hey all,

so i bought a "new" disc brake, the seller said it's 4mm thick so i thought - well, not bad, especially when mine is as thin as a potato chip.

i paid the guy and waited for the package to arrive. i got it today and... the disc brake has a pretty serious rand (not as bad as in mine but it's there) and i would say it's less than 4mm below the rand...

my question is - is it still a good idea to use it? or when a disc has that rand, it's usless (i would think so).

i will be thankful for any suggestions
cheers
Pajonk

Well, I'm going to ask the obvious...rand? The "ridge" on the edge of the disc?

The service limit for the disc is 3.556mm. Do you have some calipers to measure the thickness?

hi,
i will never understand why all over the world the same mistakes are made over an over again.

if you´ve got trouble with the breakesystems (totaly normal after 25 ears):

1. No used parts
2. new lines - rear an front
3. open the main cylinder , cleaning and remounting with ATE paste - or new cylinder from Magura (mostly 13mm)
4. open and clean the break calliper - awfull juice in there (new set of gaskets: 34112310493 )
5. disks: changing the breaking ring - or complete disk

only the addition of all mentioned points will make it.

but as always :
work on the breaksystem has to be done by someone who knows what he´s doing

mistakes meaning - do not buy used parts?

i know but come on - a new brake disc for this bike costs a fortune!

pajonk wrote:mistakes meaning - do not buy used parts?

i know but come on - a new brake disc for this bike costs a fortune!

1: you need 2

2: you don´t have to go to BMW

3: have you had contact with :

for Germany Rolf Ludwig
netherlands: http://www.hobbyist.nl/

both know what you need

it's for the rear wheel so i need only one hehe

of course i do not have to go to BMW, more, i don't want to. but still, they are damn expensive (as for me). i paid 50 Euro for this one but the seller said it's 4mm thick, but it's not...

Pajonk, try www.motobins.co.uk for another source of new brake parts. They sell Grimeca pattern rear discs for £77 and original equipment which might not break your bank.

I agree with zonenfeile about the procedure for maintaining the brakes, but I disagree about avoiding used parts.
Considering the cost of BMW parts sold outside the EU, this is out of reach for a lot of us.
2 weeks ago, I replaced my rear disk with a K1100 disk.
The disk was under the minimal thickness for a K1100, but way over the limit for a K100. The disk was slightly grooved and had a ridge on the outer part.
Here is how I proceeded:
I first filed down the ridge slightly at angle to be sure that it would not interfere with the braking surface.
I removed the ABS ring (no need of it on a 85 K100rt) and installed the disk on the bike. I check with an indicator to confirm that it was running true (not warped).
I installed a new set of break pad, took a permanent maker and wrote all over the disk. I then started the bike, put it in gear then applied the brake to see the surface of contact between the pads and the disk.
It was looking very good at the exception of the grooves.
Here is how a corrected the surface:
I remove the caliper, took a new oil stone like this one,

put the bike in first gear and started to grind the disk (by applying an even pressure on the stone) until the surface was almost flat (near perfect).
I then cleaned the disk to be sure that no grits remained on it (Very important), cleaned it with gas, measured the thickness a different areas and re-installed the caliper.
It works like a brand new brake and I am ready to use it for another 100K.
The total time for the operation was about 3 hours, and the cost was $30.

Not bad in comparison of the cost of a new disk.

Yeah, I know I am cheap, but it works for me.

Super idea CF. It would never have occurred to me to use an 1100 disc!

A similar story for me recently using secondhand parts. Needing to use the bike almost every day, and having a slightly binding rear caliper which was going to toast my rear brake disc eventually, I procured a clean, low-mileage K1100 caliper on eBay for under $30 posted to my house. I removed the ABS stub (no need for that on a 1987 K100RS) and after a thorough clean up with brake parts cleaner and elbow grease (I never run out of a tub of that) I fitted the caliper with new EBC pads and a Venhill braided hose and gave it a good bleed. The brakes now work como Dios manda (as intended). That was five thousand Kms ago. Now when the bike is idling on the centre stand the rear wheel turns slowly where as before it was stopped and would only spin if forced (even after I gave it a good bleed and clean out). Imagine what that would do to brake pads and the disc over a short period of time. I'm a cheapskate too and the total cost was under a hunnerd Aussie Shekels. Another good bit is that over time I will procure a seal kit and rebuild my old caliper as a spare for the next millennium.

Two Wheels Better wrote: I'm a cheapskate too and the total cost was under a hunnerd Aussie Shekels.

