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Please help. Made a video of my brake-dragging problem.

  • Thread starter Thread starter Smellii
  • Start date Start date
S

Smellii

Guest
Almost to tears about my brakes. Made a video of my problem. Brakes dragging bad after I cleaned everything.

http://www.youtube.com/watch?v=KLip-k_AqjA&feature=youtu.be

Should I use special lube for the pistons? If so will motor oil or WD40 work? How best can you clean the tiny fluid return hole in the front master cylinder? I have an air compressor; can I use that?
 
Hi,

Smellii said:
Should I use special lube for the pistons? If so will motor oil or WD40 work? How best can you clean the tiny fluid return hole in the front master cylinder? I have an air compressor; can I use that?
Click to expand...

Use only brake fluid on the pistons, no "special" lube. You do need special lube for the caliper axles, caliper grease, usually a copper-silicone grease is the best. But any Gunk or Permatex caliper grease will do just fine.

There's a tiny hole in the bottom of the master cylinder. It's not the larger hole that you might see, because the tiny hole is usually hidden by a baffle. You have to take the master cylinder apart and poke a very small wire through the hole to get the gunk out of there. Then spray well with brake cleaner. Re-assemble, fill, bleed, and ride safely.

Thank you for your indulgence,

BassCliff
 
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Ditto Cliff - only use brake fluid only. NOTHING ELSE (worth shouting....).

The tiny hole is really tiny and you may not even be able to see it. There's a small hole you can see (even if your eyes are not that clever like mine) - there's a smaller one. I use a magnifying glass.

You may have trouble with crap in those old lines. If they are the originals I would advise swapping for new stainless; it's night and day difference on brake feel as well. The fact that the brakes tighten up when you have been for a ride (and warmed things up) suggests crap in the line, or at the very least water (which can be catastrophic).

Plus the guy on YT is right - your fluid level is very low.
 
You only did half the rebuild job; the master cylinder needs to be cleaned and the brake lines replaced. Did you use caliper grease on the sliding pins?

Some brake/wheel drag is normal, particularly on the rear of a shafty. Your brakes look to be dragging a little more than normal but not an unusual amount for a freshly torn down system - the caliper parts mate together as you ride the bike. The fronts in particular need some miles before everything will settle down. Try taking out the bike and dragging the brakes while using the throttle to bed in the pads. That should help the situation some assuming the master cylinder isn't plugged up.

Good luck and please plan to finish the rebuild properly when you have time.
 
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Thanks guys for helping out. You are not going to believe this but I fixed it. I greased up the caliper axles per Basscliff's and Nessism's advice, poked around in that tiny-er hole in the master cylinder with a bristle from a metal bristle brush (but I don't think it was clogged because I saw it back flow fine when bleeding) -thanks hampshirehog, and scrubbed and lubed all the sliding parts in the caliper assembly (metal sliders and the back of the brake pad (per manual)). All this fixed the front only because when I came back from a spin around the block my back caliper was SMOKING :eek: (and stinky).

(So I proceed to walk around my bike pretending to look smart pressing on various parts.)

In doing so I happen to press on the rear brake peddle and it seemed to have no range. Turns out that adjusting screw on the rear brake pedal was way to tight. From this I deduce: Before I worked on my calipers it was in the correct position based on the state of the components at the time. However, I should have loosened it completely before bleeding/adding new fluid and before building pressure again in the lines. Unscrewed it and all the pressure was relieved from the rear rotor. (perhaps the caliper rebuild guide should add to check for this seemingly insignificant detail ???)

I do know, however, I need to replace/rebuild the other half of the brake system but have to make due with what I have because I'm as poor as one person can be at the moment. As soon as I can I will though. Thanks for pointing that out, Nessism.

I love love love this forum and the website. Use them aaaaallllll the time. A thousand thank yous!
 
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Great thread! Thanks guys!
Thanks for the update. I wouldn't have thought to check the adjustment on the rear brake pedal either.
 
