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Replacing Your Front and Rear Flex Discs on your Mercedes Benz
 
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Pelican Technical Article:

Replacing Your Front and Rear Flex Discs on your Mercedes Benz

Steve Vernon

Time:

3 hours3 hrs

Tab:

$90

Talent:

**

Tools:

Torque wrench, 8, 13, 17, 19mm socket, 17mm wrench, 8mm Hex

Applicable Models:

Mercedes-Benz W123 (1977-85)
Mercedes-Benz W124 (1986-95)
Mercedes-Benz W126 (1981-91)
Mercedes-Benz W201 (1984-93)

Parts Required:

Flex discs and hardware

Hot Tip:

Check your muffler hangers and CV boots

Performance Gain:

Smoother shifts, no vibrations while driving

Complementary Modification:

Replace your driveshaft support bearing

If your automatic transmission is starting to change gears a little harder, or you are getting a vibration through the transmission or center tunnel while driving, your flex disc may be deteriorating. This chassis has two flex discs that connect the transmission to the driveshaft and the driveshaft to the differential. These units will wear out over time and even if you are not noticing any signs of trouble, they should be inspected every year. The discs are made out of rubber and are designed to absorb some of the shock from the drive train. Like anything rubber, they dry out, crack and will eventually fail. If you let the discs get to that point while the car is in motion, they can cause a tremendous amount of damage.

Begin by safely raising and supporting your car off the ground. Please see our article on jacking up and supporting your Mercedes-Benz. The care will need to be in neutral while working on it, as you need to spin the drive shaft to give you access to the bolts on the flex discs.

I decided to do the rear first and then the front. It does not matter which order you do them in, but the front is a little more work. You will need to get access to the mounting bracket in the middle of the drive shaft by removing the protective cover between the drive shaft and muffler. It is held in place by three 8mm screws. Remove the screws, slide it around the muffler and set it aside.

Over the years Mercedes and the different companies that have made flex discs have used an assortment of nuts and bolts. While you may find different hardware from front to back they all have one thing in common which is they are single use, you should never reuse the hardware from the old discs. The Pelican Parts kits come with all new hardware so you do not have to worry about ordering it separately. This would also be a good time to replace your driveshaft support (carrier) bearing. Please see our article here

http://www.peachparts.com/Wikka/W123DriveShaftSupportBearing

Remove the hardware connecting the rear flex disc to the differential. With all the hardware removed, undo the 13mm bolts that hold the bracket in the middle of the drive shaft. This will allow you to lower the driveshaft and give you enough room to separate and remove the flex disc from the shaft. If the disc has been on a while it may be stuck on there pretty tight. Just be careful when separating them as the driveshaft and flange are balanced and you don't want to ding or dent them up.

With the old disc removed, apply a small amount of grease to the new fittings and install your new disc with the side that has the writing on it facing the driveshaft. Install the hardware loosely. With everything lined up, reinstall the bracket on the drive shaft and then torque down the flex disc to Mercedes-Benz specifications.

To replace the front disc you will need to support the transmission, as you're going to be removing the transmission mount. There is not enough room to access the front disc with the mount in place. Make sure you carefully support the transmission by distributing the weight over a large surface. Use a good size piece of wood and a couple of floor jack stands to help. Do not just stick a single floor jack under the transmission, as you are going to be putting a fair amount of force into torquing the bolts down and you want everything properly supported. With everything supported, remove the two 13mm bolts holding the mount to the transmission and then the four 19mm bolts holding the mount to the frame.

Undo the six nuts and bolts connecting the flex disc driveshaft and transmission. You can now slide the driveshaft back on its spindle to give you enough room to remove the old unit and install the new disc. A personal note here, I had to release the bracket on the center of the drive shaft to give me some additional room to get the old one off and new one on.

Following the same procedures as the rear, lubricate the fittings, install the single use nuts and bolts loosely and then reinstall the bracket in the center of the driveshaft. Torque the bolts, reinstall the transmission mount and the protective cover on the driveshaft.

Remove the protective cover in the drive shaft tunnel by unscrewing the three 8mm screws.
Figure 1

Remove the protective cover in the drive shaft tunnel by unscrewing the three 8mm screws. Swing the plate around the cat and set aside.

Unfasten the six nuts and bolts (yellow arrow) connecting the drive shaft, flex disc and differential.
Figure 2

Unfasten the six nuts and bolts (yellow arrow) connecting the drive shaft, flex disc and differential. Discard these bolts as they are single use and should not be reinstalled.

You will need two wrenches to remove the bolts.
Figure 3

You will need two wrenches to remove the bolts. Also the wheels will need to be off the ground so you can spin the drive shaft to give you access. Note: the muffler has been removed to get a better picture of the driveshaft bracket, but this project can certainly be done with the exhaust system on the car.

With the bolts removed from the flex disc you will need to lower the driveshaft down to give you enough space to get the old disc off and the new one on.
Figure 4

With the bolts removed from the flex disc you will need to lower the driveshaft down to give you enough space to get the old disc off and the new one on. Remove the 13 mm bolts securing the bracket (yellow arrows).

