Author Topic: Bleeding ABS Brakes  (Read 22273 times)

Offline frankenduck

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Bleeding ABS Brakes
« on: October 06, 2011, 02:08:48 PM »
People who have never bled ABS brakes often ask what the correct procedure is for bleeding brakes.  The 100% BMW way to do it is to take your bike to the dealer and have them hook your bike up to the BMW computer.  This allows the maintenance technician to modulate the ABS during the bleeding process to make sure that the very small amount of brake fluid in the modulator gets refreshed.

At $95/hour for labor with additional charges for taxes and brake fluid that gets rather expensive.  Though not the BMW proscribed procedure, I do my own brake bleeding as described herein and have never had brake issues.

The procedure for bleeding brakes it to first bleed them at the ABS modulator and then at the caliper(s). I usually use a MightyVac vacuum pump but I have also used the normal manual approach where you repeatedly open the bleed valve, s-l-o-w-l-y apply the brake, close the bleed valve and then release the brake until you've flushed the system.

If you're using the manual approach many people recommend not having the brake lever/pedal travel more than half way as there may be something in there that will get stuck in the seals and cause the master cylinder to leak.  I've never had an issue like this happen to me but if you want to err on the safe side I don't think it hurts.  It will just take you a little longer to bleed the brakes.

In order to deal with the issue of the brake fluid in the modulator I take the following approach.  Before bleeding the brakes I take the bike out and get the ABS to engage, one at a time, usually the rear first and then the front.  If you've never had your ABS engage then it's a god idea to do this anyway so that you're familiar with what happens when the ABS engages in the real world.  Try it while going straight in a nice level empty parking lot where it's safe.  Do the rear brake first and take another run and get the front ABS to engage.  I usually do each about three times before I bleed the brakes.

After I've bled the brakes, I take the bike out again and get the ABS modulators to engage a few more times.  My theory (which may not be correct) is that this at least gets the old brake fluid in the modulator at least mixed up with the fresh fluid.  It certainly doesn't hurt and practicing panic stops is a good idea anyhow.

Additional cautionary note: Do not overadjust the set screw on the rear brake pedal. Your best bet is to leave it where it is.  The reason is that if the piston in the rear master cylinder is pushed in too far it can get stuck on the set screw that holds it in - resulting in a locked or partially locked rear brake.  If this happens when you are riding PULL OVER IMMEDIATELY.  On 4 valve paralever K bikes, the rubber boot on the front of the final drive is very close to the brake rotor. If you ride with a partially locked rear brake the rear rotor gets extremely hot and in a very short distance (less than a mile) it will get hot enough to light the rubber boot on fire.  This fire is very hard to put out and can cause lots of damage - to the rotor, final drive, rear caliper and brake lines - possibly worse if you're unable to get it extinguished quickly.
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Offline enb54

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Re: Bleeding ABS Brakes
« Reply #1 on: June 13, 2012, 02:46:57 AM »
People who have never bled ABS brakes often ask what the correct procedure is for bleeding brakes. <SNIP>The procedure for bleeding brakes it to first bleed them at the ABS modulator and then at the caliper(s). I usually use a MightyVac vacuum pump but I have also used the normal manual approach where you repeatedly open the bleed valve, s-l-o-w-l-y apply the brake, close the bleed valve and then release the brake until you've flushed the system. <SNIP>

So basically you are saying that the manual way is OK? I am replacing all the fluids on my K75RT (1991) and want to ensure it's done right, there is no BMW motorcycle dealer here. I do have a Clymer's manual... Thanks in advance...
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Offline Duc750

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Bleeding ABS Brakes
« Reply #2 on: June 13, 2012, 12:14:35 PM »
Bmw dealers in the uk just bleed the manual way now as they have no access to the system to bleed anything before non servo abs ! BMW uk instructed them to de stock everything to do with the bikes pre integral abs a couple of years back. Some dealers kept it all in a cuopboard but most didn't. Software on diagnostics was often updated to get rid of that for old bikes

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Offline enb54

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Re: Bleeding ABS Brakes
« Reply #3 on: June 13, 2012, 10:30:21 PM »
Bmw dealers in the uk just bleed the manual way now as they have no access to the system to bleed anything before non servo abs ! <SNIP>
Thanks, will do it the "old fashioned" way and I'm sure it will be fine...
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Eric

Then-1966 Suzuki X6 Hustler, 1987 BMW K100RS, 1997 Suzuki GSF600 Bandit

Now-1991 BMW K75RT, 1974 Honda CB125S, 2015 Honda Grom (MSX125)

Offline RetDet

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Re: Bleeding ABS Brakes
« Reply #4 on: July 21, 2012, 04:32:37 PM »
Where do you add the fresh fluid for the rear? Guess what I am asking is where is the rear fluid reservoir located? 1993 K75RT. thanks, Ed

Offline Inge K.

