EVO brake flushing question

I recently completed flushing the ABS system in my 2004 R1150RT with EVO brakes.

I followed the procedure recommended in the manual and elsewhere, in which I removed the brake pads and blocked the calipers before flushing the wheel circuits.

So, my question is, why bother removing and blocking the calipers?

Cap

I am looking forward to the answers that you get as I never do remove them. It seems to mee that the disk does the same thing.

I recently completed flushing the ABS system in my 2004 R1150RT with EVO brakes.

 

I followed the procedure recommended in the manual and elsewhere, in which I removed the brake pads and blocked the calipers before flushing the wheel circuits.

 

So, my question is, why bother removing and blocking the calipers?

 

Cap

Afternoon Cap

No real need to remove the calipers but blocking the pads back (with wedges) serves 2 functions.

First, it reduces the dead volume space behind the pistons so that area flushes more completely (not a big deal & really not required if the brake system is flushed regularly).

Second, & most important, is that it prevents overfilling the ABS controller reservoirs.

If the brake pads have some wear on them & the caliper pistons are not pushed back during the controller reservoir final filling then there is a good chance that the reservoirs will be overfilled.

The overfilling isn't usually a problem UNTIL tire change time when the caliper pistons are then pushed back to get the front wheel off, that forces the excess fluid to flow back out the reservoir vent & vent catch container where it can drip and/or blow back on the painted rear parts of the bike & ruin the paint.

I don't normally remove the calipers but do usually pry the pads/pistons back then use some plastic wedges between the pads & rotors to hold them back during the service bleeding & reservoir re-fills.

No real need to remove the calipers but...

Thanks for confirming that it is reasonable to leave the calipers attached. I have accidently done the "pushing fluid back into the overflow drain" once on the rear circuit. So, now I am pretty careful about that. Having installed braided stainless brake lines, removing the caliper on the left front is somewhat of a PITA. I think I will just leave them attached in the future.

As an aside, a couple of years ago, I bought speed bleeders for 4 locations: the clutch, the two front wheel calipers, and the rear caliper. And initially, I couldn't get the brake bleeders to work, although the clutch bleeder worked great. After some fussing around, I got the rear brake bleeder to work, but not the fronts... And I think I finally figured out the problem:

First, the conical tips need to be filed flat on the caliper speed bleeders, to match the profile of the BMW parts. But, having done that, I still couldn't get them to work. They would not pass fluid at all, no matter how loosely I screwed them into the calipers. I went through this exercise 18 months ago when I flushed the ABS last time. But I think I solved the mystery of the non-speed-bleeders! When flushing the rear wheel circuit this time, I decided to try the speed bleeder again, after filing the tip down farther. And it still would not work. That is, until I got frustrated and jammed on the rear brake with some gusto. And then, as the sound of the ABS pump intensified, suddenly the speed bleeder gushed a bunch of frothy fluid, and then ran clear. Bingo. I just needed to increase the control circuit pressure to the point at which the ABS pump raised its output pressure.

Before doing the rear wheel circuit, I had reinstalled the speed bleeders on the front, and applied full control to the handlebar lever: no flow. So, I pulled the speed bleeders out of the front calipers and bled them the old fashioned way. But after having success on the rear wheel, I realized that I had only been able to force the ABS pump to activate at the "idle" level on the front circuit, not the more intense level. When the rear circuit worked because the ABS pump went to higher output, I realized that my front control circuit wasn't working right. And THAT was my clue that my brake master cylinder needed a new piston seal. So, it turns out that every since I bought this bike from the previous owner, the front brake master cylinder has been marginal, unable to produce full pressure. And the microswitch on the front brake lever was the only thing causing my front brakes to actuate. Wow, that is scary in retrospect.

The amusing thing is that the "idle" level of ABS actuation in my R1150RT produces better stopping than the Vstrom that I rode for years before getting this RT.

It turns out that rebuilding a master cylinder is trivial. Once I got it off the handlebars, removing the piston only takes a few seconds. Everything seems to work much better now -- I can get the front circuit to activate normally with my new master cylinder. I haven't road-tested yet, but I'm looking forward to it. I suppose I'm going to have to be gentle until I get calibrated to the new actuation force.

Cheers, Cap