Master Cylinders and Brakes
#1
06-27-2005, 09:12 PM
Master Cylinders and Brakes
Master Cylinders...
Lately I've been running into a rash of problems with master cylinders not wanting to pump fluid down to the brake calipers correctly. some of the symptoms include a spongy brake that won't quite pump up, and when you try to bleed the air out of the line, the problem gets worse. This problem can be frustrating even to a longtime pro.
The problem I have been mainly seeing is with the 1980's HD models. Disc brakes use DOT 5 brake fluid which is silicone based. This stuff breaks down over a period of time when it gets rubber particles mixed with it from normal seal wear. If you pop the cover off the top of the master cylinder and see a dark murky looking substance at the bottom, while the rest of the fluid looks fairly normal, then this is a sign of fluid breakdown.
When the fluid breaks down, it seems to coagulate (stick together) with the solid particles from the worn seals. It can and will plug or severely restrict the inlet port for the piston chamber.
What this means is, that no matter how frantically you pump the brake, only a minimal amount of fluid comes out of the port that the brake line hooks up to. It also means it's time to disassemble the master cylinder.
Source:http://sudsandbutterfly.homestead.com/HawgHelp.html
This is a fairly easy task. Precautions must be taken to protect your paint from any brake fluid that might be spilled. Brake fluid will eat paint. After the master cylinder is removed, dump any fluid out in a drain pan. Look inside of the end where the lever/pushrod assembly goes in and remove the snap-ring. Once this is done, then you should be able to pop the plunger and spring out by pushing it inward against the spring pressure by using a Phillips head screwdriver inserted in the pushrod hole, and then rapidly releasing it. You may have to repeat this process a few times before it actually comes out. Pay attention as to what order the components come out, as it will have to be reassembled in the same order.
Now that it is apart, clean out all chambers with carburetor cleaner. Then shine a light down inside the piston chamber and look through the reservoir chamber at the small ports in the bottom of it. You should be able to see the light through all of them. If not, then the carburetor cleaner did not remove all of the debris.
If this is the case, then try using compressed air through the end where the piston assembly while blocking the outlet port with your thumb. This should dislodge the debris. Now repeat the process with the flashlight.
If the port still isn't clear, then use a "torch tip cleaner", starting with the smallest bit, and rod out the port. A stiff piece of guitar string (fourth and fifth strings) works really well for this also. Once again, repeat the flashlight trick. Now your port should be clear.
Just for the sake of insurance, blow carburetor cleaner through the ports using the little straw that comes with it. Let the carb cleaner completely evaporate. Inspect your piston seals and look for cracks, splits or rough edges. Also check the flexibility of the cup seal. If it seems hard, then it's time to replace your seals.
If you're ready to reassemble your master cylinder, It goes like this: First the spring goes in. Then the cup seal goes in. Put a light coat of DOT 5 brake fluid on it and make sure the cup part faces inward, because as your brake pressure builds, the sides of the cup flare out against the cylinder wall to get a tighter seal. Next is the spool that pushes against the backside of the cup seal. The O-ring on the spool should be flexible also, and it should also recieve a light coat of brake fluid prior to insertion. Now the dust seal with the lip facing inward, and finally the snapring.
While the master cylinder is still off of the bike, fill the reservoir about 1/4 full. Hold your thumb over the outlet port, and work the piston in and out with a Phillips head
Lately I've been running into a rash of problems with master cylinders not wanting to pump fluid down to the brake calipers correctly. some of the symptoms include a spongy brake that won't quite pump up, and when you try to bleed the air out of the line, the problem gets worse. This problem can be frustrating even to a longtime pro.
The problem I have been mainly seeing is with the 1980's HD models. Disc brakes use DOT 5 brake fluid which is silicone based. This stuff breaks down over a period of time when it gets rubber particles mixed with it from normal seal wear. If you pop the cover off the top of the master cylinder and see a dark murky looking substance at the bottom, while the rest of the fluid looks fairly normal, then this is a sign of fluid breakdown.
When the fluid breaks down, it seems to coagulate (stick together) with the solid particles from the worn seals. It can and will plug or severely restrict the inlet port for the piston chamber.
What this means is, that no matter how frantically you pump the brake, only a minimal amount of fluid comes out of the port that the brake line hooks up to. It also means it's time to disassemble the master cylinder.
Source:http://sudsandbutterfly.homestead.com/HawgHelp.html
This is a fairly easy task. Precautions must be taken to protect your paint from any brake fluid that might be spilled. Brake fluid will eat paint. After the master cylinder is removed, dump any fluid out in a drain pan. Look inside of the end where the lever/pushrod assembly goes in and remove the snap-ring. Once this is done, then you should be able to pop the plunger and spring out by pushing it inward against the spring pressure by using a Phillips head screwdriver inserted in the pushrod hole, and then rapidly releasing it. You may have to repeat this process a few times before it actually comes out. Pay attention as to what order the components come out, as it will have to be reassembled in the same order.
Now that it is apart, clean out all chambers with carburetor cleaner. Then shine a light down inside the piston chamber and look through the reservoir chamber at the small ports in the bottom of it. You should be able to see the light through all of them. If not, then the carburetor cleaner did not remove all of the debris.
If this is the case, then try using compressed air through the end where the piston assembly while blocking the outlet port with your thumb. This should dislodge the debris. Now repeat the process with the flashlight.
If the port still isn't clear, then use a "torch tip cleaner", starting with the smallest bit, and rod out the port. A stiff piece of guitar string (fourth and fifth strings) works really well for this also. Once again, repeat the flashlight trick. Now your port should be clear.
Just for the sake of insurance, blow carburetor cleaner through the ports using the little straw that comes with it. Let the carb cleaner completely evaporate. Inspect your piston seals and look for cracks, splits or rough edges. Also check the flexibility of the cup seal. If it seems hard, then it's time to replace your seals.
If you're ready to reassemble your master cylinder, It goes like this: First the spring goes in. Then the cup seal goes in. Put a light coat of DOT 5 brake fluid on it and make sure the cup part faces inward, because as your brake pressure builds, the sides of the cup flare out against the cylinder wall to get a tighter seal. Next is the spool that pushes against the backside of the cup seal. The O-ring on the spool should be flexible also, and it should also recieve a light coat of brake fluid prior to insertion. Now the dust seal with the lip facing inward, and finally the snapring.
While the master cylinder is still off of the bike, fill the reservoir about 1/4 full. Hold your thumb over the outlet port, and work the piston in and out with a Phillips head
Thread
Thread Starter
Forum
Replies
Last Post
Biggzie
Dyna Glide Models
14
05-28-2016 09:03 PM
