Revshift Flex Disc Installation

  • The Revshift race flex disc is a high performance part that requires the drivetrain to be properly aligned. It is intended for race applications only.
  • FOR RACE USE ONLY! This part is very rigid and requires precise installation. The driveline must be properly aligned and all driveline components must be in good condition and properly balanced. The engine mounts, trans mounts, differential bushings, and subframe bushings must all be rigid to prevent driveline movement. We recommend a hardness of 95a or higher for these components. A new center support bearing and driveshaft centering bushing are also recommended.
  • The six supplied washers must be installed to prevent the bolts from squeezing through the polyurethane bushings causing damage to the flex disc.
  • Install three washers on each side of the flex disc. One washer under each bolt opposing the driveshaft / transmission flanges.
  • No washers should be touching the driveshaft / transmission flanges.
  • Assemble and install all 6 nuts, bolts, and washers finger tight. Do not torque bolts until fully assembled.
  • Torque the bolts in opposing sequence to 25 ft-lbs and then 50 ft-lbs.
  • Washer placement should resemble the picture below.

  • Installing the Coupler:
    Jack the car up on all four corners and use jack stands. Put it in neutral with the parking brake off because you will need to rotate the driveshaft. Drop the exhaust (mandatory, you won't be able to access the flex disc bolts with the exhaust in place). Mark the end of the driveshaft and the transmission flange, so that you can reconnect things with the same orientation. Use a breaker bar to loosen the 6 bolts. Remove the six bolts. Be ready to support the front of the driveshaft with something so that it doesn't sag more than 4"-6" (it feels like it might slide out of the central joint if it's not supported). Remove the rubber flex disc and insert the Revshift part and use all six bolts to locate things together. Install the nuts on the drive shaft side bolts. Use the extra washers Revshift includes. At this point, if you notice that the surface of the disc and the flange coming out of the transmission are not parallel (If things touch in one spot but have a gap in another, read the section below). Rotate the driveshaft and bolt it together at the top, to ensure that the extended sleeve is properly positioned before tightening each bolt. Torque the bolts in an opposing sequence to 25 ft-lbs and then 50 ft-lbs. Manually spin the driveshaft and check for runout in the center support bearing. If it is not spinning centered retorque the flex disc bolts and check again. Reinstall the exhaust, drop the car, and go for a test drive.



    Correct installation of the supplied washers is extremely important. Please inform your mechanic of these instructions.

    Incorrect installation will void the warranty of this part.

    If you have any questions please contact us prior to installation.


    Diagnosing and Correcting Driveline Vibration:

    You most likely won't need to do any of the following and your car will feel great once you install the Revshift flex disc. If not then you may be experiencing some vibration beginning at approximately 20-35 mph. It may be pronounced in the gearshift lever and you might see the gearshift moving back and forth. If so, please follow the instructions below.

    Symptom:

    • Vibration, audible rumble over 35 mph.

    Probable causes:

    • Driveshaft misaligned
    • Center bearing faulty
    • Incorrect preload of center bearing
    • Sliding coupling seized
    • Differential rubber mount faulty
    • Transmission rubber mount faulty


    Flex disc couplers mate the transmission to the driveshaft and, in some applications, the driveshaft to the differential. Flex discs are not intended to have more than a degree or so of misalignment from zero, especially in the section of driveshaft that has the flex disc in one section of a two piece driveshaft or at all in a two piece driveshaft with dual flex discs.

    The Revshift flex disc is designed to withstand extreme driving conditions. As little as .020” of misalignment can cause a vibration. It is critical to make the alignment angles zero. The factory rubber flex disc is much softer (and weaker) and will absorb some misalignment.

    The best way to do this is to use a vernier caliper. Remove the flex disc from the driveline. Align the three holes of the driveshaft flange with the three holes of the transmission flange. Measure the gap and make adjustments so that it is within .008” from top to bottom. Next, do the same horizontally and then again vertically. This takes some time as the vertical gap can sometimes change when you make the horizontal adjustment. Adjustments are made by loosening bolts and moving the center support bearing and/or transmission.

    When a high performance flex disc is too far out of alignment it can act as if you had a seized u-joint. If you have ever experienced a seized u-joint that operates on 4 degrees then you know how bad the symptoms can be.

    If your factory flex disc has failed, it is most likely due to a misalignment. Vibrations are almost always due to a misalignment unless something is seized or broken. Vibration after a flex disc install is not due to rear end or shaft balancing issues. If you are unable to correct the issue then please take your vehicle to an experienced driveline specialist.

    Correct installation of the supplied washers is extremely important. Please inform your mechanic of these instructions.

    Incorrect installation will void the warranty of this part.

    If you have any questions please contact us prior to installation.