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How To: Reline drum brakes and band brakes

May 20, 2010

I’ve always said:  “Brakes only slow you down!” 

 

But I know brakes are important.  I have loads of stories about riding some old bike with little or no brakes, and all the fun that ensued…  Riding the early Rudge into the pits at Sears Point after the old Cycle World Rolling Concours, as I tried to miss all the folks.  Or coming down Pike’s Peak with rim brakes that were wet from the (daily) 2pm rain shower.  The event that brought about this article was the 2009 SF 49 Mile Ride, when the Excelsior had to come down Lombard Street.   Here’s a video by PdO showing the basic problem:  steep hill, tight turns and lots of traffic.  I was standing on the brake pedal with all my weight, and not slowing down much at all. 

 

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The 1915-1920s Excelsior Big X was made with two rear brakes.  The primary brake is a contracting band brake that grips the outside surface of the brake drum.  A secondary brake is inside the drum, with a single leading shoe.  This brake is activated by the left foot pedal, but only after it has been depressed a little bit to unlock the gear change linkage, then depressed a little bit more to free the clutch.  The last little bit of pedal motion activates the brake.  This was done that that the pilot could put his/her right foot down when stopped on a hill.  Remember, his left foot has to put in the clutch, but the primary brake is activated by his right foot.  One foot has to come down to the pavement, or he’d fall on his noggin.

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IMG_3317In the photo above, the brake arm for the internal brake can be seen at 6 o’clock.  The lever for the external band brake is at 9 o’clock, while the brake stay that clamps to the frame is at 10 o’clock.  Adjusters for each brake can be seen (the ext one is inside that coil spring).

 

Emergency brake with “great strength”

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In this shot from the end of the axle, you can see the internal and external brake material.  The small gap between them is where the brake drum fits.

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The info above shows how the brakes are supposed to work, now here’s the trouble:

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The brake drum had some grooves worn into the outside surface.  It came right off the hub with a special nut, then a quick cut on the lathe of about .015” cleaned it up easily.   Check out the nice crack in the hollow tube axle.   We’ll get back to that later.

The brake band has some good old asbestos lining, but there wasn’t much left.  It was torn up and also worn through to the heads of the rivets.

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This is what you don’t want to see in your brakes.  The brass rivet has been rubbed by the drum, notice the grooves running across the rivet head.  This is because the brake material had worn too much.  It was also coated with some grease from the wheel bearings.  They are the loose ball type of bearing, without any seals or shields.

While that little rivet doesn’t look too bad at first glance, it was rubbing on the drum enough to begin cutting a groove in the drum.  And since the hard rivet was rubbing, it kept the soft brake lining from rubbing, hence the very poor stopping power.  Luckily, it is pretty easy to reline the brakes.

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This shot shows how small the brakes are.  Every little bit of material counts.

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Removing the material on the internal shoe was a simple job with a chisel.  On the contracting band brake, I could just pull the stuff off with my fingers, and then cut the rivets off.

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On to the rebuilding part of the project.  Brake material is available from time to time on eBay or at swap meets.  I have no idea what the modern materials are made from, but the old stuff is woven with asbestos and other good stuff.  The material on the bottom of the photo is from Raybestos.  The silver flecks in the photo are strands of lead that have been woven into the fiber material.  Lead and asbestos, that’ll get the EPA and OSHA excited.    I should probably write something here about how you shouldn’t grind up the material and eat it, or sniff too strongly while working on brakes, employees must wash hands before returning to work, etc.

Why the lead?  The dynamic coefficient of friction between lead and steel is .95  That is more friction that can be attained by almost any structurally sound material against steel.  The lead is too weak to use just by itself, but when woven into the fiber of the brake lining it provides additional friction.  Interestingly, Oak wood is a decent brake material too, which is something that I’ll explore in a future article describing the rebuild of the Premier’s rear brake.

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The brake material can be cut with typical wood working tools.  I used my table saw to rip it to width, and a hacksaw easily cut it to length.  Like Norm says, there is no more important rule than to wear these safety glasses.

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Clamp the material to the brake shoe, then mark and drill in place.  The holes need to be a tight fit on the rivets, and the material needs to fit tightly all the way around the shoe.

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Each hole needs to be counterbored to seat the head of the rivet.  The tough part is that you’ll want to cut very deep, to get long life from the brake material.  But too deep will break the brake. I set mine with about .060” of material left below the head.

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These rivets are from McMaster Carr, they are called 4/5 semi tubular rivets.  This image is from their website.  The hollow tubular part of the rivet can be peened over to lock the rivet in place, while the solid part of the rivet body provides full strength.  See in the image how the solid portion of the rivet engages both parts?  Be sure to buy the correct size of rivets for the thickness of your shoes and your brake material. 

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Support the head of the rivet well, then use a punch to set the hollow tail.  Don’t set them too harshly, or you may cut the tail clean off by shearing it on the edge of the hole in the shoe.  After the material is secured to the shoe, use a belt sander to bevel the leading and trailing edges of the brake material.  That will help prevent grabbing.  Also remove any frayed material at the counterbores and cut edges.  They will wear away eventually, but they make it hard to do the initial setup and adjustment.

To finish the job you may have to bend the band to fit the drum.  Adjust for the best fit, then spin the wheel, active the brake and check the fit.  Bend, adjust the brake linkage, check fit, repeat.  If the material is too thick, you may have to use the belt sander again to lightly thin it at certain points on the circumference (most likely at the fixed pivot point if it isn’t adjustable radially).  Go slow, it is hard to put material back on after you’ve sanded too much.  After you’ve ridden a time or two, check it all again.

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The brakes were now ready to refit, but first I had to do some work on the rear axle and the cushion sprocket…

 

 

 

 

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One Comment leave one →
  1. Anonymous permalink
    August 21, 2010 8:31 am

    Very good

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