Rear brake pressure
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6th Gear
Joined: Feb 2009
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Rear brake pressure
Hi guys , Just finished my 91 FXR , completely took it apart and rebuild it. I got myself a new pair of forward controls
these :
http://cgi.ebay.com/ebaymotors/Forwa...Q5fAccessories
I have a 4 piston brake caliper from Billet ...
I even bought a bleeding kit to make sure no air is in the lines.
I can't seem to build up enough pressure to get the piston push the brake pads. I see them move thou. I had to move the brake cylinder adjustment a bit "inside" the cylinder , make the movement shorter because the pedal was hitting the exhaust ...
I have no idea what's wrong , is it because the distance I can push the brakecylinder isn't deep enough (0.6 inch)
Don't see any leaks
I did notice that with the lid from the brakefluid reservoir pulling down the lever makes the fluid to burst out. probably because there's no other way out ...
There's a small hole in the lid , needed to get air inside the reservoir , however a rubber seal covering the whole surface of the reservoir has no hole , is that normal ?
I think if I had new brake pads it might be enough , but not an ideal situation offcourse ...
Any ideas whats wrong ?
thanks a lot guys
Raf
these :
I have a 4 piston brake caliper from Billet ...
I even bought a bleeding kit to make sure no air is in the lines.
I can't seem to build up enough pressure to get the piston push the brake pads. I see them move thou. I had to move the brake cylinder adjustment a bit "inside" the cylinder , make the movement shorter because the pedal was hitting the exhaust ...
I have no idea what's wrong , is it because the distance I can push the brakecylinder isn't deep enough (0.6 inch)
Don't see any leaks
I did notice that with the lid from the brakefluid reservoir pulling down the lever makes the fluid to burst out. probably because there's no other way out ...
There's a small hole in the lid , needed to get air inside the reservoir , however a rubber seal covering the whole surface of the reservoir has no hole , is that normal ?
I think if I had new brake pads it might be enough , but not an ideal situation offcourse ...
Any ideas whats wrong ?
thanks a lot guys
Raf
Road Warrior
Joined: Dec 2008
Posts: 1,476
Likes: 23
From: Summit, Mississippi
Did the new brake caliper specs. indicate what size master cylinder it required? I just have to guess here and you said everything was properly bled.....so you're master cylinder may be too small. If you cannot achieve a hard pedal and everything else is okay....could be an issue with a master cylinder too small for the caliper volume.
Find out what size MC is recommended and make sure the one you have on there now is large enough.
Find out what size MC is recommended and make sure the one you have on there now is large enough.
Thread Starter
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6th Gear
Joined: Feb 2009
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I got the billet (harrison) brakes installed when I had the original brakesystem (cylinder and reservoir seperate and near the end of the frame) , I had no problems braking ...
I just googled and saw that the stampede forward controls have a 5/8 master cylinder
No idea what a 4 piston brake caliper requires
Can this phenomena be related to the wrong size of bore ?
R
I just googled and saw that the stampede forward controls have a 5/8 master cylinder
No idea what a 4 piston brake caliper requires
Can this phenomena be related to the wrong size of bore ?
R
Road Warrior
Joined: Dec 2008
Posts: 1,476
Likes: 23
From: Summit, Mississippi
In a word...yes,...there is a relationship between the MC bore and caliper piston volume called master cylinder ratio, but all I am doing is guessing and taking your word that everything else is okay. It may be something butt-simple....but we don't know yet.
If the maker of the caliper cannot tell you, or list the volume of the caliper....if you will measure the diameter of the piston bores and tell me if they are opposed (two on one side...two on the other), I can tell you if it should work. Just take a ruler and measure "across" the opening in either inches or mm....as precisely as you can. If the pistons appear to be the same size....just measure one. I am guessing like 28mm, or 30mm.
What happens when you pump the pedal....do you ever get any seriously hard pedal?
What fluid do you have in there 4 or 5.
If you can't do anything but get me the measurement as described above...I can do the math and tell you there-is-or-is-not a problem there.
If the maker of the caliper cannot tell you, or list the volume of the caliper....if you will measure the diameter of the piston bores and tell me if they are opposed (two on one side...two on the other), I can tell you if it should work. Just take a ruler and measure "across" the opening in either inches or mm....as precisely as you can. If the pistons appear to be the same size....just measure one. I am guessing like 28mm, or 30mm.
What happens when you pump the pedal....do you ever get any seriously hard pedal?
What fluid do you have in there 4 or 5.
If you can't do anything but get me the measurement as described above...I can do the math and tell you there-is-or-is-not a problem there.
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6th Gear
Joined: Feb 2009
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Really grateful that you're helping me out ,
it's a 4 piston harrison billet brake , 2 pistons on each side
http://www.who-sells-it.com/cy/zodia...-fullsize.html
I have no pressure at all , I see the pistons move but don't give the force to push the pads. First I thought the distance that the pushrod travels was not deep enough in the cylinder , so turned the lever out as much as possible. hooked up the pedal but no luck
What would happen if a piston got stuck ? At first i got full pressure after pumping the pedal , after bleeding a week later , no pressure at all ...
