Brake bleeding advice please
I am fairly new to hydraulic disc brakes, but have done all my own mechanical work on my bikes for 15 years. I have two bikes with hydraulic disc brakes, a gravel bike 3 years old with about 1,500 miles total, and a 2 year old ebike conversion with 1,200 miles on it.
The Shimano 400 series brakes on the gravel bike, and the Tektro ? Model brakes on the ebike have worked well. I've replaced pads on Shimano, not yet on Tektro. My question is, should I worry about changing out brake fluid if the brakes are performing normally, or wait until I feel softness in levers or have to pump them? Having never changed bike brake fluid, I'm leery of getting into it unnecessarily, though resigned to the fact I'll need to do it some day. The Shimano manual on my brakes outlines a bizaar procedure involving 20+ steps, including multiple repositioning of the bicycle. Is there a simpler approach that applies to all brakes? I did brake work on cars when I was younger, and the bleed procedure was simple if you had one person to pump the pedal, another to open and close the bleed valve at caliper. Can you do similar on a bike? My bike work stand is not a pro caliber like Park; I can likely position bike at an angle to put hoods straight up, but doubt I could change angles repeatedly as per instructions without undue time and frustration. Anyone with a simple, practical procedure they'd care to share? Thanks in advance. I don't get on the forum often enough to chat, but will certainly check back in a couple days to see any replies. |
You don't even have to put a bike into a stand to bleed it. It might make things go a bit faster or smoother, but it is hardly a necessity.
If your brakes are working fine and feel ok, you don't need to bleed them. Just change pads and rotors as needed. Most Tektro brakes use a fitting slightly wider than Shimano, FWIW. You don't need the fancy park tool kit to do this, either, but their video demonstration is quite good: |
What is a Shimano 400 series brake? do you mean an MT400 or GRX400? you really need to be specific for questions like this as there will be different processes for each type. Same for the Tektro, best to ID exactly what you have, not just the brand name
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Bleeding shouldn't be necessary if you have no leaks. If you have leaks, then it seems like it'd make sense to fix the leaks instead of just constantly bleeding brakes. I've got way more miles on one bike with hydraulic brakes than you do with two bikes combined and I've not yet had any need to bleed my brakes. Nor do I worry about not having done so.
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Originally Posted by Iride01
(Post 22601706)
Bleeding shouldn't be necessary if you have no leaks. If you have leaks, then it seems like it'd make sense to fix the leaks instead of just constantly bleeding brakes. I've got way more miles on one bike with hydraulic brakes than you do with two bikes combined and I've not yet had any need to bleed my brakes. Nor do I worry about not having done so.
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Originally Posted by jimc101
(Post 22601694)
What is a Shimano 400 series brake? do you mean an MT400 or GRX400? you really need to be specific for questions like this as there will be different processes for each type. Same for the Tektro, best to ID exactly what you have, not just the brand name
Interesting that I got one reply saying change at intervals, another saying ride them as long as they perform well. I lean towards the latter. I was really interested in a universal procedure. Would it work to 1) screw funnel into port on hood 2) remove caliper and let it hang with bleeder at bottom 3) fill a syringe with new fluid and pump it into open bleeder to displace old fluid 4) Close bleeder, plug and remove funnel and reinsert plug on hood? |
Originally Posted by Chuckles1
(Post 22602876)
BR400 Shimano brakes on gravel bike; no model numbers that I can find on the Tektros on the hybrid ebike.
Interesting that I got one reply saying change at intervals, another saying ride them as long as they perform well. I lean towards the latter. I was really interested in a universal procedure. Would it work to 1) screw funnel into port on hood 2) remove caliper and let it hang with bleeder at bottom 3) fill a syringe with new fluid and pump it into open bleeder to displace old fluid 4) Close bleeder, plug and remove funnel and reinsert plug on hood? |
Originally Posted by Chuckles1
(Post 22602876)
BR400 Shimano brakes on gravel bike; no model numbers that I can find on the Tektros on the hybrid ebike.
Interesting that I got one reply saying change at intervals, another saying ride them as long as they perform well. I lean towards the latter. I was really interested in a universal procedure. Would it work to 1) screw funnel into port on hood 2) remove caliper and let it hang with bleeder at bottom 3) fill a syringe with new fluid and pump it into open bleeder to displace old fluid 4) Close bleeder, plug and remove funnel and reinsert plug on hood? While Shimano's mineral-oil based brake fluid isn't hygroscopic like automotive brake fluid, it still picks up contaminants (dirt, etc . . . ) that work their way past the system's seals. Over time, these can further damage the seals and other internal components of the system. This can lead to premature wear-out - or even sudden failure if a hose or caliper seal pops due to sudden high pressure (think sudden heavy braking). These recommendations from Shimano might be worth your time to read. https://bike.shimano.com/en-US/infor...sc-brakes.html https://bike.shimano.com/en-US/infor...ke-fluids.html Tektro disc brakes also appear to use mineral oil based brake fluid. Dunno if theirs and Shimano's are compatible or not. But you might find the answer here: https://www.tektro.com/faq.php |
Originally Posted by cxwrench
(Post 22602070)
Bleeding is definitely necessary at certain intervals as the fluid (whatever it is) will get contaminated and/or absorb water. Contamination and moisture will both lower boiling temperature, sometimes dangerously. For people that do a reasonable amount of mileage or ride a lot of hills I'd recommend once a year. To put this in perspective when I raced motorcycles I bled the brakes every time the bike was on the track. That's obviously extreme, but they are your brakes.
And if there are no leaks, how will moisture get in? |
DOT fluid is much more hygroscopic [sic] than is mineral oil, so if you had that, I would definitely have said flush it once a year.
