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How to fix the BMW motorcycle brakes, front or rear drum brake squeal

by Duane Ausherman

This page mostly applies to the BMW motorcycle models from 1970 and later. 

These bikes have wonderful brakes, especially for the time they were made, 30 years ago.  They are very low maintenance, last almost forever, are lightweight and stop well.  The brake squeal is usually due to one of two reasons.  Here are the usual symptoms and solutions. 

1.  When it is first ridden, especially in the morning or anytime that it has been sitting for 12 hours or more and could have collected humidity.  The first few stops will screech and be grabby, that is, hard to control.  After those first few stops, everything seems to work as before. 

Solution 1; anticipate this condition and don't allow yourself to get in a panic stop before you "dry out" the brakes.  Don't try to dry them on a gravel road.  Get up to about 25-30 and feather the brakes, that is apply

them very slightly.  Let up when they grab and do it all over again.  Each time should get better.  Usually the front is the dangerous one.  The rear is less efficient (single leading brake) and is easier to control.  The

front (double leading brake) could pitch you over sideways if you aren't expecting it. 

Alternate solution; move to the desert. 

2.  No matter how long you use the brakes they will squeal.  Usually gently braking is the loudest and hard braking is quiet or not so loud.  As you come to a complete stop and let up appropriately, they get louder. 

Solution; remove the shoes of the offending brake and chamfer the leading edge.  That is, Use a file to bevel it back so that the leading edge isn't square anymore.  Angle it for maybe 1/4" or so. 

You may hear that you should "break the glaze" on the lining surface.  To do that you MUST remove the shoes.  Lay wet-n-dry dark gray sandpaper on a smooth surface and drag the shoe over it.  Don't hold the shoe and move the paper back and forth over the shoe.  The problem with this is that it will only stop the squeal for a short time and it will be back.  Don't ask how I know. 

These comments by snobum are excellent and while one seems to contradict what I have said, it is true.  It is always up to the owner to decide what is important.  I seldom ride in the rain.  In California we have arranged all of our rain to be in 4-5 months.  Even then it isn't usually a problem.  You decide what is best for you and your riding conditions. 

snowbum's comments

I am not a fan of really tapering the sharp end of the shoe.  Breaking that edge the tiniest little bit is probably acceptable (??) (to me), although I won't do it....and any real tapering allows water that gets inside to be

forced into the shoe-to-drum interface, instead of being scraped away, causing a loss of brakes. 

Brake spring resonance can be dampened.  I actually have tried sponge, rubber, and once even tried RTV.  

Contact of the metal cam where it meets the shoe metal can be filed very gently so that a feeler gauge will show equal contacting across the cam face.  Stopping now and then from 60 or 70 mph is usually needed to treat

the surface of the shoe material...it need not be overly vigorous.  Brake actuating shaft-to-housing must not have excessive clearance.  Anything, in general, that allows high frequency vibration, will allow squeal to develop. 

Your admonition to be gentle on using the brakes in the morning is very true.  The leading shoe front brake is very conducive to reacting with condensed moisture and grabbing ...REALLY grabbing, on the first application of the riding day. 


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This page was last edited: 04/06/2006 - copyright Duane Ausherman
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