Rear brake squeal linked to front brakes? - BMW Luxury Touring Community
 
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post #1 of 20 Old Mar 30th, 2006, 10:00 am Thread Starter
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Question Rear brake squeal linked to front brakes?

I have 2003 LT with linked brakes. I don't fully understand how the system operates, except knowing that when you apply the rear brake, it applies braking pressure to the front.

I just changed my front tire and did a brake inspection (16,500 miles) I noticed that one of the 4 brake pads in the front was significantly worn, (almost to the metal). I changed the front brake pads and everything is fine.

I just rode the bike and noticed that the brake squeal that I was getting when I used the rear brakes is gone (This may be premature, because I have only ridden about 100 miles since doing the service). My question is this.. Does the linked system apply only pressure to one set of pads in the front when you use the rear brake? Could my rear brake squeal actually have been coming from the worn pad that was in the front of the bike?
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post #2 of 20 Old Mar 30th, 2006, 12:31 pm
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I have the same year bike and just changed the back brakes to EBC's because of the noise. That cleared up the noise and I've put some miles and braking on it since with no recurrence. I have not inspected the front brakes but will do so this weekend because of your post.

John changed his front brakes a couple of weekends ago since he discovered that the left most (while sitting on the bike) pad was worn to almost nothing. Is that the same pad that you had worn down?
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post #3 of 20 Old Mar 30th, 2006, 12:44 pm Thread Starter
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If you stood in front of the bike and numbered the pads (from left to right) 1,2,3,4. The brake pad that was worn in my bike was number 3.

I would estimate pad wear as follows:
1, 2 & 4 ten percent wear
# 3.. almost gone. 95% wear

In fact I ordered 4 EBC pads and when I went to change them, the old pads looked as thick as the new ones, so I only changed 3 & 4.
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post #4 of 20 Old Mar 30th, 2006, 7:36 pm
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There is only one pipe feeding each caliper so it exerts the same pressure on all pistons in that caliper.

Now why does one pad wear? A binding piston can cause it. But it can be variances in the pad material as well.

I measure mine regularly and the wear is not always even on all pads. And for some reason on my cars and bikes it is always an "inside" pad that wears first.

John
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post #5 of 20 Old Mar 31st, 2006, 12:32 am
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Simple. Inspect the brakes more often, and rotate the pads around.

Ken
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post #6 of 20 Old Mar 31st, 2006, 12:46 am
 
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As a mechanic in a former life, I can assure you that rotating the pads is a real bad idea. Each pad beds in and settles down to the shape and condition of each side of the disc, or rotor, as you guys call it, and will work more efficiently when replaced in exactly the same position it was removed from when being inspected or cleaned.
When renewing brake pads it is always best to replace them as a set, any mechanic I know would burst out laughing at the thought of just changing 2 pads out of 4 to save a few pennies. New pads should be treated as such and allowed to bed in for a hundred miles or so before being applied in anger.
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post #7 of 20 Old Mar 31st, 2006, 2:06 am
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Yes, you'd have to bed the pads in again. Maybe even a light sanding to bring up a "fresh" surface first. But if only one is wearing significantly more than the others, maybe he should really be looking for an alignment or sticking problem instead.

I also agree that replacing all is better than just replacing 2 of 4, especially if you're talking different brands (EBC versus BMW pads).

Ken
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post #8 of 20 Old Mar 31st, 2006, 3:49 am
 
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Not intending to hijack the thread, but while we are on the subject of brakes, I thought I might share a few tips I picked up while serving a 5 year apprenticeship as a mechanic. (Not wanting to preach to those who already know, but some guys/gals may learn a tip or two from this)

