another rear master cylinder question
Tourer
Joined: Apr 2010
Posts: 293
Likes: 7
So, what actually happens is.........
There are indeed 2 holes.
a small one that feeds and returns brake fluid to and from the caliper side of the brake "cup", and a larger one that allows fluid to move back and forward between the reservoir and the area between the back of the cup(effectively), and the o-ring that seals the piston from the outside.
When you initially press the brake pedal, there is no pressure build up at all, as the the cup has yet to pass over the small hole, and fluid, at this stage, is merely returned back to the reservoir(which can commonly be seen in the form of a small jet if you have the lid of the master cyl, as the smallness of the feed hole causes some pressure (volume over area), whereas the larger hole tends not to cause such a disturbance, though some turbulence may still be visible).
As the cup passes over the hole, pressure begins to rise in what has now become a closed system between the cup and the brake caliper piston, and accordingly the brake is applied. On modern systems(meaning many many years now, so not really all that modern) a quad type caliper piston seal is commonly used. This is located in a machined recess in the caliper. The recess has a relief(or chamfer) machined into it, so that there can be some deformation of the seal when the piston moves, and that when pressure is released(via the brake pedal being released, the internal spring pushing the cup and m/cyl piston back, the little hole becoming uncovered again, and the fluid being free to equalise in pressure with the atmospheric pressure of the m/cyl reservoir) the seal returns to its quad shape, and draws the caliper piston back with it, thereby preventing the pads from rubbing on the rotor.
As pads wear, the caliper piston makes it way through the quad seal, brake fluid drops in the m/cyl reservoir, and the lid diaphragm flexes to prevent a vacuum from occurring. All self adjusting up to a point.
If you have absolutely nothing connected to the m/cyl, then it will not pressurise, and fluid will not come spurting out when the pedal is depressed. You would have to hold your finger over the end, bleed the m/cyl until you have it pressurised, and then you could get fluid trying to force it's way past your finger. If you take you finger off, the pressure will almost certainly be lost immediately.
Hope the truth helps.
There are indeed 2 holes.
a small one that feeds and returns brake fluid to and from the caliper side of the brake "cup", and a larger one that allows fluid to move back and forward between the reservoir and the area between the back of the cup(effectively), and the o-ring that seals the piston from the outside.
When you initially press the brake pedal, there is no pressure build up at all, as the the cup has yet to pass over the small hole, and fluid, at this stage, is merely returned back to the reservoir(which can commonly be seen in the form of a small jet if you have the lid of the master cyl, as the smallness of the feed hole causes some pressure (volume over area), whereas the larger hole tends not to cause such a disturbance, though some turbulence may still be visible).
As the cup passes over the hole, pressure begins to rise in what has now become a closed system between the cup and the brake caliper piston, and accordingly the brake is applied. On modern systems(meaning many many years now, so not really all that modern) a quad type caliper piston seal is commonly used. This is located in a machined recess in the caliper. The recess has a relief(or chamfer) machined into it, so that there can be some deformation of the seal when the piston moves, and that when pressure is released(via the brake pedal being released, the internal spring pushing the cup and m/cyl piston back, the little hole becoming uncovered again, and the fluid being free to equalise in pressure with the atmospheric pressure of the m/cyl reservoir) the seal returns to its quad shape, and draws the caliper piston back with it, thereby preventing the pads from rubbing on the rotor.
As pads wear, the caliper piston makes it way through the quad seal, brake fluid drops in the m/cyl reservoir, and the lid diaphragm flexes to prevent a vacuum from occurring. All self adjusting up to a point.
If you have absolutely nothing connected to the m/cyl, then it will not pressurise, and fluid will not come spurting out when the pedal is depressed. You would have to hold your finger over the end, bleed the m/cyl until you have it pressurised, and then you could get fluid trying to force it's way past your finger. If you take you finger off, the pressure will almost certainly be lost immediately.
Hope the truth helps.
My provision of an accurate description of the workings of the brake system, correcting a very errant previous post, was not meaningful to you?
It should be. In fact, seeing as you claim you never need any help, why didn't you help the original poster, by offering a correction.
Do you not want the OP to know the truth, or are you happy for him to be fed incorrect info?
I want him to know the truth.
