New ATE pad wear

[Abstruse1]

[I searched the forum a bit but couldn't find anything on point.]

I put on a set of new EBC pads about 150 mi. ago. Had a new EBC disk (not stainless). Using the Magic Marker method, I wasn't able to tell much. I thought about it and decided to let the caliper adjust itself -- with the covering nut off, I simply pulled the brake and the pads immediately went to what looked like parallel to the disk and not hanging off the edge. Then I tightened the nut.

I observed two things: 1) Braking wasn't as strong as with the original pads (I have no idea how old and what kind). 2) after just 150 mi., the pads were worn in the same angular way (that is, not parallel to the backing plate) and about the same amount as were the take-off pads. I was astounded!

So, three questions: 1) Why did these pads (both sets) wear in this angular way? Is this typical? I note that the workshop manual shows used pads that also are worn like this. 2) Why in the world that much wear in a tiny distance? 3) Why the weaker braking?

What did I do wrong?

[melville]

The pads should have a taper on them as they come out of the box. Normal wear might reduce the taper a tiny bit, but it also may increase the taper.

[Rebel]

Braking distance and power could also be due to the factor of different brake pad material, and also rotor material. As I recall the ATE calipers used cast iron rotors, which in my opinion are the best rotors made. Yes, they rust, but are incredible. As far as the pads being parallel, there should be a slight taper on the face of the pad, and once everything is bedded in they should be alright. With a new rotor and new pads, it will take a few miles to wear off the crosshatch pattern on the rotor and have the pads mated. Good luck.

[Abstruse1]

Thanx, Rebel. Pads came flat (parallel sides), no taper. The disk that came on my bike looked like stainless -- can't tell for sure since some stainless alloys are magnetic, which this disk was. New EBC disk looks like not-stainless and was advertised as such. So there was a huge amount of pad material worn away in first ~150 mi. Amazing!

Here's what Bob's says about the pads:

These replacement pads fit 1974-1980 models (R75/80/90/100) with FRONT DISC brakes and the stock "ATE" brand calipers. EBC pads are made of organic materials mixed with incredibly strong Dupont KEVLAR fibers. They’re SOFTER than stock pads, which means they’re less likely to cause excessive wear to your rotors. They provide exceptional heat dissipation, long wear, and best of all, great performance! The package includes both pads needed for ONE caliper.

Here's what the vendor says about the rotor:

The worlds only complete line of direct bolt-on brake discs made in EBCs UK manufacturing plant using: Billet-steel rotor rings that deliver 18 percent more stopping power than stainless steel equivalents. EBC Pro-Lite rotors are complete bolt-on and go rotor assemblies made with forged aluminum center hubs, high friction billet steel rotor rings and sturdy riveted construction.

[Ken in Oklahoma]

[I searched the forum a bit but couldn't find anything on point.]

I put on a set of new EBC pads about 150 mi. ago. Had a new EBC disk (not stainless). Using the Magic Marker method, I wasn't able to tell much. I thought about it and decided to let the caliper adjust itself -- with the covering nut off, I simply pulled the brake and the pads immediately went to what looked like parallel to the disk and not hanging off the edge. Then I tightened the nut.

I observed two things: 1) Braking wasn't as strong as with the original pads (I have no idea how old and what kind). 2) after just 150 mi., the pads were worn in the same angular way (that is, not parallel to the backing plate) and about the same amount as were the take-off pads. I was astounded!

So, three questions: 1) Why did these pads (both sets) wear in this angular way? Is this typical? I note that the workshop manual shows used pads that also are worn like this. 2) Why in the world that much wear in a tiny distance? 3) Why the weaker braking?

What did I do wrong?

That magic marker method for aligning the pad surfaces parallel to the disk is a piss poor way of doing it, in my not so humble opinion. I invented a better way of doing the alignment only in the sense that I discovered a method on my own that others before me have discovered on their own. (Meaning that I didn't see 'my' method in any of the Airhead maintenance manuals I own.)

