REAR DERAILLEUR:
MAVIC 851 (modified) - forged 2014 light aluminum alloy construction - C.N.D. (...Couche Noir Dure) hardened anodized inner and outer link rods as well as upper and lower pivot bolts - Black anodized stamped aluminum alloy pulley cage plates with White "pinstriping" - post 1985 and pre 1989 "flat plate" outer link rod - post 1985 and pre 1989 MAVIC solid "block letter" logo on outer link rod - lower pivot housing marked with date code "8706AF" for June 1987 - adjustable chain guide system to accommodate a 21 to 32 tooth maximum freewheel cog - 12 to 21 or 13 to 32 tooth freewheel capacity (adjustable) / total chain wrap capacity rating of 26 - model 851 : Carmichael Designs - "drilled" pulley wheels - Clear anodized 6061/T6511 aluminum alloy (Silver) - ten tooth design - NMB 6265 sealed cartridge bearings - width adjustable spacers ... [Similar to its corresponding model 860 front derailleur, the first edition of these distinctive MAVIC 851 "Erector Set" rear derailleurs was introduced in late 1983 for the 1984 model year, and in this case, represent a more refined version of its predecessor the 801 series which had debuted back in 1978 and which continued on in production concurrent with the new model. One of the more interesting features borrowed from the original model 801 rear derailleur is the adjustable chain guide system which enables this component to efficiently accommodate a wide range of freewheel cog sizes in a manner similar to the pioneering Huret Success Titanium unit first offered to market in the latter half of 1975. In this instance, the model 851 is suitable for use so long as your necessary chain wrap falls within the capacity rating of 26 for this mechanism and the rear freewheel cog tooth counts fall between 12 and 32 teeth. Chain wrap capacity is used to determine whether a given derailleur has a long enough cage to take up the chain slack in your drive train. To calculate necessary chain wrap, simply determine the difference in teeth between your largest and smallest chain ring, as well as this same difference between your largest and smallest freewheel cog, and then add the two differences together. For example, if your bike is equipped with a 52/42 double crank and a 13/21 freewheel, you would need to use a read derailleur with a chain wrap capacity of 18 or more (...i.e. 52 minus 42 equals 10, and 21 minus 13 equals 8, and 10 plus 8 equals, you guessed it, 18), therefore this MAVIC 851 would prove quite capable. With regard to the particular version seen here, it would be an 851 model dating from 1986 through 1988.]
