Main.TrailIndexPage | Drive Shaft and Rear Axle | Flex Disc

Flex Disc

This component is part of Driveshaft and Rear Axle.

Function

The Flex Disc sits between the transmission output flange and the driveshaft. It aids in reducing vibration between the transmission and the driveshaft. The flex disc is considered the cousin to the u-joint. The disc is basically a thick rubber disc with 6 metal holes. They are usually very robust, but like everything else they do and WILL fail, often at the most inconvenient time. As the flex disc ages, the rubber becomes brittle and begins to crack.

Maintenance

Use a bright light and check the condition of your flex disc. Look for signs of cracking in the rubber. Look for any distortion in the disc... A fault flex disc may cause serious consequences on the drivetrain, when it breaks apart. Therefore the flex disc should be replaced for preventive causes, at any time when signs of brittle or cracks occur.

Flex Disk Replacement

To replace the flex disc, you must first do the following:

  1. Support transmission
  2. Remove the transmission support plate
  3. Remove transmission support bracket
  4. Loosen the driveshaft. Refer to Driveshaft.
  5. Ensure the car is in neutral or out-of-gear and the rear wheels off the ground (or rear of driveshaft separated from rear axle). This helps to be able to rotate the shaft and get at all of nuts and bolts of the flex disk.

Remove Flex Disc

  1. Remove the flex disc nuts and bolts.
  2. Slide the driveshaft back.
  3. Remove flex disc

Install New Flex Disc:


Ensure that the tabs on the flex disc are oriented correctly or the flex disc will not last.
  1. Attach flex disc to transmission output shaft. Ensure that the tabs are positioned correctly on the three flanges of the transmission. Refer also to page 26-1/8 of the BBB. The three tabs align on the transmission output shaft's three flanges.
  2. Ensure that the washer always goes against the rubber disc.
  3. Ensure that the longer bolts have the washer between the nut and rubber disc.
  4. Ensure that the short bolts have the washer between the bolt head and the rubber disc.
  5. Ensure that All bolts point forward with the nuts on the transmission side.
  6. There are three long bolts (different heads) and three shorter bolts.
  7. Pay attention to position of the lip on the rubber coupling.
  8. The transmission flange should align with the lips on the rubber disc.
  9. Be sure all the bolt holes in both flanges are not damaged/distorted, and use new nuts and washers.
  10. Use a torque wrench to tighten the nuts/bolts
  11. The torque spec for all bolts/nuts on flex disc is 4.3 mkp or 31 lb/ft.
  12. You may want to use some "Loctite" blue to aid in securing nuts.
  13. Slide the driveshaft forward and attach to the flex disc.
  14. Roll and bounce the car before you retightening the driveshaft.
  15. Re-install transmission plate

New-style Flex Disc

The new style flex disc is more robust. It is also symmetrical and does not need to be oriented as with the early versions. As before, it uses three long bolts and the same three short bolts. Be sure to place these correctly. Also note that the flat washer is always next to the rubber flex disc, so it is between the bolt head and the rubber flex disc on the short bolts and then between the flex disc on the and the nut on the long bolts. Two rubber seals are involved. One is on the tail shaft of the transmission, (nested in the flex disc) the other is an o-ring on the centering flange at the driveshaft. These seals keep grease from escaping onto the rubber flex disc, during normal driveshaft lubrication. Grease on the rubber can shorten the life of the flex disc. The grease nipple on the driveshaft is used to keep the centering flange lubricated.
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