All brakes dragging

SkitzyMcGee

SkitzyMcGee

Mechanical Mastermind
Joined
Aug 4, 2023
Messages
11
Location
Tampa, Florida
Bike
2005 Honda ST1300
2024 Miles
000800
After replacing the rear brake pads and rebuilding all three calipers, the brakes on both wheels are now dragging. I can only get about one wheel rotation with a hard push on the back tire, and about 3/4 a rotation on the front wheel. I’ve lubricated every surface the brake pads slide on, and bled the system in the prescribed order (while tilting the SMC). I’ve also recently rebuilt with a kit my front secondary brake master cylinder. Any help would be greatly appreciated.
 
SkitzyMcGee said:
After replacing the rear brake pads and rebuilding all three calipers, the brakes on both wheels are now dragging. I can only get about one wheel rotation with a hard push on the back tire, and about 3/4 a rotation on the front wheel. I’ve lubricated every surface the brake pads slide on, and bled the system in the prescribed order (while tilting the SMC). I’ve also recently rebuilt with a kit my front secondary brake master cylinder. Any help would be greatly appreciated.
Click to expand...
Crack the bleeders open and see if the wheels free up. If the do it's a hydraulic problem if they dont it's a assembly problem.
 
Al st1100 said:
Crack the bleeders open and see if the wheels free up. If the do it's a hydraulic problem if they dont it's a assembly problem.
Click to expand...
Releasing hydraulic pressure can also allow parts that were not assembled correctly to shift and settle into position.
So you can't always assume that if the wheel freed up, that it was a hydraulic issues and not an alignment issue ;)
 
Your post, @SkitzyMcGee , is worded such that it appears to me you "rebuilt" the SMC.
A rebuild fails more often than it succeeds.
Replacement of the SMC is the conventional wisdom, backed up by the experience of most of us.
I would suggest, as the next step, call @Igofar on the White Courtesy Phone.
That is accomplished by sending the gentleman a Provate Message with your phone number.
Click on his avatar to begin the process,... you'll be glad you did.
 
Igofar said:
Releasing hydraulic pressure can also allow parts that were not assembled correctly to shift and settle into position.
So you can't always assume that if the wheel freed up, that it was a hydraulic issues and not an alignment issue ;)
Click to expand...
But if the hydraulic system is working properly there is no pressure to release.
 
Last edited:
Al st1100 said:
But if the hydraulic system is working properly there is no pressure to release.
Click to expand...
This comment makes no sense to me :shrug2:
Cracking the bleeder will take the pressure (release pressure) from the brake line or system etc.
If the properly working system applied pressure to move the pistons against the pads, against the rotors etc. and then there was too much grease on the guide pins, which caused suction, with jammed up the caliper from moving correctly, then this pressure release may allow the suction to be released, and the caliper and components may be allowed to settle back into the correct position etc.
Just by cracking a bleeder and seeing that the rear wheel turns freely, does not always indicate that it was a pressure problem, alignment problem, or assembly problem.
You have to find what is causing the problem.
:WCP1:
 
Igofar said:
This comment makes no sense to me :shrug2:
Cracking the bleeder will take the pressure (release pressure) from the brake line or system etc.
If the properly working system applied pressure to move the pistons against the pads, against the rotors etc. and then there was too much grease on the guide pins, which caused suction, with jammed up the caliper from moving correctly, then this pressure release may allow the suction to be released, and the caliper and components may be allowed to settle back into the correct position etc.
Just by cracking a bleeder and seeing that the rear wheel turns freely, does not always indicate that it was a pressure problem, alignment problem, or assembly problem.
You have to find what is causing the problem.
:WCP1:
Click to expand...
How does cracking a bleeder open release the suction on the guide pins? "Cracking the bleeder will take the pressure (release pressure) from the brake line or system etc." what braking system has pressure to the calipers when the brakes are not being applied?
 
