sknhgy 

It's a side-pull brake on my mtb. Everything looks to be in good condition. When I apply the brake it has almost no effect on the bike. I can squeeze the lever hard but the bike barely slows down. One thing I do notice is that the levers that hold the pads are relatively close together. There's maybe an inch and a half of cable between the end of the noodle and the nut that clamps the cable. On the front this distance is about 2 and a half inches. (Both have a rubber boot over part of the exposed cable.) Any ideas?

jchabalk 

Some things to check:
- is the rim clean and clear of grease? Maybe make sure it's clean either way
- are the pads clean and clear of grease? Are they worn out?
- if you prop the rear wheel up and just squeeze the brake caliper with your hand do you get the same behavior?
- is the brake caliper loose and/or mounted improperly
- what amount of clearance do you have between the rim and the pads? I didn't get that from your description of the brake. (Is it a V-Brake?)
- is your cable properly secured to the caliper, or is it slipping by chance?

Just a few ideas, probably most of them you've done already.

I'm assuming that by side-pull on a mountain bike you're talking about a v-brake. What type of brake levers do you have? I've had a couple of mountain bikes with v-brakes and with the right setup i've been able to easily lock up the rear wheel on all of them.

Retro Grouch 

Sure it's not a linear pull? Do your brake pads have some spacers between the pad and the arm?

Look at the spacers. Most linear pull brakes have a wide one and a narrow one. See if you can fit the wide one between the arm and the brake pad. That will move your brake arms farther apart and, when yu pull the lever, the force will be directed inward tather than downward.

jchabalk 

op, a picture might be helpful too

LesterOfPuppets

If there's a noodle, that's a V Brake, not sidepull. Even though it does pull from the side.

mrrabbit 

1. Go a top of a slight hill.
2. Better yet, go to the top of a very steep hill.
3. Take feet off pedal.
4. Let 'er run freely downhill backwards.
5. Hit the rear brakes.

Assuming you are still alive, get back to us how well the stopping action was.

Thus ends today's lesson in Physic's...

=8-)

Jeff Wills

1: replace the brake pads
2: replace the cable and housing
3: adjust, following these instructions: https://www.parktool.com/blog/repair-...e-v-brake-type

Tell us what happens.

dabac

OP says :"When I apply the brake it has almost no effect on the bike."
Mrrabbit's lesson in physics is relevant to ultimate braking performance, but doesn't explain why the OP can't get the wheel to lock up.
Although all-out rear braking even at the best of times might leave the OP dissatisfied with stopping distance, the effects should be readily noticeable, i.e. rear wheel skidding. To me it sure sounds like there's more than mismatched expectations going on here.

rebuilt13

If the pads appear to be adjusted correctly and/or look similarly adjusted to the front brake, my bet is on contamination. Pull out the rear wheel and take a clean rag with some alcohol on it and wipe the entire braking surface while frequently turning to a clean part of the rag. If you can, replace the rear pads. If you can't, wipe the pads clean and scuff them with a clean emery cloth. Readjust and ride!

Chombi

One thing to also consider is, how old are the pads. some brake pads can harden up with age/exposure to elements and will not provide the neccessary friction anymore to provide adequate braking.

Chombi

fietsbob

Ah , not exactly a powerful stopper at its best 1) rear brakes just skid the tire,
when they work well . If thats the case [ambiguous description suggests it may not be the case]
real Braking power is the front brake, because deceleration lifts rear wheels unweighting them.
so the front one does most of the work.

side pulls are bendy, when made long enough to reach around fat tires..

You may be asking for too much performance from a cheap bike,
and need to go to a Bike Shop and get a bike that is better suited to your changing needs.

you may need their visual inspection of your situation, anyhow,
as im blind at this keyboard, minus pictures uploaded.

New brake pads and adjust the clearance so Its barely a dimes thickness of clearance when you let go of the lever ..

that requires quite in true wheels.

sknhgy 

^^^ The wheel is true.
I replaced the noodle and the cable, and gave the brake a general cleaning. Then I deglazed the pads with some coarse sandpaper and I lubed the little boot that goes on the end of the noodle with some silicone spray. I also gave the rim a good wipedown. Didn't help much. It seems like that boot is interfereing with the levers. Maybe I'll take it off and try it without it. Don't know what else to do. The pads look plenty thick but I guess I can change them next time I get to the store for some new ones.

Jeff Wills

That should have been your first step. Try some Kool-Stop "salmon" colored pads- they're much better than "normal" replacement pads.

Also try rearranging the spacer washers on the pads so thicker washers are on the inside of the brake arm. This will spread the arms further apart.

relyt

How much travel does the hand lever have? Is it hitting the handlebars? Is it so tight you can only move it a little bit? Either will degrade braking power.

sknhgy 

That fixed it. I had some Aztec brake pads on hand. The old pads do not appear to be worn out. There is even a wear line but there is still plenty of surface remaining. A couple of mm's at least. Anyway, now the rear is holding better than the front.
Thanks for the help.

BCRider

Rubber and elastic materials do tend to oxidize and harden over time with exposure to sun, ozone and other environmental effects. Same with tires. So if your bike is older I'm guessing that the pads just plain got old and hard and were not able to stop you as well anymore. It's not always about "wearing out".