Caliper Pistons

L

Livewir3

Well-known member
Hey Guys,

In the process of changing out front brake pads and then flushing the fluid. I noticed that upon pressing the front brake lever, not all pistons move. Some move after a few pumps. Is this normal? I don't think so but thought i'd ask as this is my first brake job :). Also with the pads removed, one piston move out almost completely ( after pumping the brake lever) while the others were still in their respective places.

See pics below for reference. This was after a few presses of the front brake lever.


xnfeig.jpg


zilnar.jpg
 
Without building pressure, typically only one piston will move. This one is the least stuck one. Once it moves there is no reason for the rest to move.

Try putting something in that is stiff but compressible, (like a piece of cedar) you should see all 4 pistons make an impression on it. If you don't get 4 impressions on the wood, a piston may be stuck.
 
The piston(s) that is(are) closest to the brake line will move first and the most.
 
I won't move the pistons too much. When you do, you're sliding them over dirt & grime. Might cause a leak
 
RockerGuy said:
I won't move the pistons too much. When you do, you're sliding them over dirt & grime. Might cause a leak
Click to expand...

I did not realize they actually come out :)
Made this mistake on one side but managed to get it back in.

I guess taking them out and cleaning them is not the way to go.
 
If you popped them out, most likely you've introduced air & grime into it
 
That piston that's sticking out in the pic is FILTHY!! You should clean all the pistons before shoving them back into the seals.
 
I agree. The pistons were filthy. They were all cleaned but now i face another issue. Before the brake and fluid change i could use one finger to bring me to a stop. But now the lever has to travel further in. And because of this i can no longer have the remaining fingers on the clip on. I need to use all fingers to brake. The bike stops fine and i can feel the difference already.

I bled the system twice..there was air initially. I left the lever compressed overnight to remove if any air that could have been in the system. It does feel better but i have to ride to really tell.

Anything else i should look at?

One more thing, the shop sold me dot
5 brake fluid. On the reservoir cap it says dot 4. Any issues mixing the two? Could this be my problem?
 
Livewir3 said:
One more thing, the shop sold me dot
5 brake fluid. On the reservoir cap it says dot 4. Any issues mixing the two? Could this be my problem?
Click to expand...

Entirely different chemistry. Unless they have changed something recently, they shouldn't be mixed. DOT 5 can eat seals too if they aren't designed for it. I would flush ASAP with DOT 4.
 
GreyGhost said:
Entirely different chemistry. ..... I would flush ASAP with DOT 4.
Click to expand...

x2. Unless it's 5.1.

Which shop sold you the DOT5 and did they not tell you that you couldn't mix it with anything else?
 
Livewir3 said:
My apologies. It's Motul 5.1 :)
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Than it is ok to mix them.

You said you left the Lever compressed over night? Did you zip tie it and then the next morning release the lever slowly?

I always found this worked wonders for me.
 
slowbird said:
Than it is ok to mix them.

You said you left the Lever compressed over night? Did you zip tie it and then the next morning release the lever slowly?

I always found this worked wonders for me.
Click to expand...

That is exactly what i did. It does feel better but i have to ride the bike to really tell. If it works for you then hopefully it will work for me too.
 
Livewir3 said:
That is exactly what i did. It does feel better but i have to ride the bike to really tell. If it works for you then hopefully it will work for me too.
Click to expand...

Keep at it. Your original issue with the excessive lever travel sounds like there's still a bit of air in the system.
 
I have had similar issues twice before where after the brakes are flushed, the lever is "softer" meaning requires more travel compared to stopping and biting with less travel prior. Even after taking to shop to 2 different shops to have them make sure no air was on the lines,

I have s theory in it not sure if it's valid but let's see what others think..
I am guessing with the new cleaner brake fluid and the Pistons are moving back off the rotor a little more when not engaged , thus requiring a bit more travel???

On a positive note and this is up for debate and preference, I have found a lever that requires more travel to be more forgiving in a hard panic braking situation,, it gives you a split second longer to get out of the "grabbing a **** load of brakesL situation in an emerge stop.
 
Livewir3 said:
I agree. The pistons were filthy. They were all cleaned but now i face another issue. Before the brake and fluid change i could use one finger to bring me to a stop. But now the lever has to travel further in. And because of this i can no longer have the remaining fingers on the clip on. I need to use all fingers to brake. The bike stops fine and i can feel the difference already.

I bled the system twice..there was air initially. I left the lever compressed overnight to remove if any air that could have been in the system. It does feel better but i have to ride to really tell.

Anything else i should look at?

One more thing, the shop sold me dot
5 brake fluid. On the reservoir cap it says dot 4. Any issues mixing the two? Could this be my problem?
Click to expand...

Did you push the pistons in before or after cleaning them? Did you remove them from the caliper?

The extra lever travel sounds like there's still air in the system. Does the master have a bleed nipple? When you said you bled the system twice does that mean two resivours of fluid?

Nothing wrong with that fluid (Motul 5.1).
 
dricked said:
Did you push the pistons in before or after cleaning them? Did you remove them from the caliper?

The extra lever travel sounds like there's still air in the system. Does the master have a bleed nipple? When you said you bled the system twice does that mean two resivours of fluid?



Nothing wrong with that fluid (Motul 5.1).
Click to expand...

Yes all pistons were pushed back in. One piston popped out (stupidity on my part) but i was able to push it back in.

Yes, about two reservoirs of fluid. There is no bleed nipple on the master cylinder.

Should i ride it when i get a chance to see if they just need to settle in? Or should i bleed the system again?
 
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