Brakes Brake loosing pressure

[pagheca]

Hey guys,

my bike's hydraulic rear disc brake suddenly started losing pressure. There are no visible leaks.

All started when I changed a flat tire a few weeks ago. When I put the wheel back on, I noticed that the brake was a little loose and elastic. Then the other day, while descending a long, steep trail, it suddenly started losing pressure and making a lot of noise. At the end of the ride the lever was touching the handle.

I'm going to take it to the shop, but I'm wondering what the problem may be. Any advice? Thx!

 

[HumanPerson]

Depending on the oil used, sometimes the oil will boil inside of the hose running from the caliper up to the brake resevoir
when coming down hills.

When the oil boils it causes bubbles/pockets of air, which causes all kinds of lack of brake problems.
This might not be your problem though..
Be careful.

 

[pagheca]

Interesting... actually the disk was so hot that I burned my fingertips by accidentally touching it to check what was going on....

Tomorrow I have a small surgery (EDIT: second EYE CATARAT... not catether you stupid autocorrector!!! probably an occupational disease), so I will not be riding for a while Plenty of time to fix it.

 

[Smaug]

Good luck with the surgery AND the brakes.
I would think that the brake fluid boiling wouldn't matter unless there was a lot of air in the system.

 

[pagheca]

Oooops, the autocorrector gave me a pretty sadistic joke: the surgery is for an EYE cataract, not a... CATHETER

Not yet at least....

 

[HumanPerson]

@pagheca ,

Heal well and we'll be here when you get back!

 

[HumanPerson]

Hey guys,

my bike's hydraulic rear disc brake suddenly started losing pressure. There are no visible leaks.

All started when I changed a flat tire a few weeks ago. When I put the wheel back on, I noticed that the brake was a little loose and elastic. Then the other day, while descending a long, steep trail, it suddenly started losing pressure and making a lot of noise. At the end of the ride the lever was touching the handle.

I'm going to take it to the shop, but I'm wondering what the problem may be. Any advice? Thx!

When i had that happen, i live in a crazy hilly town, i replaced the rotors first(thicker rotors 2.5mm iirc)....that worked somewhat...
then i went with the 4 piston caliper system (a cheap one to use LOL) which has stopped all of the bleeding early and the lever fade
and alot of heat.

So in my experience the disipation of the heat is a huge thing if you are like me and have huge hills to go up and down.
Another thing is LEARN to modulate your brakes..workm the levers like a car has anti-lock brakes..make sense?

And yet again here is another thing i changed....better hoses for the brakes....just research and learn..

 

[pagheca]

yes, I live in a really hilly place. This is the profile (incomplete) of my latest ride, when the problem developed:

Almost every ride is like that. However, I brought my bicycle to the shop today.

I also found a problem with the rear tyre while going down: a strong vibration because the tyre was slightly out of the wheel so, I decided to mount a tubeless.

Now, I have a question for you guys: the selection of tyres available is pretty limited. They suggested or Continental Kryptotal, or a Maxxis Assegai. Their cost is pretty high but (75 and 100 € ea.) Any hint? I am planning to use them on gravel and very bad terrain.

What would you suggest?? They also have a few other Maxxis models, here is a picture:

 

[m@Robertson]

I can say a Maxxis Assegai is an awesome tire, but its not a street tire. Think of it in the class of the Maxxis Minion, which is a near-legendary tire. I would say an Assegai is a slightly different tread style but the same class of tire. I use a Minion on the front of my cargo bike, because the side knobs let me stay upright when I hit sand drifts crossing the bike path. Not uncommon here where the bike path literally runs along the beach in some spots and alongside huge sand dunes in others.

You said "The tire was slightly out of the wheel" ...

 

[pagheca]

Thx a lot for your comment!

I have to say that I usually go off-road, but sometime I have to reach the access to gravel road by standard road. Here there is not very much sand but mud sometime and A LOT of volcanic ash, that behave more or less like sand. I will consider the Minion motion, althoug I prefer to optimize traction off-road.

One more question: do you think the same tyre can be installed front and wheel or it is different? I've read online that a lot of supercilious people use strange front and rear combinations. but I don't know if that's just for show (or to participate in the world championships, which I'm skipping for this year... )


So, let me explain... the tire was not properly installed in the wheel seat in one section, so the wheel was not perfectly round and on the asphalt at a certain speed it made a resonance that amplified the vibration.

