New-Old-Stock Suntour XCD (4050 Series) Roller-Cam Brake Caliper

Description

New-Old-Stock Suntour XCD (4050 Series) Roller-Cam Brake Caliper
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Product Description:
This offering is for a new-old-stock Suntour XCD (4050 Series) roller-cam brake caliper (so just a single caliper that will mount as either a front or rear brake). I have very little experience with this type of caliper, but will still do my best to explain how it mounts and functions (based on some research and conversations with others that are a lot smarter than me).
First of all, I should probably mention this caliper will not mount on traditional mountain bike cantilever posts or studs (and please keep this in mind, as this will likely limit compatibility options). As I understand it, cantilever studs are positioned slightly inward (or towards the rim), while roller-cam studs are positioned slightly outward (or away from the rim). I have also been told U-brake calipers mount similar to roller-cam brake calipers, so if your particular mountain bike or hybrid will accept U-brakes, then this roller cam brake caliper should also mount fine.
The mechanics of a roller-cam brake caliper are truly unique. I want to compare the mechanics to a traditional cantilever brake caliper, but there really are a number of differences. First, a cantilever brake caliper uses a transverse cable to move the arms, while the roller-cam caliper utilizes a triangular shaped cam to control the arms. Both cantilever and roller-cam brakes attach directly to the frame or fork studs (although, see discussion above for compatibility issues), but the roller-cam arms pivot on these studs with a see-saw like action. So the way this works is the triangular shaped cam is pulled upward by the brake cable (as you squeeze the brake levers) and each side (edge) of the triangle contacts rollers at the top of each caliper arm. As the cam pushes these rollers outward (as the rollers slide down the edge of the triangle), the caliper arms pivot. This action moves the upper part of the caliper arm outward and the lower part of the caliper arm inward (and towards the rim surface). This explains the see-saw action that converts cable movement to caliper movement and ultimately braking power to the rim surface.
Evidently, the roller-cam design gained some traction in the late 80's when there was a desire to mount the rear caliper under the chain stays. This was more difficult to accomplish with traditional cantilever brakes, because their footprint was wider and would often bump or rub against crankarms when mounted in this position. Unfortunately, I have also been told roller-cam brakes are more difficult to setup, so this can make wheel changes, etc., more of a challenge. Lastly, there is a concern that roller-cam brake shoes contact higher and higher on a rim as the pads wear. So if pads are not checked regularly, they may eventually start to rub on the sidewall of the tire, which could result in a blow-out. Again, I am just leaning on what others have written or mentioned to me in conversations, but I still hope some of this information is helpful when considering this unique brake caliper offering.
Some other observations regarding this caliper includes the following items. The caliper arms are made from a forged aluminum alloy and the mounting hardware (i.e, bolts and bosses that slide over studs) are made from a hardened steel. I also see what appear to be high quality brass components built into the caliper arms. There are the brass rollers at the top of the caliper arms that we discussed earlier. Then there are the brass sleeves in the middle of the caliper arms that slide over the bosses and represent the aforementioned pivot point for these arms. Other specs include a postal scale weight of 288 grams (for one caliper and all mounting hardware pictured) and a reach in the 35.5 mm to 42.5 mm range (depending on where the brake shoes are positioned within the slotted section of the caliper arms).
As for condition, this roller-cam brake caliper is very nice and still retail boxed. Even the original grease applied at the pivot points, etc., appears relatively fresh.
Brief discussion concerning Suntour labeling in the late 80's and early 90's...
For those that are interested, the pecking order of Suntour mountain bike groupsets with indexing capable drivetrains is somewhat confusing...due primarily to the various model number/name changes over a relatively short time period (from the late 80's to the early 90's...so the final years of the original Suntour company headquartered in Japan). To the best of my knowledge, there were anywhere from four to eight indexing capable mountain bike groupsets from the late 80's and into the early 90's...and these XCD (4050 Series) components were middle of the pack (and one step below Suntour's competition-level groupsets). So good quality bicycle components, but not designed for racing or other high-duress applications. I can also confirm Suntour originally referred to these components as part of the 4050 series groupset (and one step below their competition-level 5000 series components) in the late 80's. Although, at some point from the very late 80's to 1990, these components were rebranded as the XCD groupset (which placed them just below the competition-level XC-Comp groupset). I don't know the reason behind all the re-branding, other than it appears by the early 90's, Suntour was attempting to move away from labeling that included numbers in the branding name.
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