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1982 R100 Brake Drum Worn on Snowflake Wheel ?

R

rkildu

New member
I have researched this issue several years ago. I am hoping new alternatives are now available.

Worn Brake Drum, diameter measured a years back and found worn past Specs, a few thousandths over. The drum is an integral part of the wheel. Currently have almost no rear brakes. I have replaced shoes with new OEM and some non. Works marginally for a short time only.

Solutions found then:
New rear Snowflake wheel. Unknown availability and big bucks !, Used wheels available but it would be taking chances on drum and splines.
Oversize brake shoes: Unknown availability, and or specifications.

Has anyone successfully resolved this problem? Ideas requested.

Rod
 
I checked a few sources and no one seems to have come up with an approach for this. As you mention, I believe the rear braking area is all aluminum, so the idea of trying to sleeve in a steel section doesn't make sense. I've not heard of anyone being able to "spray in" some aluminum and then having it machined back. Likely to be pretty expensive no matter which way you go.

Since the rear wheel offers 20-30% of total braking, seems like the thing to do would be to find a way to create thicker shoes. But then the issue becomes that the rear drum has less material and can't dissipate the heat as well, leading to a potential risk.

There's a Wheels and Brakes section in the link in my signature line. Maybe a place like Vintage Brake might have some ideas.
 
Looking at a brake cam here on my desk right now

The final drive for drum wheels with brake shoes has an actuating lever with lots of adjustment available fitted to a pin running through the housing with an "S" cam on the end positioned between the brake shoe flat end castings. The other 'rounded' end of the shoes rotate off a round pin as the cam moves the brake shoes apart and into contact with the cast iron brake drum. What if one increased the lift of the cam by adding dimension to both flats? This would effectively move the shoes closer to the drum. It might be necessary to add diameter to the round pin as well or modify the shoe with the aim being to make the shoes move together into uniform contact with the drum. Actual drum thickness is a concern. I would speck thicker shoes for fleet trucks when their drums got to max. dia. and then replace the drums when the oversize shoes were gone.
 
Last edited:
I find it hard to believe the brake drum would be aluminum, but it may be!

I would consider getting the wheel bored out and sleeve the bore. Done properly it would work fine.
 
I haven't seen the innards of this wheel......When replacing rear brake shoes on my 1710 Ford tractor with aftermarket shoes, I ran into sorta the same (if I understand correctly) problem. The aftermarket shoes were a bit "thin" on the cam surface that the shoe tails ran on. A tab of 1/8" steel welded to the shoe tails allowed the travel to work the brakes just fine.
OM
 
The question is why did BMW (or any brake manufacturer) set max limits for drum diameter? There does seem to be possible ways to move the shoe surface out to meet the wear of the drum, but should you? What are the real or perceived risks?
 
rkildu said:
I have researched this issue several years ago. I am hoping new alternatives are now available.

Worn Brake Drum, diameter measured a years back and found worn past Specs, a few thousandths over. The drum is an integral part of the wheel. Currently have almost no rear brakes. I have replaced shoes with new OEM and some non. Works marginally for a short time only.

Solutions found then:
New rear Snowflake wheel. Unknown availability and big bucks !, Used wheels available but it would be taking chances on drum and splines.
Oversize brake shoes: Unknown availability, and or specifications.

Has anyone successfully resolved this problem? Ideas requested.

Rod
Click to expand...
The brake drum has a cast in iron liner that is not replaceable. It must be worn much more than a few thousands to create a problem with braking. I personally have not seen a rear drum with enough wear where the new shoes no longer engaged the drum properly. If it indeed measures beyond serviceable limits,
it should be replaced. The drum is an intregal part of the snowflake wheel, and machining or attempting to replace the iron cast in liner could weaken the casting to a point of potential failure. Best solution to the problem is replace the wheel. Surely there are some good used ones available out there.
 
Thanks for the many thoughtful comments.

I have an inquiry into Vintage Brake about making thicker brake shoe pads, and about the advisability of doing that.

If that is not advisable and replacement wheels is the only answer it brings up another issue, that of the drive spline wear. A new wheel will require the final drive splines to be repaired/replaced. A used wheel will require the drive splines fixed and the splines on the wheel replaced.

Does anyone know of a service that does these repairs?

Still seeking options
Rod
 
I'm back!

I finally got my open projects down to a minimum and put the Airhead up on the lift table so I could investigate my brake issue. I pulled the rear wheel to allow analysis.

First discovery: The brake drum is NOT over sized. The guy I had measure it for me did not get a correct reading. I measured it myself multiple times, multiple ways, and consistently came in below minimums. I show about 1 mm still usable. So Brake drum size is not the issue!

What I did find is that my brake shoes do not have even wear. It shows wear on the leading and trailing edges of the shoes for an inch or two, but nothing in the middle! I checked my maintenance records and the shoes were installed about 15K miles back. I don't have a record of manufacturer or where I got them from. Bright light and a magnifier showed them to have BMW logos on the shoe carriers and the part numbers of: 34-21-1-235-693 upper and ...694 lower. So they must be OEM parts. Those part number do not show up on any of the parts lists available on line so I expect the numbers have changed.

