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I did my first brake bleed on my '18 GTL today and found this gunk in the rear reservoir. Front brake was fine. In 30 years of owning and maintaining bikes I've never seen this before.


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Wow, I wonder what the contamination source is. Time for a flush. I’d get syringe and evacuate the contamination first.
 

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Wow, I wonder what the contamination source is. Time for a flush. I’d get syringe and evacuate the contamination first.
That is exactly what I did. Didn't want that crap in the brake line.

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I have no idea, but quick google search shows a number of car/ bike owners having the same "dandruff" white gunk in their brake oil?
 

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Good going using the syringe. I would fill the reservoir with fresh fluid and use a vacuum to draw out the brake fluid. I think a mighty vac tool would work well. Make sure you close the bleeder once your were done drawing the fluid out. Also, keep filling the reservoir as you went along with the flush. Don’t let the reservoir run dry. I’d inspect the fluid for any additional contamination once you were done. After the flush, I would then bleed the brakes using the brake pedal on the bike. Since the use of the front brakes are linked to the rear but the use of the rear brake isn’t linked to the front, you may want to flush the front brakes as well. Why leave cross contamination to chance?

If I’m not mistaken, the fluid in the abs pump won’t be flushed out during this flushing process. Now I have very limited servicing experience with bmw motorcycles but I suspect these vehicles use a diagnostic tool to cycle the abs pump to flush out the fluid. So, depending on how bad your contamination is, you may want to have a dealer do this for you. It’s a judgment call.

If I found this situation on my bike, I would flush the heck out of both the rear and front brakes. Then I would perform the final bleed to the entire system by using every bleeder screw using the force of the bikes master cylinder.

Good luck!
 

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Discussion Starter #10
I have no idea, but quick google search shows a number of car/ bike owners having the same "dandruff" white gunk in their brake oil?
This had a waxy feel to it like paraffin.

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Discussion Starter #11 (Edited)
I sucked the reservoir empty and then wiped it out. Bleed using the brake pedal into a clear glass jar. No contamination seen in fluid pumped out. Then used Motoscan software to cycle ABS pumps, and bleed system again. Everything looked good that came out. I will be keeping an eye on the rear reservoir though to see if this is a continuing problem.

The front did not look like this, but I bleed it also and cycled pump, then bleed it again.

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It looks like it, but paraffin is petroleum based, while brake fluid should not be,so still puzzled. One of the posts I read earlier somewhere else suggested it comes from breakdown or decomposing of inner break hose lining, but after only 2 years in use, I doubt it.
 

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One last thing, make sure you inspect the seal to your rear brake reservoir cap. It might be the source of your problem.
 

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Motoscan tool

I sucked the reservoir empty and then wiped it out. Bleed using the brake pedal into a clear glass jar. No contamination seen in fluid pumped out. Then used Motoscan software to cycle ABS pumps, and bleed system again. Everything looked good that came out. I will be keeping an eye on the rear reservoir though to see if this is a continuing problem.

The front did not look like this, but I bleed it also and cycled pump, then bleed it again.

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Would you recommend buying the Motoscan software?
 

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Discussion Starter #15
Would you recommend buying the Motoscan software?
So far it has done everything I've needed it to. I had a brief chance to see a GS-911 in action and the interfaces were similar. My buddy has purchased a GS-911, so I hope to be able to do a side by side comparison soon. For the money it is a good tool. Not as user friendly during set up, but if you are somewhat computer savvy you can figure it out.

From what I know at this point I would recommend it. Once I've played with the GS-911 we'll see if this is still true.

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When you do get around to doing a side by side comparison between the Motoscan and the GS-911, please shoot me a message. I plan to do my own maintenance so having someone with their unbiased review of both platforms will save me some headaches, I’m sure.

Thank you
 

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Looks like someone on the assembly line misplaced their yogurt from lunch.
 

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Since the bike is still relatively new, I have seen stuff like that in HD's, at first I thought it was from poor maintenance but I would lean more towards an assembly type lube residue. If you think about it all the components sit on shelves before they are actually used during an assembly.
When I use to rebuild calipers and master cylinders, I would clean everything in denatured alcohol, then assemble using a product called Sil-Glide, its a synthetic lubricant for brake parts, there are other products that are used and sometimes the parts come with a lube compound when rebuilding.
As fart as flushing goes is to use a denatured alcohol, it doesn't leave any residue, but I will say I have not used this on an ABS system.
 

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As fart as flushing goes is to use a denatured alcohol, it doesn't leave any residue, but I will say I have not used this on an ABS system.
Denatured alcohol most certainly leaves behind a residue. Technical grade isopropyl alcohol, on the other hand, does not.
 

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Denatured alcohol most certainly leaves behind a residue. Technical grade isopropyl alcohol, on the other hand, does not.
I just did a Google search and it seems we are both right. I found where it says does not leave a residue, and one where it says it will leave a residue that would be corrosive to a computer circuit board and terminals.
 
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