Mountain Bike Reviews Forum banner
1 - 19 of 19 Posts

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #1 ·
I was replacing the brake pads on my SLXM675 hydraulic brakes. Prior to this they were bled out perfectly with no squish and a rock solid lever on each side. I screwed up and compress the calipers without opening the bleeder valve. I knew better but for some reason I opted against better judgment. The right side did not leak that I could see but the left side squirted some out the lever cap gasket. And now that all is said and done the left side, the side that leaked out, is rock solid and works great. I assumed the rubber seal on the cap bypassed and I got safe. The rear brake, however, is full of squish and when I went to bleed it out I got a couple air bubbles out of it that I know weren't there before. Now I can't seem to bleed it out. It does not appear to be leaking anywhere but something obviously happened and I wonder if I didn't take out a seal and it may be sucking air or something? Has anyone ever done this and found out that they damaged the lever? I already know from Shimano that you cannot rebuild this stuff and when it goes you throw it away and buy new ones. I am so frustrated I am about ready to put my BB7's back on and just cut my losses
 

·
Registered
Joined
·
1,380 Posts
There is no reason to open the hydraulic system to replace pads. It sounds like you still have air in your rear brakes and need to bleed them properly. If you hadn't opened them, they would be fine.
 

·
Guest
Joined
·
1,040 Posts
This is one of the first things I managed to do. (It is also not a competely insane way to clean/flush the seals if you are having piston retraction issues). Anyway, put the old pads back in, stick a screwdriver between them, and press the pistons flush with the calipers. Then you can probably get away with a partial bleed. Just attach the syringe or funnel to the lever, put in some more brake fluid, and go through the air bubble purging ritual. It should only take a few minutes. If it makes you feel any better, this happened to me 4 or 5 years ago, and the calipers (Ultegra, which are essentially relabled XT calipers) have been absolutely fine and trouble-free since. It is extremely unlikely you damaged anything.
 

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #4 ·
That is good to know. I have tried to re bleed with no luck. I know how to properly bleed the brakes and this I just can't seem to solve. It feels like something is bypassing. I did the same thing. I.put old pads in and use a screwdriver to push both pistons back in. I can still lock up the rear brake on pavement. I mean the lever is there but if I keep.pressure applied it slowly goes down. Just spongy as if air is in it but I can't seem to get any more air out. And I do rotate the lever up on bar so bleed screw is at its highest point.
 

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #6 ·
This is my favorite Shimano bleed method:

Thank you for sharing that. I actually did that method except I didn't take the caliper loose and swish it back and forth but I opened the bleeder and let the fluid run through it. When I was working in auto shops we just called that gravity bleeding lol.
 

·
Registered
Joined
·
2,634 Posts
What do you mean by left and right? Sort of irrelevant but I'm curious.

I'd say to just keep bleeding. Just because you didn't think there was air there before doesn't mean it didn't exist. It may have been a trapped bubble that you dislodged when pushing the pistons in.

The way I bleed Shimano brakes is similar to an auto. Pump lever, hold, open bleeder, close bleeder, release lever. I'd probably suggest doing that through one of the bleed cups and see what happens. Once a year, or if I haves issues, I'll just perform the lever bleed by plopping the cup on the master cylinder and operating the lever until bubbles go away.

I think that since you did push fluid out of the master cylinder, you're fearful that the air bubble is a result when it's hard to prove that to be true.
It's cheap to bleed -see what happens. If that doesn't do the trick then maybe dig deeper.

Unless one of the few experts can suggest something that could be damaged and is sucking air.
 

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #8 ·
What do you mean by left and right? Sort of irrelevant but I'm curious.

I'd say to just keep bleeding. Just because you didn't think there was air there before doesn't mean it didn't exist. It may have been a trapped bubble that you dislodged when pushing the pistons in.

The way I bleed Shimano brakes is similar to an auto. Pump lever, hold, open bleeder, close bleeder, release lever. I'd probably suggest doing that through one of the bleed cups and see what happens. Once a year, or if I haves issues, I'll just perform the lever bleed by plopping the cup on the master cylinder and operating the lever until bubbles go away.

