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"K13GT" Technical Q&A K1300GT- Technical Questions/Answers

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  #1  
Old 11-03-2017, 01:27 PM
DMcK DMcK is offline
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Very soft front brake this morning...

The front brake on my '09 K13GS was soft this morning. Soft enough that I could pretty much pull it back to the bars. After a couple of squeezes it "pumped up" and seemed much more normal.

It was a little chilly this morning ~34F. The bike has only 15k miles.

What's the most likely culprit? The fluid level in the reservoir seems fine. What's the gold cap
on the reservoir that says "do not remove" for? Is that to stop the sponge jumping out??

cheers
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  #2  
Old 11-03-2017, 04:56 PM
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Re: Very soft front brake this morning...

When was the last time the brakes were bled and fresh brake fluid flushed though the system? Sounds like there might be some air in the brake lines, or possibly an issue with the master cylinder?
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Old 11-03-2017, 08:09 PM
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Re: Very soft front brake this morning...

The bike is rather new to me, but the dealer's records show the brakes were flushed about 18 months ago.

I've been riding the bike, cautiously, and it seems fine, but I'm not greatly happy to keep on doing so. I suppose I could try bleeding the master cylinder and see if that firms things up a bit. Even before this morning, I find the brakes a little more spongey than my other BMWs.
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Old 11-03-2017, 08:51 PM
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Re: Very soft front brake this morning...

It happened to my 06KGT 3 years ago
Check the front wheel bearing, if the wheel wobbles even just a bit, it pushes the pads off, hence the funny feeling
Keep us posted,
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Old 11-03-2017, 09:12 PM
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Re: Very soft front brake this morning...

Your brakes are due for a fluid change. I would have the dealer or a qualified shop do it. Small price to pay for peace of mind.
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  #6  
Old 11-03-2017, 10:50 PM
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Re: Very soft front brake this morning...

Hmm, the dealer told me the fluid flush interval was 2 years on that bike.

If it is, indeed, due for a flush that still doesn't explain the softness, right? It seems that there must be air in the system or some other problem.

Can someone point me to the procedure for the 2009 bleed/flush process? I've found it for the older bikes, but not one of this generation.

Regarding the possibility of wheel bearings pushing the pistons into the calipers. I don't think I have a problem with the bearings but, also, the brake was ok when I parked the bike. The softness was present after a few days of sitting in moderately chilly weather.

Thanks for the replies,
Doug
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  #7  
Old 11-04-2017, 12:32 AM
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Re: Very soft front brake this morning...

Please post with your findings. Helps others. I with the fresh brake bleed. The man said every two years, but that does not apply to a bike new to you in my opinion. Everything should be fresh. The cold weather could shrink puck seals and let air in.
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Old 11-04-2017, 09:24 AM
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Re: Very soft front brake this morning...

Start with the simple things. How worn are the pads?
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Old 11-04-2017, 09:48 AM
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Re: Very soft front brake this morning...

Also check your hoses for bulging/ballooning when applying the brakes.
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Old 11-04-2017, 09:56 AM
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Re: Very soft front brake this morning...

Quote:
Originally Posted by BAK04GT
Also check your hoses for bulging/ballooning when applying the brakes.

The 09 GT should have braided stainless lines.
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Old 11-04-2017, 10:46 AM
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Re: Very soft front brake this morning...

Quote:
Originally Posted by Beech
The man said every two years, but that does not apply to a bike new to you in my opinion. Everything should be fresh.
Exactly. After only 18 months there shouldn't be anything wrong with the brakes if the service was done correctly. I'd have the dealer completely check brakes just to ensure it's not something as simple as a bleed. A brake flush on my k13s only costs about $150. Cheap insurance.
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Old 11-04-2017, 08:34 PM
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Re: Very soft front brake this morning...

The pads are fine, the hoses are SS braided and appear in excellent condition.

I trust the dealer records, although I suppose it's certainly possible that they did a less than stellar job. I don't have a relationship with them to know how good they are.

I feel there must be a way that some air got in, and will likely be purged by a flush/bleed, which I am inclined to do. Can anyone point me to a write up for this bike? I had no trouble when I replaced the brake hoses on my GS and, unless there's something really perverse I generally prefer to do my own work.

What I'm really curious/concerned about is how the air got in there in the first place. That really shouldn't happen... If the chilly weather caused the fluid to shrink in the system, shouldn't it simply be replenished from the reservoir rather than sucking air past a seal? I presume the reservoir must have some tiny breather hole or it wouldn't be good at doing its job...

This brings me back to the question of what is that plate under the reservoir cap that says "do not remove"?. Is it a weight to damp vibration? Does it have a breather?

Thanks,
Doug
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Old 11-04-2017, 09:18 PM
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Re: Very soft front brake this morning...

Quote:
Originally Posted by DMcK

Can someone point me to the procedure for the 2009 bleed/flush process? I've found it for the older bikes, but not one of this generation.