My recipe for trouble free brakes – When cleaning or replacing the pads, use a wire brush all over the pad, paying particular attention to the metal edge surfaces where it slides in the caliper, make sure they are dust, rust and grit free. Use either the wire brush or some sandpaper to remove the glaze from the surface of the pad.
If you find you have a problem with the brakes squealing, as some LT owners do, it is perfectly acceptable and safe to chamfer the edges of the pad surface by about an 1/8th of an inch. This saves the disc (rotor) from grabbing at the pad causing vibration which leads to squeal. You can use either a grinding wheel, Dremel, or a Bastard file, which ever you have, to remove the material. Makes little, if any difference to the life or performance of the pad.
While the pads are out, check that the pistons in the caliper move freely by squeezing ever so lightly on the brake lever, and move them back with a wooden or brass implement, never screwdrivers or anything steel. If one of the pistons does not move, try and hold the others back with wooden blocks and repeat the above procedure.
A sticky or lazy piston needs to be dealt with, if it does not come out with light pressure on the lever, it sure as hell will with heavy pressure, and will more than likely stay out after the lever is released causing the uneven pad wear we are talking about. The piston is actually pulled back into the caliper by the internal seal, we are talking hundreths of an inch here, so imperative that the piston is clean and water/salt free (dealing with this problem is another full story..lol)
There are a number of ‘brake seal safe’ lubricants on the market that can be skooshed (good Scottish word) behind the piston’s outer rubber seals, work the piston back and forward until it moves with light pressure on the lever.
When replacing the pads, put a light smear of copper grease on the back metal part of the pad, even if it has a plastic coating, and along the edges where it slides in the caliper. This not only helps the pad to move but dampens vibration, and lessens the tendency to squeal. If copper grease is not available, high melting point Molybdenum grease will do the job. Make sure each pad goes back to where it came from.
Also smear any anti-rattle shims, pins and clips that hold the pads in place with the copper grease. Makes for easy maintenance next time. Avoid at all costs getting any grease on the working surface of the pad, if you do, remove it with emery, sandpaper or a wire brush.

When I picked up my LT, it had that horrendous squeal from the back brake. Servicing them as per above cured it. Not sure whether it was the copper grease or the chamfering, I did it all at once, but it worked.

The above has served me well for 30 years, and all my cars and bikes get the treatment every 6K whether they need it or not .

Just realised I have written all this before checking the HOW, sorry if it's a duplicate.
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post #9 of 20 Old Mar 31st, 2006, 9:36 am
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I have the same pad problem with my bike. I noticed a rattle in the front of my bike after a short ride with my wife. I looked at the brake shoes but could not tell anything from the inspection. After pulling the calipers I found the #2 pad (by left to right facing the bike) was gone - as in bare metal. Now I get a flashlight and check just one pad. If that looks good I feel I am ok. #2 pad is used up about two to three times as fast as the others - which from inspection - look about the same. I tried to inspect the rotor surface, but I could not find anything obvious - as if I knew what I was looking for!

Lee Nowell
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post #10 of 20 Old Mar 31st, 2006, 10:09 am
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Quote:
Originally Posted by Malki
When I picked up my LT, it had that horrendous squeal from the back brake. Servicing them as per above cured it. Not sure whether it was the copper grease or the chamfering, I did it all at once, but it worked.

The above has served me well for 30 years, and all my cars and bikes get the treatment every 6K whether they need it or not .

Just realised I have written all this before checking the HOW, sorry if it's a duplicate.
Hoot Mon - where have you been? This chamfering technique is NEW. I should have thought about it but I don't believe any one else has presented it. I will try it this week end. Thanks for the great brake post, good info and well presented! Should be it the HOW.

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
K4AN

Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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post #11 of 20 Old Mar 31st, 2006, 10:15 am
 
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Quote:
Originally Posted by jzeiler
Hoot Mon - where have you been? This chamfering technique is NEW. I should have thought about it but I don't believe any one else has presented it. I will try it this week end. Thanks for the great brake post, good info and well presented! Should be it the HOW.
total agreement from here on this being a new remedy for my little red wagon sounds from the brakes. be sure to let us know what the chamfering process does to your squeal issues.

thanx for taking the time on this Malki. I think you shoud cut and paste that entire post into a new and unique thread. will be interested in what our LT brake veterans think.
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post #12 of 20 Old Mar 31st, 2006, 10:25 am
 
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If you find you have a problem with the brakes squealing, as some LT owners do, it is perfectly acceptable and safe to chamfer the edges of the pad surface by about an 1/8th of an inch. This saves the disc (rotor) from grabbing at the pad causing vibration which leads to squeal.


Malki:

Just so I have the procedure clear in my mind. Would you explain in more detail how you do the chamfer procedure?
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post #13 of 20 Old Mar 31st, 2006, 11:03 am
 
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@ DRothermel - All you are doing is taking the the square edge off the pad's working surface all the way round each edge, the angle or degree makes no odds, neither does the amount of material removed. I would suggest the first time it is tried an 1/8th of an inch would be sufficient on a small motorcycle brake pad, on my larger car pads, I remove about a 1/4 inch. Use a hand Bastard file if you are not confident first time round. Electric grinders are a little on the vicious side if you are not careful.
I'll try and post some photos of a before and after if this procedure is not clear to anybody.
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post #14 of 20 Old Mar 31st, 2006, 11:38 am
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Question Any concerns about airborne asbestos?

