Flushing the front brakes

appliance821 · Jul 13, 2015

I'm going to flush the fluid on my front brakes - I'll be putting on speed bleeders to help with this. I have a couple of questions:

The manual calls for removing the calipers and forcing the pads apart to seat the pistons. It's unclear but I guess you bolt them back on after this process.

During this, the previously drained master cylinder is left open, and fluid is forced up and drained.

Then the standard procedure of filling the cylinder and pumping the lever is done.

2 questions:

1) Is it necessary to pull the calipers etc and seat the pistons?

2) If so - wouldn't it be easier to close the master cylinder and drain the calipers from the caliper speed bleeder?

gatdammit · Jul 13, 2015

If you're not replacing pads, I don't see a need to remove the front calipers. Might make installing the speed bleeders easier...or less messy, at least.

zibbit u2 · Jul 13, 2015

I flushed the factory fluid without removing anything except the reservoir cap. No push back of the pads, no problems arose from doing it. I did the normal pump up slowly, hold lever, close valve when the lever touches the bar. Start at the caliper with the two lines attached to it, then move on to the second caliper.

appliance821 · Jul 13, 2015

Thanks for the replies - you just saved me some time. Much appreciated.

gatdammit · Jul 14, 2015

Now the rear brake, whooooole different story...

zibbit u2 · Jul 14, 2015

True.. That one involves a bunch of steps

appliance821 · Jul 14, 2015

gatdammit said:
Now the rear brake, whooooole different story...

That's for another day. As I understand it, you have to remove a rotate the caliper to get the valve in the proper position.

gatdammit · Jul 14, 2015

If your lucky. I tried every trick from every forum and still couldn't get the bubble out.

appliance821 · Jul 15, 2015

gatdammit said:
If your lucky. I tried every trick from every forum and still couldn't get the bubble out.

did you try keeping pressure on the pedal overnight?

gatdammit · Jul 15, 2015

appliance821 said:
did you try keeping pressure on the pedal overnight?

I did not. My pocket was so stubborn that I don't think it would have mattered.

appliance821 · Jul 25, 2015

Looking at the manual - the reason they suggest pushing the pistons back is to flush fluid from the calipers and flush the abs system. Otherwise this will remain in the system. If your bubbles are in the master cylinder or brake lines , this is not an issue.

"Bleeding of the ABS hydraulic system
If brake controls feel “spongy” due to the presence of air bubbles in the system, bleed as usual, as described under Section "Changing the brake system fluid".
Before bleeding a brake master cylinder, move back the calliper pistons to let any air build-up in the ABS control unit flow into the master cylinder; as described under (Filling the brake system).
Purge must be carried out by means of the corresponding unions (A) placed on the callipers and the brake master cylinders."
The "unions" are the bleeder screws. We don't have master cylinder bleeders. Ducati must have gone to "Tranlators R' Us for the service manual.

appliance821 · Aug 10, 2015

Thought I'd follow up. Put on speed bleeders and flushed the front system without removing the calipers. The lever felt mushy regardless of how much fluid I put through so I tried the trick of tying the lever back and waiting overnight.

I didn't put tremendous pressure on the lever so as not to strain the seals. Sure enough the lever firmed up nicely. The idea is simple: bubbles in the system will, under pressure, rise to the highest point in the system - in this case the master cylinder. The thing to remember is that there is no direction to pressure - so activating the lever doesn't push bubbles downward.

Something I'd try - if mushiness persisted - would be to tap the calipers with a rubber mallet to dislodge bubbles - while the lever was pinned back.

kuksul08 · Aug 10, 2015

I recently bled my brakes and it made a HUGE difference. Here's what I did.

Remove the left side caliper and raise it up as high as possible with the bleed port pointed straight up (sort of awkward) and put in a spacer as thick as the rotor. Then bleed it. This will remove any air bubbles from the link line between the two calipers. Then, bleed the right side caliper. Then bleed the master cylinder.

I got a substantial amount of air from the left caliper and from the master cylinder. The brakes feel consistently solid.

I never fully understood tying the brake lever back. I tried it and it was nice for a little bit then went right back to being spongy. I don't see why a small air bubble will rise to the top any better than a big one.

appliance821 · Aug 10, 2015

kuksul08 said:
I recently bled my brakes and it made a HUGE difference. Here's what I did.

