Rear End

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Fitting the Swingarm
I obtained this aluminum swingarm and Ohlins remote reservoir shocks from a junked late 70’s vintage KTM 400MX.  The KTM was a “right drive/right brake” arrangement so fitting the stock TT rear wheel was a challenge. First of all the KTM swingarm was a bit wider than the TT frame so some of the swingarm had to be milled off to fit between the rails.  The stock KTM bushings would not work so my brother Jason turned some bronze bushings to fit the ID of the swingarm holes and the OD of the 5/8” axle bolt.  I will eventually install some bearings in place of the bushings when I find the right ones.

Rear Brake
This was the most challenging part of the project. I wanted to use the stock TT wheel and brake. The stock TT brake shoe assembly was held in place by a bracket which attached to the stock swingarm. This would not work because the brakes would have locked up when the suspension compressed. Besides, I had to remove the stock TT brake lever assembly because it interfered with the new swingarm. I was able to use the bracket from the CR500 and attached it to the TT frame to keep the brake shoe assembly from rotating. This corrected the geometry problem so the brakes won’t lock up. For the brake lever, I used the lever and cable from a 1978 RM125. The right footpeg mounting bolt is now also used as the brake lever pivot point. The RM lever had to be drilled out to accommodate the footpeg bolt. The RM brake cable fits perfectly with the stock TT brake actuator, including the TT adjuster.  With this arrangement I can even adjust the lever height!

Drive
A full 120 link O-ring chain is required to stretch around the sprockets due to the 5” longer swingarm. To keep the chain on track, I added a Fredette chain guide. Chain slack was a big problem with a long swingarm since the swingarm pivot point is so far from the countershaft sprocket. To fix the problem, an MSR chain roller was bolted to the frame. This took up the slack from the chain when the suspension is uncompressed. The stock TT chain adjusters were also used.

Shocks
The Ohlins shocks from the KTM are slightly narrower at the top mounting hole.   A couple of washers did the trick.

 

The ride is amazingly good now compared the kidney-jarring stock TT suspension.   It’s well suited to woods riding and an occasional trip to the motocross track.  The extra ground clearance really comes in handy too. The longer swingarm helps with the wheelie-happy nature of the stock TT500. Besides, it just looks trick!