MattTriv

After tightening the front disk cable, I gave it a squeeze to test it, and I think I squeezed too hard and cracked a bearing. Now, sometimes the brake works and sometimes it doesn't. I would say that 75% of the time it works fine, and 25% of the time I squeeze it and...nothing. So I'm thinking that I need to replace it. The problem is, there don't appear to be any published specs on my bike, so I have no idea what part to order. The brake says "PURK" on the side, and it looks like it is from a small Chinese factory, and there doesn't seem to be a way to order one. The bike I have is a Kent Thruster kz2600 mountain bike.

Is there another part I can order? Even if I could order from the factory, it would probably take weeks to get here. (My rotor is 160mm.)

My first thought was to take apart the break and put in a new bearing, but I couldn't find any instructions on the web on how to do that. So, I assume that that isn't generally done, and the brake is usually just replaced. My mechanical skills are very limited, and so I came up with this diagnosis by googling around the various bike forums, and may certainly have it wrong.

jimc101

There are no bearing in disc brakes, of that rules that out, from the look of the photos on the Kent site 26" Men's Thruster KZ2600 Dual Suspention Mountain Bike - Kent International, you have basic mechanical discs (there isn't too much info there), would suspect that if you heard something crack, it was connected /relate to a cable inner or outer, and either the routing of the outer, or where the inner connects, either at the lever (where it is inserted), or the caliper (where it's clamped on via a bolt).

For replacement/fix, if you can't sort if by checking the cable routing, going to a local co-op would probably be the best option, getting a like for like replacement will probably very difficult, and they could point you in the direction of reasonably priced replacement parts.

fietsbob

Reads like you have a low cost bike made up from many low cost parts,
verging on a "bicycle shaped object" it only looks like a dual suspension off road bike
such as from a discount warehouse.. as seen in that link..

perhaps lower your expectations accordingly?

have a real bike shop to show it to ?

Your Public Library may have books on bike repair ,


to embark on a mechanical knowledge of bicycles in general ..


Its a good place to start..








..

Crankycrank

It could be that it does have a large ball bearing inside as I have seen some of the cheap Chinese brakes use a cam type device which drives a ball bearing to press on the brake pads. For the OP it would be worth looking inside as some of the moving parts may be bolted together and just need some tightening up but I really have no idea from here how yours are made, just guessing from what I have seen on others. I think you're better off trying to find a used compatible decent quality replacement which you'll have to do some research on for fit. Some people like to replace their cable operated versions for hydraulic and sell them cheap on Craigslist, Ebay, Co-ops, etc. Chances are you'll find something of much better quality and can find spares when needed. Just noticed that the link posted above has an owners manual showing how to adjust your brake caliper. Page 24-27, may not solve the problem but worth a try. It also looks like there may be a nut holding on the actuation arm (the part the cable attaches to) which just may need to be tightened. Don't expect great braking from these even when working properly. file:///C:/Users/john/AppData/Local/Packages/Microsoft.MicrosoftEdge_8wekyb3d8bbwe/TempState/Downloads/MTN%20bike%20manual%202016-eml.pdf

Dyskolos

Here is the link to the manual that Crankycrank tried to post: https://www.kent.bike/index.php?cont...d_attachment=8

fietsbob

By reading a parts diagram on the sram site,
I saw Avid Disc brakes have a crown-like ramp ring
to turn rotational motion into a pressure force, 90 degrees from the cable pull direction ..

riding against that ring on each ramp, is a bearing ball..

FWIW..




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AnkleWork

Lets see . . .
Full suspension -- check.
Disk brakes -- check.
21 speeds -- check.
$129 at wallyworld -- check.
Front brake fails 25% of the time -- check.

Seems like your bike is perfect.

MattTriv

Well, when I squeeze the brake, the cable does indeed pull up the caliper like it is supposed to. But the pads only move a little bit toward the disk (during the times when it fails.) Also, thanks for the co-op idea.

MattTriv

Great idea; I will take a look.

MattTriv

I should have mentioned that I had the links in my original post but had to take them out because I am not allowed to post URLs yet. Sorry about that.

MattTriv

To be fair to the bike, the brakes worked fine until I broke them. I also made $3200 delivering food with it, so the bike has more than paid for itself.

Dyskolos

beyeriii

PURK mechanical disc brakes will make a clicking noise if the caliper is rotated more than about 120 degrees.

Reduce the distance between the pads to prevent the caliper from rotating more than 120 degrees

Park Tools website has instructions for how to adjust mechanical disc brakes

Search for: Park Tool Mechanical Disc Brake Alignment

Leisesturm

At the handlebar end of the brake cable should be a set of barrel adjusters to take up cable slack. Each of them has a slit that is just the width of the wire core of the brake cable. If both slots line up the cable drops inside and you get no braking. I don't know that this is your issue but I don't know of ANY other scenario where a brake might work 75% of the time. I agree with earlier advice to take bike to co-op. Do it now.

MattTriv

Thank you beyeriii and Leisesturm. I replaced the Purk with a Shimano brake that cost me $19. It works great, so all is well.

Wilfred Laurier

There are a lot of people who don't like Shimano, or greatly prefer their competitors... but in my opinion, everything Shimano makes is among the best thing of its type... need a $13 rear derailleur, Shimano Tourney works as well as much more expensive options when new... need a hydraulic disc brake; I bolted a set of SLX to my bike four years ago and have not needed to adjust it since.

I have no experience with Shimano mechanical disc brakes but I am sure they are far superior to whatever came stock on a box-store bike.

1f Jef

Purk bicycle disc brake calipers are simple in design and easy to rebuild and adjust.
Inside are 3 ball bearings set in a cam base. when the lever turns the bearings ride up the cam which pushes the platform against the caliper pad which sandwiches the disc. The center bolt on the lever holds it all together. There is a coiled tension spring inside which may be the most complicted part of the rebuild.