Hey we are not cheap, but full of resources.

Which we are willing to share, like beer and beans (or the aroma of them).

Two Wheels Better wrote:Which we are willing to share, like beer and beans (or the aroma of them).

If we ever ride together, please stay on the back of me.
It was the big joke when we stopped for lunch as I ordered a big bowl of chili! The exhaust was quit rich with some back fire after the meal. I blamed it on an unset throttle switch.

OK, you can show me the way round your neighbourhood, but NOT if you've ordered chili!

well, that is all true - if i could afford it all, i would buy a new one but motobins has only non-ABS discs...

about the one i got - i guess i just lost a bit of money. on the other hand though i am a bit confused - it looks like the new disc was 5mm thick. on the disc itself it says - min 0.18" (4,5mm) whereas in the Haynes book it's said that a new disc has 4,4mm and the min thickness is 0.14" (3,5mm). who should i believe?

pajonk wrote:well, that is all true - if i could afford it all, i would buy a new one but motobins has only non-ABS discs...

about the one i got - i guess i just lost a bit of money. on the other hand though i am a bit confused - it looks like the new disc was 5mm thick. on the disc itself it says - min 0.18" (4,5mm) whereas in the Haynes book it's said that a new disc has 4,4mm and the min thickness is 0.14" (3,5mm). who should i believe?

it depends from what bike the disks came from

ABS Bikes have different thickness than non ABS

Using "worn" ABS Disk as "almost new" in non ABS Bikes is very common

sweet, that means i bought a piece of crap for 50 euro...

pajonk wrote:sweet, that means i bought a piece of crap for 50 euro...

you did it by your own choice

Rtfm first.....



Again :
Call the guys in Holland (English & German spoken) they know exactly what you need

http://www.hobbyist.nl/contact.php/

but believe me - my disc brake is probably less than 3mm now... so i guess i will survive until i am rich again

Any recourse with the seller pajonk?

nope... the guy never replied to my emails... so meh, screw him, but thanks for asking

Sorry to reopen this can of worms but can anyone tell me if the two alloy (brass coloured) screws holding the disc to the final drive body are re useable, they seemed very soft when I undid them (at the hex
drive)
RT

Those screws is a one time use.

Inge K.

Whoa, missed that one on my FD service. Thanks for the safety tip Inge!!

OG

Thanks Inge, you are certainly a mine of information.
Keep warm
RT

I've just received my new Grimeca rear brake disc from Motobins and have two new tapered screws for it. They can be got from any nut and bolt source in stainless but the OEM screws from usually priced-outta-this-world BMW Australia is actually cheap at cents, not dollars (the BMW distributor sets the suggested price, boys, not the conscientous dealers - though plenty of unscrupulous dealers do add the extra margin. My advice is to let them know you're onto them and avoid them). Some new Ferodo pads back there, a good flush of the not-too old brake fluid of the recent replacement second hand K1100 caliper and we'll be laughing.

nice one gith .....better order me a couple for the brake refurbish in a few weeks

good to receive parcels in the mail

Brown paper packages tied up with string. These are a few of my favourite things. Julie Andrews was hot once upon a time.

Guest wrote:Pajonk, try www.motobins.co.uk for another source of new brake parts. They sell Grimeca pattern rear discs for £77 and original equipment which might not break your bank.

The motobins price does not include the dreaded VAT, which makes them £92.40, which is the same price as James Sherlock for Grimeca.
James Sherlock are currently testing a cheaper range of disks and they are going to let me know the results. Don't know the final price yet, but they will be on a service exchange.

Bryan

but us foreigners dont pay the dredded " various added taxes " so its all good from down under, and strange ports of call

AU$150 from the boys at the 'Bins to my doorstep for a disc brake (locally of varied sources and dubious quality) that would otherwise cfost a minimum of $229 here.

Inge K. wrote:Those screws is a one time use.

Inge K.

Why? They only hold the disc in place during assembly, surely the four wheel bolts clamp the disc in place.
Paul.

They are soft and easily damaged. BMW recommend them to be replaced after each use, like many fasteners on the various models. But we do still have free will and can smoke our cigarette right down to the filter, hell, we can roll our own!

Agree with you Paul - these are only there to assist during assembly, my K only has 1.

Being ham fisted I ended up damaging the hex head getting them undone, I don't think I want to be trying that again in 27 years time.

RT,
Nowadays I only tighten mine a little more than fingertight, to save destroying the hexagon.
Paul

I use stainless screws and antisieze done up just firm after all the wheel prevents the things comming out.