Chuckles1

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.

Polaris OBark

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:

jimc101

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

Iride01 

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.

cxwrench

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.

Chuckles1

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?

cxwrench

How will you discover they don't work? Most likely when you try to use them on the road. This is why we have service intervals for cars and motorcycles, so you maintain these systems and they always work properly. Would you run your car til the engine blows up then change the oil? Along with rebuilding the engine? I can't understand why people are too lazy to maintain things, especially important things like brakes.

Hondo6

cxwrench can be a bit brusque, but he has a point regarding your brake fluid requiring periodic changes.

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

Iride01 

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?

Polaris OBark

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.

Polaris OBark

The same way dirt can get in. Through the piston seals. This is a bigger issue for DOT fluid-based braking systems. Dirty fluid is a good proxy for evaluating water contamination for this reason.

Iride01 

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?

Atlas Shrugged

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.

cxwrench

Obnoxious rant: You don't know what you don't know. Ever seen the once red Shimano mineral oil that comes out of a brake after a year or so of use? Probably not. Ever had a brake get really soft on a long downhill because there was moisture in the DOT fluid which turned into air bubbles because the boiling point went down a couple hundred degrees due to the water? All you guys that pretend to know so much have so little experience it's beyond laughable. If you'd just stay in your damn lane and understand the limits of your knowledge we'd all be a lot better off. I wouldn't be a **** and you might learn something. End obnoxious rant.

Hondo6

Can't speak for aircraft brake systems, but every auto brake system I've ever owned had a brake fluid reservoir with a cap to allow for the owner to add brake fluid. These are never 100% airtight. Neither are cylinder or caliper seals.

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.

Kai Winters

My rule of thumb is fluid replacement every year or two.
It doesn't take long, is inexpensive and your brakes feel great.

Badger6

Intervals. Sudden loss of braking is quite rare, but catastrophic when it happens. I realize that brakes only slow you down...but, the thing is, most experienced riders slow only when they need to slow, so it stands to reason that you want them to slow you when you apply them. 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. That said, I ride between 16-20k kms per year, across 3 bikes. I go through 1-2 sets of pads per year (winter is gnarly on them), and do a fluid replacement/system bleed whenever I swap the pads.

Iride01 

Sounds about like my experience. However I don't change brake fluid and all I do is change pads when needed.

I might be more green than you since I'm not using as much oil!

Chuckles1

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?

Iride01 

Have you looked at the Shimano manuals for your brakes? They give everything needed to know how to do it. The DM's are what you want to read.

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.

cxwrench

I follow each manufacturer's instructions, but they're fairly similar. I can't see a normal bleed taking any more than 10-15mins. For Shimano you have the cup at the lever and the syringe at the caliper. 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. If it's not been bleed for a while this will usually come out dark grey. When fresh fluid starts coming up into the cup I close off the caliper and remove the syringe. I'll dump the old fluid from the cup and put a little new fluid in and 'burp' the lever. I always get some more air out this way. I'll rotate the bike in the stand to change the angle of the lever. A minute or 2 of this and it's done. SRAM is similar but uses a syringe at both ends. This is not hard and should only take a few minutes. If you're spending 30mins or an hour to bleed a single brake you're doing it wrong.

Badger6

TBF, cxwrench my 30 minute estimate was both ends. Chuckles1 follow that general instruction, it'll get it done every time.

TakingMyTime

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.

Chuckles1

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.

cxwrench

You can do the top down method too, or you can pump fluid from the lever out the caliper, both work. I'd always finish w/ 'burping' the lever with just the cup attached.