Sunday, December 21, 2008

Yes, it really is that easy...

We Mavic fans often tout rebuildability as a major win over other options. Want to convert that clamp on front derailleur to a braze on? Just pop the circlips, press out the body, and pop a braze-on body on! Simple! Convert a rear derailleur from a short cage 840 to a medium cage 841? Pop a circlip, drive out a pin, replace the cage and there ya go!

Right. Maybe its simple once you've done it, or seen pictures of it being done. I recently picked up a set of 841 cages, and set about replacing the cages of an 840 with them. Here are pictures I took along the way.

On the left, we have a standard 840 short cage derailleur. On the right, the plates that make up the medium cage for the 841 derailleur. The only difference between the two are the cages.

Step one - remove the bolts holding on the pulleys and the back portion of the cage.

Step 2 - remove the circlip pointed to in the picture above. It'll pop off easily with a set of needle nose pliers.

Step 3 - drive the pin out. I use the handle of a screw driver to push it out. Try twisting the cage - at the stop position, the spring's 90 degree bend is in contact with the pin, and will make it hard to remove. Once you pivot the cage, it should be easy to push the pin out.

The hinge pin slides in the groove pointed to by the white arrow. It butts up against the tension spring pointed to by the red arrow. This keeps the cage from unspinning and losing tension, without any additional limit pin.

Replace the cage, lining up the spring. Press it inward, rotate it in place, and press the hinge pin back in. Replace the circlip, and you're done.

Now, what used to be an 840 short cage derailleur is now an 841 medium cage derailleur. Perfect to use with your 631 triple crank and 870 front derailleur. Total time elapsed, including pictures, was 13 minutes. Without documenting the process, it's easily a sub-10 minute procedure.

Tuesday, December 16, 2008

Mavic 451/Suntour Superbe Pro/Dia Compe BRS500 Instructions

As previously discussed, the Mavic 451 brake was one of many brakes that was a rebranded Dia Compe BRS500. Some consider them the pinnacle of single pivot design, combining excellent stopping power, precise modulation, and the clean lines that come with its hidden spring.

Those of us who've used them know they can be a serious pain in the butt to adjust. It's a little easier when you have three hands and the proper instructions

Here's a parts explosion, just in case you accidentally disassembled your brakes when you tried to adjust them.

If you've emailed to me asking how they hell to make your Mavic 451's work, I apologize for my rambling responses. Hopefully these instructions will make things a little easier. Enjoy!

Saturday, December 06, 2008

Dura Ace EX headset

In 1978, Shimano introduced the Dura Ace EX series of parts. In it, Shimano introduced a lot of new concepts to their line. This included the introduction of the Shimano Uniglide cassette. While Shimano wasn't the first to introduce the cassette, they definitely made the concept popular, and stuck with the cassette concept for a number of years before it gained in popularity. Other little things they introduced in EX included one-key crank releases, standardization on all hex-key bolts, shaved teeth to improve shifting under load.

Also introduced was the UA-110 headset, better known in later years as the HP-7200. This headset is mostly known as the one with the funny wrench scallops.


While it doesn't require a special tool, a 32mm wrench isn't the greatest fit, and probably would result in marring the headset.

The HP-7200, and the closely related UB-110/HP-6200 differed only in their stampings, and in the use of an alloy crown race in the HP-7200. This resulted in a 44 gram weight difference. They were both available in parallel with an AX version, which was the same headset with a plastic fairing over the top assembly.

The Dura Ace and 600 EX headsets are often sold on eBay in conjuction with the word "rare". They were available from 1978 until 1984, so they're really quite common. Finding ones new-in-box, however, is a little less common.

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