Odd behaviour from brakes - BMW Luxury Touring Community
 
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post #1 of 9 Old Feb 9th, 2012, 3:41 am Thread Starter
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Odd behaviour from brakes

I was coming into work this morning in light city traffic. I was feathering the front brake but it behaved as if I had pulled had on the lever and even after releasing the lever the brake stayed on. I turned the bike off and it seemed that the brakes 'released' them selves. The two lights on the dash do not flash or stay on when in movement.

I put new front pads on about 5K KMs ago, and the brake lines were swapped over to the braided Aeroquip type last year. The reservoir on the handle bar is showing fluid.

Any sugestions?

1999 BMW K1200LT "Galatea"
1976 MERCEDES-BENZ 280S "Lady Genevieve"
1993 MERCEDES-BENZ S320 "Lady Audrey"
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post #2 of 9 Old Feb 9th, 2012, 3:53 am
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Re: Odd behaviour from brakes

If it were me, I would take the front calipers off, clean them really well with some brake cleaner, then get an air hose and blow them dry with the compressor. I would also check the levels of the reservoir under the passenger seat on the right side of the bike just for fun. You mentioned you had the lines replaced, and had the pads done, was that both the front and the back? How about the abs unit being flushed? How long ago was that done? Just going down a list of things I would do.

Courage doesn't always roar. Sometimes it is the quiet voice at the end of the day saying " I'll try again tomorrow".


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post #3 of 9 Old Feb 9th, 2012, 4:03 am Thread Starter
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Re: Odd behaviour from brakes

The front brake lines were changed about 4 months ago, both F + R Pads were changed around November/December. I shall have a look at the reservoir under the seat...Isn't that for the rear brake?

Just a simple question. Would the ABS sensor have anything to do with this, or is it a mechanical issue?

1999 BMW K1200LT "Galatea"
1976 MERCEDES-BENZ 280S "Lady Genevieve"
1993 MERCEDES-BENZ S320 "Lady Audrey"
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post #4 of 9 Old Feb 9th, 2012, 4:16 am
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Re: Odd behaviour from brakes

I do not think it is a sensor problem, I will let John Z. Answer some of your questions when he gets on here as he is well versed in the braking system of these bikes. As yours is a 99 and mine being a 02 there are some differences and I do not want to tell you something incorrect.
Calipers retract by the pads pushing back as the rotor turns, if the pistons have dirt, dust, small rocks etc around the piston, then they will not retract. If it were me, I would clean them really well and see if that fixes the issue.
Get back on here later on and see what other suggestions other members can give you to solve this issue. You can also send a message to John directly explaining your problem.

Courage doesn't always roar. Sometimes it is the quiet voice at the end of the day saying " I'll try again tomorrow".


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post #5 of 9 Old Feb 9th, 2012, 6:56 am
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Re: Odd behaviour from brakes

The cut of the groove in the caliper that holds the piston seal is designed so when applied the seal is under tension. This is what causes the piston to retract when the brakes are released. The seal could be getting hard and loosing it's elasticity and/or dirt build up is causing the piston to stick. When replacing brake pads the piston(s) should be cleaned before they are retracted to avoid pushing dirt into the seal.
It can also be caused by crud in the master cylinder port or the piston not fully retracting keeping fluid under pressure.
The other condition I have seen is the inner liner of a brake line separating and acting like a check valve trapping fluid under pressure and again keeping the brakes applied.

Because you replaced your brake lines I would think it to be one of the first two mentioned.
It's something that needs to be looked into to avoid cooking your rotors. If it's one caliper sticking focus on that caliper if it's both focus on the master cylinder.

The ABS without whizzy is a flow through design so I wouldn't think that to be the problem but it should be checked for operation just the same.
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post #6 of 9 Old Feb 9th, 2012, 4:06 pm Thread Starter
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Re: Odd behaviour from brakes

I popped in to the mechanic's on the way home The pistons moved easily within the calipers just by pushing them by thumb, the pads are more than 50%. Therefore, diagnosis is that the 'new' areoquip lines must be at fault.

1999 BMW K1200LT "Galatea"
1976 MERCEDES-BENZ 280S "Lady Genevieve"
1993 MERCEDES-BENZ S320 "Lady Audrey"
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post #7 of 9 Old Feb 9th, 2012, 7:46 pm
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Re: Odd behaviour from brakes

This is unusual behaviour for a 99 since it is not power assisted and any activation of the ABS only "modulates" what ever pressure you apply to the brakes. New lines of the stainless steel variety would not cause this issue but they do give you a firmer "lever" when applying the brakes.

I agree it could be the master cylinder not releasing. Might try to force fluid up from the caliper and see if there is any resistance to flow at the master cylinder.

John
2009 K1300GT Red Rocket
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But lack DE, MA, RI and CT with the 2005 LT

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post #8 of 9 Old Feb 9th, 2012, 10:07 pm
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Re: Odd behaviour from brakes

Also, look inside the master cylinder reservoir and check that the small fluid return hole at the bottom of the reservoir is open -- if it clogs, pressure in the brake circuit cannot be relieved, so the calipers won't release (same symptom as an internally collapsed/failed brake hose).

When you do this, put a paper towel over the top of the reservoir, and a plastic trash bag over the tupperware under the grip. You will no doubt squeeze and release the front brake lever with the reservoir cap off -- when you do, if the main hole between the reservoir and the master cylinder piston bore is not plugged, you'll get a brief, strong fountain-like spurt of brake fluid shooting up a foot or more into the air, then onto your tupperware or windshield. I had this happen with my '02 LT -- when it was in for warranty brake work, the tech allowed a "spurt," which permanently marred the right windshield winglet. The paper towel over top of the reservoir minimizes the spray.

Mark Neblett
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post #9 of 9 Old Feb 10th, 2012, 4:00 am Thread Starter
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Re: Odd behaviour from brakes

Quote:
Originally Posted by mneblett
Also, look inside the master cylinder reservoir and check that the small fluid return hole at the bottom of the reservoir is open -- if it clogs, pressure in the brake circuit cannot be relieved, so the calipers won't release (same symptom as an internally collapsed/failed brake hose).

When you do this, put a paper towel over the top of the reservoir, and a plastic trash bag over the tupperware under the grip. You will no doubt squeeze and release the front brake lever with the reservoir cap off -- when you do, if the main hole between the reservoir and the master cylinder piston bore is not plugged, you'll get a brief, strong fountain-like spurt of brake fluid shooting up a foot or more into the air, then onto your tupperware or windshield. I had this happen with my '02 LT -- when it was in for warranty brake work, the tech allowed a "spurt," which permanently marred the right windshield winglet. The paper towel over top of the reservoir minimizes the spray.
I'll give this a try too. I hope it's just some dirt in the system. The aeroquips shouldn't have collapsed after just a few months usage unless they were sub-standard to start with.

1999 BMW K1200LT "Galatea"
1976 MERCEDES-BENZ 280S "Lady Genevieve"
1993 MERCEDES-BENZ S320 "Lady Audrey"
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