1999 K1200RS breaks soft - K-Bikes.com - Excellence in Motion
 
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post #1 of 5 (permalink) Old Mar 17th, 2020, 3:57 am Thread Starter
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Question 1999 K1200RS breaks soft

Greetings,

I'm new here, and this is my first post, now I have spent a number of hours looking over the various post trying to find a solution, but I can't see anything that looks like its similar to my issue, never the less. If I have repeated the question, please feel free to gently correct me and provide me with the relevant information.

So here is the situation, I purchased a new to me 1999 K1200RS, and now I need to get it passed its vehicle inspection before I can transfer ownership. The bike is generally in good shape, however, the rear breaks where a little soft and required to be pumped two or three times to get them to work, after about 20 minutes of riding they would fade again. So I decided to replace all the brake lines, replace the seals and also replace the master cylinder. I checked the shoes, and they are still in pretty good condition, so I didn't replace them. I vacuum bled the whole system, but this hasn't made much difference.
If anything the situation is worse because now the front breaks are also soft (I replaced the lines and Seals in them as well). It definitely seems like there is air in the system. But I have spent literally days trying to fix this with no success. I have a full workshop manual, and I have followed the procedure as outlined, I have a vacuum bleeder, but it just doesn't seem to want to bleed properly, I can't see any bubbles in the line at either the calliper of the ABS unit, so it should be perfect. BUTÖ it's not.
Is there a trick?
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post #2 of 5 (permalink) Old Mar 17th, 2020, 5:10 am
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A couple of things to check/do. Make sure you have removed the callipers, pushed the pistons all the way back and blocked them so they cannot move when bleeding the lines. Also, you can crack open the banjo at the front MC, treating the process as if itís a bleed nipple. Air is known to get trapped here.
Always a good idea to thoroughly wash the pistons with a toothbrush before pushing them back to avoid damaging the seals. Others will definitely chime in on this.

2002 K1200RS Owned from new. Pacific Blue, Ohlins. 183,000kmís
2016 K1300R Black, Remus hexacone. 6000kmís
The family history
1951 AJS 500 single - my Dads
1916 Triumph Type H, Western front, France WW1 - my Grandads
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post #3 of 5 (permalink) Old Mar 17th, 2020, 11:26 am
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Do a complete bleed but don't use the vacuum bleeder, use the old fashion lever pressure, crack the bleed nipple, flow fluid, seal bleed nipple, release lever pressure. Cover the front reservoir lid area as it can spray fluid up. Bubbles can be very troublesome to get out of the system. I have found sometimes the rear brake takes some force (quick) lever movement to get the fluid moving with enough energy to carry small bubbles with it. As mentioned to get trapped fluid in the front calipers out of the circuit it is best to wedge the pucks back for one bleed session then install on the bike to fill and a small flush again. I have had to move large amounts of brake fluid through some systems to get pesky bubbles out.

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post #4 of 5 (permalink) Old Mar 17th, 2020, 6:59 pm
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If the good suggestions above don't produce results, you can use a large syringe and some flexible clear tubing to fill the brakes (and clutch slave if you've a mind to) from the bottom up.

The oldest suggestion in the book is to compress the brake lever, tie it in compressed state, park the bike on the sidestand so the brake master is the highest point on the bike, and leave it overnight. Small bubbles can need a lot of time to work up through the viscosity of brake fluid and past the inner surface stickiness of small diameter brake lines.
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post #5 of 5 (permalink) Old Mar 18th, 2020, 3:05 am
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Out of interest, what brake lines did you replace the oem lines with?

2002 K1200RS Owned from new. Pacific Blue, Ohlins. 183,000kmís
2016 K1300R Black, Remus hexacone. 6000kmís
The family history
1951 AJS 500 single - my Dads
1916 Triumph Type H, Western front, France WW1 - my Grandads
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