I'm sorry, you missed my point.
Lets try a simpler version.
Lets say the rear caliper pistons are dirty, and sticking unevenly, which causes the pad to be tilted or crooked, which causes the rear wheel to drag etc.
Releasing the rear bleeder allows the pressure to be released, thus releasing pressure off the piston(s) that are stuck, letting the pads shift, allowing the rear wheel to spin freely again etc.
So...was it a pressure issue with the return port not allowing the pressure to return through the system, and building up pressure?
Or was it an alignment issue because something got crooked because it was dirty or greasy causing things to get grabby?
 
Igofar said:
I'm sorry, you missed my point.
Lets try a simpler version.
Lets say the rear caliper pistons are dirty, and sticking unevenly, which causes the pad to be tilted or crooked, which causes the rear wheel to drag etc.
Releasing the rear bleeder allows the pressure to be released, thus releasing pressure off the piston(s) that are stuck, letting the pads shift, allowing the rear wheel to spin freely again etc.
So...was it a pressure issue with the return port not allowing the pressure to return through the system, and building up pressure?
Or was it an alignment issue because something got crooked because it was dirty or greasy causing things to get grabby?
Click to expand...
Your missing my point , a cocked piston can not hold fluid pressure but fluid pressure can hold a piston. You said it in your reply"Releasing the rear bleeder allows the pressure to be released" What pressure? Fluid pressure?
 
Fluid pressure in the brake lines can be as a result of any of 4 blocked compensation ports; blocked brake lines; overfull reservoirs; non returning master cylinder pistons; lever/pedal issues.
Releasing the pressure at the bleed valves (without introducing air) may remove the symptoms at the caliper and may help to eliminate jammed up components as the cause.

There is of course another reason for the fluid pressure. That would be the thick rubber guy that is wrapped around the front brake lever overnight to help get rid of air bubbles. Or the Pendle parking brake.
Me, no. Only once.
 
I do enjoy a brake thread for the pedantry. I've missed you guys.

As an aside, I will have to remember the "crack the nipple" trick for when I finally move the 13. It's sat still for probably 8 months at this point.

Please, continue :smile-popcorn:

(@SkitzyMcGee - see the RAN list, Igofar is on it, give him a call. Without even looking at your bike he'll whisper to it down the phone and find a laundry list of things wrong with it that you weren't even looking at, as well as telling you how to solve the sticky brake issue).
 
In an ideal system - picture a heavy steel hydraulic cylinder and an incompressible fluid with a piston atop it. Press down on the piston and pressure is transmitted to the walls of the cylindrical vessel. Again, this system is ideal so there can be no movement (fluid does not compress and the heavy walls do not flex) of the piston. Lock the piston in this position and crack a bleed valve and you will get very very little fluid out - it cannot expand because it did not shrink in volume under pressure.

Brake fluid, like water, is essentially incompressible. However, the system of pipes and rubber hoses (especially the latter) will store some energy when the brakes are applied. Blocked ports prevent the fluid from flowing back into the reservoir and relieving the pressure, and the very slightly ballooned rubber hoses will keep pressure on the fluid. This is the source of some of the pressure that will be relieved by cracking the bleed nipple. Caliper pistons have a square cross section O-ring sitting in a groove. Hydraulic pressure forces the piston outward slightly distorting the shape. This rubber ring is trying to pull the piston back into the bore (only a few thous, but that's enough to allow the disk to turn freely). This is a second source of stored pressure, as is any flex in the caliper or mechanical distortion of the brake assembly.
 
SMSW said:
Brake fluid, like water, is essentially incompressible.
Click to expand...


To be pedant....

Brake fluid, just like water, is compressible, just less than air but more than steel.

If you care to run the numbers, you'll find that under emergency braking where the brake line pressure can reach 1000 psi, it will take about 1 in of travel (end of lever) just to build up to this pressure., not negligeable (on top of moving the pistons and expanding the lines).
 
OK folks, move along here, there's nothing to see....move along
Lets not high jack the OP thread.
I've got him on speed dial, and we are sorting issues.
Will report back when it happens, as it happens, stay tuned to this station.
 
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