Another joyous hydraulic brake thread

[Profpointy]

Please please please read the 3rd post in this thread.

The one that says you have to pull the lever several times. That sounds quite like air in the system, albeit with slight variances from the "classic" symptoms. Doubt I can understand but I think your certainty is misplaced from what we've heard

What is your explanation for these symptoms ? , Or for that matter care to explain yor reasoning for your certainty that it's not air? This would actually be helpfull to have a more refined test as it were

 

[Drago]

And to think I was poo poohed for suggesting that while hydro's can be very reliable, they can be a right royal PITA when they do go wrong.

 

[Yellow Saddle]

And to think I was poo poohed for suggesting that while hydro's can be very reliable, they can be a right royal PITA when they do go wrong.

Only if you don't understand the symptoms and misinterpret them.

 

[I like Skol]

Lever feels fine.....

The lever is as normal at its usual bite point, no change in its feel but there is no bite to the pads.....

Prof. You are barking up the wrong tree entirely and unfortunately your suggestion to bleed the brakes is likely to introduce an unnecessary variable I to the problem. The info to rule out air in the system is fairly conclusive.

 

[Profpointy]

Prof. You are barking up the wrong tree entirely and unfortunately your suggestion to bleed the brakes is likely to introduce an unnecessary variable I to the problem. The info to rule out air in the system is fairly conclusive.

Well yes, that is evidence against. But the works better with repeated pumps is evidence for. Given conflicting evidence I'm reluctant to rule it out. Also is "pedal feels fine" actually "pedal slightly but not very spongy". When debugging things you've got to be awfully careful eliminating things prematurely.

Is bleeding bike brakes particularly hard? I've only done cars, and though mildly tedious isn't hard - unless of course you snap the bleed nipples off, and then snap the brake pipes off on the subsequent replacement of the wheel cyclinders. Said car had been standing for 7 years so shouldn't happen here

 

[Oldfentiger]

I believe brake fluid readily absorbs water, which can also play havoc with braking performance.
In this situation I would replace the brake fluid, so then I would know that any problems remaining cannot be attributed to air or water in the fluid.
It's good practice to replace fluid every couple of years anyway.
That's it, stuck my head up above the ramparts. I'll run and hide now

 

[Yellow Saddle]

The one that says you have to pull the lever several times.

No, the one that says: "The lever is as normal at its usual bite point, no change in its feel but there is no bite to the pads."

Had there been air in the system, the lever would not have reached bite point and went all the way down to the handlebar with very little pressure.
Jody clearly says there is bite (feel/pressure/resistance) in the lever but it is the pads that are not biting i.e. not applying friction to the discs.

"Feels like when you have to bed a new set of pads in but every ride."

This clarifies it and shows an understanding of how new pads react before having been bedded in.

That sounds quite like air in the system, albeit with slight variances from the "classic" symptoms. Doubt I can understand but I think your certainty is misplaced from what we've heard

What is your explanation for these symptoms ? , Or for that matter care to explain yor reasoning for your certainty that it's not air? This would actually be helpfull to have a more refined test as it were

The test is simple and has been described on this forum. I'll repeat it. To test if there is air in your brake system do the following:

1) Approach the bike after it has been standing for some time - 20 minutes is enough. Position yourself at the bars and concentrate.
2) Pull both brake levers and hold. Notice how the levers feel viz a vie each other and with respect to how far they advance towards the bars.
3) Now pump them repeatedly and try and feel whether they/it are "pumping up". In other words, does the bite point improve and do the levers feel harder after pumping?
4) Let the bike stand for a while and do the exercise again. Has the levers gone "flat" in the interim?

There is air in the system if:
1) The lever feel hardens up with pumping.
2) The levers lose the feel after standing and require pumping again to get them to bite.

That's it. No other brake problem presents like this. No other brake problem can be fixed by bleeding. The need to bleed is rare.
The only reason you would bleed brakes that don't have air in the system is if the brakes use DOT fluid and a relatively short run using the brakes caused the fluid to boil and had the brakes fail on you due to vapour in the system. The diagnosis for this is the symptom described and the fact that the brakes returned to normal once they have cooled down.

