Shimano actively sold the M733 brake levers in the 1991 and 1992 model year. They were discontinued in the 1993 model year and have had legs ever since. The reason for their continued success is there are still quite a number of serious riders who use "above the bar" thumb shifters and these are a high quality, heavy duty replacement that are made in Japan, yet inexpensive. The M733 is made using a forged aluminum handle and clamp assembly.
The handle is held to the clamp section by a steel bolt. The black bolt has a 4mm hex fitting for tightening with 6mm by 1mm threads. The bolt threads into a steel hex nut with a 10mm outer hex shape, (replaceable with our part # 06-91-010). Their are friction reducing washers used on both sides of the handle. Nearest the handle is a thin brass washer. A nylon washer smooths over the top of the brass piece and fits tightly down into the handle making the action of the handle and clamp firm but smooth.
The lever return spring is enclosed in a two section telescoping plastic assembly that houses a small coiled spring of the sort used in a retractable ball point pen. The spring pushes against a tiny steel rivet on the handle at one end and against a recess in the clamp piece for the other. The lever fastening bolt is fairly traditional. It has 6mm by 1mm threads with a 15.5mm length, a 5mm hex fitting for removal and a 4.5 gram weight.
The M733 uses a two piece cable convenience adjust system. The adjusting barrel is made of machined brass that is chrome plated. The barrel has 7mm by 1mm threads with a slot cut lengthwise through the piece for easy cable replacement. Each of these brass originals weigh 11.5 grams each and would be a great candidate for replacement by Titanium (our part # 06-91-CA-S) which weigh only 5.5 grams each. The fixing nut is made of Black plastic. The lever is 95mm long between the center of the bolt holding the handle to the clamp and the handle end. The area for fingers to grip the handle is 60mm long.
Carbonworks makes a carbon fiber replacement for the handle section of these levers. The Shimano original weighs 43.5 grams while the carbon fiber version weighs just 18.5 grams. We told you this was a heavy duty lever, that's why the handle is so heavy. The M733 has an unusual reach adjustment. As you've read about the other levers, continually a small set screw has been used to force the lever into a smaller profile. The M733 has an internal square plastic cam, with its axis off center. A bolt from the top of the lever revolves this square cam so that their are four defined depths of reach for the levers. The M733 comes with a rubber hood that covers the cable barrel adjusters. Black only, this lever pair weighs 271.5 grams per pair and the rubber adjuster hoods add another 14.5 grams for a total of 286 grams. These were made in Japan but are no longer available as the Rapid Fire style has replaced anything that once used a thumbshifter. We sold these for $39.99.