Disc brake swirl pattern

[wirespokes]

I've had the 87 LM1000 almost two years now and just before this last rear tire change noticed the rear brake disc was mounted backwards.

Most discs I've seen have holes drilled in an arc starting from the center, arching towards the outside edge. The discs are normally mounted with the arc swirling outwards - the hole nearest the axle being the leading edge.

So when I changed the rear tire yesterday, i also pulled the disc. I didn't realize those button head allens were installed with loctite - it wasn't easy removing them. After that, the job was mostly janitorial, lube and re-install.

I thought someone in the previous 29 years had removed the disc and accidentally replaced it backwards. But now I've seen several more LM1000s and every one of them also has the disc oriented backwards. Of course it works either way, but might there have been a reason for them being mounted that way? I'm now thinking they must have come from the factory reversed. 

[guzzisteve]

No, the rest of the world is wrong. I can't check my LM3, that wheel is on the Cal2. It also has no buttons.

[Huzo]

Sounds like you have a Southern Hemisphere model.
It's like the swirling water coriolis principle...

[Moto]

I've had the 87 LM1000 almost two years now and just before this last rear tire change noticed the rear brake disc was mounted backwards.

Most discs I've seen have holes drilled in an arc starting from the center, arching towards the outside edge. The discs are normally mounted with the arc swirling outwards - the hole nearest the axle being the leading edge.

So when I changed the rear tire yesterday, i also pulled the disc. I didn't realize those button head allens were installed with loctite - it wasn't easy removing them. After that, the job was mostly janitorial, lube and re-install.

I thought someone in the previous 29 years had removed the disc and accidentally replaced it backwards. But now I've seen several more LM1000s and every one of them also has the disc oriented backwards. Of course it works either way, but might there have been a reason for them being mounted that way? I'm now thinking they must have come from the factory reversed.

I don't see how it could make a bit of difference. Some discs have spiral grooves cut into them, and for those the "correct" direction you describe could help eject scraped-off material via "centrifugal force." But discs that are merely drilled are different. Each hole is a self-contained element rotating in a circular motion; the spiraling effect is only an optical illusion that we perceive when the wheel rotates. Each hole does its work in isolation, no spiraling involved.

That's how it seems to me.

Moto

[wirespokes]

I don't see how it could make a bit of difference. Some discs have spiral grooves cut into them, and for those the "correct" direction you describe could help eject scraped-off material via "centrifugal force." But discs that are merely drilled are different. Each hole is a self-contained element rotating in a circular motion; the spiraling effect is only an optical illusion that we perceive when the wheel rotates. Each hole does its work in isolation, no spiraling involved.

I totally agree. It seems like a matter of aesthetics more than anything else. However, if you take the arced sections individually (cut at the dotted lines), one direction would be pulling it through the disc, the other would be pushing. Mine's been fine for 36K so doubt there's a problem either way but who knows? Perhaps in a really quick stop the forces on it would be better applied pulling the sections rather than pushing.

All conjecture. But I am something of a slave to aesthetics, so turned it around.

[Moto]

I totally agree. It seems like a matter of aesthetics more than anything else. However, if you take the arced sections individually (cut at the dotted lines), one direction would be pulling it through the disc, the other would be pushing. Mine's been fine for 36K so doubt there's a problem either way but who knows? Perhaps in a really quick stop the forces on it would be better applied pulling the sections rather than pushing.

All conjecture. But I am something of a slave to aesthetics, so turned it around.

Good for you. Beauty is truth, truth beauty.

[wirespokes]

I don't know about beauty being truth - I trusted my X  - maybe because she was beautiful - but the truth to her was something to be molded and massaged to serve her own personal purpose. Funny thing is, she's an ugly tank now. Hard to believe the transformation - karma I guess.

My perception of beauty has gone through a few changes over the years, and my ability to deal with truth has as well. But I wouldn't say truth and beauty go hand in hand.

[notbent]

nbv





The first pic is the rear disc on my 89 LM V.

Only 5 holes not 6 like the 2 front discs.

Plus there are no springs and circlips. The bobbins look the same both sides.

Anyone seen this before?