 

[I like Skol]

I believe brake fluid readily absorbs water, which can also play havoc with braking performance.
In this situation I would replace the brake fluid, so then I would know that any problems remaining cannot be attributed to air or water in the fluid.
It's good practice to replace fluid every couple of years anyway.
That's it, stuck my head up above the ramparts. I'll run and hide now

Shimano use mineral oil rather than DOT brake fluid. Mineral oil does not suck up water like DOT so that shouldn't be a problem here. Now you know

 

[Oldfentiger]

Shimano use mineral oil rather than DOT brake fluid. Mineral oil does not suck up water like DOT so that shouldn't be a problem here. Now you know

Thanks.

 

[Drago]

It does, but the process is many, many, many times slower, and the mechanisms that hold the water in suspension are different.

 

[I like Skol]

Just as an aside while we are on the topic, something that really gets my brakefluid boiling is when people start spouting shoot about brake fade
As described by YS, if you boil the contaminated brake fluid by heating it up (This usually only occurs when there is a high water content) the pedal/lever will feel spongy, as if there is air in the system.
Brake fade is where you overheat the pads and they start to outgas causing them to float on the disc rather than bite. This feels like the brake pads have been replaced with blocks of slippy ice but the pedal will feel normally hard. This is scary shoot as it normally happens just when you really, really need your brakes to work (like just when you are enthusiastically negotiating the hairpin bends at the bottom of Holme Moss on the Holmfirth side. Luckily I somehow managed to keep my car on the road).
The number of times people have been on here claiming knowledge and getting the two things mixed up or not even knowing it was a separate issue!

 

[Yellow Saddle]

Brake fade is where you overheat the pads and they start to outgas causing them to float on the disc rather than bite. This feels like the brake pads have been replaced with blocks of slippy ice but the pedal will feel normally hard.

I wish that myth would go away. There is no way on earth that a little pad can produce so much gas at such force that it prevents the pad from making contact with the disc. This myth is perpetuated by car disc brake designs with slots and holes that supposedly lets the gas escape. However, solid discs work just as well (better actually).

There are three types of brake fade and none of them concerns a gas bearing.

 

[Jody]

Well yes, that is evidence against. But the works better with repeated pumps is evidence for. Given conflicting evidence I'm reluctant to rule it out. Also is "pedal feels fine" actually "pedal slightly but not very spongy". When debugging things you've got to be awfully careful eliminating things prematurely.

Is bleeding bike brakes particularly hard? I've only done cars, and though mildly tedious isn't hard - unless of course you snap the bleed nipples off, and then snap the brake pipes off on the subsequent replacement of the wheel cyclinders. Said car had been standing for 7 years so shouldn't happen here

The brake in question had a new hose (due to longer forks) at Christmas. All fluid replaced and re-bled. No issues with the lever feel, travel or operation.

 

[Jody]

Brake fade is where you overheat the pads and they start to outgas causing them to float on the disc rather than bite. This feels like the brake pads have been replaced with blocks of slippy ice but the pedal will feel normally hard. This is scary shoot as it normally happens just when you really, really need your brakes to work (like just when you are enthusiastically negotiating the hairpin bends at the bottom of Holme Moss on the Holmfirth side. Luckily I somehow managed to keep my car on the road).

Had that in my old turbocharged Mini. Even with 4 pot brakes and grooved/drilled discs. Absolutuely sh*t myself

 

[I like Skol]

I wish that myth would go away. There is no way on earth that a little pad can produce so much gas at such force that it prevents the pad from making contact with the disc. This myth is perpetuated by car disc brake designs with slots and holes that supposedly lets the gas escape. However, solid discs work just as well (better actually).

There are three types of brake fade and none of them concerns a gas bearing.

I'm always ready to learn so please put me right on this. All I have read in the past pointed at outgassing so what is the true mechanism for the overheated pads to lose bite? By the way, I always understood the grooved discs where to remove dust and keep the friction interface clean but suspected that was also just sales BS! Never been tempted to fit nasty 'upgrade' parts when genuine or reputable OEM have always done me proud.