Momentary brake release while stopping - Help - BMW Luxury Touring Community
 
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post #1 of 15 Old Oct 21st, 2008, 10:24 am Thread Starter
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Momentary brake release while stopping - Help

Ok.. I have been living with this issue for a few weeks, but I am starting to get nervous about it. (My co-worker just told me that he lost his power steering on BMW M-roadster while driving last night and nearly crashed)

When stopping the brakes will sometimes release pressure on the pads for a split second which extends the room needed to stop. At first, I thought this was happening because I was using just the rear brake and I thought that maybe the battery was weak and the servo wasnt getting enough power. I thought would clear up after the battery charged. ( I have an Odssey battery) I have been driving the bike regularly and leaving it on trickle charge each night. The battery seems fine, but my braking surge continues. It happens when I use the front or back brakes. It doesnt happen all the time, maybe 50% of the time. The pulse varies, but the brakes definetely let go for a split second. (I have been allowing for more stopping time until I figure this out)

There are no warning lights blinking on the dashboard. Everything seems normal. The bike is a 2003 with 23,800 miles on it. I am worried that one day the brakes will just fail entirely.. Any ideas on what could cause this and what to look for? Failing servo? Air in the lines? low fluid?

I replaced the pads at one point, and needed to add a few ccs of fluid to the resevoir behind the right foot peg, but no other work has been done to the braking system at this point.
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post #2 of 15 Old Oct 21st, 2008, 10:45 am
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Re: Momentary brake release while stopping - Help

I experience the same thing...always at the same spots! To me it means that the ABS system is doing its job and releasing the wheel while hitting a slippery spot. A very uneasy feeling indeed, but much better than locking up.
The Balboa off-ramp on the 101 SB is downhill and I have to stop hard at the light. I never really paid attention to the pavement until the ABS released a couple of times. That is then that I noticed a very uneven layer of tar on the road, with waves going sideways. I wondered what it would be like without ABS... Probably not a good scenario!!!

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post #3 of 15 Old Oct 21st, 2008, 10:53 am
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Re: Momentary brake release while stopping - Help

You might check the rear sensor gap. Use the guage in your tool kit. I had the same thing happen often on my '03 around the same mileage. Usually on rough pavement,and always when I hit a bump while braking. My rear sensor went out completely at about 38,000 miles. Replaced it and don't notice the release as much anymore. It still happens,but always on bad pavement.

dan
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post #4 of 15 Old Oct 21st, 2008, 10:56 am
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Re: Momentary brake release while stopping - Help

I will agree that it is most likely the ABS doing its job. There are several places on my daily commute where there are bumps in the braking area and the ABS pulses - good to know that it is working and will be there when I really need it. While it is unnerving the first couple of times, I don't believe that it significantly adds to the braking distance.

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post #5 of 15 Old Oct 21st, 2008, 11:05 am
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Re: Momentary brake release while stopping - Help

Seems to me everything is working just fine... maybe I missed something here.

What you didn't say is how hard you are braking or what the pavement conditions are like at the time of braking.

If you brake aggressively I would say that "50% of the time" would be about right for the ABS to kick in.

If you are just doing normal, gentle stops you've got something seriously wrong - and should stop riding the bike until it is professionally diagnosed. That means taking it to a BMW shop, paying the big bucks to find out EXACTLY what is wrong and not taking advice from anyone here.

Since you are already compromising and allowing extra space for stopping you are currently riding in a very dangerous zone... whether it is in your head or in the bike it doesn't matter.

I'm not trying to scold you, just concerned for your safety.




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post #6 of 15 Old Oct 21st, 2008, 11:14 am
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Re: Momentary brake release while stopping - Help

Quote:
Originally Posted by DanMartin
You might check the rear sensor gap. Use the guage in your tool kit. I had the same thing happen often on my '03 around the same mileage. Usually on rough pavement,and always when I hit a bump while braking. My rear sensor went out completely at about 38,000 miles. Replaced it and don't notice the release as much anymore. It still happens,but always on bad pavement.

dan
I'm always learning new things. Gauge in the tool kit? I bought my LT used and it's missing some things, including (apparently) this gauge. Can I use a feeler gauge instead? What thickness should it be?

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post #7 of 15 Old Oct 21st, 2008, 11:21 am
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Re: Momentary brake release while stopping - Help

Quote:
Originally Posted by Vince_nj1
... When stopping the brakes will sometimes release pressure on the pads for a split second which extends the room needed to stop. At first, I thought this was happening because I was using just the rear brake and I thought that maybe the battery was weak and the servo wasnt getting enough power. ...It happens when I use the front or back brakes. ...
First of all, you are stopping the bike with rear brake? Hopefully not ONLY rear - that would explain why the rear wheel tends to lock and the ABS kicks in.

