felt throughout the car but seeming to emanate from the rear center of the car. I have recorded the noise and will attempt to post that if it would help with the diagnosis.

If the car is rolling but my foot is not on the accelerator, the "rumble" disappears. It also seemed to lessen as my speed increased over 45 MPH.

I am open to any thoughts or ideas. Transmission mounts? Flex disc? Rear differential? Where should I start looking?

TIA,
glenn

vstech · #2 12-11-2014, 09:53 AM

I would first off STOP DRIVING THE CAR!!!

get under it, and grab the driveshaft. if you can move it up and down in the center, the center bearing support may have failed. it's simple to change, but requires disconnecting one or both of the flex discs.

it could also be the flex discs themselves. get a look at them. if there is any cracking, or cord sticking out, they gotta come out before they destroy the car!

take pics and post them if you are unsure of the issue.

Mxfrank · #3 12-11-2014, 10:56 AM

If it's not the center bearing, check your engine, differential and transmission mounts. The engine and differential have to be exactly in-line, but can shift around as a result of decayed mounts. There is a u-joint in the middle of the driveshaft, which is an unfortunate affliction of German drivetrain engineering. A single U-joint really isn't useful for correcting mismatched driveline angles. If the engine and differential aren't lined up exactly, you will get a shuddering vibration.

1987-300TD · #4 12-11-2014, 12:28 PM

Thank You both for your replies! I will get pictures posted this evening as this is my daily driver. :-)

1987-300TD · #5 12-11-2014, 12:45 PM

Extra question. As I do not have service records from previous owners, should I just replace the flex discs (126-410-04-15-M57 front and rear) and the drive shaft bearing (008-981-43-25-M34)?

Is there anything else I should replace whilst I have this apart?

Thank You!

capflya · #6 12-11-2014, 01:07 PM

Look at the discs... if you can start to see the cord showing through the rubber, or the rubber looks like it is cracked replace the discs.

The center bearing/bearing mount is probably the original stuff. If you're changing the bearing you should put a new support in around the bearing. Part# 124-410-07-81

Quahog · #7 12-11-2014, 04:11 PM

x2 on center bearing support

replacing flex discs is cheap insurance against catastrophic failure, especially when age is unknown.

use good quality/oem parts here

do make sure transmission is filled properly

sixto · #8 12-11-2014, 04:33 PM

Can't put too fine a point on this - get the best quality flex disks available. Mind that there's an unscrupulous knock-off brand called OEM that has nothing to do with any original equipment manufacturer.

Sixto
MB-less

jay_bob · #9 12-11-2014, 10:27 PM

And the other important safety tip on these:

If you study the new flex disk you will see that 3 holes have a raised lip and 3 are flat on each side.

Raised lip holes mate with the "ears" on either the transmission flange, the drive shaft flanges, or the differential flange. The flat holes should have bolt heads (or nuts) resting against them.

Factory spec is to have the bolt heads facing the center of the car (i.e. transmission end - bolts threaded back to front, differential end - bolts threaded front to back).

Do not mix this up!

And to repeat what others have said: Use only the Genuine MB part on this. Not one of those things you want to cut costs on.

1987-300TD · #10 12-12-2014, 02:54 AM

Here are pictures of my flex discs...

First, the front...

1987-300TD · #11 12-12-2014, 02:55 AM

Now the rear...

1987-300TD · #12 12-12-2014, 02:57 AM

I am going to go out on a limb here and say the rear flex disc is bad. :-)

Does anyone have a write-up or procedure to replace these?

Again, Thank You for the assistance! This board is invaluable for DIY projects!

jay_bob · #13 12-12-2014, 08:06 AM

In case you were wondering, DO NOT DRIVE IT AGAIN (except maybe to move it from one parking spot to another) !!!!

Replacement is pretty straightforward
Jack up and support back of car
Apply AeroKroil to the bolts and nuts
Remove hardware
The drive shaft has a short lengthwise adjustment ability so you can just push the drive shaft end forwards enough to give clearance for removing the flex disk.
Arrange support for the drive shaft, don't let it hang down while swapping the disk.
Install your new disk, remember to watch the arrangement of the flats and flanges on the holes.

Hate to be the bearer of bad news, but your differential is leaking fluid based on the oil caked deposits on the outside. That may be the source of your noise more so than the flex disks. I would venture a guess that your differential is seriously low on fluid and the gears are cooked.

1987-300TD · #14 12-12-2014, 04:21 PM

Thank You for all the insight!

I have ordered 2 Febi flex discs. Lemforder's were unfortunately out of stock. A few lingering questions...

Are there torque specs on the bolts for the discs?

For the center bearing, does the brand matter? Is genuine MB worth the extra $?

Regarding the rear diff, which oil should I use (001-989-33-03-12-M22)? Is synthetic better? How does one check/change the rear diff oil? How much oil does the rear diff hold? How often should it be changed?

Again, Thank You All!

sixto · #15 12-13-2014, 02:51 PM

The diff has a drain plug along the bottom and a fill plug about halfway up. Don't remove the drain plug until you remove the fill plug. The diff takes a touch more or less than a quart - that's all I remember. Might as well get synthetic.

jay_bob is right, you should address the diff leak. My guess is one or both axle seals. Nasty job dropping and refitting the diff with that d@mn vent in the way. Maybe keep topping the diff until you're ready to drop the rear subframe for new bushings.

Sixto
MB-less