Magura Piston Question

[aj2four0]

I broke the little nub that holds the brake pad on one of my hs-33 pistons. I have a few spare pistons laying around, so i grabbed one and tossed it on. Bled etc. And my lever pull is significantly longer than before. After a fresh bleed w/ no tpa adjustment the pull is far to close to the bar for my liking. If i move the pistons any closer to the rim they rub.

My real question is, are all magura pistons the same? or do some have a larger internal diameter or something to that affect. The piston i used was dark gray in color. Much darker than the silver hs-33 pistons. Almost like a gun-metal color. (I got these used so i have no idea what they came from.)

Let me know if you have any ideas. Thanks.

[Simonk]

if the two pistons were different diameteres i have a feeling that one would move much further than the other.

[pav]

2005 model HS33's have same diametre pistons, 2004 have different diametre. Look on the piston it should say something like M6 or M8 or 6/6 or 6/8, something along those lines to help you work out which piston it is, have a look around till you find the right one, if not try bleed it as best as you can or something.

[greyghost]

As long as they are in the same position with respect to the piston housing, one pad will not hit the rim faster than the other, 'cause hydraulic pressure will distribute equally.

[Simonk]

If one of the pistons has a higher area, the same pressure will exhert a stronger force on the pad housing for that piston (force=pressure x area). Since the pads are pushed back by springs (as far as i'm aware) a stronger force would mean that the it would retract further than the smaller cylinder.
Also when you actually squeezed hard on the lever one pad would push stronger than the other pad and it would probably push the rim to one side.

[greyghost]

If one of the pistons has a higher area, the same pressure will exhert a stronger force on the pad housing for that piston (force=pressure x area). Since the pads are pushed back by springs (as far as i'm aware) a stronger force would mean that the it would retract further than the smaller cylinder.
Also when you actually squeezed hard on the lever one pad would push stronger than the other pad and it would probably push the rim to one side.
No. I've never ripped apart some Maguras, but if it was a spring that pushed it, it wouldn't make any difference at all, because the area of the piston would have nothing to do with it, as long as it was the same length, so as not to affect the spring.

[Simonk]

maybe this diagram will confuse you

[pav]

F2 has to be greater than F1 because the oil flows through F1 first then F2. It most likely would not distribute the oil and force evenly. And when you squeeze your brakes hard it does push the rim to once side. loosen out cones and you can really see this. There is a spring in the lever that retracts the lever becuase it pushes out on the piston. Pushing out on the piston would retract the pads because it owuld create a vaccume otherwise and all that bullshit.
SimonK is too smart is my conclusion.

[felix]

Both slave piston have the same diameter!

[smudge]

Yup, they're both the same diameter.

In reference to pressure equalization being the answer...:rolleyes:

Aren't theories great? The thing about them is that they make everything seem so clear right? But it's so easy to overlook other underlying factors such as friction around the piston seal, or the I.D. of a barbed outlet going to one side of the slaves. While it may seem obvious that pressure equalization would move both pistons at the same time, it's just not true due to other circumstances.

[aj2four0]

my wheel does shift slightly away from the replaced cylinder, but the frame also flexes, so i cant tell what the movement is caused by. there is slight movement in the other piston away from the wheel as well, ill play w/ it more today and give more details.

im an me major, i understand the fluid dynamics of the system, i was really hoping someone could tell me if magura made pistons w/ diff internal diameters. cool diagram btw :)

[aj2four0]

2005 model HS33's have same diametre pistons, 2004 have different diametre. Look on the piston it should say something like M6 or M8 or 6/6 or 6/8, something along those lines to help you work out which piston it is, have a look around till you find the right one, if not try bleed it as best as you can or something.

sorry, missed this, im reading and typing on my pda in heat transfer class... im such a bad student... *sigh

ill check for numbers :)
i know all the pistons are older.. at least pre 2002 probably more like 99.

[aj2four0]

the light grey (newer ones) say 00 on them ('im guessing from 2000) and the dark grey one (the one i just installed) says 95 (so i'm guessing its from 1995) ;).. anyone know if the pistons charged over these years?

these are the only numbers i can find on the pistons to differentiate them from the other.

[felix]

the light grey (newer ones) say 00 on them ('im guessing from 2000) and the dark grey one (the one i just installed) says 95 (so i'm guessing its from 1995) ;).. anyone know if the pistons charged over these years?

these are the only numbers i can find on the pistons to differentiate them from the other.

The slave pistons are the same on all Maguras and weren't changed in the last years; the only difference is the master piston/lever.

[rush]

OMFG nerds.


Put the brake on and pull it to stop.

[aj2four0]

The slave pistons are the same on all Maguras and weren't changed in the last years; the only difference is the master piston/lever.

thanks!

[Simonk]

Yup, they're both the same diameter.

In reference to pressure equalization being the answer...:rolleyes:

Aren't theories great? The thing about them is that they make everything seem so clear right? But it's so easy to overlook other underlying factors such as friction around the piston seal, or the I.D. of a barbed outlet going to one side of the slaves. While it may seem obvious that pressure equalization would move both pistons at the same time, it's just not true due to other circumstances.
As a matter of fact thories can explain just about everything, the problems arise if the people making them fail to use them correctly or dont take everything into account.
The internal diameter of a barb should make absolutely no difference, friction would make one of the pads lag a bit. As long as you actually know how the whole thing works you should be able to explain it all.