I think that since you did push fluid out of the master cylinder, you're fearful that the air bubble is a result when it's hard to prove that to be true.
It's cheap to bleed -see what happens. If that doesn't do the trick then maybe dig deeper.

Unless one of the few experts can suggest something that could be damaged and is sucking air.
Left and right meaning left lever which is my front brake and right lever which is my rear brake. I forced fluid out of the left lever when I compress the front caliper piston. I did not force fluid out of the rear brake when I did it the same way but it is the rear brake that is giving me problems now. I have tried gravity bleeding with my cup screwed into the bleed port and mineral oil in it, I have tried opening the bleeder and pushing the lever to the handlebars and closing the bleeder (a more traditional bleed method), and I have tried screwing my cup into the bleed port with mineral oil in it and pumping the lever to let air bubbles come out the top of which I can't get any. 3 different styles of bleeding and the only thing I have to try now is to remove the caliper and let it hang down while I'm gravity bleeding and see if I can get any air out that way.

My background is in automobiles and in a car a master cylinder is never filled all the way to the top so you have air space for the fluid to compress into especially when the brake pads are worn which means the level is even lower yet. But on a bike they're filled all the way to the top with no air space so when you compress the caliper that fluid has to go somewhere.
 

·
psycho cyclo addict
Joined
·
3,201 Posts
Left and right meaning left lever which is my front brake and right lever which is my rear brake. <snip>

My background is in automobiles and in a car a master cylinder is never filled all the way to the top so you have air space for the fluid to compress into especially when the brake pads are worn which means the level is even lower yet. But on a bike they're filled all the way to the top with no air space so when you compress the caliper that fluid has to go somewhere.
The brake handle side of the system contains a small device similar to a "master cylinder" that compensates for heat, brake wear, etc. so that there is sufficient fluid to apply braking consistently.

I suggest you have someone familiar with bleeding bicycle brakes assist you so you can learn how to do it properly. Improperly bled brakes can fail at any time and "do it yourself" concussion, tooth loss or worse is not advisable...
 

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #10 ·
I gravity bled this morning with my caliper hanging free at the rear wheel, pads removed. I probably ran around 2-3 ounces through. I rocked the caliper back and forth to try and dislodge any air. None came out. I sealed, cleaned, reinstalled pads, then to the rotor, repositioned brake lever to its normal position on the bars and gave her a try. Same. If I apply enough pressure to throw me over the bars or lock the rear tire on pavement it feels pretty firm. I have more than half a lever when I grab hold. But I can squeeze harder and get the lever to "sponge" closer to the bars and that doesn't feel normal. So again moderate pressure (enough to lock them up and then some) feels good but bear down and you get the sponge. The front feels more solid. That said I can't get the lever to bleed down with the moderate pressure applied. It will hold steady and not sink. I got a set of mountain BB7's with less than 200 miles on them and I may just switch them and say to heck with it for peace of mind. They work nice. I just had these hydros on another bike that doesn't get ridden so I thought I would use them when I switched from drops to Jones bars.

I'm on the fence about whether what I am feeling is even anything not normal. I suppose anyone with a strong grip could squeeze hard enough and bend something. Maybe I am overthinking it and my mind is playing games on me since I forced some fluid out and now I am looking for a problem that doesn't exist. Wouldn't be the first time. I am overly anal normally

This is the same caliper/lever setup that i mentioned in another thread had more travel before engagement than the front brake caliper did. At that time it felt solid but just had considerable more free travel than the front lever had. 1/4 lever travel compared to 1/2 lever travel on the rear. The rear caliper appeared to be retracting more after release or something.
 

·
Registered
Joined
·
200 Posts
Are you absolutely sure they weren't like that before? The rear brake has much more hose to flex under pressure, so some amount of sponginess compared to the front is to be expected.

Sent from my Pixel 2 using Tapatalk
 

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #12 ·
Are you absolutely sure they weren't like that before? The rear brake has much more hose to flex under pressure, so some amount of sponginess compared to the front is to be expected.

