1995 K75 rear brake flush problem - with ABS

[dbamberger]

Hey folks.

I went home after BT last night, changed the oil, flushed and bled the front brake all of which went fine.

The rear brake won't flow any fluid through either the ABS modulator or the rear caliper. I was using a one-way valve to help with the process (and it was brilliant for the fronts).  Here are some symptoms

* I got a very minimal amount of fluid out of the ABS modulator initially, maybe a tablespoon, and then nothing
* Pedal has no pressure
* Can't get fluid out of either rear caliper or ABS modulator
* Even under vacuum - I've got some big syringes and in a bit of desperation I bought myself a MightyVac vacuum diagnostic hand pump which is good for bleeding brakes.
* Can't push fluid back up the system either (filling the syringe and pushing through the rear caliper)

I'm beginning to wonder if I ever had any rear brake.  Thoughts? Master cylinder?  Some blockage in the piping or ???

Would love to try and fix this so that I can ride off to the BMWMOA nationals today but can also fallback to the KLR if needs be.  Thanks for your ideas.

Regards.
dbam

[Laitch]

I'm beginning to wonder if I ever had any rear brake.

Because you're asking for thoughts, I'll provide one. That's either a troubling statement or a comedic punchline I've quoted above.
Help will be arriving soon. I don't have ABS; it seems a bit pesky so I'm living without it, so far anyway. 

[Past-my-Prime]

When flushing the rear brake, might you have some crap in the master cylinder that clogged up the outlet? In my case, I did have to rebuild both MC and caliper for the rear brake (on a BMW F650, if that makes any difference) and it took me a day to do the job. I’m a slow mechanic.
On my K75, with these symptoms, I would be removing the brake line at the attachment to the ABS pump and see if I can squirt any fluid out but “have no pedal” implies to me that you’re unable to pressurize the line, which gets me back to the master cylinder.
I’ll wait for the brake professionals to chime in or possibly you’ve already fixed it.
Finally, if everything I just wrote doesn’t make sense, I am blaming sleep deprivation, to possibly be explored on another story line!

[dbamberger]

To close this loop. 

I ended up pulling off the ABS system, getting some stainless/braided lines made up.  I still had problems pulling brake fluid through the rear so I swapped out the MC with the cheap Chinese universal as [described here][/https://www.motobrick.com/index.php?topic=9364.0].  Bled the rear and will give it a shake down ride tomorrow.  Thanks for the help.

[mmc_meneses]

With the metal hose is a bit different to purgue...

To make it easier i used the old rubber hose, remove the bleeder completaly, conect the rubber hose to the bleeder exit directly (yes !!! it is the same nut size) then connect the bleeder nut to the other side of the rubber hose (yes!!! again is the same size) and now with the circuit open (bleeder open) make the circuit flow (pump-metal hose-rubber hose-bleeder) pressing the brake pedal at intervals (1-1-0) and at the zero close the bleeder everytime with your finger (use gloves) so the air don't go back to the system.
Repeat the process until you feel the brake pedal is tight (takes max 1 min)

In my experience rubber hose close itself around when you release the pression in the line and makes it easier to purgue the air in the system with no extra tools.. but metal one when system is open puts air back in the system everytime you release the pedal.

Big hug

[stokester]

I purge the braking system on both my ABS-equipped K75S bikes and vehicles every two years

What I have found with my airheads, bricks and vehicles is that using a vacuum system will make it a much easier process.  I've use the MityVac with limited success in the past but have found that a system using shop air will flush and bleed a system quickly and without complications.

Flushing a brake system in all vehicles is so important these days.  Even more so than in the past where the complication (and expense) of an ABS system is involved.