Brake Bleeding Question

[kennetht]

So I bled my brakes this weekend with the beautiful weather that was here along the east coast. Back to cold now... grrrrrr.

The rear brake bleeding went great, however I have a question regarding the front break.

Prior to the bleed, I did not have to squeeze the brake lever much to apply the front break. It was very pressurized and applied the brake with even the slightest pull of the brake lever. However, now, I really have to pull in on the lever to apply the brake. It is not as sensitive as it was prior to bleeding it.

I made sure there was no air in the lines as I went through two brake cylinders of brake fluid to bleed the brakes and no air bubbles came out.

What could be the issue?

Thanks in advance for the help

[csmith12]

Most likely, they still have air in the lines somewhere. How did you bleed them? Vac, reverse pumped, somehow else?

[kennetht]

Originally Posted by csmith12

Most likely, they still have air in the lines somewhere. How did you bleed them? Vac, reverse pumped, somehow else?

Neither. I just emptied the entire system of the old brake fluid, as it was never changed since I purchased the bike, and the previous owner could not tell me when it was last done.

Once I emptied out the entire system of the old fluid, I began to bleed the system with new fluid. Put new in the reservoir, pumped the brakes till I felt a little pressure, then began to bleed the system. I went through about 2 reservoir fills during this entire sequence. Squeeze brake, open bleeder valve, close bleeder valve, release brake, repeat. Repeated that sequence about 20 times but to no avail the brake lever never went back to the same pressure that it was before the bleed. Throughout this whole process I only saw air bubbles in the beginning, but never saw them after about 5 cycles of bleeding the valve. I now have to squeeze the lever quite a bit more to really get good braking power.

[csmith12]

It is very, very difficult to pump bleed brakes like that on a bike without being "creative". Sometimes we get lucky and it works, other times... not so much. If you don't have a vac or pump, you can give this method a try. Did it this way for many years, hell... still do sometimes.

[csmith12]

This is basically the process.

Link to original page on YouTube.

[kennetht]

Originally Posted by csmith12

It is very, very difficult to pump bleed brakes like that on a bike without being "creative". Sometimes we get lucky and it works, other times... not so much. If you don't have a vac or pump, you can give this method a try. Did it this way for many years, hell... still do sometimes.

That is actually exactly how I did it this weekend.

I just found the wiki and read this section:

If you can't get all the air out
If all else has failed, and you still can't get the brake lever to be firm, air may have collected at the top banjo bolt. You have two options:

Dirty, faster: Lean the bike so that the banjo bolt becomes the highest point in the system. Wrap a slightly damp rag around the bolt, then bleed... meaning squeeze the lever, open the banjo bolt (the fluid will come out and be soaked up by the rag), close the banjo bolt, and release pressure on the lever.

Cleaner, slower: Remove the caliper from the bike. Tie it up to something so it's the highest point in the system and let it rest overnight. Then you can bleed as normal to get the last of the air out.

Option 3: Zip-tie the brake lever to the bar overnight. This opens the bleed valve at the master cylinder and can let air escape. For the rear, connect the lever to the horizontal bar on the center stand using two zip ties while standing partially on the rear brake. Take the zip tie(s) off in the morning and check to see if it helped.


And 4: After bleeding the caliper to the best of your abilities, make sure the caliper bleeder is closed. Fill up the master cylinder about 75% of the way to the brim with brake fluid, then reinstall the master cylinder cover and tighten it. Next, squeeze and release the brake as fast as you can while turning the wheel from side to side. This doesn't necessarily mean complete squeezes; the goal is to severely agitate and shock the stuck air bubbles so you can bleed them. Re-bleed after this.


I think I am going to give the wire tie option a try. Question though, for the wire tie, do I need to have the reservoir cover on or off?

[csmith12]

Ah, I see... I guess I have been lucky over the years and never had to do the zip tie thing. Although, I may try it on my 4wheeler. I can never seem to get a good brake feel on that thing.

[tfkrocks]

Tapping on the brake lines might help the bubbles along to the top. Bleeding from the banjo bolt has been the most useful trick for me.

[Motofool]

Originally Posted by kennetht

........I think I am going to give the wire tie option a try. Question though, for the wire tie, do I need to have the reservoir cover on or off?

The reservoir cover and rubber seal should be in place, as well as the cap of the bottle with which you refill.

Air humidity is the other big problem that can lead to spongy brakes.
While the brake fluid is in direct contact with humid air (and all air is humid to certain degree), it is absorbing that water.
With braking heat, that water becomes steam, which acts as air in the lines, ....... or worse.

Think of your problem as two fluids (air and brake fluid) inside a container (caliper, hose, master) and under the influence of gravity.
Previously, you did fill that container completely with the fluid named air.
Then, you did pour some brake fluid into the container.

