BMW K bikes (Bricks)


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Rabidchiwawa007

Rabidchiwawa007
Platinum member
Platinum member
Hi all,

The bike in question is a 1991 k100rs 4v abs.

I've been through 3 sets of bobbins on my bike in the last year or so. Each time it's around $120 USD in parts and I'm getting a bit tired of it.  They last about 3 trips around town until the discs get really (*really*) rattly again, and I just let it stay that way till it feels unsafe because the bobbins are just completely destroyed.  The discs themselves have plenty of meat left on them. It's likely that the holes themselves,where the bobbins go, are very worn out.  This seems unnecessary due to the following:

I see that the older K100 / k75 models do not have floating discs on the front.  The calipers don't seem to be of the floating variety either from what I could tell in pictures.  This seems like a bit of a sturdier design and I'm interested in altering my front end for that purpose.

-Are there non-floating discs that I could put on my current front end with no ill-effects?  Why do the discs have to float anyways?
-If something's gotta float, are there floating calipers I could get that would bolt on correctly?
-If neither of those is an option, then I'd be looking at changing the entire front end from triple tree down, which would be kind of silly.

The rear brake doesn't have anything floating.

Thanks!


__________________________________________________
1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

BobT

BobT
Life time member
Life time member
If you are going through bobbins at that rate then there is something wrong somewhere, perhaps with the bobbins that you are being supplied with. Floating discs were an update and you would go to loads of hassle to downgrade your bike. All 4 valves including the K100 and K1100 had floating discs and the bobbins last for years. do you cover your front brake lever with your fingers while you are riding? Could that be dragging the discs without you realising it?
I fitted new EBC discs to mine and they came fitted to the new carriers with bobbins as a complete unit.
The rear brake is not a floating disc because it does very little work.

    

sidecar paul

sidecar paul
Life time member
Life time member
The bobbins on EBC discs are not circular; they have flat sides, giving a much larger surface area to take the load. As such, they should last the life of the disc.

Here's a pic. 
https://i.servimg.com/u/f37/17/23/83/39/downlo10.jpg

Paul.


__________________________________________________
'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
'51 Vincent (since '67),'72 Montesa Cota (from new), '87 Honda RS125R NF4 (bought 2015) 
....No CARS never ever!
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Are the bobbins showing a lot of wear?  On my K100RS they sometimes rattle slightly even though they aren't significantly worn.  They do need to have some play in them in order to work as intended.

I would suggest that if the rattle really bothers you, you might want to reassemble the bobbins onto the disc assembly with a tiny dab of silicone gasket material.  Once it hardens, it should dampen the rattle, but still allow enough movement to allow the disc to float in the caliper.


__________________________________________________
Present: 1991 K100RS "Moby Brick Too"
 
Past:
1994 K75RT "Ilsa, She Wolf of the SS"
1988 K100RS SE "Special Ed"
1994 K75S "Cheetos"
1992 K100RS "Moby Brick" R.I.P.
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Rabidchiwawa007

Rabidchiwawa007
Platinum member
Platinum member
No no, I mean *destroyed*:

https://imgur.com/gallery/dWci8

These bobbins are maybe around 1k miles old...


__________________________________________________
1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

BobT

BobT
Life time member
Life time member
Where are you buying those bobbins from? They look like alloy ones!

    

Rabidchiwawa007

Rabidchiwawa007
Platinum member
Platinum member
From Max BMW motorcycles, via the parts fiche.


__________________________________________________
1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Motorbike Mike

Motorbike Mike
Life time member
Life time member
I had the exact same discs on my Cobas bike before I changed the wheels but the bobbins (I think) are stainless steel. They stood up to some long hard braking at circuits like Spa and Donnington and never gave any problems or showed any signs of wear. The parts you were supplied are surely not fit for purpose and look positively dangerous to me, please don't use them again!
I have a saying I use "Buy cheap, buy twice!"

Here it is on those discs at Spa.
Replacing floating discs with non? _vdc2410

    

Rabidchiwawa007

Rabidchiwawa007
Platinum member
Platinum member
Wow, cool build, Mike.  That looks great.
Yeah, I certainly believe that.  There's no way these things are up to the task.  I'm baffled by these types of things sometimes.  Things that shouldn't be allowed to fail in the way they are.  My handle bar mounts just snapped recently, about a week apart from each other.  The U shaped part just popped right off of the bolt part.  I had to take them out and weld them back together.  

Anyways,
Might this be the rotor set I'm looking for? http://www.beemerboneyard.com/abm305kitwc.html
With the square / flat style bobbins?


__________________________________________________
1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Motorbike Mike

Motorbike Mike
Life time member
Life time member
Ouch! Expensive.

Try this page on Motorworks website.
https://www.motorworks.co.uk/vlive/Shop/Parts.php?T=5&NU=15&M=40&Ct=IA&SbCt=BA_15_40_IA_50&spPage=1

I know it's in the UK but all their kit is very good quality and may save you a few $

Mike.

    

Rick G

Rick G
admin
admin
I have stainless bobbins on my K1100 discs and they are very firm but after a bit of hard braking they become slightly loose as in they don't rattle but move easily on the bobbins from side to side but immediately centre when moving again.
Don't grab the disc with bare fingers to find out if it is loose.
The discs don't rattle but at low speed I sometimes hear the pads rattle.
If the bobbins are loose when cold the carrier and maybe the disc will need replacing. I have over 100K on the same stainless bobbins. The disc should be very firm and not rattle but be able to expand when it gets hot and not warp.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1999 K1100 LT with a Big Block 1200
    

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