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Front and Rear Flex Disc Replacement
 
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Pelican Technical Article:

Front and Rear Flex Disc Replacement

Steve Vernon

Time:

3 hours3 hrs

Tab:

$80 to $160

Talent:

**

Tools:

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

Applicable Models:

Mercedes-Benz W124 (1986-95)

Parts Required:

Flex discs and hardware

Hot Tip:

Carefully support the transmission

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. The W124 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.

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.

Begin by safely raising and supporting your car off the ground. Please see our article on jacking up and supporting your W124. The car will need to be in neutral while working on it, as you need to spin the driveshaft to give you access to the bolts on the flex discs.

Remove the protective cover in the driveshaft tunnel by unscrewing the three 8mm screws (red arrow).
Figure 1

Remove the protective cover in the driveshaft tunnel by unscrewing the three 8mm screws (red arrow). Swing the plate around the cat and set it aside.

Unfasten the six nuts and bolts (red arrow) connecting the driveshaft, flex disc and differential.
Figure 2

Unfasten the six nuts and bolts (red arrow) connecting the driveshaft, 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 (red arrow).
Figure 3

You will need two wrenches to remove the bolts (red arrow). Also the wheels will need to be off the ground so you can spin the driveshaft to give you access.

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 (red arrows). Note: the exhaust is removed for photographic purposes. You should be able to get access to the bolts without removing the exhaust.

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 with a large flat piece of wood. 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'mm bolts holding the mount to the frame (yellow arrows).

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

In this photo you can see the lumber we used to support the transmission (red 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 (yellow arrow). With the disc free the driveshaft 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 driveshaft 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. Installation is the reverse of removal.


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Comments and Suggestions:
quest1966 Comments: Still not answering the question directly - is the block in the picture "on the pan" or "not on the pan?"
October 10, 2016
  Followup from the Pelican Staff: The block will (is) sit(ing) on the transmission. (my previous response with items in parenthesis added. - Nick at Pelican Parts  
quest1966 Comments: Yes, I understand the wood block is between the jack and the transmission. The question is about the position of the block on the transmission. Is the block directly supporting the transmission oil pan? In other word, is the weight of the transmission being held by the transmission oil pan?
October 9, 2016
  Followup from the Pelican Staff: Ok, sorry missed that part of your question.

The block will sit on the transmission. You can also build a wood bracket that supports the trans where the pan bolts up, avoiding pressure on the pan. - Nick at Pelican Parts
 
quest1966 Comments: Regarding support for the tranny in Figure 7, it's hard to tell exactly how the wood blocks are being used. Is there a large, wide board spanning the whole area of the pan to hold up the tranny? Or, is the wood block holding up the back edge of the tranny, off of the pan? Thank you!
October 7, 2016
  Followup from the Pelican Staff: The wood blocks are sitting on a jack, the wood providing a soft buffer between the jack and the trans. - Nick at Pelican Parts  
Tom Comments: Hi Pelican, my shop is telling me that labor to replace the flex disc will be quite high because they first need to remove the exhaust system on my 1995 E320 wagon. Based on your instructions, this doesn't seem to be the case. Does the exhaust need to be removed?
September 19, 2016
  Followup from the Pelican Staff: Our article is for a sedan. Your vehicle may be different. - Nick at Pelican Parts  
TonyC124 Comments: Good Progress.... but...
Driveshaft Support Bearing - you mention up top that whilst replacing the flexdiscs done it's a good time to check/change the centre bearing. Well the rubber around mine is cracking so time to change the mount, but how easy is it to change the actual bearing? Is this a home or a workshop job? Do you have a tutorial? Any advice gratefully received!
Oh and by the way is it feasible to replace just the UJ or is that a new driveshaft?
July 24, 2016
  Followup from the Pelican Staff: The driveshaft has to be separated when removed, pull it apart, the splined shaft should slide apart. Then the bearing is pressed on and off. You will need a puller to remove, possibly installed without a press using a soft-faced hammer. As long as you don't damage the bearing. - Nick at Pelican Parts  
TonyC124 Comments: Oh - me again, secondary question - on the flexdiscs, is there a right or wrong way to fit the bolts? I.e. should they be all front-back, or alternate, or back-front? Or doesn't it matter? And one last point re Greg's posting - is that true? Can we reuse the bolts and washers?
June 19, 2016
  Followup from the Pelican Staff: Trans bolts face trans. Diff bolts face diff. - Nick at Pelican Parts  
TonyC124 Comments: I have a question to Pelican - Today after hopefully successfully replacing my front engine mounts I used the non-raining time under the car to take a look at the front flex disc and trans mount. My trans mount is clearly kaput and the flex disc is quite hard not sure why the dealer/stealer only replaced the rear one last year and not the front... :-. So, I need to get a new mount and disc and hopefully replace next weekend, but the question is on positioning of the mounting strut you show in Fig 6. Mine has slotted holes all round, so how do I know when it is in the correct position? Do I just follow the old grease marks, or is there a more scientific method? I guess left-right position is quite important for prop shaft balance..... :-
June 19, 2016
  Followup from the Pelican Staff: Get the mounting bracket fasteners finger tight, then lower the jack supporting the trans to lower in onto the bracket. Once centered, tighten the fasteners for the body, then the mount. - Nick at Pelican Parts  
Neels Comments: P with the rear bolts removed and the centre bearing loosened I still can not mote the drive shaft forward to get it out of the differential. Exhaust has been removed and there is ample space but still the rear is not sliding forward on the spline as supposed to be. Any suggestions ? I am at wits end .
May 25, 2016
  Followup from the Pelican Staff: What vehicle are you working on? The article covers models with a flex-disc at the rear. - Nick at Pelican Parts  
Greg Comments: Quick remark: The bolts and washers are reusable, it's the nuts which must be replaced.
March 25, 2016
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
golfinator Comments: It would be helpful if Lemforder would include some info in their packaging as to why the different colored and sized bolts.
December 3, 2014
  Followup from the Pelican Staff: Send them an email. There are likely different size bolts on your vehicle. Match the new ones up when you remove the part. - Nick at Pelican Parts  
Ron Comments: On the front flex disc, why are there six bolts when only 3 attach to the transmission yoke?
November 28, 2014
  Followup from the Pelican Staff: Three attach to the driveshaft as well. - Nick at Pelican Parts  

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