Weak back brakes

[Kapil Jadva]

Hi all, I'm new to this forum I'm looking for some help. My back brakes just won't bite strong enough. I have gone as far as taking off the rotar sanding it wiping it down with de greaser and putting in new brake pads bedding them in (the old were not worn but slightly contaminated. I have adjusted the brake cable so it's adjusted properly at the handle bars. I have also aligned the pads and adjusted everything that can be adjusted.

The issue I have is when applying the brake the pads move and pinch the rotar as they should but the brakes just don't bite and I can easily move the wheel with the brakes applied it's as though the pads are just gliding along the rotor. The system is only mechanical not hydrolic so I'm unsure what's going on? I have also changed the inner brake cable today hoping that would help and re adjusted everything and still the breaks are pretty weak only slightly better. The cable is pulled as tight as it can be (I haven't tried pushing the brake lever slightly so it bites better ass the park video says to keep the bike lever at its normal loose position. Any help would be appreciated!! I will add the front brakes work nice and sharp like they should and when the bike was purchased (1 year ago) they were both working fine. When I first purchased the bike the back brakes were nice and sharp so I could skid if I hit them too hard since then I don't know what I'm doing wrong.

[Jesper]

(06-26-2020, 11:56 AM)Kapil Jadva Wrote:  Hi all, I'm new to this forum I'm looking for some help. My back brakes just won't bite strong enough. I have gone as far as taking off the rotar sanding it wiping it down with de greaser and putting in new brake pads bedding them in (the old were not worn but slightly contaminated. I have adjusted the brake cable so it's adjusted properly at the handle bars. I have also aligned the pads and adjusted everything that can be adjusted.

The issue I have is when applying the brake the pads move and pinch the rotar as they should but the brakes just don't bite and I can easily move the wheel with the brakes applied it's as though the pads are just gliding along the rotor. The system is only mechanical not hydrolic so I'm unsure what's going on? I have also changed the inner brake cable today hoping that would help and re adjusted everything and still the breaks are pretty weak only slightly better. The cable is pulled as tight as it can be (I haven't tried pushing the brake lever slightly so it bites better ass the park video says to keep the bike lever at its normal loose position. Any help would be appreciated!! I will add the front brakes work nice and sharp like they should and when the bike was purchased (1 year ago) they were both working fine. When I first purchased the bike the back brakes were nice and sharp so I could skid if I hit them too hard since then I don't know what I'm doing wrong.

Hello Kapil,
Welcome to the club.
I have never used disc brakes, so I do not have experience with setting them up or maintaining them, but your problem intrigued me. I do however have years of experience with automotive disc brakes, both cable and hydraulic types so I will try and help. Had any any work been just before you noticed that the brakes were failed? Did you have an accident Did they just stop working one day, or did they get progressively worse after a period of time (hours, days, months)? If you remove the wheel and then engage the brakes, can you see the brake pads make contact with each other? This should be something simple.

Jesper

[CharleyFarley]

(06-26-2020, 11:56 AM)Kapil Jadva Wrote:  Hi all, I'm new to this forum I'm looking for some help. My back brakes just won't bite strong enough. I have gone as far as taking off the rotar sanding it wiping it down with de greaser and putting in new brake pads bedding them in (the old were not worn but slightly contaminated. I have adjusted the brake cable so it's adjusted properly at the handle bars. I have also aligned the pads and adjusted everything that can be adjusted.

The issue I have is when applying the brake the pads move and pinch the rotar as they should but the brakes just don't bite and I can easily move the wheel with the brakes applied it's as though the pads are just gliding along the rotor. The system is only mechanical not hydrolic so I'm unsure what's going on? I have also changed the inner brake cable today hoping that would help and re adjusted everything and still the breaks are pretty weak only slightly better. The cable is pulled as tight as it can be (I haven't tried pushing the brake lever slightly so it bites better ass the park video says to keep the bike lever at its normal loose position. Any help would be appreciated!! I will add the front brakes work nice and sharp like they should and when the bike was purchased (1 year ago) they were both working fine. When I first purchased the bike the back brakes were nice and sharp so I could skid if I hit them too hard since then I don't know what I'm doing wrong.

I have mechanical disc brakes on my fat bike. There should be a hexagonal hole on one side of the caliper. It is usually reached from the other side of the spokes. It may need to be adjusted. You can hear and feel clicks as you tighten it with a hex wrench. The cable will only pull the brakes so far, and if it isn't adjusted properly, the brakes won't work well. Try turning it a few clicks and see if it improves. You may have to turn it several clicks.

