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Weak rear brake


silverbird1100

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Front brake stops the bike fine, but the weight of my leg is hardly enough to hold it on a hill. Very low miles, stored well.  The rear reservoir is about half way between full and min, fluid is slightly bronze. Doesn’t seem to have air but I don’t know how the linked parts work together. A friend said try sanding the pads?

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Should be enough to hold you on a hill, how long since the fluid was changed? Sounds like something might be sticking, caliper or a piston. I'd start with flushing the system. Even with glazed pads there should be enough to hold it on a hill.

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Rear caliper only has a piston on one side so caliper has to slide on pins when activated, so it could be this action that's jamming or piston inside caliper or master. Agree with above, the front is only a small percentage transfer.

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1 hour ago, paul99xx said:

Should be enough to hold you on a hill, how long since the fluid was changed? Sounds like something might be sticking, caliper or a piston. I'd start with flushing the system. Even with glazed pads there should be enough to hold it on a hill.

 

I think the fluids are original,  I haven't have it for long but the fluids look good so I haven't tried that yet.  Plus the front lever works so well but I'll try and flush the whole system. Anything I can do to the caliper that isn't too invasive? 

 

@Furbird How can I investigate the rear master? Bike only had 8K on it and everything else is literally perfect. 

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2 hours ago, blackhawkxx said:

The rear brake on mine have never been strong but maybe you could give more details.  If you are riding and hit just the rear brake (yes I know they are linked), what happens?

 

If I really stomp on it I think it slows the bike as it should. It just takes way more pressure that it should. 

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14 minutes ago, silverbird1100 said:

 

I think the fluids are original,  I haven't have it for long but the fluids look good so I haven't tried that yet.  Plus the front lever works so well but I'll try and flush the whole system. Anything I can do to the caliper that isn't too invasive? 

 

@Furbird How can I investigate the rear master? Bike only had 8K on it and everything else is literally perfect. 

So really old fluid, they recomment changing every 2 years, it absorbes moisture. First I'd flush the system. I like to syringe everything out of the masters and replace, replace cap on resevoir then open nipple with a tube on it, gently squeeze lever and tighten nipple while lever compressed. Or just open nipple and let it bleed itself, check back every 10 minutes and top up resevoir. Can't recall servicing the pins, it's been a while and memory failing :) But if you get someone to press on brake pedal while you hold the caliper you should feel a tiny amount of movement.

Anyway while bleeding and squeezing pedal you should get an idea if any of the pistons are seized.

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20 minutes ago, silverbird1100 said:

 

If I really stomp on it I think it slows the bike as it should. It just takes way more pressure that it should. 

If I really stomp on mine I can lock the back wheel.

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1 hour ago, silverbird1100 said:

 

If I really stomp on it I think it slows the bike as it should. It just takes way more pressure that it should. 

If you stomp on it the tire should lock.

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5 hours ago, paul99xx said:

If I really stomp on mine I can lock the back wheel.

I don't know if I have tried the "stomp" but I'm guessing that mine will not lock.

3 hours ago, superhawk996 said:

If you stomp on it the tire should lock.

Have you done it on a Bird on dry pavement?

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8 hours ago, paul99xx said:

So really old fluid, they recomment changing every 2 years, it absorbes moisture. First I'd flush the system. I like to syringe everything out of the masters and replace, replace cap on resevoir then open nipple with a tube on it, gently squeeze lever and tighten nipple while lever compressed. Or just open nipple and let it bleed itself, check back every 10 minutes and top up resevoir. Can't recall servicing the pins, it's been a while and memory failing :) But if you get someone to press on brake pedal while you hold the caliper you should feel a tiny amount of movement.

Anyway while bleeding and squeezing pedal you should get an idea if any of the pistons are seized.

Sounds good will one bottle be enough?

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5 hours ago, blackhawkxx said:

Have you done it on a Bird on dry pavement?

Yes, but then remembered that it was de-linked so not the same.  I imagine the linked one will, I'll try it next ride.

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Rear brake sucks for sure.  The pads are probably original, as well.  I recommend changing or light sanding, and check them for any oil or other fluid that would reduce friction.

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12 hours ago, silverbird1100 said:

 

I think the fluids are original,  I haven't have it for long but the fluids look good so I haven't tried that yet.  Plus the front lever works so well but I'll try and flush the whole system. Anything I can do to the caliper that isn't too invasive? 

 

@Furbird How can I investigate the rear master? Bike only had 8K on it and everything else is literally perfect. 


My fluids have only been replaced once in 21 years, maybe.  Bike has over 50k and probably a thousand passes at the dragstrip.  And this was an 1/8th mile with a short shutdown, so you had to use a lot of brake.  8k miles on a 20 years old bike is scary to me, that's why I always say mileage should not be anywhere near the top of a list of requirements for purchase, no matter what it is, and especially not a bird.  But don't be like me, change the fluid FIRST and do a full bleed to make sure it's not the easiest fix of all.

The easiest thing to check of hard parts is the caliper.  Center stand, put in first gear, get the rear wheel speed up  to maybe 20-30mph, clutch in and hit rear brake.  Rear wheel should stop almost immediately.  If not, pull the caliper and make sure the pads are easily removable.  Could be the pad is just stuck on the pin(s) or is corroded and causing excess friction.  It's pad on one side and slot on the other.  Hell you might get lucky and it just have a rock stuck between the pad plates!

Next, collapse the pistons on the rear caliper.  I have always used the old pads to do this but whatever you have that will fit in there and allow you to close them.  If it moves smoothly then the caliper is probably fine.  If you feel things grinding,  I would suspect it's got water intrusion and has surface rust on the piston on the inside.  Never taken a bird caliper apart but have seen this happen before on other bikes.  Normally you would have a leak as it tears seals but it depends on how the caliper is assembled.  The rear reservoir cap needs to be off to allow the fluid to easily flow back into the master cylinder during this step, in case you aren't aware.

If all that is good, I would replace the rear master cylinder.  It's $100 from Ron Ayers and while they do sell rebuild kits for that, I would just buy the entire assembly if it gets to that point.  I'm referring to the actual piston part, not everything.  Hell, Joe probably has 15 laying around he'll sell you.

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11 hours ago, blackhawkxx said:

I don't know if I have tried the "stomp" but I'm guessing that mine will not lock.

Have you done it on a Bird on dry pavement?

I just tried and it did lock.  I didn't stomp the pedal, but pressed it, and it took a pretty hard press.  I think the Gille's pedal gives a little less leverage than the stock pedal does so it may be a little easier on a stocker.  I was shocked by how much front brake it applied, it slowed pretty hard.

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10 hours ago, silverbird1100 said:

Sounds good will one bottle be enough?

More than enough, dot 3 or 4 good. Stay away from dot 5.

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6 hours ago, superhawk996 said:

I just tried and it did lock.  I didn't stomp the pedal, but pressed it, and it took a pretty hard press.  I think the Gille's pedal gives a little less leverage than the stock pedal does so it may be a little easier on a stocker.  I was shocked by how much front brake it applied, it slowed pretty hard.

Thanks for the experiment.  If it ever stops being 50F and rainy around here, I'll give a go also.  Just for the record, yours is also a 97 with the stock braking system, right?  Any idea which brand of pads?  I have the green EBC HH.

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2 hours ago, silverbird1100 said:

I can hear the rear pedal clamping the front but not the rear. Does that say anything about the rear master?

Hear it how?

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