As you know, rotating the eccentric bolt head (under the dust cover at the bottom of the fork leg) is physically what you turn to align the pads to the disk. With the magic marker method there is always some ambiguity as to whether the brake pad surfaces are truly parallel to the sides of the disc. To do the alignment you need a helper, or a home made inner tube rubber band, or perhaps a simple bungee cord (without the hooks) wrapped around the brake lever and handle bar grip. What you're trying to accomplish is to put continuous pressure on the brake lever while freeing your hands and whatever else you need to do the alignment.

With the brake lever 'on' you rotate back and forth that eccentric adjuster bolt at the bottom of the fork leg. You will quickly discover that the brake pads 'want' to be in only one position of the adjuster. That 'want-to-be' place happens to be with the surface of the brake pads dead flat against the disk. It takes extra pressure to rotate the adjuster elsewhere. That's because, in so doing, you are levering the brake pad away from the disk. Leaving the adjuster in the wrong position, which I would expect to actually wear the pads more as they wear to accommodate the mis-alignment.

When you get the pads where they need to be you button things back up and you're good to go.

Not quite. The eccentric actually has two places where it 'wants' to be. One position moves the brake pads forward relative to the disk and the other position rearward. You want the forward position. That's because (on at least one of my bikes) the brake pad was positioned rearward and the brake pad surface extended slightly beyond the periphery of the disc. That meant, of course, that the pad didn't wear there. The braking probably wasn't significantly compromised, but later when you service the brakes you will likely need to re-flatten the pad surface, such as on a stationary belt sander.

Ken

[Abstruse1]

An "AHA!" moment.

Here's what I think I learned. Since the caliper pivots about a vertical bolt, the pads have to wear into wedge shapes.

Most calipers stay pretty much fixed with respect to the caliper (except for a small amount of float), so the pads start out with parallel surfaces and stay that way. As was observed earlier, BMW pads come in a wedge shape (I didn't catch this on first reading). The EBC pads I bought do fit, but have to wear into the wedge shape.

So, if I'm right, what I am seeing is normal.

[Ken in Oklahoma]

An "AHA!" moment.

Here's what I think I learned. Since the caliper pivots about a vertical bolt, the pads have to wear into wedge shapes.

Most calipers stay pretty much fixed with respect to the caliper (except for a small amount of float), so the pads start out with parallel surfaces and stay that way. As was observed earlier, BMW pads come in a wedge shape (I didn't catch this on first reading). The EBC pads I bought do fit, but have to wear into the wedge shape.

So, if I'm right, what I am seeing is normal.

I'm not sure I understand your AHA, but I'm sure you're going to find that EBC pads arrive factory fresh in the same wedge shape as the BMW stock pads. You are quite correct that the geometry of the swinging caliper used with a fixed plane disk will result in wear as the pads are consumed. But the amount of wear is not going to be so much, such that at the end of the brake pads life they will become substantially less keystone shaped than at the beginning of their lives. In other words, all of the new brake pads I've seen have started out keystone shaped and the old worn out pads that I've removed, though worn, have still been markedly keystone shaped.

As you surmised, it all has to do with the distance of the eccentric bolt from the disk, coupled with the fact that one pad is hard against the caliper and the opposing pad is driven by a piston towards that fixed side.

Or so I think. Perhaps I misunderstood what you wrote and we're both trying to say the same thing.

Ken

[chasbmw]

I agree with Ken.....

many years ago I had to have pads resurfaced because I could not get new pads In Bolivia, they were made parallel and so did not work, I had to go back to the workshop and get the pad surfaces ground to a taper.

P.S all BMW OEM brake discs are Stainless steel.

[Abstruse1]

My EBC pads came with parallel sides. No wedgies.

[Ken in Oklahoma]

My EBC pads came with parallel sides. No wedgies.

Well, I don't know what to say about that. However upon reading it I went through a couple boxes of my Airhead spares and I found a new set of EBC FA22 brake pads in an unopened package that I had put in stock. They are definitely for the 'swinging' ATE calipers and both pads are definitely wedge shaped.

Ken