The second pic is one of my front discs... they were rattling like crazy it took me ages to narrow down the clunking noise every time I hit a bump in the road ie all the time.

I thought it was the fairing so it's been off like a hundred times... rubber washers etc etc.

THEN I realised it was the discs by lightly holding the front brake [de-linked] as I rode merrily along. No noise!

THEN I realised that the clunking was the sideways disc rattle being amplified by the shape of the fairing, which is like a speaker horn.

So I bought new Belleville washers and circlips and switched them over. You can see the wear marks in the pic.

I put the bobbins through the opposite side so both sides are unworn. Swapped the discs lefty for righty [keep the swirl pattern] so the clip side is inside.

No more clunking over speed bumps and other road detritus.

You have no idea how that cheered up my day!

[Moto]

I don't know about beauty being truth - I trusted my X  - maybe because she was beautiful - but the truth to her was something to be molded and massaged to serve her own personal purpose. Funny thing is, she's an ugly tank now. Hard to believe the transformation - karma I guess.

My perception of beauty has gone through a few changes over the years, and my ability to deal with truth has as well. But I wouldn't say truth and beauty go hand in hand.

Yeah, well, John Keats never met your ex.

Moto

[Rusnak_322]

nbv





The first pic is the rear disc on my 89 LM V.

Only 5 holes not 6 like the 2 front discs.

Plus there are no springs and circlips. The bobbins look the same both sides.

Anyone seen this before?

The second pic is one of my front discs... they were rattling like crazy it took me ages to narrow down the clunking noise every time I hit a bump in the road ie all the time.

I thought it was the fairing so it's been off like a hundred times... rubber washers etc etc.

THEN I realised it was the discs by lightly holding the front brake [de-linked] as I rode merrily along. No noise!

THEN I realised that the clunking was the sideways disc rattle being amplified by the shape of the fairing, which is like a speaker horn.

So I bought new Belleville washers and circlips and switched them over. You can see the wear marks in the pic.

I put the bobbins through the opposite side so both sides are unworn. Swapped the discs lefty for righty [keep the swirl pattern] so the clip side is inside.

No more clunking over speed bumps and other road detritus.

You have no idea how that cheered up my day!

you are supposed to have some movement in those bobbins. they are floating to allow for radial expansion. 
I had a few Honda GP race bikes and the brembo rotors on them were very loud (when pushing the bike around - you couldn't hear anything from them when the bike was running)

[wirespokes]

Notbent - My 87 rear disc could be removed from the carrier, unlike yours. The buttons have spring washers and C clips holding them together. Yours are like the ones on some of my airheads - permanently attached.

Where did you get the new buttons, washers and clips?

[notbent]

https://www.gutsibits.co.uk/pr/TheShop/index.php?q=bobbins&f=d&Model=7&search=SEARCH

I didn't buy the bobbins. When disassembled the outer discs only had .5mm play radially and I didn't see any wear.

It was the axial play was causing me grief.

I'm guessing you know this site... I had to dick around to find the circlips but they delivered to Australia in a week!

[wirespokes]

At a little over 8 BP each a whole set would be $60. Expensive little buggers!  For that kind of money I'd make them myself.

How did you remove the old ones?

[Antietam Classic Cycle]

Notbent - My 87 rear disc could be removed from the carrier, unlike yours. The buttons have spring washers and C clips holding them together. Yours are like the ones on some of my airheads - permanently attached.

Where did you get the new buttons, washers and clips?

MG Cycle has them:
http://www.mgcycle.com/index.php?main_page=product_info&cPath=110_134&products_id=1030
http://www.mgcycle.com/index.php?main_page=product_info&cPath=110_134&products_id=1033
http://www.mgcycle.com/index.php?main_page=product_info&cPath=110_134&products_id=1340

[notbent]

At a little over 8 BP each a whole set would be $60. Expensive little buggers!  For that kind of money I'd make them myself.

How did you remove the old ones?

I undid the circips then pushed them out with my thumb.

[wirespokes]

Thanks, Charlie - that's more reasonable.

Notbent - I thought you said previously they didn't have clips, but were solid. With clips it's a no-brainer.