If you've not replaced the hoses, as Nessism has suggested in his Top 10 Mistakes link, please do so. The rubber lines were scheduled to be replaced every 2 years. I've never ever seen them replaced. Ever. Including by my self unless they got ripped off for stainless lines (highly suggested, not only better, but cheaper than OEM). The lines will not only expand as they age, but they can also collapse, preventing back-flow and overpressurizing the system causing symptoms you describe as well.
As to bedding in your pads...
There are as many theories on proper bedding as there are people to tell you about them, so I'm not going to say what Nessism is suggesting is wholly wrong. But I will respectfully disagree. As has been explained through a couple of sites, and links on this very board, a method that I have used pretty much every time and has always worked is a bit different than Eds suggestion.

Some gear-heads would suggest that what Ed is describing as a break in proceedure would actually cause glazing of the rotor and the pad. Leaving trace amounts of pad material embedded in the rotor, causing chatter, un-even wear, poor lever feel etc etc.
The method I've used requires you to slow from around 30 MpH to nearly stopped, without stopping, and then immediately speed up to 60, then on the brakes hard (but don't kill yourself) to a near stop, then back to 80. Again, slowing hard (hey, you can use this as an opportunity to practice emergency braking) and then back to thirty. Repeat the process once more.
The theory is it properly heats the pads and discs to allow bedding, but also allows both to cool as to prevent glazing, and stopping completely is a no no as it will leave said pad deposits on rotor. Just one of many theories, and as I said they're about as good as opinions....
 
Ed's version of brake bedding isn't really all that different.

It heats the pads to bed them, just like yours. The only difference is the number of times and the duration/temperature.

I have seen a variation that includes both methods. Drag the brakes a bit to warm them up, then speed up and use them moderately hard a few times. Just don't do the "moderatly hard" stops on cold pads.

.
 
Smelli, your rear pedal adjustment was likely placing that master cylinder piston too far forward in the bore such that the compensating port was not open to the forward portion of the cylinder. You likely already know this but in case someone is not aware, there are two small/tiny holes in the bottom of brake master cylinder bores which lead downward from the reservoir into the piston bore.

The hole which is further forward and is the subject of the reference in this thread is called the compensating port. This is usually obvious because it typically has a structure around it such as a plastic/metal deflector. When the brake is applied, this is accomplished by applying mechanical effort to press the brake master cylinder piston forward into the master cylinder bore. The forward movement displaces fluid.

Some close observation of a normally adjusted and operating master cylinder will reveal that there is some flow out of the compensating port into the reservoir during the initial movement of the master cylinder piston but the flow stops after a short movement of the piston.

As the piston moves forward into the master cylinder bore, it displaces fluid and, initially, the fluid moves upward out of the piston bore into the reservoir which can usually be observed as a disturbance in the reservoir fluid. In some cases the fluid will squirt upward with some force.

As the master cylinder piston moves further forward, the piston rubber seal passes the compensating port which is then sealed off from connecting the bore ahead of the piston into the reservoir.

It is from this point onward that the master cylinder piston movement pressurizes the brake system which is intended to apply pressure to the brake caliper pistons, wheel cylinder pistons (in drum brakes), clutch slave cylinder piston (in clutch systems), or ABS components, etc.

When the brakes are applied, the purpose of the brakes is manifest and, if the machine is in motion, the friction resulting from the action of the brake friction material acting with the rotor or drum begins the conversion of kinetic energy into heat which, in part, enters the brake friction material (pad or shoe) and transfers into the caliper or wheel cylinder.

Increasing temperature within the caliper or wheel cylinder causes the brake fluid to expand, but this is not usually observed by the rider. The amount of expansion of the fluid can be quite significant evidenced by the following experiment.

If one adjusts the master cylinder piston's return (battery) position so that the piston is unable to return past the compensating port and then the brakes are operated, the expanding fluid will, as before, expand within the caliper. The expansion will, if application is continued sufficiently, apply the brake when the piston has been released because there is no mechanism available to release the pressure.

This expansion, manifest by pressure will continue to apply the brake which will continue to convert movement to heat and continue to heat the fluid. In the case stated in this thread, this is the likely cause of the dragging rear caliper.

In extreme cases, the bike will be dragged to a stop and be unable to move until the system has cooled enough that the fluid contracts to the initial volume at the time that braking began.

We used to see this frequently when 1970's Fords had a master cylinder replaced onto power brake boosters. If the power brake booster's push rod were not properly adjusted, the vehicle would often be found on the roadside.

This condition can also occur, as I think someone suggested in an earlier post, if the compensating port is blocked.

So what is supposed to happen if the piston is adjusted to the proper return position and the compensating port is open?

