- Parts List
- Front Brake Assembly
- Front Brake Design
- Install Brake Arm Cams
- Install Brake Shoes
- Align Brake Arms on Brake Cam Shafts
- Install Brake Carrier and Mount Front Wheel
- Install Front Brake Torque Arm Assembly
- Install Handlebars and Right Control Perch
- Install Front Brake Cable
- Adjust Front Brakes
Now that I have the front forks aligned and installed, and you can read about how I did that here,
it’s time to put the front brakes back together and install them. I also add the new handlebars and have replaced some worn parts in the right control assembly or perch.
Here is the list of parts I used for this work.
|34 11 2 311 079||Brake shoes, Front, set||1|
|32 73 1 234 515||Front Brake Cable||1|
|61 31 1 351 646||Front Brake Switch, Rubber Cap||1|
|32 72 1 230 868||Handle bar grip, Magura, round, right||1|
|07 32 R kit 002 SS||Perch mount Kit SS, Allen head bolts, M6x16
(Hucky’s Part #)
|32 72 1 231 610||Felt Ring||1|
|32 71 2 307 401 F||Handle bar, USA Chrome, Fehling
(Hucky’s Part #)
The tools needed are standard workshop tools. I also found (was directed to) a neat template created by Scott Scott Lydiard that simplifies alignment of the two brake arms. His site, www.BMWScotter.com is temporarily off-line, but I have his permission to include a PDF file of his template.
Here are links to resources I used in preparation for this work including my link to a correct sized PDF file of Scott’s alignment template.
- Scott Lydiard, Front Brake Arm Template, Version 8.0
- Duane Ausherman, BMW motorcycle front drum brake adjustment and repair
- Robert Fleischer, BMW Airhead Motorcycle Brakes
Front Brake Assembly
I cleaned up the front brake carrier and all the mounting hardware previously so everything is nice and clean.
Note in the picture above of the inside of the face plate there are two circular, hollow pins on the left and right sides. The front brake shoes have holes that mount over these. The brake came shafts go through the holes next to the pins (at the 4:00 position of the left pin and the 1:00 position of the right pin). Just below and to the right of the left side cam shaft hole is a circular pin that looks like a very large nail head. This is an adjustment cam that I show more clearly later on.
Here is the brake shoe assembly parts.
Unlike the rear shoes where there is a different top and bottom shoe, the front brake shoes are the same shape. Between the shoes from the left are the polished brake arms and their cable nipples above them. The two arms are the same and above them are cable nipples and a wire bracket that routes the brake cable along the right fork tube. There is a picture of where the wire bracket goes later on.
To the right are the two brake cams that attach to the brake arms and push the shoes outward against the brake drum which is part of the hub. Each brake cam is different and I show them more clearly later on. The circlips (i.e., snap ring, c-clip) above them secure the shoes on pivot pins on the back side of the brake carrier plate.
The two springs are different. One has thicker diameter wire with fewer coils (the darker colored one on top) so it is a weaker spring. The other spring has smaller diameter wire and more coils so it is a stronger spring. The stronger spring goes in the holes in the brake shoes that are toward the rear of the bike (which is on the left in the picture above) while the weaker spring goes in the holes toward the front of the bike.
The reason for different size springs is to engage the the lower shoe against the drum first (the one with the curved right edge) and then the top shoe (the one with the vertical right edge). The provides more progressive braking than if both shoes contact the brake drum at the same time due to the design of the brakes.
Front Brake Design
The brake design is called double, or twin, leading shoe brakes. The term “leading” indicates that as a shoe pivots on a pin on one side, the other side of the shoe is pushed against the spinning brake drum in the hub. Based on the direction of rotation of the brake drum (clockwise or counter-clockwise) a force is created that acts on the brake shoe but in the opposite direction. For example, if the drum rotates clockwise, the force on the shoe is a counter-clockwise rotation.
Standing on the right side of the bike, if rotation of the hub is clockwise (which is true when the wheel is rolling forward) and the brake shoe rotates counter-clockwise on it’s pivot when the brake is applied, then the resulting force on the shoe as it contacts the hub is a counter-clockwise rotation of the shoe which pulls it tighter against the rotating brake drum so the braking force increases.
Some brakes have a leading and trailing shoe so the brake works equally well when the wheel is rolling forward or backward. For most efficient braking when the bike is moving forward, double leading shoes are used, but they are very weak when stopping while backing the bike up as the force created on each shoe tries to rotate the shoe away from the spinning brake hub.
Install Brake Arm Cams
I put some brake grease on the shafts and the cam face of the brake arm cams before I insert them into the holes. I also put some grease on the outside of the brake shoe pivot pins. I wiped off the excess grease to keep it from getting on the brake shoes and brake drum.