Remove the left side caliper and raise it up as high as possible with the bleed port pointed straight up (sort of awkward) and put in a spacer as thick as the rotor. Then bleed it. This will remove any air bubbles from the link line between the two calipers. Then, bleed the right side caliper. Then bleed the master cylinder.

I got a substantial amount of air from the left caliper and from the master cylinder. The brakes feel consistently solid.

I never fully understood tying the brake lever back. I tried it and it was nice for a little bit then went right back to being spongy. I don't see why a small air bubble will rise to the top any better than a big one.

What you did is closer to the what the manual instructs - so I did cut a corner here. I'm pretty much working on the street so getting too involved can be complex.

So far the lever is firm and it's been a week. Not sure what you're referring to regarding bubble size - the pressure just forces bubbles to the top. The reason is that there's a small air gap in the master cylinder and stuff flows to the area of least resistance.

I do think the issue is air trapped in the hoses related to the ABS - your method addresses this directly. This time my method worked too, and for someone in a bind, it's worth trying.

kuksul08 · Aug 10, 2015

appliance821 said:
What you did is closer to the what the manual instructs - so I did cut a corner here. I'm pretty much working on the street so getting too involved can be complex.

So far the lever is firm and it's been a week. Not sure what you're referring to regarding bubble size - the pressure just forces bubbles to the top. The reason is that there's a small air gap in the master cylinder and stuff flows to the area of least resistance.

I do think the issue is air trapped in the hoses related to the ABS - your method addresses this directly. This time my method worked too, and for someone in a bind, it's worth trying.

When you squeeze the lever, it's going to make any air bubbles in the system smaller. The only forces acting on it are atmospheric pressure, hydraulic pressure, and buoyant force. So if you make the bubble smaller by pulling the lever, the buoyant force will be even less. I don't see how it solves any problem with making the bubbles move or go away.

I actually read somewhere that squeezing the lever makes the air dissolve into solution. They will eventually reappear as the fluid heats up and with time. I tend to believe this. In mountain biking with hydraulic brakes (very small fluid volume and very sensitive brakes), it's a common procedure to put brand new fluid under vacuum in a syringe and allow it to rise to the top. You'd be surprised just how much air is trapped in fluid.

Anyway, just some thoughts.

appliance821 · Aug 10, 2015

That might be why it takes around 8 hours to be effective. I'm an empiricist and it seems to work. But, if the softness returns I'll post it.

gatdammit · Aug 10, 2015

appliance821 said:
Something I'd try - if mushiness persisted - would be to tap the calipers with a rubber mallet to dislodge bubbles - while the lever was pinned back.

I beat the crap out of my rear caliper with a dead blow, while elevated/ inverted/ etc., with no results.

But my fronts were a piece of cake. I only removed the calipers to install new pads and did the fluid change with them re-installed.

appliance821 · Aug 10, 2015

gatdammit said:
I beat the crap out of my rear caliper with a dead blow, while elevated/ inverted/ etc., with no results.

But my fronts were a piece of cake. I only removed the calipers to install new pads and did the fluid change with them re-installed.

I'd guess that when you put the new pads in you pushed the pistons back and forced fluid from the ABS circuit. I'm guessing by having the lever tied back overnight I got air out of the same system, though not the fluid.

I'm happy with my results up front. The rear will wait a bit.

appliance821 · Aug 18, 2015

Well I just came back from a brief, but demanding camping tour through the Green Mountains, and the brakes held up fine. I'm calling it good.

One thing I'll note is that I didn't tie down the lever with a lot of force out of concern for the seals. Just a nice pressure (whatever that means) for about 5 - 6 hours. I then opened the MC and drained some fluid as it was a little high.

Hope this is helpful.

zippy49 · Feb 2, 2016

appliance821 said:
Thought I'd follow up. Put on speed bleeders and flushed the front system without removing the calipers. The lever felt mushy regardless of how much fluid I put through so I tried the trick of tying the lever back and waiting overnight.

I didn't put tremendous pressure on the lever so as not to strain the seals. Sure enough the lever firmed up nicely. The idea is simple: bubbles in the system will, under pressure, rise to the highest point in the system - in this case the master cylinder. The thing to remember is that there is no direction to pressure - so activating the lever doesn't push bubbles downward.

Something I'd try - if mushiness persisted - would be to tap the calipers with a rubber mallet to dislodge bubbles - while the lever was pinned back.

I'm about to flush the front brakes, can you post a link to where you found those speed bleeders? The company's website does not list our 821s.

Flushing the front brakes

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