The liquid tends to occupy the lowest point in the container, while air goes up and some bubbles stay trapped in any geometry that creates a pocket for it.
Think like a bubble trying to reach the surface of the fluid at the master cylinder: if you cannot mentally, you may have air trapped at that point.

The traditional flushing system works by dragging some of that air out with the high speed of the fluid, but it seldom eliminates 100% of the trapped air.

[kennetht]

Originally Posted by tfkrocks

Tapping on the brake lines might help the bubbles along to the top. Bleeding from the banjo bolt has been the most useful trick for me.

I am going to give the wiretie method a shot tonight, and if that does not work, next chance i get I will give tapping the brake lines a shot to get the bubbles to raise to the top. Thanks for that recommendation

[kennetht]

Originally Posted by Motofool

The reservoir cover and rubber seal should be in place, as well as the cap of the bottle with which you refill.

Air humidity is the other big problem that can lead to spongy brakes.
While the brake fluid is in direct contact with humid air (and all air is humid to certain degree), it is absorbing that water.
With braking heat, that water becomes steam, which acts as air in the lines, ....... or worse.

Think of your problem as two fluids (air and brake fluid) inside a container (caliper, hose, master) and under the influence of gravity.
Previously, you did fill that container completely with the fluid named air.
Then, you did pour some brake fluid into the container.

The liquid tends to occupy the lowest point in the container, while air goes up and some bubbles stay trapped in any geometry that creates a pocket for it.
Think like a bubble trying to reach the surface of the fluid at the master cylinder: if you cannot mentally, you may have air trapped at that point.

The traditional flushing system works by dragging some of that air out with the high speed of the fluid, but it seldom eliminates 100% of the trapped air.

Thanks for that detailed response. I did read somewhere that the brake fluid does absorb water quickly. I even read somewhere that once you open a fresh brake fluid container, once finished with it you should consider it contaminated and not use the remaining fluid again at any time. Just buy a new bottle for the next time I change the fluid.

[Motofool]

Originally Posted by kennetht

Thanks for that detailed response. I did read somewhere that the brake fluid does absorb water quickly........

You are welcome.

http://en.wikipedia.org/wiki/Brake_fluid#Boiling_point

Yes, DOT 3, 4, and 5.1 are a very hygroscopic mix of fluids.
DOT 5 is not.

[Racer x]

When bleeding next time just pump new flidd through until it is clear. That way you never introduce air into the system. On some bikes it is really impossible to bleed them. I have resorted to removing the caliper until I can hold it above the master cylinder. Then the air goes up and out. Usually this is back brakes though.
And yes it absorbed moisture like a sponge. The moisture eats metal parts. But it also will boil. This is a big problem on race cars. So change it every spring and in the fall. Just clean out the resivour with each oil change.

[RedPepper64]

@Motofool @kennetht helpful info! We have a vacuum pump to do our brake flushes so I haven't run into this problem before with the air bubbles but we are doing a traditional flush at a friend's soon. Great to know.

[kennetht]

So I gave the wiretie method a shot, and let it sit for the last 48 hours (since we had a snowstorm).

Took the wiretie off this morning to ride to work, and walah! It worked.

Only problem, it worked too well. haha. The break pads are slighly applied, even with no squeeze of the brake. So, I am going to relieve a little bit of the pressure by letting out a little bit of brake fluid, and then we should be good to go.

Originally Posted by kennetht

I am going to give the wiretie method a shot tonight, and if that does not work, next chance i get I will give tapping the brake lines a shot to get the bubbles to raise to the top. Thanks for that recommendation

[kennetht]

Originally Posted by Racer x

When bleeding next time just pump new flidd through until it is clear. That way you never introduce air into the system. On some bikes it is really impossible to bleed them. I have resorted to removing the caliper until I can hold it above the master cylinder. Then the air goes up and out. Usually this is back brakes though.
And yes it absorbed moisture like a sponge. The moisture eats metal parts. But it also will boil. This is a big problem on race cars. So change it every spring and in the fall. Just clean out the resivour with each oil change.

Yeah, thats what I plan on doing from here on out. I just bled them the first time becasue I was unsure about what brake fluid was previously in there, and didnt want to mix new with old, even slightly.

So now that I know what fluid is in there, I plan on using the same fluid all the time now. So that way a little old can be mixed with new.

[kennetht]

Originally Posted by kennetht

So I gave the wiretie method a shot, and let it sit for the last 48 hours (since we had a snowstorm).

Took the wiretie off this morning to ride to work, and walah! It worked.

Only problem, it worked too well. haha. The break pads are slighly applied, even with no squeeze of the brake. So, I am going to relieve a little bit of the pressure by letting out a little bit of brake fluid, and then we should be good to go.

***UPDATE***

Didnt even have to relieve any pressure by opening the bleeder valve.

I just went outside to ride home for lunch, and it seems like the pressure relieved itself as it sat there for the past few hours with the wiretie off.

So I'm back to normal!