I just yanked the giant master cylinder off of my CB750 and replaced it with a Buell Blast MC and now my lever is spongy. I drained all the old brake fluid out of the line and pumped it out of the caliper, topped it off with new stuff and bled. Now the lever builds pressure and stops the wheel (just rolling it in the garage) but I can pull it all the way to the grips without it stopping. Any ideas?
Squishy front brake.
- Thread starter Yamanube
- Start date
At a guess there is still air trapped in there somewhere.
There are a few places where little air bubbles can get caught.
The other reason is water in the fluid, but since you hav e flushed it all, thats one out of the way.
Just keep bleeding and gently tapping the lines, caliper and master cylinder to move any air through the system.
Cheers.
There are a few places where little air bubbles can get caught.
The other reason is water in the fluid, but since you hav e flushed it all, thats one out of the way.
Just keep bleeding and gently tapping the lines, caliper and master cylinder to move any air through the system.
Cheers.
You should invest in a speed bleeder for your calipers - eliminates all the open/close coordination.
When I bleed my BMW's brake, I open the speed bleeder, put a hose on it into a jar, open up the master cylinder and start pumping new fluid through it.
I just keep pumping the lever and filling the cylinder with new fluid, till nothing but nice new fluid is coming out the bottom end with no bubbles. Probably go through a whole bottle of fluid doing it. Maybe overkill, but it works for me and my brakes are great.
When I bleed my BMW's brake, I open the speed bleeder, put a hose on it into a jar, open up the master cylinder and start pumping new fluid through it.
I just keep pumping the lever and filling the cylinder with new fluid, till nothing but nice new fluid is coming out the bottom end with no bubbles. Probably go through a whole bottle of fluid doing it. Maybe overkill, but it works for me and my brakes are great.
crazypj
Split personality, I fake being smart
johnnylaw said:
That's just stupid. :
There is supposed to be a hole in the cap and a bellows under it so as fluid level moves (pad wear, heat/cool, etc) the pressure remains 'constant'
Anyway, back to original 'problem'
What size is the Blast m/c?
You probably have air in it, but, if it's wrong size piston it will never work right/You don't need a speed-bleeder, all you need is about aoot of fuel line.
Just form a loop into it so air rises to high spot then drains into container.
I use Teflon tape on bleeder threads, prevents air leaking back in and also prevents bleeder seizing in place
PJ
Newer brake set-ups usually require less fluid flow to operate - hence they will have a smaller MC size compared to older ones.
The size will be stamped on the MC either in metric (11, 14, 16, etc) or imperial (1/2, 5/8, 11/16, etc). Compare the new V old and see if it is smaller. Could also just be air in the lines still.
The size will be stamped on the MC either in metric (11, 14, 16, etc) or imperial (1/2, 5/8, 11/16, etc). Compare the new V old and see if it is smaller. Could also just be air in the lines still.
crazypj
Split personality, I fake being smart
Newer systems don't need 'less' flow, the master cyl to piston area is just worked out better to give more 'feel'.
If Blast caliper piston is different size to Honda one you'll have to do some math on volume of fluid moved compared to surface area
You probably want 1~2mm smaller than stock size (do conversion if it's in inches)
PJ
If Blast caliper piston is different size to Honda one you'll have to do some math on volume of fluid moved compared to surface area
You probably want 1~2mm smaller than stock size (do conversion if it's in inches)
PJ
crazypj
Split personality, I fake being smart
Sorry for very long post, hope you all manage to get to end OK
Basically there are only two types of caliper, opposed piston (rigid mount 2, 4, 6, 8 piston) and sliding mount, usually single or twin piston. (3 piston designs /sometimes usually have linked brake with center piston operated by footbrake, some 6 piston calipers do same)
Good idea to check before buying used.
Early Honda used a single piston pivot mount (Yamaha used similar as well at one time)
Which is better?
Well............................ I don't think anyone uses single sided calipers on supersport bikes (VFR Honda is Sport Tourer)
Whatever type you have, the surface area of caliper piston is matched to master cylinder piston.
When new, the 'pivoting'/'floating' type won't have excessive clearance and will feel very similar to fixed type and have same travel at lever (or whatever manufacturer decided)
You don't use an oversize master cyl to move more fluid, if you did the 'leverage' (pressure ratio's) would increase to get adequate pressure at pad..
You'll find rotor to pad clearance is deciding factor how far lever moves
I think the Buell uses smaller diameter caliper pistons than the Honda
Floating rotors are a different thing all together and dont require any extra fluid or lever travel.
Several bikes use or used floating rotors with sliding caliper (eg, Suzuki Katana, 1998~2007)
The reason is, float is to prevent distortion (due to thermal expansion), not to centralise the rotor between pads.
The only bike's that used true 'FLOATING' (actually siding) rotors was the inside out disc Honda, particularly CBX550, VF400, etc. (may have been a few more but I spent a lot of time making those particular ones work)
Basically there are only two types of caliper, opposed piston (rigid mount 2, 4, 6, 8 piston) and sliding mount, usually single or twin piston. (3 piston designs /sometimes usually have linked brake with center piston operated by footbrake, some 6 piston calipers do same)
Good idea to check before buying used.
Early Honda used a single piston pivot mount (Yamaha used similar as well at one time)
Which is better?
Well............................ I don't think anyone uses single sided calipers on supersport bikes (VFR Honda is Sport Tourer)
Whatever type you have, the surface area of caliper piston is matched to master cylinder piston.
When new, the 'pivoting'/'floating' type won't have excessive clearance and will feel very similar to fixed type and have same travel at lever (or whatever manufacturer decided)
You don't use an oversize master cyl to move more fluid, if you did the 'leverage' (pressure ratio's) would increase to get adequate pressure at pad..
You'll find rotor to pad clearance is deciding factor how far lever moves
I think the Buell uses smaller diameter caliper pistons than the Honda
Floating rotors are a different thing all together and dont require any extra fluid or lever travel.
Several bikes use or used floating rotors with sliding caliper (eg, Suzuki Katana, 1998~2007)
The reason is, float is to prevent distortion (due to thermal expansion), not to centralise the rotor between pads.
The only bike's that used true 'FLOATING' (actually siding) rotors was the inside out disc Honda, particularly CBX550, VF400, etc. (may have been a few more but I spent a lot of time making those particular ones work)
I know the theory, and yes it should be true, but when I put an R1 MC on an old XJ750 I was expecting it to stand on it's head....but the lever came back to the bars. The R1 has a 14mm MC. I went to a 16mm MC on the XJ and the brakes came good. All I could suspect is that the floating calipers required more fluid to "operate" than the fixed ones because there's no way a single piston XJ floating caliper has more piston area than an 4 spot R1 caliper.
