Brake Flush Question - K-Bikes.com - Excellence in Motion
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post #1 of 18 (permalink) Old Mar 14th, 2011, 1:00 pm Thread Starter
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Brake Flush Question

I flushed both front and rear brakes over the weekend on my 2008 K1200GT and have a few questions. While a fairly easy maintenance task, I was somewhat surprised to note the lack of material that accompanied a search of the K12/K13 Forum.

I've owned the bike since it was new and performed all the maintenance myself (save a faulty fuel strip that was fixed under warranty by my dealer) and have never flushed the brakes. I know, bad on me. Felt it was about time to give a little love to the all important system that slows the bike down from the joyful warp speeds we all take for granted.

Per my GS-911 the build date of the bike was March of 2008 (if memory serves - I'm at work). Was surprised to note how vibrant and clean the original fluid looked in both reservoirs. Granted, the effectiveness could have been compromised over the years (we all know the hygroscopic issue with brakes) but the fluid wasn't discolored and I still had a firm feel in both brakes.

I also went overboard and removed everything necessary to easily access the rear reservoir. It's tucked in tight on the right side of the bike under the rear seat and even after removing the reservoir from the clip holding it in place I didn't have sufficient wiggle room to adequately clean or refill. Suppose next time I can skip that step and use a funnel with a curved tip to top it off.

So here are my issues:

I used the same large volume fluid extractor that I change the oil with to suck out the brake fluid at the caliper bleed screws. In other words, I didn't do the old pump the lever and open the bleeder screw trick. Seemed to work just fine with no introduction of air. Any reason why this isn't on par with the time honored tradition of pumping the lever and opening the bleeder screw?

Inside the front brake reservoir I noted a bar graph picture denoting a Min/Max level for the fluid. How should the handlebars be oriented when measuring this? Keeping the front wheel pointing straight ahead wasn't the best way to keep the fluid even across the reservoir, rather turning the bars to the left accomplished that. When using the round site glass on the reservoir to check your fluid level, how should the bars be positioned? Again, I'm at work and don't have access to my manual.

I did not remove my calipers in order to fully re-seat the pistons. Have I not removed all the old fluid?

And finally, after the procedure I was somewhat disconcerted to note the lever feel was no different than when I began. Wasn't expecting a night & day difference but a more firm feel was hoped for. Do I need to bleed the smaller screw outside the front reservoir? Could I have possibly trapped some air thus explaining the lever feel? I've often wondered why BMW chose to place that tiny bleeder screw there.

All in all an enjoyable bit of maintenance that was long overdue. Just wondering what other folks thoughts and experiences are.
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post #2 of 18 (permalink) Old Mar 14th, 2011, 4:48 pm
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Number one on my list is the risk of oil contamination by using a tool that had previously had oil in it. Not sure what the real risk in your case is, but I would be very careful not to introduce even small quantities of oil into the brake lines.

Also, it seems from your description that you didn't pump new fluid through the system, a necessary part of replacing the fluid and the only way to bleed the system. I believe forcing the pistons back will help because you decrease the volume of the fluid in the system, so less needs to be pumped thru.

I vaguely remember the bleed screw at the master cylinder is a help because you can get air out of the system before you pump it down into the slave, most useful if you suspect air is in the line or replacing the master. Sometimes it's difficult to get a bubble to travel downhill, so the bleedscrew at the top will help.

Guy Howard
K12LT 05 (sold)
K12GT 07 - build 12/06 BMSK-P ECU (ASC retrofit), V.3 airbox, new o2 sensor @18k, PowerFrk module @25k
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post #3 of 18 (permalink) Old Mar 14th, 2011, 10:45 pm Thread Starter
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Quote:
Originally Posted by howfly
Number one on my list is the risk of oil contamination by using a tool that had previously had oil in it. Not sure what the real risk in your case is, but I would be very careful not to introduce even small quantities of oil into the brake lines.

Also, it seems from your description that you didn't pump new fluid through the system, a necessary part of replacing the fluid and the only way to bleed the system. I believe forcing the pistons back will help because you decrease the volume of the fluid in the system, so less needs to be pumped thru.
I should have been more clear. I placed a new section of tubing on the end of the extractor and sucked the dirty brake fluid out each reservoir first. After refilling with fresh fluid I used the extractor to then suck the fluid out of each caliper. I filled the reservoirs countless times during this flush process ensuring I had pumped new fluid throughout the system.

Thanks for the response.
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post #4 of 18 (permalink) Old Mar 15th, 2011, 6:59 pm
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Bleeding motorcycle brakes can be tricky because of the small amount of fluid in the system the typical pump it and bleed it off method we all use before on our old Cheys will not be effective. You only need one guy to do vacuum method and I use a cheap vacuum pump you can get at any auto parts store. Mine is the Mityvac 4000 and it can be found on Amazon.com for about $50 but I didnít pay that much.