The brake arm cams are different and the one with the lever opposite the cam face goes in the front facing hole (to the left in this picture).
The lever rests on the face of the large nail looking adjusting cam. You can see the adjusting cam better in the picture below.
Here is the rear brake arm cam installed.
Next, I temporarily install the brake arms on the serrated end of the brake cam shafts to hold them in place. I’ll adjust the arms on the shafts later.
Install Brake Shoes
Installing brake shoes with springs can be like wrestling an over-caffeinated alligator while standing on a slippery river bank. The alligator wins 🙂
Here’s how I did it. I put the stronger spring into the brake shoe holes that are toward the front of the bike (to the left in this picture). Then I slip the end of the brake shoes with holes onto the pivot shafts. This is easy since the shoes can overlap and you aren’t fighting the spring.
Then I use a screw driver to pry the end of the shoe with the flat face that rides on the cam onto the cam face. Then I just tap the shoes down until they are fully on the pivot shaft and the cam face. This isn’t too hard because you only have one spring to overcome.
I use my circlip pliers to install the circlips in the groove on the end of the pivot shaft to keep the brake shoes on the shaft.
Now I install the weaker spring (the one that is toward the rear of the bike, or the right side in my pictures) into the hole of the top brake shoe and with my vice grips, I clamp the bottom hook so the the spring wire rides in a groove of the serrated jaw. Then I sit down on the floor, brace the brake carrier plate with my feet and lean back to stretch the spring until I can hook the curved end into the hole in the lower shoe. Be sure there is nothing behind you should the grips let go or the spring brake and wear eye protection as well. There is a lot of force and spring steel can break sending shards of steel flying.
After I installed my springs I read that you can put both springs on the shoes and then mount them on the pivot shafts with the shoes overlapping. They use a large screw driver to lever the ends of the shoes with the flat faces onto the cams.
Align Brake Arms on Brake Cam Shafts
I received a template created by Scott Lydiard (www.BMWScotter.com) via the Micapeak airhead forum from two of the “Headz” and a link to Scott’s site, www.BMWSCotter.com. However, Scott’s site is temporarily unavailable. I contacted Scott and he gave me permission to provide a link to his template which is stored in PDF format. One of the copies I received from one of the Headz had shrunk somehow and didn’t line up correctly. The one I got from Scott lined up correctly. The link I provided in the Resources section above has the correct size template I received directly from Scott.
Here’s what it looks like.
I cut the template out along the dotted lines and place it on the front side of the brake carrier plate oriented so the two brake cam shafts and the 13 mm nut that holds the adjustment cam are aligned. Then I orient the brake lever arms so they line up with the blue (3) line since I don’t have the brake cable installed.
I don’t have pictures of doing this on my work bench, but here are pictures I took after I mounted the wheel with the brake carrier on the bike. I did a final check to be sure everything was correct.
You can see the rear lever arm on the left clearly aligned along the blue #3 line and if you look carefully, you can see the front brake lever arm poking out along the the blue #3 line on the right. The template is designed to be used with the wheel installed so it’s is easy to check the brake arm alignment when you want to adjust the brake cable. However, you can’t remove the rear brake lever arm as it interferes with the right fork lower slider. You have to remove the brake arm from the brake carrier plate and rotate the carrier plate so you can remove the rear brake lever arm.
When you have brake lever arms aligned on the brake cam shafts, tighten the Allen head bolts to secure them. I didn’t find torque settings for these so I snugged them to a firm feel, but didn’t oink on them. The lever arms are aluminum and I don’t want to strip the treads.
Install Brake Carrier and Mount Front Wheel
Although I wore nitrile gloves when applying the brake grease and was careful to wipe off any that got on the gloves, I clean the brake hub and brake shoes with brake cleaner. Before I do that, I use 320 grit wet paper and lightly sand the brake hub and the outside surface of the new brake shoes to remove any old brake binder from the drum and any surface contamination from the shoes. Then I clean the hub and shoes with brake cleaner and dry them off. Then I put the brake carrier into the wheel hub.
Here is the front axle assembly.
There is a spacer sleeve that slides over the axle. The lip on the sleeve rests against the left side bearing cover under the chrome hubcap. I put a light coating of wheel bearing grease on the axle and the outside of the spacer sleeve before installing the sleeve in the wheel using the axle to guide it through the bearings.
Then I inserted the axle from the right side through the hole in the lower fork slider, through the wheel hub and through the left lower slider hole.
Install Front Brake Torque Arm Assembly
Here is the polished brake torque arm assembly that keeps the brake carrier from rotating.