Thread Starter
|
Seasoned HDF Member
Joined: Mar 2008
Posts: 5,134
Likes: 146
From: texas
irongear---when i said im probably gonna regret this i meant getting further into this nonsense.....but i think if i dont it will continue...and since i am the original poster i will try and end this here.
about using syringes----bike shops uses them.certified harley mechanics uses them.there procedures to use them in mechanics books such as haynes/clymers etc. to come here and put someone down for using one is absurd.if you dont like them then voice your opinion why...theres no need to make a big deal other than that.would you have the same attitude if you were having this conversation with someone you just met in a bar someplace?would you walk into someones house acting like that?c'mon.you know that aint right.thats essentially what you did.
ive no doubt you have alot of knowledge regarding mechanic work,but dude you came in here guns blazing for no reason.i consider everyone who replied to my post/plus others on this site to be my personal friends.these guys have helped me out plenty of times.especially when i first got here.....i am glad they had the helpful attitude they have.
i usually try and help people by telling them somthing that doesnt work.i generally will work on anything....bikes,autos,trucks,tractors....anythin g really.i dont consider myself a mechanic by any means.i keep plugging away til i get it sometimes.somewhere in life i learned to try and listen to people.i realized that everyone...EVERYONE...knows somthing i dont.even people i dont like can teach me somthing.somtimes its just the fact that i dont want to be like them...thats somthing.i beleive you have info i/others could learn from....but for you to ASSUME that you cant learn from everyone else here(probably everywhere else) is shortsighted on your part.
o and btw i did like your description of the master cyl. if you would have left it at that you would have been aces.
about using syringes----bike shops uses them.certified harley mechanics uses them.there procedures to use them in mechanics books such as haynes/clymers etc. to come here and put someone down for using one is absurd.if you dont like them then voice your opinion why...theres no need to make a big deal other than that.would you have the same attitude if you were having this conversation with someone you just met in a bar someplace?would you walk into someones house acting like that?c'mon.you know that aint right.thats essentially what you did.
ive no doubt you have alot of knowledge regarding mechanic work,but dude you came in here guns blazing for no reason.i consider everyone who replied to my post/plus others on this site to be my personal friends.these guys have helped me out plenty of times.especially when i first got here.....i am glad they had the helpful attitude they have.
i usually try and help people by telling them somthing that doesnt work.i generally will work on anything....bikes,autos,trucks,tractors....anythin g really.i dont consider myself a mechanic by any means.i keep plugging away til i get it sometimes.somewhere in life i learned to try and listen to people.i realized that everyone...EVERYONE...knows somthing i dont.even people i dont like can teach me somthing.somtimes its just the fact that i dont want to be like them...thats somthing.i beleive you have info i/others could learn from....but for you to ASSUME that you cant learn from everyone else here(probably everywhere else) is shortsighted on your part.
o and btw i did like your description of the master cyl. if you would have left it at that you would have been aces.
Tourer
Joined: Apr 2010
Posts: 293
Likes: 7
Hear me clearly.
I am neither for nor against any individual.
But the truth must out.
And when people post rubbish, and I can see the OP has no way of telling, I feel a bit sorry for them.
I have been very clear regarding the ills of backbleeding, and I do not care if some moron that owns 3 bent spanners and a home made shop sign uses that method.
It cannot be universally used without risk.
And it is true. Everyone knows something. But I pretty well have motorcycles covered, so it really is unlikely that I am going to read a procedure, or theory of operation, and think, I did not know that.
So I am not assuming that I cannot learn from EVERYONE here, I know for a fact that I cannot. The vast majority here really have no idea. The sad thing is a lot of them think they do. Sad because they try to instruct others from a position of total ignorance.
But no matter.
I do not have my guns blazing, not even close. Not even close to close.
Catch you in the posts.
I am neither for nor against any individual.
But the truth must out.
And when people post rubbish, and I can see the OP has no way of telling, I feel a bit sorry for them.
I have been very clear regarding the ills of backbleeding, and I do not care if some moron that owns 3 bent spanners and a home made shop sign uses that method.
It cannot be universally used without risk.
And it is true. Everyone knows something. But I pretty well have motorcycles covered, so it really is unlikely that I am going to read a procedure, or theory of operation, and think, I did not know that.
So I am not assuming that I cannot learn from EVERYONE here, I know for a fact that I cannot. The vast majority here really have no idea. The sad thing is a lot of them think they do. Sad because they try to instruct others from a position of total ignorance.
But no matter.
I do not have my guns blazing, not even close. Not even close to close.
Catch you in the posts.
Tourer
Joined: Sep 2007
Posts: 400
Likes: 1
From: se ohio
i did not respond to the original post because im not a expert in the breakdown on how to describe how this system works, i do know that i have always been able to bleed any kind of brakes with either pressure or my hand held vacuum pump, any way im over it with your attitude you will be flamed soon enough and peace will be restored! lol
Last edited by shepdog; Aug 25, 2010 at 07:03 PM.
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