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Sunday, January 5, 2014

SRAM Automatix 2 Speed Hack

A couple of months ago I purchased a SRAM Automatix 2 Speed hub to replace my old 3 Speed Sturmey Archer on a '74 Raleigh Sports.
I loved the idea behind the design. Simplify the function and style of the bike by eliminating the shifters, brakes, and cables, while still allowing for a gear change.
After installing it on my Sports I noticed a problem right away. It shifted way too early, before you could get up to speed it would kick into high gear, robbing you of all momentum. Hill climbing was nearly impossible and it made the bike feel sluggish.
I went online to see if others had the same problem and found this article: http://mccraw.co.uk/sram-automatix-review/. Someone else had the same issue and was able to modify the timing and correct the problem. After reading the article I was interested in attempting to modify the hub but I was hesitant due to not fully comprehending the instructions and the fact that this was a brand new purchase, vs. some old junk I had laying around.
Once I got started it turned out to be pretty easy to do. The whole operation took about 30min.
I included some pictures of the disassembly and created a couple diagrams to help answer some of the questions that I had before attempting this modification.

This fix can be done with the hub still laced to the wheel. Just remove the wheel from the bike and start by removing the nuts on the non-drive/sprocket side of the hub.
Once the nuts are removed the coaster brake arm will slide straight out. Make sure your work area is clean there are a lot of greased moving parts in here that would be a pain to dig cat hair and dust out of.
Now that the brake arm is removed it should look like this. You should now be able to slide the entire unit out of the shell.
The hub shifts by centrifugal force. The weights labeled "1 & 2" are held down (towards the spindle/center) lightly by a spring labeled "4". When the wheel is spinning fast enough the weights are forced outward (pushing against the spring) by the centrifugal force engaging them into the higher gear.
So the goal is now to bend the spring to give a little more resistance against the weights so the the wheel has to be going faster to engage the higher gear. Only one weight has the spring on it. It is held together by a small clip labeled "3".
Remove the clip "3" by sliding it out sideways with a very small flathead screwdriver. Then you can slide the weight upwards to remove it and the spring with it. Then slide off the spring (highlighted in green) and unwind it slightly at about a 45° angle as the image below. You want to bend it enough that it stays in the 45° position before you reinstall it. Remember unwind it to push the weight toward the spindle/center. Do not unwind it over the 45° or you will not be able to shift into the higher gear.
Now reassemble the hub and reinstall the wheel. You should notice a significant difference. The potential this hub had is now realized. Great design and manufacturing overall just needed a slight adjustment on one spring. Not too bad.

Cheers to Dave McCraw for pioneering this method and sharing it on his blog!
http://mccraw.co.uk/sram-automatix-review/