 

[Smaug]

Thx a lot for your comment!

I have to say that I usually go off-road, but sometime I have to reach the access to gravel road by standard road. Here there is not very much sand but mud sometime and A LOT of volcanic ash, that behave more or less like sand. I will consider the Minion motion, althoug I prefer to optimize traction off-road.

After reading this, I would recommend the most aggressive off-road tread pattern; that is, the ones with the larger lugs spaced further apart. The reasons:

• It sounds like you're off-road more than on, so it makes sense to have the more aggressive tread pattern
• You live in a hilly area. When climbing hills, you will not go fast no matter what. When descending hills, that aggressive tread will act like a bit like an air brake to save your brakes a bit when going fast.

One more question: do you think the same tyre can be installed front and wheel or it is different? I've read online that a lot of supercilious people use strange front and rear combinations. but I don't know if that's just for show (or to participate in the world championships, which I'm skipping for this year... )

I think it is mostly because the tires are so expensive, they only want to replace them one at a time. Rears tend to wear twice as quickly as fronts.
Of course there will be some difference in handling, but you will get used to it.

So, let me explain... the tire was not properly installed in the wheel seat in one section, so the wheel was not perfectly round and on the asphalt at a certain speed it made a resonance that amplified the vibration.

Well, good that it was an easy fix. I have a tire that's not quite seated right and it's not always as easy as it seems to be to get it right. (mine is an old Schwinn from 1972 and the OEM tires are no longer made so it has some Kendas on it that are marked as the right size, but are just a bit different.

 

[pagheca]

only problem is the CRAZY cost of this stuff here. They sell it at 100€, when you can find it at less than 50 online (and they do NOT pay VAT here...). No alternatives, though. And installation is another 20. Per wheel!

 

[pagheca]

After reading this, I would recommend the most aggressive off-road tread pattern; that is, the ones with the larger lugs spaced further apart. The reasons:

• It sounds like you're off-road more than on, so it makes sense to have the more aggressive tread pattern
• You live in a hilly area. When climbing hills, you will not go fast no matter what. When descending hills, that aggressive tread will act like a bit like an air brake to save your brakes a bit when going fast.

Good points. Actually, I do not know exactly what's the downside of a real off-road tyre when on-road, at least for a user like me.

I think it is mostly because the tires are so expensive, they only want to replace them one at a time. Rears tend to wear twice as quickly as fronts.
Of course there will be some difference in handling, but you will get used to it.

As above!

 

[Smaug]

Good points. Actually, I do not know exactly what's the downside of a real off-road tyre when on-road, at least for a user like me.

When used on-road, off-road tires will have less traction due to having less rubber in contact with the pavement. The knobby lugs don't dig into pavement like they do dirt, sand, etc. Braking and cornering performance will be diminished. I don't think you will notice, except maybe under emergency braking on dry pavement. They will also make more noise and wear down faster on pavement. These are all compromises that are worth making in your case, since they are better in every way off-road.

 

[pagheca]

thanks again. Looks reasonable too. Actually I do ride on sealed road, but try to avoid them and in any case the fun is mainly off-road here ... I think I will go with the off-road tyres...

BTW, I did the eye catether catarat . Quiet environment, excellent assistance, and very kind and funny nurses, one even quite pretty (Venezuelan, not a case...), which to be honest doesn't hurt, to rest your eye on (singular, the other was shut down ). And all paid for by the Spanish health service. I am now at home relaxing and dreaming about my future ebikes adventure!

 

[munirider]

Did you figure out what was wrong with your brake?

Glad to hear your cataract surgery went well.

Happy solstice everybody!

 

[pagheca]

as an Astronomer I can't do other than thank you twice! Today I am going back to the shop to give them instructions. I do not know yet what happened to the brake.

 

[munirider]

I get that! It's Friday the 22nd there where you live on the other side of the international date line.

 

[pagheca]

Did you figure out what was wrong with your brake?

They just called me. The bike is ready. There was air in the circuit. Probably it got in when I changed the tube last time, but I wonder why it increased the other day. Does it sound reasonable or could I get the same problem again in your opinion?

Regarding the tubeless conversion, they told me that they can do it even if I buy the tires myself online.

 

[HumanPerson]

I just cannot wrap my head around how you would have gotten air in the brake lines from changing a tube lol