It won't hurt to bleed mineral oil brakes yearly, but there isn't the same imperative as there is for DOT fluid. Full disclosure: CXWrench is a pro mechanic. I am not anywhere close. |
Originally Posted by Iride01
(Post 22603215)
IAnd if there are no leaks, how will moisture get in?
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Well all my motor vehicles use DOT brake fluid of some flavor. Use to be mostly DOT 3. Nasty stuff and AFAIK, very hygroscopic. It loved moisture. However in my vehicles, it never was a problem. Perhaps if I bled them annually to change the fluid I might have save myself the replacement of a set of calipers. But one set of calipers in 50 years and a dozen vehicles it seems like I will have paid more money on fluid changes than I did for just changing out the brake calipers after they stuck.
Do you get your brakes bled regularly on your motor vehicles? There's more to go wrong on them with their steel brake lines that do rust on the inside from moisture than the plastic hoses on my bike. Just keep your wiper seals clean and un-crudded on the piston and you'll keep out a lot of any imagined dirt getting in the system. I'm not going to fault you if you wish to change your fluid often. However don't tell me that it's necessary. While it might be preventive maintenance, what are you really preventing? |
Originally Posted by Polaris OBark
(Post 22603238)
DOT fluid is much more hygroscopic [sic] than is mineral oil, so if you had that, I would definitely have said flush it once a year.
It won't hurt to bleed mineral oil brakes yearly, but there isn't the same imperative as there is for DOT fluid. Full disclosure: CXWrench is a pro mechanic. I am not anywhere close. |
Originally Posted by Atlas Shrugged
(Post 22603299)
That doesn't excuse being obnoxious but does explain being ridiculously judgemental. Millions of hydraulic braking systems are not being flushed once a year or even once a decade, working just fine. That was a massive overreaction to a simple and innocent question. Other than creating work, I can't see any reason to flush a bike's hydraulic brakes yearly or even every other year.
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Originally Posted by Iride01
(Post 22603215)
I've bled a lot of brakes on motor vehicles and even aircraft. However only when it was necessary to open up the brake cylinders and allowing air to get into the system. Same for the airplanes I worked on and helped do annual inspections and other routine maintenance on. None had a requirement for regular changes of the fluid of any corporate jet, private aircraft or any motor vehicle that I worked on. Air in the lines shouldn't be there if there are no leaks and it was properly bled before.
And if there are no leaks, how will moisture get in? I'm also reasonably certain that every major auto manufacturer has had a recommended brake fluid change interval of 2 or 3 years since the 1980s. Reason? Brake fluid absorbs water from the air. And that is not a good thing for either brake system longevity or brake performance.. Since needing to have a brake system redone on a 5 y/o vehicle some decades ago, I have indeed had brake fluid changed regularly - every 2 or 3 years. And I've not had to have much if any brake work other than new pads since. |
My rule of thumb is fluid replacement every year or two.
It doesn't take long, is inexpensive and your brakes feel great. |
Originally Posted by Chuckles1
(Post 22602876)
Interesting that I got one reply saying change at intervals, another saying ride them as long as they perform well. I lean towards the latter.
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Originally Posted by Hondo6
(Post 22603477)
Since needing to have a brake system redone on a 5 y/o vehicle some decades ago, I have indeed had brake fluid changed regularly - every 2 or 3 years. And I've not had to have much if any brake work other than new pads since.
I might be more green than you since I'm not using as much oil! |
How you do it in 30 min?
Originally Posted by Badger6
(Post 22603941)
Replacing fluid is quite easy on Shimano systems, and takes all of 30 minutes if you take 5 minutes to set up the work area in advance. It's time well spent.
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Originally Posted by Chuckles1
(Post 22604121)
Was really hoping for some experienced mechanic or amateur to summarize HOW they do it in 30 minutes. Videos I've seen use various approaches, and all seem quirky. I doubt cxwrench or other experienced bike mechanics follow model specific instructions after they've done hundreds of bleeds/fluid changes on various models of brakes. Why isn't there a simple method that just varies slightly on different models, and if there is, what are the essential steps?
https://si.shimano.com/ And Park Tool usually has pretty good information and videos that can be trusted. Though I haven't watched theirs on hydraulic brakes https://www.parktool.com/en-us/blog/...a%5B%5D=153809 Don't overthink it. Hydraulic brakes are more simple than many want to make them out to be. Regardless of any of my discussion here for whether it's needed on a regular basis, perhaps you should just do bleed your brakes a few times so you'll know what to do when actually needed. Though if your DIY experience involves frequent missteps and having to do things several times to get stuff working again, maybe that's a bad idea. |
Originally Posted by Chuckles1
(Post 22604121)
Was really hoping for some experienced mechanic or amateur to summarize HOW they do it in 30 minutes. Videos I've seen use various approaches, and all seem quirky. I doubt cxwrench or other experienced bike mechanics follow model specific instructions after they've done hundreds of bleeds/fluid changes on various models of brakes. Why isn't there a simple method that just varies slightly on different models, and if there is, what are the essential steps?
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I think the reason there is so much apprehension regarding brake bleeding is due to the fact that a majority of us just began riding bikes with disc brakes. Although we may be proficient in other bicycle repairs we all get a little nervous when doing something for the first time. At least I know that's how I am. I may require a bit of "hand holding" to get me through it the first time. After that I'm good.
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Originally Posted by cxwrench
(Post 22604267)
I'll pull a little vacuum at the caliper to make sure there isn't any air and then push fluid up to the lever.
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Originally Posted by Chuckles1
(Post 22605279)
So new fluid goes into the bleeder on caliper, which makes sense. I think a lot of folks add new fluid into cup and let it run out bleeder by gravity, as my instructions say to do. I like your bottom up approach, and will try it when it gets too cold to ride in the Fall.
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