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Re: Bleeding ABS Brakes
« Reply #5 on: July 21, 2012, 04:53:43 PM »
Behind RHS battery cover.

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Offline RetDet

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Re: Bleeding ABS Brakes
« Reply #6 on: July 21, 2012, 09:46:31 PM »
Thank you, appreciate the response. Ed

Offline voodooskin

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Re: Bleeding ABS Brakes
« Reply #7 on: August 29, 2012, 01:35:28 AM »
Does anyone know what model of speed bleeder replaces the OEM fitting on a K1100?  Thought I'd replace the original part since I have to bleed the brakes anyway.   Thanks!
http://www.speedbleeder.com/size.htm
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Offline TimTyler

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Re: Bleeding ABS Brakes
« Reply #8 on: January 22, 2016, 01:11:59 AM »
The BMW K75 / K100 Rapair Manual says:

Quote
Remove brake pads (see page 34- 12.0)
Insert piston setting-back device BMW 34 1 500 in brake
caliper and push the piston back into the brake caliper
with adjusting screw. (Only in this way can the brake fluid
behind the piston be changed.)

Does anybody do this?

Offline The Mighty Gryphon

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Re: Bleeding ABS Brakes
« Reply #9 on: January 22, 2016, 09:54:33 AM »
Ummm...uhhhh...uhhh...well, ummmm, no.
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Offline mlytle

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Re: Bleeding ABS Brakes
« Reply #10 on: January 22, 2016, 10:31:51 AM »
that is technically the correct way to do a complete flush.  compressing the pistons pushes out more of the old fluid that would be in "dead" spots inside the caliper.  the normal bleeding process mixes some new fluid in with the old but does not do a complete flush. 

I do compress the pistons every couple of fluid bleeds, which I do twice a year.  this applies to cars or bikes.

special tools not needed.  a couple of pairs of pliers will get the pistons in, then just stick a piece of wood or something else in the caliper to keep the pistons in while bleeding.
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Offline Martin

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Re: Bleeding ABS Brakes
« Reply #11 on: January 22, 2016, 02:11:45 PM »
Wouldn't a vacuum achieve the same thing. I don't have ABS but vacuum bleeding should remove all the old fluid? Thoughts anyone
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Offline mlytle

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Re: Bleeding ABS Brakes
« Reply #12 on: January 22, 2016, 02:26:20 PM »
no.  vacuum or pressure does not matter.  neither will get all the old fluid trapped in the calipers.  bottoming out the pistons is the only way to get most of it.  only way to get all of it is to remove the pistons when replacing the seals during rebuild.
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Offline TimTyler

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Re: Bleeding ABS Brakes
« Reply #13 on: January 22, 2016, 04:22:00 PM »
I was able to depress the pistons easily using my fingers. Calipers were removed from the bike first (and hose disconnected at the master cylinder).

When I had the new brake hose made the other day, the guy mistakenly used a banjo fitting that was 8mm thick instead of the OEM 10mm thick. (The opening is the proper 10mm though). Consequently this turned out to be a happy accident since I'm now able to use two 1.5mm thick aluminum sealing washers instead of the thinner 0.75mm OEM copper sealing washers. In my experience the aluminum sealing washers require less torque to properly seal than the copper washers, and it's very easy to strip the threads in the $200 master cylinder.

Offline mlytle

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Re: Bleeding ABS Brakes
« Reply #14 on: January 22, 2016, 06:49:41 PM »
if you had caliper off, don't forget to recheck the abs sensor gap.
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Offline piptravels

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Re: Bleeding ABS Brakes
« Reply #15 on: April 09, 2018, 10:55:03 PM »
Does anyone know what model of speed bleeder replaces the OEM fitting on a K1100?  Thought I'd replace the original part since I have to bleed the brakes anyway.   Thanks!
http://www.speedbleeder.com/size.htm


Did you ever find out what size speed bleeder works? I have a 1996 K1100LT
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Offline Laitch

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Re: Bleeding ABS Brakes
« Reply #16 on: April 09, 2018, 11:36:20 PM »

Did you ever find out what size speed bleeder works? I have a 1996 K1100LT
How about believing this chart at Aerostich?
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