When the port is open, on release of the piston, the port will open to connect the reservoir to the piston bore such that pressure within the bore will disperse due to fluid flow back from the bore into the reservoir. If braking heat causes (when it causes) expansion of the brake fluid within the caliper (wheel cylinder or in the clutch slave), accumulated pressure will release on return of the master cylinder piston.

If the master cylinder reservoir is over filled, pressurizing of the brake system will occur in a similar manner.

Another concern regarding the compensating port needs mention: If the reservoir lid is not in place when the brake is applied and rapidly released, a squirt of fluid my be discharged upward with enough velocity to escape the reservoir. The resulting spray can distribute brake fluid widely onto surrounding areas resulting on damage to paint and other surfaces. Many have paid this price.

In master cylinders which have some wear to the sealing cup or cylinder bore, or are simply gummed up by deposits, there may be enough leakage past the piston cup on release to vent the fluid back so all may appear to be well until such time as something such as a master cylinder service or even pad change affects the condition. This is why dragging brakes sometimes occur after some other intervention.

Of course, misaligned caliper mountings, binding caliper pistons, too think brake pad material and many other factors can cause brake drag. One clue to the possibility of a blocked compensating port is to open a bleeder nipple when the brake drag is manifest because opening the nipple will release the accumulated pressure. Opening a nipple will not alleviate a binding mount and so on.

The other master cylinder port, just to close this subject to some degree, is the breather port. The compensating port "compensates" for differences in fluid volume within the system while the breather port's purpose is to vent fluid from behind the master cylinder piston when the piston is returning to battery on release.

If some means is not provided to release fluid which has accumulated behind the piston, the resulting pressure can cause slow release in some cases but almost always earlier leakage from the piston bore as the piston end seal is over powered by the pressure. A seal in top condition can withstand this but as time goes on leakage can occur.

If someone is interested, remind me to discuss the "pump-up" action of the piston seals on rapid and repeated application as well as the role of rapid application in sealing a compromised seal.

HIH, time to get some work done,


Norm
 
cowboyup3371 said:
I finally figured out what you are saying here:dancing:...HIH = Hope it Helps.

Wow, I'm getting old.:rolleyes:
Click to expand...
Cowboy...I've been wondering the same thing. Guess who doesn't carry a cell phone or text message? Hmmm, maybe I AM getting old.
 
Great writeup, Norm.

I am definitely interested in what you have to say about "pump up"
 
I must say. I'm impressed of your knowledge and more impressed of your willingness to share. Thanks for teaching me how to fish when it comes to my brakes. You, Sir, get a gold star.

BTW. Took it out on the road today. Absolutely no problems and being able to smoothly coast without dragging is a wonderful thing. Brakes work great.
 
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The term "pump-up" or without the "-" as I can't recall the correct form,:o refers to a separate action involving the main sealing cup. When the brake (or to a lesser extent, the clutch) is applied, it is accomplished, as we all know, by forward movement of the master cylinder piston which displaces fluid until all clearance is removed from the system.

From that point, further application of force to the piston builds pressure with the system. If there is excessive clearance within the system, the piston will reach the limits of travel and no further pressure will build.

If we relax the lever or pedal, the master cylinder piston returns to battery (the resting position) and reapplication results in the same limited or no action regarding the slave cylinders (clutch servo, brake wheel cylinder, or brake caliper).

In order to allow for emergency application by moving additional fluid forward in order to take up clearance, designers create a lip type piston seal which has some side clearance between the body (main diameter) of the sealing cup and the master cylinder bore. In this fashion the rubber seal is in the form of a tapered cup with the lips of the open end spead against the surface of the bore.

In normal release, the cup and piston simply return to battery as already stated but in a rapid release the inertia and density of the fluid cause it to resist rearward movement being applied by the sealing cup. In this condition, the sealing cup's lips flex inward allowing some fluid to by-pass the cup in the forward direction, so that the fluid moves into the area ahead of the piston before the piston clears the compensating port.

Rapid partial release and application of the linkage cycles the piston forward to create pressure/take-up clearance and then rearward to by-pass more fluid. With each repetition the piston's forward movement acts on an increasing volume of fluid forward of the piston sealing cup so that the piston is able to apply more pressure due to the reduction in clearance.

