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Thread: Final Drive

  1. #1
    tricyclerob
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    Final Drive

    Hi all, I guess this could be a dumb question, but ... Does anyone know if a later mdl. final drive, [/5 or?] would fit on a "/2"? Actually on a R69? They look identical, except for having a shock mount stud, instead of a bolt.
    I'm looking for a lower ratio for sidecar use, and have been watching E-bay, etc for a while, and have not seen any for "/2", in the lower ratios.
    I had a 26/6 which I tried for a bit but it seemed way too low for general use.
    Thanks, rj

  2. #2
    '99 '03 '06 National Co-Rally Chair Friedle's Avatar
    Join Date
    Mar 2003
    Location
    Poughkeepsie, NY
    Posts
    883

    Final Drive

    Yes it can be done, but it is not quite a "bolt on"swap.

    As you have already noted, the rear suspension mounting points for a /2 and the later final drives (/5,6,7) are different. It requires a bracket to mount the later FDs to fit the rear shock botom mounting point of the /2 suspension. It will probably be necessary to change the driveshaft inside the /2 swingarm to mate with the later FDs.

    There are "kits" out there for making this swap. I have had one in my R75/2 conversion rig with Steib S-500 for a long time. The kit included a modified /2 swingarm with a newer driveshaft and the mounting bracket for the rear suspension. It eliminated the need for an adaptor plate between the newer motor and the original /2 driveshaft and rear end. When you install a newer motor to gain some extra horsepower to pull the chair in traffic safely, you will be putting more horsepower through the drive train and also increasing the strain on the entire original drivetrain components. Something will give up the ghost soon, usually the rear end. Not sure if these "kits" are still available today, but you might try searching the USCA, IBMWR or MOA sidecar lists or even e-bay.

    Friedle
    Ride fast safely

  3. #3
    tricyclerob
    Guest
    Friedle, Thanks for your reply. It did look like the mount would be an issue. After adding a Ural to my R69, I can now see why the later engine conversions are poular with the "/2's". I guess I'll keep looking for the correct rear. thanks again, rj

  4. #4
    Registered User
    Join Date
    Apr 2006
    Posts
    93
    You can buy new gearsets of various ratios for the current final drive. The 25:7 (3.57:1) used on the R50S would be better, it would result in about 56 mph at 4000 rpm with a 4.00 X 18 rear tire. A wee bit more expensive than the /5 final drive conversion though - $722 + shipping etc. from Mark Huggett.

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