Disc brake bleed question

[Willy]

I have 25,000 miles on my bike with dura ace disc brakes and have replace the pads a few times but never bleed the brakes. Are there any rules as to when to bleed the brakes or is this one of those that you “don’t fix it unless it’s broken items?”

[nmrt]

I usually bleed when that "taut" lever feel is not there. Also, when there is a lot of lever travel (even after changing the brake pads), I will bleed.

I have 25,000 miles on my bike with dura ace disc brakes and have replace the pads a few times but never bleed the brakes. Are there any rules as to when to bleed the brakes or is this one of those that you “don’t fix it unless it’s broken items?”

[CTracer]

I usually bleed when that "taut" lever feel is not there. Also, when there is a lot of lever travel (even after changing the brake pads), I will bleed.

+1 If the lever travel is still good with new pads I would not do a bleed.

[mcteague]

25,000 miles? :eek: How many each year?

Tim

[Clancy]

With that many miles I would have to believe the brake fluid has become contaminated. I would definitely do a brake bleed, fairly easy and quick as long as you follow Shimano’s procedures step by step.

There’s no reason not to. Preventive maintenance

[ColonelJLloyd]

+1 I think I would just do a bleed as a matter of course/preventative maintenance. It's quite possible it's such a slow degradation that you won't realize they're not at 100% right now until you do a bleed, then ride, and "whoa".

[Willy]

25,000 miles? :eek: How many each year?

Tim

4,000 to 5,000/year

[merlinmurph]

Highly recommend getting a bleed kit and doing it. I'm sure you'll find an appreciable difference in the lever. Lots of videos on YouTube to help you out.

Good luck!

[Clancy]

Highly recommend getting a bleed kit and doing it. I'm sure you'll find an appreciable difference in the lever. Lots of videos on YouTube to help you out.

Good luck!

The first video that pops up is by Cycling Magazine. Follow his instructions and I can almost promise you that you’ll end up with air in the lines and no brakes. He leaves out multiple steps. Shimano has a dealer manual PDF easily found and downloaded. Follow those steps and you’ll have happy brakes.

I’ve always found Shimano’s manuals the surest way to end up with quality results. For example I’ve seen complaints on Shimano’s Front Derailleur Set-up but I found following Shimano’ dealer manual step by step it’s very straightforward. YouTube videos can often be helpful but I always look over Shimano’s instructions. Dry and dull no doubt but easy enough to follow.

[eddief]

before taking my bike to the LBS. next time i will try his approach.

https://www.youtube.com/watch?v=JXQKx4S_eoI

he's not my fave online bike guy but this is the most complete vid i've seen. this is a full bleed when installing new levers but the steps are instructive regardless.

[eBAUMANN]

Just curious --- Assuming everything is installed correctly and the brakes still feel good...why would the brake fluid be contaminated after ______ miles of riding?

Does mineral oil "go bad" after a certain amount of miles?

If the brakes still feel/work fine, that should mean the seal on the hydraulic system is still good and not letting in air or other contaminants.

My general rule of thumb with hydraulics is to leave em alone if they are working correctly. Even contaminated fluid will still do its job, it's what that contamination suggests (a breach in the system) that will eventually lead to air bubbles where you don't want em, which will effect braking feel/performance. If you aren't noticing funny feel in the lever, I wouldn't touch it.

Just my 2c. I could be wrong.

[eddief]

i'm not touching mine unless braking becomes less than effective.

Just curious --- Assuming everything is installed correctly and the brakes still feel good...why would the brake fluid be contaminated after ______ miles of riding?

Does mineral oil "go bad" after a certain amount of miles?

If the brakes still feel/work fine, that should mean the seal on the hydraulic system is still good and not letting in air or other contaminants.

My general rule of thumb with hydraulics is to leave em alone if they are working correctly. Even contaminated fluid will still do its job, it's what that contamination suggests (a breach in the system) that will eventually lead to air bubbles where you don't want em, which will effect braking feel/performance. If you aren't noticing funny feel in the lever, I wouldn't touch it.

Just my 2c. I could be wrong.

[Ken Robb]

"Brake" fluid is hydroscopic and will absorb moisture from the air through tiny pores in lines and seals. When brakes get hot enough the water boils and the resulting steam/vapor is compressible so braking is greatly compromised. Even if you never get the fluid hot enough to boil the water it contains that water will cause corrosion in the brake hydraulics.

OTOH I know some bicycle brakes use mineral oil which may not absorb water so those brakes may be in the "leave well enough alone" or "if it ain't broke don't fix it" category. :)

[eddief]

i am thinking bicycle brake hoses are plastic, not metal, so maybe less chance for "corrosion."

"Brake" fluid is hydroscopic and will absorb moisture from the air through tiny pores in lines and seals. When brakes get hot enough the water boils and the resulting steam/vapor is compressible so braking is greatly compromised. Even if you never get the fluid hot enough to boil the water it contains that water will cause corrosion in the brake hydraulics.

OTOH I know some bicycle brakes use mineral oil which may not absorb water so those brakes may be in the "leave well enough alone" or "if it ain't broke don't fix it" category. :)

[eBAUMANN]

Yea OP was asking about Shimano disc brakes, which use mineral oil.

"Unlike DOT fluid, Mineral Oil is hydrophobic and does not absorb moisture from the environment. ... This is because as the fluid repels any water ingress, it causes it to pool at low points within the brake system, usually the caliper, since water is heavier than brake fluid it will settle at the lowest point."


"Brake" fluid is hydroscopic and will absorb moisture from the air through tiny pores in lines and seals. When brakes get hot enough the water boils and the resulting steam/vapor is compressible so braking is greatly compromised. Even if you never get the fluid hot enough to boil the water it contains that water will cause corrosion in the brake hydraulics.

OTOH I know some bicycle brakes use mineral oil which may not absorb water so those brakes may be in the "leave well enough alone" or "if it ain't broke don't fix it" category. :)

[vespasianus]

Yea OP was asking about Shimano disc brakes, which use mineral oil.

"Unlike DOT fluid, Mineral Oil is hydrophobic and does not absorb moisture from the environment. ... This is because as the fluid repels any water ingress, it causes it to pool at low points within the brake system, usually the caliper, since water is heavier than brake fluid it will settle at the lowest point."

Yeah, I have run my mountain bikes for years without doing a full bleed (Shimano). I only do it when I am altering the cable length. One bike is going on 9 years since installation without any issue. The trick that was linked works wonders and may be the only thing you need to do.