I think everyone will recall the effect of short rapid pumping which moves the lever outward or the pedal upward at the point where application force is stopped by the resistance of the brake?

If one experiences a malfunction such as forgetting to bleed the air from the system this pump-up action can be a life saver because it allows one to literally pump up the system pressure sufficiently to obtain some brake application. Slow or normal application rates will not accomplish this effect.

Similarly, if one does repeated hard braking with contaminated brake fluid which boils, this may save the day.....or not so change the stuff every year. Please!

HIH

Norm
 
cowboyup3371 said:
I finally figured out what you are saying here:dancing:...HIH = Hope it Helps.

Wow, I'm getting old.:rolleyes:
Click to expand...

BigD_83 said:
Cowboy...I've been wondering the same thing. Guess who doesn't carry a cell phone or text message? Hmmm, maybe I AM getting old.
Click to expand...
I'm not getting old, I AM old. :rolleyes:

I'm tired of showing off my ignorance of "texting" lingo. I figure if it's not important enough to type it out, it's not important enough to worry about.
shrug2.gif


Thanks for the translation, cowboy.

Norm, thanks for the write-up. Now we just need to get some pictures attached to that tome and get it posted in the "Brakes" section of BassCliff's library. :D

.
 
Here's some more brake master cylinder stuff which might be useful to someone:

Everone knows how disk brakes self-adjust because the pistons do not return as far on release as the fruction material wears down. Of course this is why the fluid level drops as the pads wear and why we need to suction out some fluid from the master cylinder reservoir before pushing the caliper piston(s) back in order to install new pads.

Likely should make sure that everone understands the action of the caliper's square sealing ring and the need to make sure that the piston is free.....

I'm sure that most people have also noticed the difference in shape between the master cylinder sealing cup(s), caliper seal rings, wheel & slave cylinder seals and likely know why they are differently shaped?

Here's a point which can save some grief:

Sometimes, after replacing brake pads or otherwise having pushed a caliper piston back or when bleeding brakes, one may have trouble obtaining a hard brake. In other words, the lever or pedal has a spongy feel and full pressure can only be obtained by pump-up. Air is often blamed but the cause may lie elsewhere.

In normal braking action, the master cylinder sealing cup moves through a limited range and never beyond. If there is water present in the system it will drop out of solution under colder temperatures. Remember your college physics? The solubility of a gas in a liquid, solid in a liquid?

The water will collect and remain in low areas within the braking system, one of which is along the bottom of the master cylinder bore. Hope no one will advance that silly myth about brake fluid not needing to be changed or the one that silicone brake fluid is better!:eek:

If the water lies within the stroke of the piston cup, it will be pushed forward where it will remain, corroding & pitting the master cylinder bore. When something happens to require an increased piston stroke, the sealing cup will slide forward being expanded by increasing pressure, over the corroded/pitted area. The contact will wear/abraid the sealing lip surface of the cup compromising its ability to seal to the bore. It can require only one stroke into a corroded/pitted area to fatally damage the sealing cup, especially when combined with normal wear to the sealing lip.

When one next tries to apply light braking, the cup is unable to seal effectively so that fluid leaks back, past the sealing cup and the lever/pedal sinks, perhaps all the way to the end of the bore and no braking pressure is created. A rapid application, sometimes requiring some pump-up to move the piston cup back to a smoother area, with hard application will often create enough pressure on the cup to affect a seal.

Most of us have experienced a brake lever of pedal which gradually sinks unless it is applied quickly and hard. Some have experienced a clutch which will disengage if the lever is pulled quickly but the clutch will begin to gradually apply as though one was slowly releasing the lever. This can be a quite humerous condition if one observes a riding buddy dealing with a misbehaving clutch of this type.:D

Old timers have learned not to stroke a used master cylinder further than it is used to do in order to avoid this happening. The obvious problem though, is that the system may let one down unless the master cylinder is repaired or replaced.

It has always troubled me that so many people will avoid doing a valve adjustment or cleaning carburetors because these are complicated and intricate operations but the same people will fly at a brake job with no understanding of the systems. What's the worst from a too tight valve or flooding carb.? Death is unlikely:confused:

HIH someone. I will see what else pops into mind.

Norm
 
Thanks, Norm! I know the importance of understanding how my braking system works; now I actually understand how my braking system works.
 
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