Simply put some fluid in the cup so the supplied hose is submerged and attach it to the pressure side of the pump. Probably not required since the vacuum pump has back flow valve but Iím kinda anal that way. Attach the vacuum side of the pump to the zurk fitting. Add fluid to the reservoir and start pumping until the fluid is clear after opening the zurk ľ turn. Close the zurk when you are done with that caliper. Hint use a closed end 8mm wrench and have it on the zurk before you attach the hose to the vacuum. Make sure you keep the reservoir full and always start at the caliper that is farthest way from the reservoir. Bleed/ flush all three calipers and your done.

Donít know much about the level indicator line at the reservoir but it would be reasonable that the line should be level to the ground when testing the fluid level?
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post #5 of 18 (permalink) Old Mar 15th, 2011, 8:43 pm
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On the post 2007 models without the power assisted brakes, is the ABS setup like the prior where they are two separate systems or are they coupled together now? i.e. Master cylinder to ABS as one circuit to bleed; and the ABS to brake caliper as the second? I know mine with the power assist ABS unit is a total PITA to bleed all the damn circuits and bleed nipples (something like 10 in total to bust open?). Takes about a quart of brake fluid too.

Supposedly, the S1000RR is a lot like a straight through brake system and not separate circuits. The ABS unit on it is about the size of a pack of cigarettes without the half dozen fittings all over it like on my GT.


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post #6 of 18 (permalink) Old Mar 15th, 2011, 9:41 pm
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The newer non-servo ABS has just two circuits, for front and rear. There are no "internal" ABS circuits like on the older power-assisted brakes.

So it's just a "normal" brake bleed, as long as you maintain fluid levels and don't allow any air into the ABS pump then all is good.

Ken
Pacific NorthWet
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032

All lower 48 states plus Alaska on the K13GT in two weeks . . .

Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...
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post #7 of 18 (permalink) Old Mar 16th, 2011, 9:55 am
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Quote:
Originally Posted by Meese
The newer non-servo ABS has just two circuits, for front and rear. There are no "internal" ABS circuits like on the older power-assisted brakes.

So it's just a "normal" brake bleed, as long as you maintain fluid levels and don't allow any air into the ABS pump then all is good.
I've been trying to figure out the straight goods an the non-servo brakes on my 08 GT. My owners manual still describes them as integral brakes and states the front and rear are linked off the front M/C. They are deffinitely not the servo brakes and do not have the seperate resevoirs etc. at the ABS modulator, but are they in fact still linked? As near as I can tell, they don't seem to be.

Ed Miller,
Calgary, AB, Canada
2008 K1200GT, 2009 F800GS
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post #8 of 18 (permalink) Old Mar 16th, 2011, 11:41 am
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They are not "Linked" in that they do not share any common brake fluid. There are still two distinct brake fluid circuits here for front and rear.

They are "Semi-Integral" according to BMW. Integral means that the ABS unit has a proportioning valve that allows some brake input from either lever to be applied to both wheels. Semi means that the front brake lever will apply some braking force to the rear wheel, but the rear pedal does not apply any force to the front brakes. This configuration allows for more "sporty" riding, such as smooth trail braking into corners without upsetting the chassis stability.

In contrast, the LT has Full-Integral brakes, meaning the rear pedal also affects the front brakes.

Integral also refers to the fact that the amount of braking force applied to the "other" wheel is proportional, depending on the bike's speed, loaded weight, available traction, etc.

This is a much more sophisticated system than older "Linked" systems that used a simple mechanical valve to apply all brake inputs to all calipers, or that hook the front brake lever to some front and some rear caliper pistons, and the rear brake lever to some rear and some front caliper pistons.

The older Servo-ABS system also added hydraulic pumps that amplified the effort put in at the levers and gave a stronger (and quicker) response at the calipers, especially during full-on panic braking. This system, used on '06 GTs and '02 and up LTs, has four separate brake circuits. There is one for each lever/pedal, and one for each set of calipers. All four of these circuits needed to be bled separately.

Welcome to the wonderful world of German engineering excellence (and expense).

Ken
Pacific NorthWet
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032

All lower 48 states plus Alaska on the K13GT in two weeks . . .

Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...
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post #9 of 18 (permalink) Old Mar 16th, 2011, 12:58 pm
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I presume then that this linking action will only take place when riding, i.e. with the ABS system powered up. That would explain why sitting in the garage, I could not discern any rear brake application with the front lever.

Thanks.

Ed Miller,
Calgary, AB, Canada
2008 K1200GT, 2009 F800GS
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post #10 of 18 (permalink) Old Mar 16th, 2011, 1:37 pm
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Again, it is speed dependent . . .

The system is fairly complex in design, but works very well in practice. Most folks don't even know it's there . . .

Ken
Pacific NorthWet
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032

All lower 48 states plus Alaska on the K13GT in two weeks . . .

Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...
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