Shimano refers to these as the Super M70 cartridge brake shoe and pad. These were first introduced in the 1994 model year on the M737 XT cantilever brake. In the 1995 model year, they will also become standard issue with the XTR cantilevers. In fact using this enhanced brake pad is the only scheduled change for the XTR brake in 1995. First we'll describe the brake pad (shoe) holder. It is made of two pieces of aluminum, the non-threaded mounting stud is 6.92mm in diameter with 29mm of useful length.
The stud is riveted to the pad holder which is 70mm long and curved to mimic the shape of the rim. The holder is 14.5mm high with a "V" shaped channel for the pad to slide into. The channel is closed at one end. The pad's fit begins to tighten as it reaches the closed end, achieving a very tight fit at the end of the travel. (Edward Scott's alloy finned brake pad, introduced in the mid 1980's was the first to use this slide into place/replaceable pad design.) To prevent the pad from sliding out of the holder in use, there are very strict instructions on how each curved holder is to be positioned, either front or rear and the proper forward facing direction. When they are installed properly, braking actually pushes the pad into the holder. Shimano also taps threads into the back of the holder and a small steel screw tightens into a 3.3mm deep concave hole to make the pad slipping out accidentally impossible. A thread lock compound holds the screw securely in place. Removing the screw allows the pads to be changed, and a replacement set of four pads is available separately.
We imagine that Shimano will one day release brake pads of different compounds and hardnesses to personalize further the users bike. At the moment, there is just one compound available. The Black rubber pad tested to a fairly hard A/89 harness. The metal stud is left Silver, the holder is painted Black. The weight of a pair of the M70 pads is 56 grams, of which 32 grams is the holders and 24 grams is the pads.
The M-System (Multi-condition) brake pads come with the LX cantilevers. These replacements however are of better quality than the original pads that come with the brake. They have a more substantive pad and a ribbed back to add more structure to the molded rubber. The M-System uses an aluminum, non-threaded, mounting stud that's 6.94mm in diameter and has a 29mm useful length. The rubber pad is molded around the mounting stud. leaving it imbedded in the pad and giving the rubber pad structure over its 70mm length. The pad is 16mm tall with a 10mm high rim contact surface broken up into four sections. The pad has a curved shape that mimics the rim's curve.
The mounting stud is placed closer to one end of the pad, so pressure is more firmly applied at one end. These pads come as a set of four, each of them is labeled, "front" or "rear", "left" or "right" so the mounting stud is positioned closest to the wheels on coming rotation. The Black rubber pad tested to have an A/92 hardness. A pair of them weighs 47 grams, the set of four weighs 94 grams.
set of 4 M-System pads $ Price in Catalog
The XTR brake pads appear to be physically the same as the M-System brake pad. The rubber is slightly darker, but these pads are physically the same length, height, use a 6.94mm diameter non-threaded, aluminum mounting stud that is imbedded into the rubber pad. They are marked exactly the same as the M-System but these say "XTR" on the top.
We found them to weigh just 45 grams per pair and can't explain the weight difference unless the density of the rubber has somehow affected the weight. We however found the rubber to also have an A/92 hardness. The XTR pads, like the M-System come as a set of four, and have an un-explainable higher price. The M-System would seem the better buy of the two types. Remember, in the 1995 model year XTR brakes will come with the M70 pads used on the XT cantilever.
set of four XTR M900 pads $ Price in Catalog
At the moment these are still made and available, though Shimano hasn't made a U-brake in three seasons. These pads are sold in a pair, each pad is physically 53mm long and 16.4mm high with an 11mm high rim contact surface. The pad is slightly curved to mimic the rim's curve. The pad has a threaded steel stud which the pad is molded around. This imbedded cadmium plated stud has 6mm x 1mm threads with the threaded section 12.5mm long.
Mounting nuts are not included, save the ones you have. The Black rubber pad tested to an A/91 hardness. The pair without nuts weighs 44.5 grams.
pair of threaded U-brake pads $ Price in Catalog