What I do is to tighten it up, then back it off a click or two. Then I slacken the caliper bolts, pull on the brake lever, and while it's still pulled, tighten the caliper bolts. Bear in mind that the front brake does about 70% of the stopping, while the back brake does about 30%.

[Jesper]

(06-27-2020, 11:01 AM)CharleyFarley Wrote:  I have mechanical disc brakes on my fat bike. There should be a hexagonal hole on one side of the caliper. It is usually reached from the other side of the spokes. It may need to be adjusted. You can hear and feel clicks as you tighten it with a hex wrench. The cable will only pull the brakes so far, and if it isn't adjusted properly, the brakes won't work well. Try turning it a few clicks and see if it improves. You may have to turn it several clicks.

What I do is to tighten it up, then back it off a click or two. Then I slacken the caliper bolts, pull on the brake lever, and while it's still pulled, tighten the caliper bolts. Bear in mind that the front brake does about 70% of the stopping, while the back brake does about 30%.

Please excuse my ignorance Charley, but seeing that I don't brake very often l have no need of discs; but I would like to be more knowledgeable regarding their set up. Is the "hex" hole a bolt head that keeps the pad from fully retracting? Does it allow for automatic compensation regarding pad wear? Would it "suddenly" go out of adjustment causing the poster's poor brake performance? Is the front caliper the same?

Thanks,
Jesper

[CharleyFarley]

(06-27-2020, 12:36 PM)Jesper Wrote:  

(06-27-2020, 11:01 AM)CharleyFarley Wrote:  I have mechanical disc brakes on my fat bike. There should be a hexagonal hole on one side of the caliper. It is usually reached from the other side of the spokes. It may need to be adjusted. You can hear and feel clicks as you tighten it with a hex wrench. The cable will only pull the brakes so far, and if it isn't adjusted properly, the brakes won't work well. Try turning it a few clicks and see if it improves. You may have to turn it several clicks.

What I do is to tighten it up, then back it off a click or two. Then I slacken the caliper bolts, pull on the brake lever, and while it's still pulled, tighten the caliper bolts. Bear in mind that the front brake does about 70% of the stopping, while the back brake does about 30%.

Please excuse my ignorance Charley, but seeing that I don't brake very often l have no need of discs; but I would like to be more knowledgeable regarding their set up. Is the "hex" hole a bolt head that keeps the pad from fully retracting? Does it allow for automatic compensation regarding pad wear? Would it "suddenly" go out of adjustment causing the poster's poor brake performance? Is the front caliper the same?

Thanks,
Jesper

Looking at the right side of the caliper, from the drive side of the bike, there is a threaded plug about the size of a quarter with a hex hole in it. Only one caliper piston moves in when the brake lever is pulled. The inner brake pad inside the plug with the hex hole is stationary and it's adjusted by turning that plug to push the pad in. It needs to get the inner brake pad as close to the rotor as possible without binding it. If that plug has backed out, then the outer brake pad is doing all the work, and may even push the rotor inward as it's turning. So the inner pad may be doing no work at all because the outer pad doesn't move very far.

A rotor may be very slightly out of true but it doesn't seem to hurt. If the inner pad is pushed very close to the rotor, when you wheel the bike, you may hear the rotor brushing the pad very lightly when the high spot comes around. I haven't found that this is a problem but the pad could be backed out a click or two to stop it from brushing the disc.

The mechanical brake doesn't have an automatic adjustment, and I don't believe the adjusting plug (for want of a better word) will move out by itself. It has click stops so it's highly unlikely to move out by itself.

Being that new pads have been installed and broken in, and the rotor being thoroughly cleaned, it's the only reason I can think of why the performance is so bad.

[Jesper]

Thanks for the explanation Charley, I understand fully. Appreciate you taking time to educate me. I have no frames that can mount discs, even my monocoque carbon frame is still designed for "old school" calipers being that it is a road bike and we're all about speed and lightweight. I like to be able to help the "kids" at the bike co-op since most are getting bikes with discs but don't know how to maintain them. I worked on enough old Jags to be familiar with discs before anti-lock brakes were in vogue and I see the similarities between car and bike versions, but I need to work on a few to become more familiar with the different features and set-ups, be they cable or hydraulic types.
I'm up in north FL where temps have been sweltering, hope it's not too bad where you're at.

Take care,
Jesper