I use dot 5 fluid
piston sizes = 31 mm
Is the original master cyliner the same bore as my current aftermarket ?
R
it's a 4 piston harrison billet brake , 2 pistons on each side
http://www.who-sells-it.com/cy/zodia...-fullsize.html
I have no pressure at all , I see the pistons move but don't give the force to push the pads. First I thought the distance that the pushrod travels was not deep enough in the cylinder , so turned the lever out as much as possible. hooked up the pedal but no luck
What would happen if a piston got stuck ? At first i got full pressure after pumping the pedal , after bleeding a week later , no pressure at all ...
I use dot 5 fluid
piston sizes = 31 mm
Is the original master cyliner the same bore as my current aftermarket ?
R
Last edited by Raf_666; May 24, 2011 at 01:20 PM.
Road Warrior
Joined: Dec 2008
Posts: 1,476
Likes: 23
From: Summit, Mississippi
This is helpful. 4 piston opposed calipers with 31mm bores should work just fine with that 5/8 master cylinder. 5/8 was likely stock on the bike.....so we can rule that out. We can also rule it out since you say it worked at one time. It being a multi-piston caliper, it is highly doubtful that all of them stuck.
As long as you use EITHER 4 or EITHER 5 you will be fine, but if you ever mix them....you will have a mess. Have the brake lines, or any of the components ever had 4 in them? It won't take much to gum-up the works if you get it mixed.
Here is what I would do to isolate the problem and I know it's a pain in the butt, but you have to start somewhere. Put an old caliper (if you don't have the original) on and....re-bleed and see what you have. You don't even have to put it back on the bike. You can get it close enough to bolt the brake line on it and stick a piece of paneling, wood or something about as thick as the rotor in between the pads to do the test. If this substitute caliper will clamp...you know your MC is good, if it don't, you can suspect your MC. Or...go the other way. Put your old MC back on and see if it works. I know this is all a bunch of trouble, but you have to isolate the problem.
I know you said they were...but it sounds a lot like they are not bled, or you have an issue with the new MC, or brake fluid contamination. You said something about having to change the rod adjustment to prevent it hitting your pipes. If the pedal is not going full stroke....maybe that should be looked at. Maybe take the pipe off to clear the pedal and make sure it is going down through it's full range. However....since you said it has worked before...I go back to the other things mentioned.
For sure....I can tell you that that 5/8 MC should work with the 4-piston opposed 31mm bores.
As long as you use EITHER 4 or EITHER 5 you will be fine, but if you ever mix them....you will have a mess. Have the brake lines, or any of the components ever had 4 in them? It won't take much to gum-up the works if you get it mixed.
Here is what I would do to isolate the problem and I know it's a pain in the butt, but you have to start somewhere. Put an old caliper (if you don't have the original) on and....re-bleed and see what you have. You don't even have to put it back on the bike. You can get it close enough to bolt the brake line on it and stick a piece of paneling, wood or something about as thick as the rotor in between the pads to do the test. If this substitute caliper will clamp...you know your MC is good, if it don't, you can suspect your MC. Or...go the other way. Put your old MC back on and see if it works. I know this is all a bunch of trouble, but you have to isolate the problem.
I know you said they were...but it sounds a lot like they are not bled, or you have an issue with the new MC, or brake fluid contamination. You said something about having to change the rod adjustment to prevent it hitting your pipes. If the pedal is not going full stroke....maybe that should be looked at. Maybe take the pipe off to clear the pedal and make sure it is going down through it's full range. However....since you said it has worked before...I go back to the other things mentioned.
For sure....I can tell you that that 5/8 MC should work with the 4-piston opposed 31mm bores.
Thread Starter
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6th Gear
Joined: Feb 2009
Posts: 10
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I took apart the cylinder and will check tomorrow if the cylinder is mounted correctly, could that be damaged inside? So the fluid is not going in the brakeline?
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Road Warrior
Joined: Dec 2008
Posts: 1,476
Likes: 23
From: Summit, Mississippi
Anything is possible. I worked with one guy for two weeks and he finally took his rear brake line off and found a kink. Never know, but known good parts for substitution seems easier than taking stuff apart. The more you pull pistons and seals...the more likely you are to get a grain of sand, or some other debris in there.
Good luck and keep us posted. All I can say is that component wise...your stuff should work.
Good luck and keep us posted. All I can say is that component wise...your stuff should work.
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Thread Starter
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6th Gear
Joined: Feb 2009
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I can't get it right , decided to bring the bike to a shop , tried the original bracket , seems a bit better. Installed the 4 piston billet again, I do feel the pistons move a bit , but just very little ...
I thought if a piston , was being pushed against the brake pad , it would continue to push till it reaches the disc. Or (as is the case now) that it goes back in the original position once the pedal is released , so witha limited movement (1mm)
R
I thought if a piston , was being pushed against the brake pad , it would continue to push till it reaches the disc. Or (as is the case now) that it goes back in the original position once the pedal is released , so witha limited movement (1mm)
R