Sent from my Pixel 2 using Tapatalk
exactly! That's what I am wondering. You know how something unexpected can happen and you start looking for a problem that isn't even there? That's what I am thinking.
 

·
Registered
Joined
·
2,634 Posts
Left and right meaning left lever which is my front brake and right lever which is my rear brake. I forced fluid out of the left lever when I compress the front caliper piston. I did not force fluid out of the rear brake when I did it the same way but it is the rear brake that is giving me problems now. I have tried gravity bleeding with my cup screwed into the bleed port and mineral oil in it, I have tried opening the bleeder and pushing the lever to the handlebars and closing the bleeder (a more traditional bleed method), and I have tried screwing my cup into the bleed port with mineral oil in it and pumping the lever to let air bubbles come out the top of which I can't get any. 3 different styles of bleeding and the only thing I have to try now is to remove the caliper and let it hang down while I'm gravity bleeding and see if I can get any air out that way.

My background is in automobiles and in a car a master cylinder is never filled all the way to the top so you have air space for the fluid to compress into especially when the brake pads are worn which means the level is even lower yet. But on a bike they're filled all the way to the top with no air space so when you compress the caliper that fluid has to go somewhere.
Thanks for clarifying. I wasn't sure if you were referring to the left piston and right piston at the caliper.
 

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #14 ·
Well I found the problem and yes there is a problem. If you apply pressure and leave it for several minutes (a velcro strap assists this) you can see mineral oil leaking out the front corner of the cap (the silver part with "SLX" printed on it). It's got a leak. I disassembled and inspected it and the seal looks intact but it sure wants to "seep" with constant pressure applied. Granted I will never be in a situation where I hold hard brake pressure for 10 minutes or more but still.......it's a leak and that's not good. It's a leak that wasn't there before I compressed the calipers and given that is where the front brake lever blew fluid out I am sure I did the same on the rear lever and just never noticed it at the time. Any way it is what it is i guess.
 

·
Registered
Joined
·
1,380 Posts
Well I found the problem and yes there is a problem. If you apply pressure and leave it for several minutes (a velcro strap assists this) you can see mineral oil leaking out the front corner of the cap (the silver part with "SLX" printed on it). It's got a leak. I disassembled and inspected it and the seal looks intact but it sure wants to "seep" with constant pressure applied. Granted I will never be in a situation where I hold hard brake pressure for 10 minutes or more but still.......it's a leak and that's not good. It's a leak that wasn't there before I compressed the calipers and given that is where the front brake lever blew fluid out I am sure I did the same on the rear lever and just never noticed it at the time. Any way it is what it is i guess.
And anywhere there is a leak of fluid out, it's replaced with air. At least now you know what to fix to make it go away.
 

·
Registered
Joined
·
1,611 Posts
Discussion Starter · #16 ·
And anywhere there is a leak of fluid out, it's replaced with air. At least now you know what to fix to make it go away.
Yes I'm aware of that. :)
Unfortunately from things I have read online as well as what Shimano told me on the phone the other day was that they do not make rebuild kits for these things. So I'm under the impression that when something finally happens that involves a faulty seal or O ring all you can do is throw them away. It boggles my mind why they would not make a rebuild kit or a seal kit for this stuff.
 

·
Guest
Joined
·
1,040 Posts
That is good to know. I have tried to re bleed with no luck. I know how to properly bleed the brakes and this I just can't seem to solve. It feels like something is bypassing. I did the same thing. I.put old pads in and use a screwdriver to push both pistons back in. I can still lock up the rear brake on pavement. I mean the lever is there but if I keep.pressure applied it slowly goes down. Just spongy as if air is in it but I can't seem to get any more air out. And I do rotate the lever up on bar so bleed screw is at its highest point.
Then something is leaking. That is the classic symptom. Might be worth taking it to a bike shop and paying to make it someone else's headache.

Edit: Sorry, posted this before I read your post # 14.
 
1 - 19 of 19 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top