Boxerworks.com

I'm a bit puzzled to see this thread at all. All of my own rear drum brake drums have looked fine to me. No signs of any significant wear at all. And I'm puzzled to hear that low drum wear rear wheels are kind of thin on the ground as spares nowadays. I've bought a short handful of such used wheels through IBMWR, and aside from a little surface rust all have been fine. In fact I never even thought to pay much attention to the drum condition (which I should have). Maybe I was just lucky.

Rear wheel splines are, of course, another story. I have paid attention to them and turned down wheels because of spline wear.

So how do the worn drums get so worn? I'm thinking that it can only be from a long period of excessively heavy rear wheel braking. Since the front brakes stop the bike so much better, if only because of weight transfer while braking, I've developed the habit of light braking on the rear while braking more heavily on the front (road condition permitting).



Ken

Can I ask, without measuring and comparing against the factory no-go spec why you are even inquiring about this?

Upon closer inspection, "jjwithers" look at your last picture. I'd bet anything and people that know will be able to confirm or deny this, but I would think the steel insert in those hubs most certainly are machined AFTER they are installed. If you look at you last picture, if the wear you are worried about is really wear, why to the left does there seem to be little wear or ridge by where the hole is? that much deviation if it were from wear would pulsate so badly you'd likely never be able to modulate the rear brake apply enough for it to not want to lock up. Surely if nothing else, it would vibrate like a SOB.

I cannot imaging that **if** what you are showing us is really wear and not what it appears to be, the simple post insertion process refacing/machining of the steel, that it could wear by say an 1/8' in a place only a few inches from where it appears to have worn very little. I think what you are looking at is not at all what you think.

High res pictures of the entire drum all the way around, or better yet, your own eye combined with some gray matter should be able to confirm, or deny my theory here...

It'd be interesting to hear from people that actually know these answers rather than my pure speculation on the matter from some fragmented pictures and guessing the steel that lines the hubs would have "had" to be turned/trued up after it was inserted to insure it was perfectly aligned all the way around with respect to the center axis (axle).

Up until now, i never considered the brake lining an issue either. I just slapped on a true wheel with good bearings and good splines and called it a day.
That was... until i got a /5 with both drum fronts and rears. My rear brake isn't that effective (not that i use it THAT often but if i stomp on it, i want it to STOP, not glide slower). My front could be better but it works.
So i started looking into better 'stock' brake options.
I have some extra wheels sitting around and i am considering lacing them up with some Akront rims and having the hubs powder coated. Before i go to all that trouble, i wanted to make sure the hubs are worth it. \
So... i dug deeper. A local mechanic clued me into this tidbit:
There is a number stamped on the outer edge of the hub.
It says something like MAX 7.92"
That number is the maximum tolerance of wear allowed for the drum's lining. If you put a caliper and measure in there (accurately), it is an indication of how much life you have, or don't have...
I have no idea what happens after you go beyond that tolerance. Perhaps you will hit rivets? I don't know.
I also have no idea why BMW has this number stamped on there in inches and not metric. Maybe the USA required they put it on there for safety reasons? (I was being conceived and born around the same time these hubs were made so i can only speculate.)

The mechanic had some calipers so we measured my wheels. They were very close to being out of tolerance but after 35+ years of braking on the hub, i have no idea how much actual wearing goes on after a year, 2 years, 5 years (i know riding habits vary wear)?
If you look closely (and clean the inside), you can see where the drum's lining started when it was new, and how much wear has taken place... and of course, how much is left.

I did hear back from Vintage Brake. They said that it would cost about 150 British Pounds to have the brake hub re-lined. That is about $250 + shipping. Brake hubs start at about $400 New. so... i'd say your best bet is to take a chance on the used wheels out there....

If any experts can chime in on this, please do. All this information is new to me.
-Josh

I am wearing into my FRONT drum lining on my slash five. Every time I check...the ridge gets deeper. I am running more aggressive linings. I will replace the hub when it gets too far.

More aggressive linings???

This sounds interesting. I'll bet your idea of more aggressive and mine "could differ." More aggressive (in a favorable manner) used to mean you put even softer material in. If your wheel is wearing out due to hard linings that are NOT asbestos or a similar soft organic compound, well then usually that is a less aggressive brake for stopping, but far more aggressive brake for wearing one's drum out. Linings were meant to be replaced, drums were not... I'm not going to bore people here. I'd think this is enough on the topic to already light a fire...

I guess no one told anyone to use asbestos in these bikes? I suppose that could be the OP's issue here. Yeah, be worried; it could be all worn to bits if someone put hard-ass shoes in instead of the original asbestos or comparable organic substitutes...

Also of course maybe I have atypical brakes along with my charging system? Can no one else lock up their BMW's drum brakes? Rears are a piece of cake. Fronts too, I just TRY MY BEST to not do so, even in a panic stop... (as I lay my body over the tank and handlebars to prevent such a lock-up...)