Nothing special.
Suck out most of the old fluid from the reservoir and refill with new.
Press the brake lever, open the bleeder, close the bleeder, release the brake lever.
Repeat until the reservoir is low.
Do this a couple times.
You can probably do it in 30 minutes with a helper.
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Old 11-04-2017, 10:21 PM
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Re: Very soft front brake this morning...

Ok, a traditional bleed/flush is no problem.

Thx,
Doug
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Old 11-04-2017, 11:46 PM
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Re: Very soft front brake this morning...

That weight and the internal sponge are part of a recall for a vibrating reservoir that made the fluid foam. The sponge does enough, I filed the weight. The bellows rubber cap seal is the system that allows for expansion and contraction of the brake fluid system, that is why it is a bellows. There is a tiny vent system in the cap on the "exposed/top" side of the bellows. There can be no vent to the liquid side as the fluid would get contaminated over time. When you flush use wedges or puck compressors to push back the pads and pucks to reduce the volume in the calipers. Otherwise you are just flushing in a circle where the banjo fitting connects the line to the caliper as you will see the bleed nipple is on top of the banjo fitting. Fit the caliper back on the bike, pump up the brake until the pucks firm up. Do a little bleed to make sure no air entered. Keep an eye on the reservoir lever of course. The correct procedure is to also activate the ABS, flush a second time and check for bubbles. Many folks don't bother though. So to do a complete bleed it takes more time than just cracking the nipple and working the lever.
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Old 11-04-2017, 11:51 PM
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Re: Very soft front brake this morning...

Ok, That makes sense. A bellows is what I'd expect, but I guess it's hidden under the weight, which I haven't yet removed.

Is the ABS unit cycled by test riding, or by a GS911?
Doug
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Old 11-05-2017, 12:50 AM
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Re: Very soft front brake this morning...

ABS activation, either one, easy with a gs911 but a stretch of dirt will do. Just put that brass 150 gram weight on your desk where it should be, return the sponge after your finished bleeding. It will take up room so don't top up until the sponge is in place. (drain old fluid out of it too). Just as an aside, I have only once seen bubbles after activating the ABS. But I do think it stirs up the old fluid and helps move it along.
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Old 11-05-2017, 07:10 PM
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Re: Very soft front brake this morning...

The weather wasn't conducive to working on the bike today. I'll follow up when I get some time on this, and some updates to share.
doug
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Old 11-05-2017, 08:46 PM
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Re: Very soft front brake this morning...

Something just occurred to me...

If I recall correctly, the solubility of gas in organic liquids decreases with decreasing temperature (unlike water). This means that a lower overnight temperature could have made some dissolved gas (air) come out of solution and form bubbles. Unlike dissolved gas, actual bubbles have the observed effect on brake lever feel.

The fix would be a flush/bleed, as discussed, but this is interesting because it gives a plausible explanation for what might have happened.

Any chemists out there? What's the temperature dependence of gas solubility in polyethylene glycol?
Doug
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Old 11-06-2017, 04:24 AM
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Re: Very soft front brake this morning...

You're over thinking the problem mate, just bleed/flush the brakes.
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Old 11-06-2017, 08:31 AM
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Re: Very soft front brake this morning...

Were the brake parts warm/hot when you parked the bike?

If hot metal had expanded then retracted.Sure doesn't take much of a gap between pads & rotors for the lever to come all the way back on first/second pull.

GS911 or dealer's? For a bleed pressure test?Pass or fail?
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Old 11-06-2017, 09:35 AM
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Re: Very soft front brake this morning...

Quote:
Originally Posted by paulmogs
You're over thinking the problem mate, just bleed/flush the brakes.

Sure I'm going to bleed/flush the brakes, and I expect that will sort things out.

But, I disagree about "overthinking" the problem. First, I enjoy figuring things out. Second, I think that brake weirdness is a good thing to understand!

cheers,
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Old 11-06-2017, 09:41 AM
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Re: Very soft front brake this morning...

Quote:
Originally Posted by pbegin@burton
Were the brake parts warm/hot when you parked the bike?

If hot metal had expanded then retracted.Sure doesn't take much of a gap between pads & rotors for the lever to come all the way back on first/second pull.

GS911 or dealer's? For a bleed pressure test?Pass or fail?

I understand your point, but this was not the take-up of mechanical play, which feels different. This was "spongey".

It's probably time to get a GS911. I have a fondness for middle-aged BMW motorcycles (I currently have 3!), so it's about time...
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Old 11-06-2017, 01:47 PM
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Re: Very soft front brake this morning...

Middle aged motorcycles (). GS-911, get the yellow one and save some bucks. The Red one is for newer bikes and wifi. There are threads on the subject. Your trust in previous dealer work is borderline and you don't know what happened at other times after that. Even the best dealership service departments make mistakes occasionally, personally seen it with just what you are discussing in this thread.
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