The torque arm mounts on the stud in the brake carrier and to the right fork lower slider using the bolt, lock nut and washer. I mount the brake torque arm to the brake carrier first and then attach the other end to the left fork lower slider.
I torque the brake arm nuts to 12 FOOT/pounds. Then I torque the large 22 mm axle nut to 25 FOOT/pounds followed by the single axle pinch bolt on the bottom of the right fork tube to 12 FOOT/pounds.
Here is what the front looks like now.
Install Handlebars and Right Control Perch
I install the new handlebars and torque the handlebar clamp nuts to 15 FOOT/pounds.
Now I can install the right side control perch assembly.
Note this picture below does not show the V-shaped serrated steel wedge described below. I had the control perch powder coated and had to remove the powder coat inside the perch with a drum sanding attachment on my Dremel tool. I install the small serrated steel wedge into the V-slot on the inside of the perch.
Then I slide the perch on the right handlebar end and tighten Allen head bolt to clamp it on the handlebar.
Install Front Brake Cable
The wire bracket is installed under the top, right, fork boot strap.
Here is the new front brake cable assembly.
The end that connects to the brake lever goes through a ferrule and has a felt cylinder wiper that fits on the cable.
The ferrule is slotted on one end and has a larger hole on one side that captures the end of the cable inside the ferrule. The felt is split down one side so it slips over the cable.
I thread the handlebar end of the cable through the right control perch and attach the felt wiper as shown. The felt slides inside the cable adjuster. It keeps dirt our of the assembly and is NOT oiled nor is the brake cable as it uses an outer Teflon sheath over the braided cable.
I remove the handlebar lever and flip it over and then slide the end of the brake cable inside the lever so the cable is visible in the hole for the ferrule.
I insert the ferrule into the hole in the lever with the large side of the hole in the ferrule pointing toward the end of the brake lever so the slot in the ferrule passes over the cable as the ferrule is inserted into the hole in the brake lever. I pull the cable out of the lever to seat the end of the cable into the ferrule before turning the lever over.
I twist the lever over and mount it into the slot in the right control perch. I insert the threaded pivot pin into the hole and then tighten the nut and lockwasher on the bottom of the perch.
I route the cable behind the upper brace and lower yoke. I insert the cable into the wire bracket using a pair of pliers to open the loop so I can slip the cable inside.
This what it looks things look like now. I’m ready to install the lower end of the brake cable in the brake lever arms and adjust the brakes.
Adjust Front Brakes
I start with adjusting the brake cable adjuster barrel on the control perch all the way into the control perch so I have maximum slack in the outer sheath.
Part way up from the other end of the cable near the rubber boot is where the sheath ends. The sheath mounts in the rear brake lever ferrule. The ferrule has a cut in the bottom to slip over the braided cable and a larger hole to capture the sheath in the ferrule.
At the other end, the cable has a threaded sleeve with an adjusting nut on the end.
I remove the adjusting nut and thread the cable into the other ferrule in the front brake lever. The threaded sleeve has a flat on one end so I can hold it with a small crescent wrench as I tighten the adjusting nut onto the end.
To get enough slack so the sleeve sticks out far enough from the front brake arm ferrule to let me thread the adjuster nut, I push the rear brake lever forward with my left hand and then thread the nut a couple turns with my right.
Then I tighten up the nut using a crescent wrench to hold the threaded sleeve while I use a 10 mm socket on the adjusting nut.
I tighten the adjusting nut until the rear shoe starts to touch the drum and then back the adjusting nut off a turn. I loosen the 13 mm nut on the cam adjusting screw. I pull the brake lever at the handle bar until the front shoe just touches the drum. Then I turn the screw with an Allen wrench counter-clockwise until it stops. Then I turn it clockwise a small amount and set the lock nut.
Now I check the movement of the brake arms as I pull the brake lever at the handlebar. I want the rear brake lever to move, stop and then the front lever move. The distance each lever moves should be about equal and about 4 mm. I adjust the adjuster nut to change the movement of the rear brake lever and the cam adjuster to change the movement of the front brake lever. When the brake arms are moving equally I tighten the brake cable adjusting barrel at the handlebar (turn the barrel so it extends from the control perch) so there is about 1/8 inch movement of the lever before the rear shoe touches the drum. I get a solid locked up brake when the handlebar lever is about 1/2 way to the handlebar. When I release the handlebar lever the brake shoes aren’t dragging on the drums and the front wheel spins freely.
That does it for now. I’ll tweak the brake adjustments when I get the bike on the road again.
2017-03-31 Corrected error in location of brake torque arm.
2020-07-30 Corrected error in spring strength vs wire size and number of coils.