This picture shows the old disc removed along with the driveshaft lowered.
Figure 5

This picture shows the old disc removed along with the driveshaft lowered. Grease the fittings on the new flex disc and install the new hardware.

The front flex disc is hidden by the transmission mount.
Figure 6

The front flex disc is hidden by the transmission mount. You will need to remove this to replace the disc. Slightly lift and support the transmission. DO NOT just place a floor jack under the sump plate, you may damage the transmission and it is not very stable for the amount of force you may need to use to remove the disc. Once the transmission is safely supported you need to remove the two 13mm bolts holding the mount to the transmission (red arrows) and the four 19mm bolts holding mount to the frame (yellow arrows).

In this photo you can see the lumber we used to support the transmission (green arrows).
Figure 7

In this photo you can see the lumber we used to support the transmission (green arrows). You will need to use two wrenches to get the bolts off as well as have the driveshaft free to spin so you can get access. You can see the damage to the old disc here (red arrow). With the disc free the drive shaft will slide back on its spindle. This should give you enough room to remove the old disc, but if you need more you can always lower the drive shaft bracket again.

Here is the transmission and driveshaft flange with the old flex disc off.
Figure 8

Here is the transmission and driveshaft flange with the old flex disc off.

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Comments and Suggestions:
63soni Comments: Hi I have a 1996 c280 , when downshifting when on incline or decline sometimes level there's a chunk noise from 2 to 1 transmission is fine , after inspection the flex discuss look ok but the center bearing mount has a lot of play no cracks , it can be moved with 2 fingers and there's a thuk noise when I do this any ideas?
August 5, 2016
  Followup from the Pelican Staff: I would replace the center support bearing. - Nick at Pelican Parts  
Joe Pau Comments: Where is the drive shaft bracket? Is it under a cover? This is for an 88 190e 2.3
July 6, 2016
  Followup from the Pelican Staff: I think the author is referring to the differential flange. - Nick at Pelican Parts  
Tony Comments: are there any special tools needed for replacing the center support bearing on a 91 190e auto, and does the drive shaft just slip apart by pulling the rear section out.
April 4, 2016
  Followup from the Pelican Staff: It should slide apart, then you will have to press the bearing on and off. - Nick at Pelican Parts  
cyberbach Comments: I found this article very informative but was surprised there were no links to order the parts.... I was really hoping to find DIY info and source for flex discs and drive shaft support bearing. You info and pics were great, sure wish I could have found the parts though. Paul
August 28, 2015
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Greg Comments: Before replacing the rear flex disk the drive train had a clunk sound if the transmission shifted while not accelerating. After replacing rear flex it has a loud ticking sound when slowing down.
June 3, 2015
  Followup from the Pelican Staff: Check if a heat shield is hitting the driveshaft. - Nick at Pelican Parts  
sherri Comments: My driveshaft came apart upon replacing my flex disc, i cant seem to get the flex disc back connected to trans and proper drive shaft alignment
September 10, 2014
  Followup from the Pelican Staff: You didn't mention what vehicle you are working on. Where did the driveshaft come apart (which component)? - Nick at Pelican Parts  
Sandy Comments: Replaced a front flex disc with these great instructions and even better pictures. Had to undo the centre bearing bracket and remove cross piece on front section of propshaft 'tunnel' then gently prise the old disk hammer and old screwdriver from the gearbox and propshaft mounts. A real uncomfortable job without a lift but done now for another 100,000 miles maybe. Remember to mark the transmission bracket and propshaft clearly it's dark under there.
Thanks again guys...
August 31, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
rbs8f Comments: Working on my 1990 300SE. Replaced the drive shaft flex discs, center bearing & carrier, and centering bushings.
Problem is, now that I am putting it back on the car, it appears to be TOO LONG!

The shaft is compressed at the gland nut/splines. The front flex disc is bolted to the front end of the drive shaft- and to the transmission. The center bearing carrier is not bolted to the floor frame.

When I use a pry bar to get the rear flex disc over the differential centering pin, I feel a little compression as I strain the universal joint, but the compression stops a good 1/2" before fitting over the pin.

Any ideas??? BTW- this car has had an engine swap before I bought it... it has a 617.951 from a ~1985 300SD. I have assumed this would not have caused a drive shaft length change- since they were both W126 chassis. Anyway... the !@##$@#$ drive shaft fit before I put the new parts on!
May 21, 2014
  Followup from the Pelican Staff: I would compare the old parts to the new. You may have a wrong part installed. That is the only thing that makes sense to me. - Nick at Pelican Parts  
bnthdntht Comments: are there any marks to replace your driveshaft exactly the way you removed it -for dynamic balance-if you took it off not knowing it is balance ,so you didn't mark it-?
February 17, 2014
  Followup from the Pelican Staff: I prefer to make my own marks, that is if the factory marks are not visible. - Nick at Pelican Parts  

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