My first thought was that I may have an incorrect part from another model? I don't know?

My only option seems to be replace. I am not equipped to modify the shoes I have! OEM are very pricey at over $200. I see that EBC is everywhere on line and much more reasonable cost. However there is a thread here about a similar problem on a set of EBC's on a /5 front brake???

What's the general opinion on the EBC replacement parts? And/or other options.

Thanks
Rod
 
Rod -

Those aren't part numbers...very rarely did BMW put part numbers on items. These numbers represent a batch or mold number of some kind that BMW used for internal tracking.

So, do the existing shoes have a lot of material left? If so, why not look into getting the shoes arced to match the mating with the drum lining. We had a discussion about that on EBC shoes...maybe that's what you read about:

https://forums.bmwmoa.org/showthread.php?93841-EBC-brake-shoes-R75-5

Much less expensive if you still have life in the shoes.
 
If so, why not look into getting the shoes arced to match the mating with the drum lining.
Click to expand...

You've already been in touch with the best. Call Vintage Brake again. and have the shoes arced to the drum.
 
Arcing the shoes will not fix the problem of undersize shoes. Arcing is a sanding/grinding operation to deal with the high spots present with newly riveted linings.
 
rkildu said:
I'm back!

I finally got my open projects down to a minimum and put the Airhead up on the lift table so I could investigate my brake issue. I pulled the rear wheel to allow analysis.

First discovery: The brake drum is NOT over sized. The guy I had measure it for me did not get a correct reading. I measured it myself multiple times, multiple ways, and consistently came in below minimums. I show about 1 mm still usable. So Brake drum size is not the issue!

What I did find is that my brake shoes do not have even wear. It shows wear on the leading and trailing edges of the shoes for an inch or two, but nothing in the middle! I checked my maintenance records and the shoes were installed about 15K miles back. I don't have a record of manufacturer or where I got them from. Bright light and a magnifier showed them to have BMW logos on the shoe carriers and the part numbers of: 34-21-1-235-693 upper and ...694 lower. So they must be OEM parts. Those part number do not show up on any of the parts lists available on line so I expect the numbers have changed.

My first thought was that I may have an incorrect part from another model? I don't know?

My only option seems to be replace. I am not equipped to modify the shoes I have! OEM are very pricey at over $200. I see that EBC is everywhere on line and much more reasonable cost. However there is a thread here about a similar problem on a set of EBC's on a /5 front brake???

What's the general opinion on the EBC replacement parts? And/or other options.

Thanks
Rod
Click to expand...

Hi Rod,
I replaced my shoes with Motobins parts. Not BMW OEM but from an Italian maker. You can tell the difference by the price. :laugh
Go here: https://www.motobins.co.uk/
and search for 24800. That's their part code number.

They fit and work well on my 81 R80G/S. The original shoes were ruined by a fluid leak caused by the O ring seal for the actuator lever that travels through the final drive. There is also a felt washer in there. These two parts need to be monitored since when they break down and leak you have almost no rear brake at all and the shoes get ruined.
 
I had to replace my brake shoes due to a oil leak also. That was 15K miles back. The bike has 115K total miles on it now.

Anyway, I cleaned up both shoes and did a "chalk test" on it yesterday, with interesting results. It shows pretty even contact on the lower shoe, but there is almost no contact on the upper shoe. Just a very little at the leading and trailing edges. That explains the poor braking action! There is something very wrong with this set of shoes. I am just not comfortable with trying to Arc the shoes my self and I think I want to go with the latest technology braking material.

I just got off of the phone with Bob's BMW and I ordered a set of EBC's, after discussing the problem with them.

I will report back when it get it back together.

Thanks
Rod
 
Just to close this thread out,

I have installed the new EBC Brake shoes, and a bunch of other maintenance, and took it out for a test ride the other day. I still don't completely understand what was wrong, but I have plenty of brake drum wear left and the new shoes have given me back my rear brakes! The shoes I removed only had about 15 K miles, and had plenty of wear left on the braking surface, but for some reason that wear was uneven! They were BMW OEM brake shoes. Old Stock ? Who knows.

Thanks for the input,
Rod
 
BMW specifications for rear drum are ...

new drum ... 200 mm diameter

maximum oversize after wear ... 201.5 mm

This applies to all large frame Airheads through 1984, spoke or cast wheel

Do not have data on hand for R65, R80G/S, R80ST.
 
I have to wonder if you are looking in the wrong place. I find it hard to believe that the brake shoes and drum could be bad, or be bad enough to give you pretty much no breaking. Have you looked over the linkage well and made certain it is in good condition and properly installed? I wonder if something is wrong with the linkage, binding, or perhaps installed wrong giving you a wrong ratio, wrong action?
 
Uneven wear (or incorrect installation) of the brake cam? Item 21 on the MAX fiche.
New shoes would temporarily mask this.
 
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