Heat88

The front disc brake isn't working properly because when you squeeze the brakes, instead of the brake pads being squeezed(well they are being squeezed, but not enough) the caliper is being pulled to the side. That's happening because the caliper has a design that doesn't make sense to me. Its not one solid unit. Between the mounting bracket that has the two screw holes and the rest of the caliper, there's a spring. which causes the caliper to pull to the side. Why isn't the caliper one unit? Why does that spring have to be there? The caliper for the back desk brake is all one unit, so why can't the front one be?


Another thing:

With both the front and back brake, only the pad on the side where the cable comes in actually moves. Is that how its supposed to work? It still grabs the disc with no problem, but disc brakes on a car don't work that way do they?

The brand of the caliper is Twins DA5 or DAS.

mpetry912 

suggest you loosen the caliper bolts that hold it to the frame / fork.

then squeeze the lever - a couple times. have a friend hold it or put a rubber band around it

and then tighten the bolts to spec

your objective is to align the caliper and pads with the disk.

/markp

Iride01 

Are you sure it's malfunctioning? I thought some brakes only pushed on one side of the rotor. So the rotor will have to flex to get pressure from both pads.

Do your brakes to stop you and otherwise would be no issue if you hadn't noticed this peculiarity?

andrewclaus

Auto brakes do work that way--a hydraulic piston on one side of a caliper that moves on pins. I've seen that once on an old bike, and it still worked.

ivangobike

I'm pretty sure I know what cable caliper this is, it comes with screws for adjusting the angle of the caliper. They are found rarely on lower end bikes and have low durability. I recommend replacing them at a local bike shop.

streetsurfer

Usually there is a fastener on the back/inboard side of the caliper to adjust the gap between the inboard pad and the disc. Set that first, then the outboard pad.
This should reduce the flexing of the disc, to the minimum needed.

FBinNY 

From your description, this is how auto disc brakes work.

There is a single piston which pushes against the disc, and the reaction force draws the caliper across so the rear pads now also press on the disc. The spring recenters the caliper when the brake is released.

Bike disc brakes the same way, except that most hold the caliper rigidly, and depend on the flexible disc to get pushed into the back pads.

Either design is fine, and as long as it's working, you can trust that the designers know what's what. If it's not working properly, adjust or fix it accordingly. In your case, I suspect it's simply a cable adjustment.

Bill Kapaun

Maybe 2 pictures of the brake assembly?
One with the brake lever squeezed & one NOT.

Heat88

Alignment isn't the problem and its not moving on the frame. Its moving on a spring that connects the mounting bracket on the caliper to the rest of the caliper. You can sort of see what I mean in the third picture.

You could also see a compartment with a cover held on by 3 screws. I hope nobody is gonna suggest that I remove that cover and take a look around. I'm scared to because there's springs in there and I highly doubt that I'll be able to reload the spring for the arm if it comes out because it takes a lot of strength to pull the arm. I probably could remove the spring for the mounting bracket and fill the space that it occupied with something so the bracket doesn't move anymore, but I'm scared to go in. Having said all that, I'm dying to know whats in there.

In the first picture, you can see the part from the other side of the caliper that holds the other brake pad. Why is the magnet installed so complicatedly? Its held in by a spring or whatever that is. In the second picture you can see whats on the other side. But I think its actually a fake screw because I had a very hard time turning it. When I finally did turn it a little, it didn't get looser. I'm guessing that if I removed the spring holding the magnet in, the fake screw would fall out. Why would they use a spring to hold the magnet in instead of gluing it in or or something else cheaper? Doesn't they fancy way the magnet is held in indicate that its not a low end caliper?

Looking at the first picture is probably gonna hurt your eyes because its a tad blurry. Sorry.

RocThrower

If I understand correctly, I think you are missing a bolt or bolts that keep the left and right sides of the caliper body together as one unit. When you pull the brake, the piston is pushing the caliper apart because there is no resistance. The front brake should be identical to your rear brake, one solid unit.

andrewclaus

By "fake screw" do you mean the hex adjuster? The leaf spring in the first photo provides a detent every sixth turn of the adjuster. If the adjuster isn't turning, it's dirty or corroded. If you can't free it up, replace the caliper.

ScottCommutes

Look up "fixed vs. floating caliper".

ivangobike

After reviewing the photos, it looks like one half of the caliper, that being the half that mounts to the fork, is 2 pieces of press fit metal. That press fit has come loose and is causing the caliper to slide along it left-to-right, making it operate kinda like most automotive calipers.

