Some improvement after new rear brakes installed

[George inMinneapolis]

installed a nice new set of EBC rear brake shoes. I adjusted the brake adjustment and pedal adjustment as Duane Ausherman says to, http://w6rec.com/duane/bmw/rear_brake/.

The brake adjustment is set to just start to have a bit of drag when the wheel is spun.

When I press the pedal all the way down, the last 1/2 inch of pedal, the brakes start to be affective. Above 1/2 inch they work somewhat.

Is there something I could have installed wrong? Maybe something amiss with the brake cam? I'm thinking if they work at all, I must have installed them correctly. Either the brakes are extended by the cam or they are not.

So, they are a bit better than before, but certainly I cannot come close to locking up the back wheel.

I don't think it could be a worn brake drum since the brake adjustment has some drag on the drum.

Any ideas of what the problem could be?

Thanks!
George

[Bamboo812]

Could be the new shoes don't match the arc of the worn drum, so small contact patch.

[Major Softie]

installed a nice new set of EBC rear brake shoes. I adjusted the brake adjustment and pedal adjustment as Duane Ausherman says to, http://w6rec.com/duane/bmw/rear_brake/.

The brake adjustment is set to just start to have a bit of drag when the wheel is spun.

When I press the pedal all the way down, the last 1/2 inch of pedal, the brakes start to be affective. Above 1/2 inch they work somewhat.

Is there something I could have installed wrong? Maybe something amiss with the brake cam? I'm thinking if they work at all, I must have installed them correctly. Either the brakes are extended by the cam or they are not.

So, they are a bit better than before, but certainly I cannot come close to locking up the back wheel.

I don't think it could be a worn brake drum since the brake adjustment has some drag on the drum.

Any ideas of what the problem could be?

Thanks!
George

Tim's correct (Bamboo). Also, the angle of the arm is important. Go to Duane's site and look it up if the logic isn't immediately apparent.

You said: "I don't think it could be a worn brake drum since the brake adjustment has some drag on the drum." I have no idea what you mean by that, but Tim is correct that this can do it: if the arc of the drum is greater than the arc of the shoes, then only a little of the shoe will touch. This can be corrected by having the shoes "arced," or you can wait the few thousand miles it will take for the shoe to wear in to the arc of the drum.

[Duane Ausherman]

This could be a can of worms. Of the various possibilities, the most likely is the arc of the drum doesn't match the shoes. It is very easy to prove this with an examination of the shoes. You will see that the wear area is far less than the virgin area. This means that your energy put into the brake lever is attempting to warp the shoe to fit the drum. Better not happen.

Or, it is also possible for the linkage near the brake lever to be wrong. Not very common.

It is also possible for the cam that actuates the shoes is worn incorrectly and fails to transmit the energy to the shoes in the proper amount.

The last two are not common and should be ignored for now. Of course you should find no evidence of oil on the shoes.

Even with a very good job of grinding the arc to match the drum, you won't have great brakes at first. Use the brake gently after the shoes are ground.

[George inMinneapolis]

The term I have heard before is wait for the shoes to "bed in". So in a few thousand miles, the shoes may wear to fit the arc of the drum and have more contact. I'll see how this goes. Thanks for the advice.

By the statement , "I don't think it could be a worn brake drum since the brake adjustment has some drag on the drum", I was trying to communicate that I have adjusted the wing nut on the brake adjustment rod to the point when I spin the rear tire, there is just a touch of drag by the brake. The thinking was that there is at least some contact with the brake drum by the shoes without even pressing the pedal.

[Duane Ausherman]

George, over this forum we can't judge the amount of drag that you mention. There is a simple test for it. The risk is that the drag can increase with heat. That makes it a downward spiral. This was especially true of the stock linings on the /2 series.

I have no idea about the variety of materials used today on the various offerings.

Go for a ride on the highway, on a cool morning, where you won't need to use the rear brake for at least 15-20 miles. Stop without the brake and park it. Test the temperature of the drum, by hand or by a laser gauge. It will be warm due to the heat off of the final drive, but not over 160 F on a day of 70-80 degrees. If the drum is hot, then check the drag the same way that you set it initially. It should drag the same, or less.

Keep in mind that you have new shoes. Why do you trust the shoe casting where the cam lifts it? I have seen errors several times with new shoes. That is partially why I prefer to have my material bonded on my old shoes.

I suggest that you remove the wheel and take a good look at the wear pattern now, before you expect it to get better in a few thousand miles. A proper job will lock up the rear wheel in the first one or two hundred miles. You risk having a poor match and causing hot spots that can glaze over your new linings.

Removing the wheel is the hard part, as the shoes pop on and off easily. Just be sure to tap the washer flat again after installing shoes.

[Curt Henry]

I sent George an E-Mail recommending that he has his new brake shoes radius cut to fit the drums. You want full contact with the friction material to the drum to achieve maximum braking force. I have had this work done with Harleys that I have owned in the past.

The below link explains the process of re-radiusing brake shoes.

<http://www.bremsenundkupplungsteile.de/ ... fen_en.pdf>

[George inMinneapolis]

I had no idea that just popping in a new set of brakes shoes would not simply take care of the problem.

I'll check the shoe castings, though I would hope that EBC knows how to make shoes. I've put on a few miles, so maybe I can see where the contact is on the shoes.

I'll look into radius cutting.
George

[Kurt in S.A.]

I've never had a small amount of drag when adjusting the rear brakes. I usually run the wing nut in with the wheel spinning until I begin to hear some noise of shoe contact. Then I back off the wing 1/2 to a full turn. You really don't want drag going down the road. I suppose that drag will more or less disappear with the constant rubbing; so if it's going to end up that way, why not just start with the right adjustment?

I agree with the arcing of the shoes. I had new shoes installed on my R25/2...Vech rivet his new material to the metal shoes. I assembled, spun the wheel, then used the brake. I disassembled and noted what parts touched. It wasn't bad but still I found the appropriate sandpaper and used a sanding block to radius the shoes myself. I iterated on this many times until I got the entire surface to be wiped on when I applied the brake. It seems to have done a good job.

Kurt in S.A.

[Duane Ausherman]

When sanding a glazed shoe, it is often done incorrectly. It seems natural to hold the shoe in one hand and sand with the paper in the other hand. Nope, that doesn't work well at all.

Lay the paper on your flat glass plate. Now, rub the shoe against the paper in an even sweeping motion. This does the job better and faster than the former way.