NoWhammies

When do I need to change the hydraulic brake fluid on my road bike? Is it done by mileage? Age? Another factor?

And is this a job that I can do myself? I have Zinn's book which seems to give good step by step directions. I have Shimano hydraulic road brakes. Thank you.

jp911

There's a big "it depends" on this one. It's subjective, but some will go for several years without flushing the system. However, you have to consider how often you ride, the type of terrain you ride, your body weight, how hard you use your brakes, and even average temperature.

Personally, I like to bleed the discs on my gravel bike every 6 months, but I live in a very hilly area, I weigh about 200 lbs, and I tend to be a bit of a grandma on really fast descents. If you bleed on a regular interval, which flushes air bubbles trapped in the system and introduces a small amount of fresh fluid, you should be fine going about 3 years between full system flushes.

gsa103

For Shimano, if it's working well, probably about as often as you repack hubs.
Annually isn't a bad idea, but you could probably go 3-4 years on a lightly ridden road bike.
SRAM should be bled annually because it's automotive fluid that is hygroscopic.

NoWhammies

When I bought the bike I was told I could probably get away with flushing the system every 2 - 3 years. That said I do a lot of hill climbing and I am on the brakes when I come down. Already gone through one set of front brake pads.
Just trying to be a bit proactive. I have over 5,000k on the bike so far this season and will close in on (maybe) 6k before it's all said and done.
If I don't need to flush them, then that's fine. Sounds like 3 years might be a good interval.

gsa103

Do a touch up bleed top-down. If the fluid coming from the front caliper is still a nice pink color you should be good for a while longer. If the fluid is darker, then it's had high heat and would benefit from a bleed.

fietsbob

Mostly you bleed to get out air bubbles , because being an open system ,
it happens..

but unlike oil for your car engine it is not contaminated by combustion of fuel..

NoWhammies

In your experience/opinions, does the Zinn manual do a good job of explaining of how go about doing the work?

@gsa103 re the touch up bleed, my concern with doing something like that is I would introduce air in to the system, as opposed to taking air out of the system. I have a fear that as soon as I open the system up, air will in. So once I start, I need to complete the whole thing.

Cyclist0108

With mineral oil, I don't think there is any compelling reason to change it, if everything is still working properly (no leaks, isn't squishy after fresh pads and rotors). (Even then, it is often sufficient to purge the system of dissolved air and top it off.)

It has been several years since I bled my Ultegra brakes, and I burn through pads and rotors on an embarrassingly regular basis, i.e., they are very heavily used.

With DOT fluid (like SRAM uses), I think the recommendation is to change it annually, as the fluid is somewhat hygroscopic.

NoWhammies

Well thanks to @wgscott I learned something new today. I wasn't aware that the fluid in my Shimano brakes is/was mineral oil. I figured it was DOT fluid and that it would be hygroscopic. Interesting...And that's good to know about heavily using the brakes and not having to bleed them on an annual basis.

It sounds like I might be able to away with bleeding the brakes every three years. Maybe, and that's a big maybe, if I suddenly end up doing tons of mileage between now and then. But good to know I don't have to worry about it at the end of this season.

@gsa103 when you talk about high heat, would you be referring to hard braking coming down a hill?

Cyclist0108

@NoWhammies I am very vigilant and pro-active about brake maintenance. I climb and drop 2000 ft minimum per day, and apply the brakes like a clinically paranoid grandmother. It certainly would do no harm to bleed them more frequently, but it isn't clear to me it would benefit unless the braking characteristics change. (I can tell how worn brake pads and rotors are now just from the feel of my brake levers, so I am fairly tuned into it.) The good thing is bleeding Shimano brakes is extremely easy to do, and safe, thanks to it being mineral oil. One trick that I find makes it easier is to use two syringes, and a threaded Leur lock on the top one, with some high vacuum grease in the threads to make the seal air-tight. You can then purge air bubbles out of the line just by creating negative pressure by pulling up on the stopper.

NoWhammies

Thanks for the information. Perhaps if I need a winter project I'll look in to it. That said, my bike is braking well without any brake fade. Oh and by the way, that is a lot of climbing per day! Well done.

BTW, I am no bomber going downhill either. Having come off my bike while heading down a hill has brought a good level of fear/paranoia to my descending. I can climb ok. It's the descent that I'm not the fastest at.

PDLandis