This old beater bike is missing one part.

old bike

The front rotor and caliper are there.

front rotor and caliper

But the rear caliper is missing.

rear rotor

What model of rear caliper do I need?

If you are able to identify the model (ideally with a pointer to https://www.bicyclebluebook.com/ or similar sites), do mention it.

I'm also curious about the technical name of hubs that are absolutely silent, such as those on this bike, and the noisy clicking hubs that are on almost all other hubs.

  • Not sure on the exact year/ model but the shape looks to be a 2009-2012 Specialized Hardrock. The fork looks better than the original SR Suntour that likely came with it. Earlier models had fatter down tubes and later models got the new logos.
    – DWGKNZ
    Nov 19 '21 at 17:53
  • Whatever you get, make sure it has the right mount interface. The fork uses a post mount, the rear uses an IS mount. You'll probably need an IS/post adapter (I don't think there are any brakes that fit IS mounts directly). Some brakes come with the adapters in the box. But there are also flat mounts, which will not fit this bike.
    – Adam Rice
    Nov 19 '21 at 19:23
  • 3
    @AdamRice the adapter is still on the frame, it's only the calliper that is missing.
    – DWGKNZ
    Nov 19 '21 at 20:16
  • @AdamRice Some do, but they're all out of production now.
    – MaplePanda
    Nov 19 '21 at 20:43
  • @DWGKNZ I see it now.
    – Adam Rice
    Nov 19 '21 at 20:57

Almost any mechanical disc brake caliper will work as long as it's not a road or short pull model and will also work with a generic 160mm rear IS adapter like the one you have. That might sound specific, but the vast majority of mechanical disc calipers meet those criteria. The cable pull needed will be "mountain", "v-brake", or "long-pull", all different names for the same thing, but it's the more common type so it might not have any of those names in the description.

The front caliper is a random low-end OEM one. There's no point trying to match it.

Ones that would work: TRP Spyke, Tektro Aries, Shimano BR-M416A or BR-M375 (or any other Shimano mechanical brake caliper that has an "M" before the number part of the model number).

If the cable is still moving in the housing freely, all you need is a new brake cable because the one you've got is frayed. If not you'll need a new housing, and there are many questions about that.

"Silent clutch" is the most common name for click-free freehubs. Different companies have made them at different times and have their own buzzwords for the "technology" used. Shimano had an old line of them called "Silent Clutch," then also a newer iteration called "Scylence" that they hyped and then cancelled before widely releasing. The Stealth hub line by True Precision Components are time-tested, ultra high quality, and reliable, but expensive. They're the main option if you want a silent hub to my awareness.

  • In my experience the Onyx Vesper is the most popular silent hub. Uses a sprag clutch design.
    – MaplePanda
    Nov 20 '21 at 3:53

Any mountain bike disc brake will be suitable for your bike. Personally I would steer away from cable disc brakes and select a hydraulic set. When purchasing a disc brakes make sure you select either a front or rear brake as they come in different cable/ hose lengths.

  • Can you confirm that disc brake calipers are front/rear specific? I am not seeing that they are, or that cables and housing are typically bundled with them.
    – Weiwen Ng
    Nov 19 '21 at 19:13
  • 1
    @WeiwenNg - I'm not sure where you are looking that you don't see that? Mountain bike brakes are sold as sets with lever, calliper and hose. If you would like to buy a component individually you have to buy it as a spare part.
    – DWGKNZ
    Nov 19 '21 at 20:08
  • D’oh. I was looking at the TRP Spyre, which is a drop bar cable disc brake not paired to a brake lever, because ours are integrated.
    – Weiwen Ng
    Nov 19 '21 at 20:18
  • 2
    The bike has integrated shift/brake levers (ST-EF series) so upgrading to hydraulic will require new shifters too.
    – JoeK
    Nov 20 '21 at 10:17
  • 1
    @JoeK with the laser vision once again, great point!
    – Swifty
    Nov 20 '21 at 11:08

Contrary to the other answer, recommend to use a mechanical brake caliper, when your front one is already a mechanical one. Otherwise the investment will be much larger (hydraulic lines, hydraulic brake lever). It would only make sense if you wanted to change the whole braking system (both front and back) to hydraulic. Before that I recommend to compare the investment required with a price of a new (even if second-hand) bike. The front brake is more important anyway so it would make more sense to change the front one to hydraulic first (if not both).

As far as I can see, the bike is ready to accept a post mount caliper. If you stay with mechanical, suggest using a caliper that has two movable brake pads, even if they are somewhat more expensive. Most mechanical brakes only move one pad and that is an inferior design.

Oh yes, and it must be an MTB brake caliper, not a road one. Basically, one compatible with your lever. I wanted to write that, but somehow forgot when writing the answer. The only exception would be a lever that is compatible with traditional cantilever brakes or one that can be set to use both pulls (e.g. V-brakes and cantis). As Nathan wrote in his answer, the key term is "long pull".

I do not like recommending any specific products, but the two movable pads recommendation is specific enough.

  • You could buy a pair of Magura MT Sport hydraulic brakes or nearly a pair of SRAM Level for the price of one "double pad moving" mechanical caliper so I'm not sure it's such a great recommendation on scales of economy.
    – JoeK
    Nov 20 '21 at 10:14

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