Second: I'd say that a 2003 bike should have its fluid changed (you mention that no work like that took place). This should not have an effect on your issue, though.

Otherwise, what you describe sounds like ABS action. Whether it was warranted - you'll have to decide. It would be very likely if you used only rear - if you have the problem with front, I am surprised unless you are on loose surface

I live nearby; if you'd like I can ride on the stretch that you have problem with and see if my bike fires up the ABS (I assume that it is a particular spot, rather than anywhere).

If you experience ABS activation anywhere, you are either too aggressive on the rear brake or you have an issue that should be looked at by the dealer.

Robert in Northern NJ

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post #8 of 15 Old Oct 21st, 2008, 11:22 am
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Re: Momentary brake release while stopping - Help

Quote:
Originally Posted by Lare
I'm always learning new things. Gauge in the tool kit? I bought my LT used and it's missing some things, including (apparently) this gauge. Can I use a feeler gauge instead? What thickness should it be?
0.45 - 0.55 mm. (0.018 -0.022 in) is the gap

Yes, you can use a feeler gauge.

No, I did not have that arcane bit of knowledge stored in my brain.


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post #9 of 15 Old Oct 21st, 2008, 12:00 pm
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Re: Momentary brake release while stopping - Help

Thank you, Ron.

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post #10 of 15 Old Oct 21st, 2008, 12:21 pm Thread Starter
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Re: Momentary brake release while stopping - Help

Originally I was using the rear brake a little more than the front. ( I was getting lazy). I went back to using both.. and my braking is usually agressive to very aggressive... So I will check the sensor..

Is it the sensor on the rear wheel/brake?
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post #11 of 15 Old Oct 21st, 2008, 12:23 pm Thread Starter
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Re: Momentary brake release while stopping - Help

Quote:
Originally Posted by rdwalker
I live nearby; if you'd like I can ride on the stretch that you have problem with and see if my bike fires up the ABS (I assume that it is a particular spot, rather than anywhere).

If you experience ABS activation anywhere, you are either too aggressive on the rear brake or you have an issue that should be looked at by the dealer.
Robert, thanks for the offer.. But it happens anywhere.. I will take notice about rough pavement.. But I have been riding the bike pretty hard since I bought it and this issue has only surfaced recentl...
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post #12 of 15 Old Oct 21st, 2008, 12:32 pm
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Re: Momentary brake release while stopping - Help

Could it be that the shocks are shot, causing the wheels to lose contact with the ground and triggering the ABS?

Kevin

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post #13 of 15 Old Oct 21st, 2008, 1:17 pm Thread Starter
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Re: Momentary brake release while stopping - Help

Quote:
Originally Posted by kevincook
Could it be that the shocks are shot, causing the wheels to lose contact with the ground and triggering the ABS?

Kevin
That is an interesting theory... I will have to see if I can reproduce it on smooth pavement. It definetly feels like an ABS over-ride, but I don't think I'm locking up the tires..
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post #14 of 15 Old Oct 21st, 2008, 7:09 pm
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Re: Momentary brake release while stopping - Help

Quote:
Originally Posted by rdwalker
First of all, you are stopping the bike with rear brake? Hopefully not ONLY rear - that would explain why the rear wheel tends to lock and the ABS kicks in.
On an 03 you cannot use ONLY the rear brakes since with any large force on the pedal it will also activate the front brakes.

+1 on system should be flushed if you have no record of it ever being done.

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post #15 of 15 Old Oct 22nd, 2008, 9:41 am Thread Starter
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Re: Momentary brake release while stopping - Help

Quote:
Originally Posted by jzeiler
On an 03 you cannot use ONLY the rear brakes since with any large force on the pedal it will also activate the front brakes.

+1 on system should be flushed if you have no record of it ever being done.
Thanks for adding that in. I am well aware of the need to use the front brakes.. After all they provide 70+% of the stopping power. When I said I was using the rear brake a little more than the front, I was basically relying on the integrated braking system to apply my front brakes. My real goal was to make my rear brake work a little harder in an effort to clear up the occasional brake squeal. My theory was that I was probably causing more of a power drain on the system by just using the back brake. Either way, I went back to using both front and back brakes and the problem is still there.
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