As we’ve stated before, Truvativ HammerSchmidt is one of those products that we could barely wait to get our hands on. When we finally did, there was no doubt that the HammerSchmidt was a high-quality execution of a clever design. Truvativ has brought a planetary two-speed gearbox to the masses. We have loved it, both out on the trail and at the local freeride park.
One thing we can’t stop doing is thinking of different ways to do things here at Competitive Cyclist. While we don’t claim to be engineers, we do like to tinker. We had an enthusiastic local customer who bought a HammerSchmidt from us to install on his single speed dirt-jump bike. His only hesitation was that he wanted to keep the handlebars as aesthetically clean as possible. He doesn’t run a front brake, so the left side of the bars are normally devoid of anything but a grip. One of our shop guys assured him that the HammerSchmidt was just a dumb ol’ hunk of metal, and that it didn’t know if it was getting shifted by the proprietary SRAM trigger or an 8-ball shifter on the top tube. As long as the correct amount of cable gets pulled, it should work. With that assurance, our brave customer shelled out the dough, and our handy fabricator got busy. We were eager to meet the challenge head on.
We had theorized that one could shift the HammerSchmidt with a PushLoc shifter. Old XC Pro thumbshifters were likely donors too, but we elected to keep it in the SRAM family. After a brief inspection, we found the PushLoc to be suitable, except that it didn’t work at all! No problem, we just needed to modify the cable pulley inside to limit the total amount of ‘throw’. The PushLoc, as it is in its factory configuration, pulls in too much cable for the HammerSchmidt and wouldn’t reach the detent at the end of its lever stroke unless there was excess cable slack to start with. That caused problems with the cable ferrule popping out of the PushLoc body and snagging at the rim when the lever was pushed. We resolved to make it work.
It seemed simple enough. We’d just need to limit the cable pull by modifying the pulley and limiting its throw inside the PushLoc body. The PushLoc mechanism is pretty simple. The lever rotates a plastic pulley (for lack of a better term) that directs and pulls the cable. We determined that we could glue a stop inside the body to limit the amount of cable slack that can be fed back out of the PushLoc.This is the part that actually sets the total amount of cable travel. All that was left was to redefine the spring path on the pulley so that the detents would be consistent with the new, shorter cable throw.
Some close encounters work with some rifler files and some creative J-B welding gave us the desired result. Our old pulley, with its new spring path, matches the reduced travel and pulls the right amount of cable to shift the HammerSchmidt.To be fair, the PushLoc lever is designed to work with RockShox Motion Control dampers. The spring on those damper shafts is quite stiff in order to control the lockout feature. The HammerSchmidt doesn’t have a strong spring return on the inner three pawls that shift the unit into overdrive. That said, the PushLoc doesn’t briskly snap back like it’s intended to on a fork application. It does work, however, and it works fine. If we were engineers, or had more time, tools, and know how, we’d figure out a way to get a supplemental return spring in that little PushLoc body.
We fixed a Jagwire barrel adjuster into the PushLoc to make incremental tension adjustments as the wire stretches. Our customer is very proud of his new HammerSchmidt. He’s been all over the local dirt jump park with it and says that the low gear is great for trails or pedaling back up to the roll-in. He prefers to shift into the overdrive when he attacks the big jump lines just in case he needs to fire off a few crank revolutions across the bottoms to clear the next double. His left side bar is still clean and so far, his custom PushLoc lever is working great. We had some fun with this little project. Perhaps we won’t be the only ones trying simple modifications to push the direction that the awesome new Truvativ HammerSchmidt can go, be it dirt jump, freeride, trials, street, all mountain, or cross-country.