Do our brake pads (BMW, EBC's etc) contain Asbestos?

If so....you should take some pre-cautions if you do this. Dust mask...maybe do it outside so the dust isn't all over your garage/workbench...rinse off pads/hands/tools with water.

Just a thought.

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post #15 of 20 Old Mar 31st, 2006, 11:55 am Thread Starter
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I was under the impression that all origian equipment brake pads sold in the United States had to be Asbestos free. The laws used to allow aftermarket pads to contain Asbestos... My knowledge dates back to early 90's.. So I would assume that Aftermarket pads are probably asbestos free.

Either way, it is good advice to take precautionary measures when grinding the pads.
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post #16 of 20 Old Mar 31st, 2006, 12:17 pm
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Hmmmm. Did a little research and, while not suprising, it seems there is some conflicting information out there. It appears that asbestos was indeed banned at one time (1989) from use in brake pads, but there seems to be evidence that the ruling was overturned (circa 1991).

Here's an excerpt from a document titled;
" EPA Asbestos Materials Bans: Clarification May 18, 1999"
Products not banned –
Asbestos-containing product categories no longer subject to the 1989 TSCA ban include: asbestos-cement corrugated sheet, asbestos-cement flat sheet, asbestos clothing, pipeline wrap, roofing felt, vinyl-asbestos floor tile, asbestos-cement shingle, millboard, asbestos-cement pipe, automatic transmission components, clutch facings, friction materials, disc brake pads, drum brake linings, brake blocks, gaskets, non-roofing coatings, and roof coatings..

That document was found here --> http://www.mde.state.md.us/Programs/...stos/index.asp

Don't know what to believe. Perhaps we could contact a brake pad manufacturer to the get the real "skinny".

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post #17 of 20 Old Mar 31st, 2006, 1:15 pm
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At one point, BMW changed the factory rear pads to have a significant chamfer on the front and rear edges, maybe 1/2". It seemed to help on some bikes, but not all. I don't know of anyone else who's tried to chamfer all the way around the pads.

Ken
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post #18 of 20 Old Mar 31st, 2006, 3:00 pm
 
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Smile Do BMW garages have the knowledge?

Hi Malki

Can't remember who told me about the chamfering and Copperslip method- but it was many, many years ago and I can confirm it helped to cure my cars woes.

My LT's rear brake is having it,s first squealing fit after two years of ownership, so I guess it is time to test the technology again.

I am curious if BMW bike mechanics have "the knowledge" and apply the same technique?

Now back riding after 6 months serious illness. Will be in Scotland on the LT with my wife from 28/4 to 6/5.

Aviemore for two days, then cottage in the middle of no where above Ullapool. Can't wait.

Cheers Gillboy
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post #19 of 20 Old Apr 1st, 2006, 3:17 am
 
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@ gillboy - Judging by the number of complaints on this board about brake squeal, it might take more than this little procedure to cure everybody's problem. If it was as simple as this, BMW would have had it sorted a long time ago. I fear it may be more of an inherent fault in the design of the disc/caliper mounting or similar, but will we ever know?

Enjoy your trip to God's country, and take your waterproofs when going to Ullapool, a nice wee place, but I've never seen it in the dry
Be aware the A9 road to Inverness has speed cameras and is heavily patrolled by unmarked cars. If you are caught over the Ton, you WILL go to jail. Give me a shout nearer the time, could meet you in Aviemore for a coffee/pint and a blether.
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post #20 of 20 Old Apr 2nd, 2006, 10:37 am
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Quote:
Originally Posted by Malki
@ gillboy - Judging by the number of complaints on this board about brake squeal, it might take more than this little procedure to cure everybody's problem. If it was as simple as this, BMW would have had it sorted a long time ago. I fear it may be more of an inherent fault in the design of the disc/caliper mounting or similar, but will we ever know?
I think you are right. I feel dumb, pulled the pads to chamfer the edges and they were already done from the factory. I think I already knew that from my previous measurements just forgot about it. I guess we will just keep trying other things.

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
K4AN

Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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