Help! Replaced Cracked Flex Disk, Now Vibration
 

I HAVE A 1993 500SEL WITH 95,000 MILES.

I HAD MY CRACKED FLEX DISK (FRONT) REPLACED, NOW I HAVE A VIBRATION AT SPEEDS OVER 50MPH.

THE PART NUMBER OF THE OLD DISK IS 129 411 00 15.THE NEW PART NUMBER IS 129 410 01 15. BOTH UNITS LOOK THE SAME. ONLY DIFFERENCE IS THE BOLT HEADS. THE OLD ONE HAD SOCKET HEADS AND THE NEW ONE IS A ALLEN HEAD.

WHAT COULD HAVE HAPPENED? DO THE BOLTS HAVE TO BE TIGHTENED IN A CERTAIN ORDER AND TORQUED? THE MECHANIC INSTALLED THEM WITH A AIR GUN.

ANY HELP WILL BE GREATLY APPRECIATED.

Not only is there a front face and rear face to the flex disk, three of the flanges are designed to attach only to the transmission while the other three attach only to the driveshaft. Nuts, bolts and washers can only go one way or the new disk will be flexing in ways not intended, and yes, you can get vibrations from it. Is the mechanic that installed it an experienced MB mechanic? Did he use new bolts? If there is any play between the sleeves and the bolts, the bolts must be replaced. Also, I always replace the self locking nuts.

FLEX DISK PROBLEM! VIBRATION
 

How do you tell which side is front and rear? On my old or the new one nothing says front or rear? The flanges that attach to the driveshaft and transmission...........would it not be very hard to mess this up as the flanges fit inside the transmission yoke and driveshaft yoke, right?

If the unit has been installed backwards, is it now damaged?

The mechanic did use the new bolts as the new ones were large allen head and the old ones were standard head. He placed the washers like on the driveshaft yoke, they were placed on the bolt side and not the nut side and vice versa on the transmission side.
So on the driveshaft yoke the four nuts were screwed down with the washers below the bolt head and not on the nut side. THE NUT IS SCREDED DOWN DIRECT TO THE YOKE. Is this correct?

Thanks for any input as I need to get the car back to hime first thing in the morning.

It's been a while since I replaced one, but I remember that there is a German word on it that indicates which way it goes in. Even if it is in backwards, I doubt that it would cause vibration. It would allow slack.

What may very well have happened was that the driveshaft slipped apart at the splines during the operation. If this happens without the two pieces being marked, it could have been slipped back in place in a different position. This will spoil the balance of the entire assembly.

Good luck,

I don't believe ALL flex discs have that German word. Only some must face a certain way, and I don't believe 124's are (at least for a diesel). When I took mine off to remove the driveshaft, I found three bolts that did not even have washers and I did not have any vibration. If a bolt is loose, that is very prone to vibration. Since air guns don't get torque evenly distributed, I would check on the bolts first. If any are loose, they must be fixed.

MB dealer part for flex disc includes the bolts, washers, and nuts (again, at least for '87 diesel). If aftermarket was used, it may not have included the new bolts.

But, I would check that the two flanges are seated properly to the flex disc and that bolts are toqued as appropriate.

Its also possible that the center support bearing mount was loosened, moved, or the 41 or 46 mm bolt that tighens the driveshaft halves together was loosened and not put back correctly.

-brian

And to add to what Larry said, the way to check if the halves were reassembled correctly, there is a /\ on one and a | on the other near where they meet. The | should be aligned inbetween the /\.

This is exactly what happened. See quote.

Now, how they can determine the proper alignment -- I don't know.

brookspw,

Are you saying the flex disc was put on backwards or the driveshaft was not aligned correctly or both?? As mentioned, the /\ and | marks on the driveshaft ends are used for alignment.

I bet the driveshaft is NOT aligned. Just replaced mine and made sure to mark it.

HELP!!! CRACKED FLEX DISK (FRONT) REPLACED, NOW I HAVE A VIBRATION
 

THE DRIVE SHAFT IS ALIGNED CORRECT AS IT WAS NOT TAKEN APART WHEN THE FLES DISK WAS REPLACED. I WATCHED HIM INSTALL IT. TOTAL TIME WAS ONLY 15 MINUTES.

ON THE ORIGIONAL ONE, ONE SIDE SAYS, MADE IN GERMANY & THE OTHER SIDE SAYS, 129 411 00 15, CAD 138, SGF 12, & THE MERCEDES STAR. (WHICH IS FRONT AND BACK)

THE PART NUMBER ON THE NEW ONE IS 129 410 01 15 & THE BRAND IS LEMFORDER. IS THE PART NUMBER WRONG??

THANKS FOR ALL THE IMPUT GUYS AS I NEED TO KNOW WHAT I'M TALKING ABOUT WHEN I TAKE IT BACK TO HIM.

Please do not use all caps when you type :)

According to the Fastlane parts ordering system, you have the correct part number for the flex disc. Lemforder is a supplier to Mercedes for parts. There is no ordering sequence to tightening the bolts. Its most important that none are loose. One possibility is that fixing the front flex disc exposed a problem somewhere else. This is not uncommon. (i.e. Check the condition of your center support mount and bearing.)

I would take it to the mechanic and explain you started having a vibration after the front flex disc was changed and you'd like him to check it out. Don't assume the front flex disc was incorrectly installed. Or more importantly, don't accuse him of installing it incorrectly. Let him check it out and see what he finds.

Check the condition of your center support mount and bearing
 

Check the condition of your center support mount and bearing.

Are these two items common to go out?

Is the bearing in the tail of the transmission?

And does the support mount hold the transmission twards the rear?

If one of the above was bad, wouldn't I have still had a vibration???

Thanks!

The center support bearing (also known as carrier bearing;cutlass bearing) is located just about where the two drive shaft halves join. If the bearing is bad you will have a vibration, if real bad the shafts could knock against the tunnel.

Etiquette: all caps is akin to yelling. Thanks for taking the cap lock off.

Re: HELP!!! CRACKED FLEX DISK (FRONT) REPLACED, NOW I HAVE A VIBRATION
 

It had to be taken apart. The flex disck goes BETWEEN the two parts of the drive shaft.

Could the center support bearing gotten damaged while replacing the flex disk? He bearly even moved the drive shaft. Just eased it back a little to get the flex disk out. Is this bearing difficult and expensive to R & R? How else would you know if it's bad? And should it be replaced at so many miles?

Sorry about the caps, was not yelling, just disappointed about having to take the car back again.