Ducati Monster Forum

For the last week or two the front brake lever on my ST2 has been coming back almost an extra inch before generating any pressure.  A sure sign that there is an air bubble or two in the hydraulic lines.  Since I have a big trip planned in a few days, I needed to fix that right away.

It's a real bother to properly bleed brakes.  You need to hook up a tube on each caliper to catch the brake fluid, then go through the process of squeezing the brake lever, releasing the bleeder valve to let some fluid and hopefully an air bubble or two out, then tighten the valve again before releasing the lever.  Then you need to make sure you don't run the master cylinder dry in the process.  But you can't just leave the master cylinder open or you might spray brake fluid all over the front of the bike.

In addition, since the air bubble has usually migrated to the top of the hydraulic line, it can often be a big job just to get it to go down and out the bleeder valve two feet below.

So I had a different idea.  Based on my experience with changing brake pads in the past, I decided to just push any air bubbles out of the brake lines and directly back into the master cylinder.  I grabbed my 8mm allen wrench, removed the two bolts holding the left caliper to the fork leg and took the caliper off of the rotor.  It was then a small matter of pushing the four brake pistons back as far as they would go, which also pushes a bit of brake fluid, and hopefully the bubbles, back into the master cylinder.

Pushing the pistons back in once was enough to make the brake much firmer.  I set the caliper back over the rotor and pumped six or eight times to get the brake pads back into place and it was a big improvement.  I went through the process a second time "just to be sure", then tightened the caliper back into place.

The bike had recently received new front brake pads when it was serviced less than two thousand miles ago, so I had no worries about the pistons not being clean enough to push back in three or four millimeters.  And checking the brake after the bike has sat overnight, the lever is still nice and firm.

Any comments about this method of removing air bubbles from brake lines?

It's sort of like 'Reverse' bleeding... without the hassle.  And i guess it's not actually bleeding them, but it makes a lot of sense to me.  On our front brake systems about the only place to air to hide is in the bores for the pistons - which we then try to force out by pumping fluid down (when the air would want to go up) and out some inconveniently place bleeders.

By forcing the fluid back into the lines like you did you've got a much better chance of clearing air if you did bleed them.  And you've also got a good shot and the air just working it way up the line and out on it's own.  It's a bit like leaving the clutch lever pulled in and strapped to the bar method for dealing with a mushy clutch.

Combine what you did with a vac bleeder on the master and you've got a realy good shot clear 99% of any air out. 

It's an extra hassle - but it makes sense to me -especially if you've got brakes that are being stubborn about getting all the air out.

The only negative, which should not apply to any of our bikes since we are meticulous about changing brake fluid, is you could be pushing dirty fluid up into the master.  The plus is this method is great for getting air bubbles out of the master.  

Don't get me wrong.  I'm not attacking anyone, I'm not knocking this method at all, and I don't mean to thread jack but...

I really don't find bleeding brakes all that hard.  A piece of vinyl tubing, an empty jar to catch the excess, and a can of brake fluid.  Fill, pump, drain, repeat.  I know it can be hard if the master runs dry but routine bleeding is easy, I've been doing it since I was 15 years old.  Do people really find it that difficult?

Scott

What I like most about ScottR's suggestion is that it can be done relatively easily when out in the wild.  If the brakes are feeling less effective than expected, pop 'em off and squeeze the Charmin (so to speak).  No fuss, no muss, no messy applicator brush.  Great suggestion, imo!   [thumbsup]

Not difficult, but time consuming.  I really didn't have the time to do a proper job, which would probably take me 45 minutes to an hour.  My alternate method took less than 15 minutes.

It's definitely better to do on the road.  At home I'd rather crack open the bleeder than remove and compress the caliper.  Only takes me a few minutes but maybe that's just me.

Scott

I've been using a pneumatic one person bleeder for a couple of years now and I can bleed the brakes and clutch on both bikes and the cage in under an hour.  It's been the absolute easiest method that I've used by far but it requires an air compressor.

All I do is hold the trigger down and there is constant suction until I'm done... very nice

(http://s7d4.scene7.com/is/image/GriotsGarage/35714?$detail$)

btw, the pic from griot's garage happens to be a monster  ;)

How do you make sure you have the right amount of brake fluid in the master cylinder while you're doing this?

you have a free hand and don't have to be kneeling down so I just watch the fluid and use a little squirt bottle

This page is a good list of tips and tricks for bleeding brakes: http://www.tawvehicle.com/brembo_tech_info.htm.  I think they describe a similar process in section 4b, paragraph 2.

I've been having the same problem with mine so I tried this before I went to run some errands tonight.  Worked like a charm.  I still need to change the fluid and bleed it the right way, but this is a good intermediate way to keep things tight.

It's the way I get the last of the air out it if I'm starting from scratch, IE rebuilt caliper or brand-new empty caliper.
I'll do it if a conventional bleed job isn't getting the job done on a system that's already 'full', like what Scott had.

Sometimes the bubbles will get stuck in a banjo bolt, or high spot in the hose.
You can bleed in the conventional fashion for a *long* time, and get nowhere.

Also, it's a very handy method for the S*R rear calipers, as the hose has several high spots.

Is that this thing?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92924

I need one.

Here's another simple way to bleed them from the bottom up.   Go to the parts store and buy a simple pump oil can (like this http://tinyurl.com/5vkxrl (http://tinyurl.com/5vkxrl)) and a piece of tubing.  Fill the oiler with brake fluid, hook the tubing to the bleeder and open it.  You can now pump fluid into the brakes from the bottom up.   A large syringe would also work and you can get those at most veterinary stores.  The only downside is you have to watch the master cylinder, but it's not a big deal.

yup!