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K1300GT Front Brake Lever suddenly different

D

dn325ci

New member
Guys, I started my 2009 K1300GT this weekend after it has sat on the battery tender for several weeks without being started. The front brake lever is completely “gone” - it immediately pulled all the way to the throttle grip without any back pressure. I pumped it several times but it never built any pressure. Interestingly it still exherted force enough on the pads to stop the bike, at least from 25-30 mph, so I rode it slowly around the block. It never built pressure. From the feel of it you would have predicted it wouldn’t brake the bike at all. Also interesting that the rear brake is unaffected- rear brake level and position seemed fine. At the time this happened I really had no time to investigate further, and now at work today, but any ideas what this could be?

Thanks,
Don
 
Check at calipers, master cylinder, and line connectors to see if you have a leak, and also check fluid level at the handlebar reservoir. This sounds like you have air in the system and need a good bleeding, but first you want to see if you have points where fluid is leaking out and air getting in. If you don’t find any leaks then bleed the front brakes and see if the system will build and hold pressure at the lever. If you can’t build pressure, or if it fades if the bike sits for a day or three, then I’d suspect the piston in the master cylinder has lost or diminished sealing capability.

Best,
DG
 
GTRider said:
Check at calipers, master cylinder, and line connectors to see if you have a leak, and also check fluid level at the handlebar reservoir. This sounds like you have air in the system and need a good bleeding, but first you want to see if you have points where fluid is leaking out and air getting in. If you don’t find any leaks then bleed the front brakes and see if the system will build and hold pressure at the lever. If you can’t build pressure, or if it fades if the bike sits for a day or three, then I’d suspect the piston in the master cylinder has lost or diminished sealing capability.

Best,
DG
Click to expand...

That’s terrific advice. I’m on it. Yes there wasn’t any fluid leaking anywhere. Thanks.
 
Is it very cold where you store the bike?

A worn master cylinder piston seal can allow fluid to bypass when very cold. BTDT! The cold rubber doesn't flex enough to allow the lip of the seal to push out against the bore of the cylinder sufficiently or to conform to irregularities in the bore. It might start sealing again once it warms up abit.

A little more wear, and it will bypass all the time (with disastrous results). Might be time for a rebuild.




:dance:dance:dance
 
Guys, I finally got around to looking at this yesterday - too much travel going on it my life right now. I bled the brake using new DOT 4 fluid and a pump bleeder and could not build any pressure at the handle. I did it again just using the 2 person hand process to bleed the brakes. Still no pressure. I'm suspecting possibly that thin rubber diaphragm in the master cyclinder. Does anybody have a parts list for these parts? I don't know what to order and some generic search phrases online have not really helped.

Thanks,
Don
 
dn325ci said:
Guys, I finally got around to looking at this yesterday - too much travel going on it my life right now. I bled the brake using new DOT 4 fluid and a pump bleeder and could not build any pressure at the handle. I did it again just using the 2 person hand process to bleed the brakes. Still no pressure. I'm suspecting possibly that thin rubber diaphragm in the master cyclinder. Does anybody have a parts list for these parts? I don't know what to order and some generic search phrases online have not really helped.
Click to expand...

BMW does not make available a rebuild kit (piston & seals) for the K1300GT brake or clutch master cylinders. So, you get to replace the entire front MC at a cost approaching $470. Yowch! But before ordering a replacement I’d try one more bleeding, using the tried and true old-school procedure of squeezing the lever with bleeder closed, opening bleeder and quickly closing, etc. etc. etc. I don’t find vacuum bleeders to be of any use on modern BMW brake systems—the factory certainly doesn’t use them, they inject brake fluid from a grub screw location to fill the system and drive out air.

As for looking up parts, arm yourself with the VIN# of your bike then visit any one of the three most common BMW parts fiche locations:
http://RealOEM.com (nice big diagrams but ignore the prices, they are WAY outdated)

http://maxbmw.com

http://bobsbmw.com

Good luck,
DG
 
dn325ci said:
I bled the brake using new DOT 4 fluid and a pump bleeder and could not build any pressure at the handle.
Click to expand...

Do you have the tiny bleeder to the left of the reservoir, where the hose attaches? If so, bleed there. It's a high point in the system which collects air. With the new diaphragm valve master cylinders, you need that to get air out of the cylinder itself.
 
GTRider said:
BMW does not make available a rebuild kit (piston & seals) for the K1300GT brake or clutch master cylinders. So, you get to replace the entire front MC at a cost approaching $470. Yowch! But before ordering a replacement I’d try one more bleeding, using the tried and true old-school procedure of squeezing the lever with bleeder closed, opening bleeder and quickly closing, etc. etc. etc. I don’t find vacuum bleeders to be of any use on modern BMW brake systems—the factory certainly doesn’t use them, they inject brake fluid from a grub screw location to fill the system and drive out air.

As for looking up parts, arm yourself with the VIN# of your bike then visit any one of the three most common BMW parts fiche locations:
http://RealOEM.com (nice big diagrams but ignore the prices, they are WAY outdated)

http://maxbmw.com

http://bobsbmw.com

Good luck,
DG
Click to expand...
Thank you DG. I will try that.

Don
 
AntonLargiader said:
Do you have the tiny bleeder to the left of the reservoir, where the hose attaches? If so, bleed there. It's a high point in the system which collects air. With the new diaphragm valve master cylinders, you need that to get air out of the cylinder itself.
Click to expand...

Yes, I have that tiny bleeder. I did not have a hose that small and didn't try that, but didn't recognize it's importance. I will give that a try.

Thanks,
Don
 
Guys, a simple follow up to say this advice worked! Not only is the problem solved, but I have the firmest front brake lever than I have had in 5 years I've owned my '09 GT.

Moral, for posterity:

I don't know which of these two things mattered more, but I believe firmly now that both mattered:
1. That tiny little bleeder near the master cylinder is a big deal. I bought 6 foot long piece of fish tank airline hose from the local Petsmart to bleed that tiny thing. Thanks AntonLargiader.
2. The method of squeezing the brake handle first, then quickly cracking open and closing the bleeder was pretty effective. Thanks GTRider.

Happy riding, guys.
Don
 
The bleeder is important. Usually there's no chance to get air into that location to begin with, but once air is there you need that bleeder to remove it. It's just a tiny amount of air and you can just use a rag to absorb whatever fluid comes out. What is it, like a 6mm wrench size? It's tiny. I'll just hold a rag over it with the same hand that operates the wrench, squeeze the lever with the other and cycle the wrench once. That's all it ever needs.

EDIT: next time I have one of those bikes in the shop I'll try to remember to make a short video of it.
 
dn325ci said:
I bought 6 foot long piece of fish tank airline hose from the local Petsmart to bleed that tiny thing.
Click to expand...

Now the big question - was that fresh water hose or salt water hose? :laugh

Glad you got it fixed up and that your brakes are better than ever. :thumb
 
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