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What Could Cause a Weak Rear Brake

2159 Views 21 Replies 9 Participants Last post by  Vinish
My wife's 2012 Cross Country Tour (XCT) has just started exhibiting a weak rear brake. When the rear brake pedal is pressed, there is some braking action but not as much as there should be. If I compare it to my 2012 XCT, her bike has significantly lower rear braking action. I have checked the rotor and it is fine (proper thickness and no scoring). I have checked the fluid level in the reservoir and it is full. The fluid is fairly new and not discolored. I have examined the brake pads and they are practically new with large amounts of the wear grooves still present. This reduced braking action occurs starting with the very first press of the rear brake lever so it is not overheating of the fluid. When the rear brake lever is pressed, it has firm resistance and does not go down real far as it might if there was air in the system.

Any suggestions for possible sources of this problem would be appreciated. Thanks.
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I clean the rotors from time to time by wiping them with a cloth and brake parts cleaner.
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Might have one or more stuck pistons in your rear caliper. They get hung up from road crud sometimes on some bikes. Then you have a 1,2 or 3 piston caliper instead of 4 piston which equals out to 1/4, 1/2 or 3/4 the force on the pads when you apply the brakes.
HD twin cams were famous for this. I believe there are YouTube videos that show
how to clean them on sport bikes that would be applicable to a Vic.
It’s fairly straight forward once you watch it done.. Just be certain to do it outside. Brake cleaner is bad ju ju.
Nitrile glove. Hold your breath. Etc.
You remove the caliper from the rotor but don’t take the caliper apart or remove the brake line when cleaning it. As best I remember.
I’ve always used chlorinated brake cleaner for this.
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AS depot picker said, and the pads could be glazed over (use sandpaper on them).
Thanks, guys. Does anyone know if the caliper can be easily removed from the mounting bracket on a XCT? To remove the entire mounting bracket, I have to remove the rear axle so I am hoping that I can just remove the caliper itself from the large black mounting bracket.
pull retainer pin for pads should be able to seperate caliper also grease pistons an slide pins with high temp grease
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I had the same issue removing the rear brake caliper. If my memory serves me I removed the pads and pushed the pistons all the way in. Then I had enough "wiggle room" to pull the caliper off far enough and as it hit the rim I could angle it enough to remove it.
I will give that a shot and, if I can't make it work, will remove the rear wheel and brake caliper bracket. Thanks.
Check for air in the rear brake line (ie bleed rears, realizing that if there is air in the antilock brake actuator, it needs to be cycled during the bleeding process). Air in brake system will always give a " soft or weak" feel.
I am familiar with how air in the brake line makes the brakes feel. This does not seem to be that problem. The pedal is not "soft", it does not travel further than normal, and it does not take two or more pumps to become firm. Instead, the pedal acts completely normal. When I press the pedal, it travels only a small amount - about 3/4 inch before stopping and being very firm at this stopped position. The ~3/4 inch of pedal travel might seem low but I tested my XCT (same model year) and the rear brake pedal travel was the same ~3/4 inch.

Yesterday, I took off the rear wheel to access the brake caliper. I removed the caliper from the bracket but left it attached to the brake line. I pushed the pistons out much further than they would normally go, cleaned the exposed piston surfaces, and greased them with a silicone grease. I removed the brake pads and cleaned them, the brake pad pin, the two retaining springs, and the caliper in general. I very lightly sanded the surface of the brake pads (there was no glazing (sp?) apparent. I inspected and cleaned the rotor. It looked good and had no grease or other liquid on it. I reassembled the parts and test road the bike.

The symptoms remain the same. While the brake pedal feels firm, the stopping ability of the bike using the rear brake seems low.

I am wondering if this is just a perception issue. Perhaps I am just imagining things. I am going to wait for a rain (supposed to happen later today) and then take the bike out, get going on a straight downhill road and hit the rear brake very hard. On a wet/slippery road, I want to see if I can get the ABS to activate. If it does, then I will conclude that this entire problem is in my head and I wasted three hours yesterday doing the brake cleaning. My back ached all evening yesterday from the three hours spend stopped over this awkwardly accessed area of the bike.
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Is there a chance that when the pads were changed last that a less aggressive pad was used?
I set of organics in place of a set of metallics will definitely lower braking force.
That is possible. My wife's bike has less than 20k miles on it, we bought it used with pretty low miles, and I have never changed the pads. There is a LOT of life left in the pads so it is possible they were changed before we bought it but it is also possible that these are the original stock pads. There were some numbers/letters on the back of the pads but I did not make note of it so I cannot look up the part number now unless I took the pads back out of the bike .... something I do not intend to do :)
Did you notice if they were metallic often copper looking or just gray or black fiber looking by chance?
Assuming you are asking about the part of the brake pad that touches the rotor, they were somewhere between gray and black with some lighter colored inclusions that were a lighter shade of gray.
Went out and looked at the wife’s Vic that has stock pads and they too are grey.
On most of my bikes the aggressive metallic stock pads have a copper cast to them. These are an exception.
Well, I suppose you could just swap pads with the wife bike. Clean the rotor before and after that test.

There is no issues activating ABS on rear with dry pavement for your test. I've done it by accident.

The mentioned possibly less aggressive brake pads were a preference of the guy from North West that left the forum. He purposely went with softer pads because he thought the rear was too grabby stock.

I can stop my bike easily with the rear so it's indeed very grabby on stock pads.
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Went out and looked at the wife’s Vic that has stock pads and they too are grey.
On most of my bikes the aggressive metallic stock pads have a copper cast to them. These are an exception.
Please pardon my confusion but I do not understand what you are saying here. Are you saying that my pads are likely stock and that they are "aggressive metallic stock pads" or are my pads an exception to this? Sorry, I just do not follow what you are saying. I hope you will clarify as your input is valued. Thanks.
Well, I suppose you could just swap pads with the wife bike. Clean the rotor before and after that test.
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Now that is a darn good idea. Thanks, Indy.
Now that is a darn good idea. Thanks, Indy.
I would not do that. The pads tend to form to any irregularities on the surface of the rotors. If you swap the pads the surfaces won't match.
I would not do that. The pads tend to form to any irregularities on the surface of the rotors. If you swap the pads the surfaces won't match.
Good point. It could reduce performance much like when people swap pads on cars without fresh rotors it takes time to break in.

Plan B, just buy quality fresh pads. If that fixes it then hooray. If not, mark them assigned to whatever bike you were testing them on and use later.
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