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[Solved] R75/5 Front Brake Shoes Won't Go On the Posts

Justin Handfield
(@justinh)
Active Member

Ahead of a planned camping trip this weekend, I decided it was finally time to replace my (original) front brake shoes with some new ones I've had sitting around for a while on my '72 R75/5. Like clockwork, I've run into problems... The old shoes came out without too much hassle - pop the clips, detach the springs, and out they came; no muss, no fuss. Getting the new shoes ON, however... I've provided them some blood, some sweat, and am about ready to add tears to the mix!

Try as I might, I simply cannot get the new shoes to slide down over the posts; no matter the amount of grease, the amount of cursing, they just feel like the holes aren't quite large enough. I've checked with calipers, the old shoes had 14mm holes, same as the new ones so it wouldn't appear to be a machining issue. Am I just probably ever-so-slightly off-kilter and not trying to slide these straight on? Is there a trick I'm missing to getting them on? Am I just going too easy on it? I can get them to slide at least partway on, but they're so incredibly stiff to rotate that I can't imagine the springs would be capable of pulling them back away from the drum...

Any suggestions appreciated, save me from having to ride a borrowed bike this weekend!

Quote
Topic starter Posted : 05/18/2021 20:06
Justin Handfield
(@justinh)
Active Member

Sometimes you just need to write it out to realize the simple answer of “if the holes are a little too small, just make them bigger…”

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Topic starter Posted : 05/18/2021 23:14
David Elkow
(@4949)
Estimable Member

I have never worked on those brakes. I looked at some images online. My first check would be - are the tops of the posts somehow “mushroomed” a bit?  Perhaps that is the only point of interference. If so, they could be dressed by hand. I wouldn’t go any further than that on the posts. Don’t want to mess those up. Just be sure they are clean and slick. 

That leaves the 14mm bore in the shoes. How to make those slightly larger, hmmm, at home. Knowing me, and my tools, I would probably be trying to lightly/evenly whisk out some material with a dremel tool w/grinding or sanding drum attachment. They just need to fit and move freely.

just my thoughts. 

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Posted : 05/19/2021 10:29
Richard Whatley
(@wobbly)
Member Moderator
Posted by: @justinh

Sometimes you just need to write it out to realize the simple answer of “if the holes are a little too small, just make them bigger…”

The new shoes should slip right over the posts. Justin is correct, you're holes are probably 0.002" undersized. You probably got 3rd party shoes, but not to worry.

If you'll drill out the hole with a 14mm (0.551") drill bit, it will probably leave a 0.553" hole. That's exactly what you need. It would help to have a drill press, but it can be done in a vice.

Hope this helps.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 05/19/2021 16:08
Justin Handfield
(@justinh)
Active Member
Posted by: @wobbly

If you'll drill out the hole with a 14mm (0.551") drill bit, it will probably leave a 0.553" hole. That's exactly what you need. It would help to have a drill press, but it can be done in a vice.

Yup, that's exactly what I ended up doing, they slipped right on like a charm after that. These were actual BMW shoes, actually - somewhere there's some retired German machinists shaking their heads over an error like this.

ReplyQuote
Topic starter Posted : 05/19/2021 20:49
Richard Whatley
(@wobbly)
Member Moderator

Glad to hear it all worked out.... and in time for your outing ! 🙂 

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

ReplyQuote
Posted : 05/20/2021 14:00

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