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Pelican Technical Article:

Flex Disk Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$45 to $120

Talent:

**

Tools:

17mm, 13mm socket, extension, 19mm, 17mm wrench, 8mm Allen,

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Flex disk (Giubo)

Hot Tip:

Put a piece of wood between the jack and transmission

Performance Gain:

Proper drive shaft alignment

Complementary Modification:

Check your transmission mount

If the automatic transmission in your W123 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 W123 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 that it completely fails while the car is in motion, they can cause a tremendous amount of damage.

The hardware on the flex disks are considered to be single use only, make sure you check when ordering that your kit includes all new hardware. Also the hardware can vary from disks and manufacturers, so make absolutely sure you are using the right tools for the fittings on your vehicle.

To change the disks you will need to remove the transmission cross-member and I prefer the transmission mount as well. Begin by safely raising and supporting the vehicle. Please see our article on safely raising and supporting your W123.

The transmission mount mounts by a single 19mm nut to the tail of the transmission (red arrow) and two 13mm bolts to the cross-member (yellow arrow).
Figure 1

The transmission mount mounts by a single 19mm nut to the tail of the transmission (red arrow) and two 13mm bolts to the cross-member (yellow arrow).

Begin by placing a piece of wood across the transmission to help distribute the load and safely support the weight of the transmission.
Figure 2

Begin by placing a piece of wood across the transmission to help distribute the load and safely support the weight of the transmission. Set the wood back far enough so it will not interfere with accessing the disk

Use a 13mm socket and remove the two bolts holding the mount to the cross-member (red arrows).
Figure 3

Use a 13mm socket and remove the two bolts holding the mount to the cross-member (red arrows).

Next remove the four 17mm bolts holding the cross-member to the chassis.
Figure 4

Next remove the four 17mm bolts holding the cross-member to the chassis. Use care as once the last bolt is out, the cross-member will fall. There is a bridge late between the cross-member and mount (red arrow); do not lose it and do not forget to reinstall it when installing the new mount.

Use a 19mm wrench (preferable geared because of the tight working conditions) and remove the single nut holding the mount to the transmission (red arrow).
Figure 5

Use a 19mm wrench (preferable geared because of the tight working conditions) and remove the single nut holding the mount to the transmission (red arrow).

You can now inspect the transmission mount.
Figure 6

You can now inspect the transmission mount. This mount is fine but if your mount is starting to go you will see, rips, tears, cracks and general degradation in the rubber.

Make sure you have set up your wood to support the transmission so it does not interfere with access to the disk (red arrows)While you can get your wrenches in with the mount in place I like to take the two minutes and remove it and inspect it.
Figure 7

Make sure you have set up your wood to support the transmission so it does not interfere with access to the disk (red arrows)While you can get your wrenches in with the mount in place I like to take the two minutes and remove it and inspect it. Here you can see how the disk is failing as there should be no space between the hardware and rubber (yellow arrow). You will need to rotate the drive shaft to get access to all of the hardware.

With the hardware off you should be able to compress the drive shaft back far enough to remove the disk.
Figure 8

With the hardware off you should be able to compress the drive shaft back far enough to remove the disk. Note the position of the disk and how three of the openings will have elevated flanges which sit in the drive shaft flange (red arrow). Make sure you install the new disk so these elevated flanges sit in the driveshaft flange.

This disk is shot and in dangerous shape to have still been in the vehicle; don't let yours get to this shape by making sure you inspect and replace it before it looks like this.
Figure 9

This disk is shot and in dangerous shape to have still been in the vehicle; don't let yours get to this shape by making sure you inspect and replace it before it looks like this.

If you cannot compress the drive shaft enough, you may have to lower the drive shaft bearing by loosening the two 13mm bolts holding it in place (red arrows).
Figure 10

If you cannot compress the drive shaft enough, you may have to lower the drive shaft bearing by loosening the two 13mm bolts holding it in place (red arrows).

Replacing the rear disk (red arrow) is the same as the front, but you do not need to remove any mounts.
Figure 11

Replacing the rear disk (red arrow) is the same as the front, but you do not need to remove any mounts.

Again, check what type of hardware you have on yours and then remove it, rotating the drive shaft as necessary (red arrow).
Figure 12

Again, check what type of hardware you have on yours and then remove it, rotating the drive shaft as necessary (red arrow).

Installation is the reverse of removal making sure that the raised flanges sit in the drive shaft flange.
Figure 13

Installation is the reverse of removal making sure that the raised flanges sit in the drive shaft flange.

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