:EDIT: It might be designed to operate like this, there could be a spring behind that plate being held by 3 screws.

Heat88

Its actually not a fake screw. I didn't try hard enough to turn it the last time because I was worried about damaging something. I was able to remove it this time.

Heat88

No, nothings missing.

Heat88

I don't know about that. It just feels like there's a spring where there doesn't need to be one.

However, I discovered that the bracket that the screws go through is actually two pieces. Is that the 2 pieces you're talking about? I guess I'll remove that cover after all. If there's anything to fix, it's in there. If have to replace the caliper, I have nothing to lose. And I'll get to see what's in there.

ivangobike

My curiosity remains heightened...

Heat88

Here's everything that was under that cover. There's still a washer inside the housing. The thing on the right above the springs goes on top of the thing next to it. The arm mounts on the thing on the right. The thing on the left has the magnet that holds the brake pad on the other side of it.

As you can see, the mounting bracket is one piece. I was wrong about that.

I'm no mechanical engineer, but isn't that more complicated than it needs to be? Also, why does the mounting bracket that the screws go through have to be part of the arm mechanism?

Nothing is broken but there were a couple tiny pieces of metal, so maybe something is worn.

Can a caliper with mechanics this complicated be low end?

Heat88

A man (or woman) after my own heart.❤️

ivangobike

O.o

Anyways, it is like I partially suspected. It's a miniature car-style mechanical brake. Thing is, without 2 caliper pins, it just flops around once it wear out a bit. Caliper pins would solve that if this were built to scale.

Very neat idea, but for bicycles, the average tektro and shimano disc caliper works quite well.

grumpus

Maybe it's intended to avoid infringing IP and licensing fees, or a genuine attempt by a manufacturer to add value to his product. It is an odd design. Clean it up, grease the right places and chuck it back on the bike. I wish you luck. :-)

Heat88

It is odd, but I love the spring design. I managed to get it back together. It was actually pretty easy. I was expecting to have to get a new caliper just because I couldn't get this one back together. The screws for the cover are long enough that I didn't need to push the cover much to get the screws to bite. The hardest part was reloading the springs. I have no idea how I did it. I can't even tell where it happens. At first it was reloading in the wrong spot, so I decided I was gonna start in one spot and keep adjusting until it was right, but the spot I started at was the right spot. Its working like it was before. The same tension and everything. I would love to know how it works. I guess I'll have to find a physics or engineering forum and ask there.

I have it all put back together. I'll have see how it works tomorrow. One design change I made was I put a piece of metal between the brake pad on the arm side and the magnet that holds it because when you pulled the arm all the way back(before I put the caliper back on the bike), the distance between the pads was about half a mm less than the thickness of the disc. Which means the arm uses 95% of its track before the pads start to grab the disc. There's about 2mm of resin or whatever you call it on the pad, so I don't think that's the problem. But I guess it's possible that even though it looks like there's plenty of pad left, a significant amount of it has been used up. How thick is the resin on a brand new pad?

Heat88

I should've mentioned this on the first post because it's why I started on the adventure with this caliper'

There were about 5 times in the last 6 months or so when I was riding my bike and I went to use the brake ab

Heat88

I should've mentioned this on the first post because it's how I started on the adventure with this caliper.

There were about 5 times in the last 6 months or so when I was riding my bike and I went to use the brake and as the disc was about to be squeezed, it felt like the brake cable slipped through the screw that holds it to the caliper arm a little. After that happened the caliper was useless until I fixed it. The first four times, I thought it was the cable slipping so I just loosened the screw and adjusted the cable to fix it. The 4th fix lasted a lot longer than the previous 3 fixes, so I thought it was finally fixed. But then I felt the slipping again. This time I decided to do a closer inspection. The cable hadn't slipped. Then, squeezing the handle several times and watching the movement of the caliper is how I noticed that the caliper was moving more than the pads. This post feels like an origin story episode of a TV show that's made several years into the show.LOL

I forgot to mention that I think maybe the two or three tiny pieces of metal that I found in the mechanism were the cause of the slippage. I don't know where they came from, but the mechanism feels different since I put it back together. But I won't know for sure until tomorrow.

Heat88

I just meant that I appreciate your curiosity. There seems to be fewer and fewer people who are curious about how the world works.