Hi,

Stupid question maybe but is it possible to replace just the rear brake fluid reservoir (34311451863) without replacing the master cylinder as well?

Reason I ask is because today my son was playing around the bike and he accidently kicked the fluid reservoir. It smashed into pieces as if it was made of glass; guess the plastic was hardened by years of exposure. Fluid everywhere around the right peg bracket and now I do not have use of a rear brake. I'm hoping for a cheap fix instead of the expense of replacing the entire rear brake MC. TIA.

Several on Ebay right now. Here's a couple:

http://cgi.ebay.com/ebaymotors/86-BMW-K100-K100RT-REAR-BRAKE-MASTER-CYLINDER-_W0QQcmdZViewItemQQhashZitem1e631edb40QQitemZ130511985472QQ

http://cgi.ebay.com/ebaymotors/BMW-K75-K100-Rear-Brake-Master-Cylinder-_W0QQcmdZViewItemQQhashZitem256314a394QQitemZ160576086932QQptZMotorcyclesQ5fPartsQ5fAccessoriesptZMotorcyclesQ5fPartsQ5fAccessories

Rob, no problem at all to do so. BMW had to modify the rear brake reservoir after a few years because they became so brittle that just vibration could break them. They were replaced with a round version that was placed (rigged up) behind the right hand battery cover.

I bought just the reservior and new bellows from Munich Motorcycles in Perth. No good to you, but replaced it after doing a thorough clean of the master cylinder piston and spring. So much gunk. It wasn't expensive at all. Mine just smashed like yours, as did the one of my spares bike.Grrrrrrrr. Anyway, I'm a jubbo and managed to fix it so anyone can.
Regards RT.

Perso I have make this and no problem -->

The volume of this little Brembo jar (?) is widely enough

looking good segafredo .....good work !!

SEGAFREDO wrote: Perso I have make this and no problem

very innovative, Segafredo. Ahh, I see; the light dawns in the ol' slow brain . The reservoir is connected to the rear MC through the braided hose. All this time, I was thinking that the reservoir was an integral part of the MC and the braided hose disappearing behind the peg plate was the high pressure brake line. I didn't realize the two components were separated. I had imagined a difficult time maintaining MC integrity after replacing the reservoir but such is not the case.

I'll obtain a replacement after this Easter long weekend. I can't afford to have the bike disabled for repair long because I'm dependant upon it now that the season is here (commuting, errands, etc.).

If you change the fluid reservoir, do it slowly with patience. It is just a fluid reservoir then the air bubbles have no importance (not like the MC) you have to hit the braided hose with a finger to evacuate the bubbles in the new fluid reservoir.

Heh Segafredo,

The fluid reservoir you used -- was it the new reservoir, P/N 34312314082? I've been searching around MaxBMW's fiches and found this reservoir part is used on many current BMW models. If this is the improved design, I'd like to try and adapt it to my bike (to avoid this problem in the future). The only concern that I have is that the images on the fiche doesn't show a plastic tang. This is the tang you have used to secure the reservoir to your home-made bracket. Instead, there is a metal sprung bracket into which you clip the reservoir. If you are using another reservoir container with integrated mounting tang, what part number should I search for? TIA.

Excuse me but I have a problem with te word "tang" ...
The fluid reservoir that I show is not a BMW part but a BREMBO that I have bought in te 90's. I think that you can find it or another on the web.
To fix it I have just make a "L" in a piece of aluminium.
If you want another photo more clear I can make it

Oh, ok. Another photo won't be necessary. I understand that the container is not necessarily a BMW part. The word "tang" refers to the piece of plastic jutting out from the side of the container into which you have put a bolt. This bolt secures the container to the bracket. You have then secured the bracket to the battery plate. I believe all the BMW containers don't have this piece of plastic on them and I will need the special metal bracket as well. Thanks for replying.

You can make this system without the plastic tang with a plastic tie

The important bit of the BMW modification was that it was fitted away from direct light. That's why they fitted it behind the battery cover. And indeed the new reservoir was a round one.

Yes, I've been reading that direct sunlight will (1) cause changes to the plasicity of the container by exposure to UV light and (2) cause changes to the characteristics of the brake fluid by UV (although there is controversy to this theory).

Today, I priced out the OEM brake reservoir and a used substitute. I ended up buying a used Yamaha YZF R1 rear brake reservoir and installing that unit. It is a temporary fix at the moment and I will be making it more permanent when I have the time. It looks very similar to Segafredo's picture above. If I could find the Tygon 2075 hose locally, I'd even experiment with a brake reservoir delete as is popular for SS type bikes (just because I could).

On that topic, does anyone know if 6mm neoprene fuel injection gas line (3R90?) can be used as lead-in from the reservoir to the master cylinder. I've been getting different, conflicting advice concerning this.

Rob, I saw your post on another forum (took me a while to work out what FFS meant!).

Motobins in the UK sell the brake hose (part no: 23540, UK3.50). Wouldn't that be the easiest way to get the correct hose?

You're right Neil. Maybe I should just bite the bullet and order the BMW part from the local dealership. It is inexpensive enough considering all the hoops I'm going through just trying to find an approved substitute at the local bike shops here in Toronto. I'm not getting a clear answer from the other forums either. Seems that brake hose understanding is a bit of a black art at the moment, perpetrated by guys who frequent the track and want to emulate the professionals (eg. "reservoir delete" where you remove the brake reservoir and substitute with a length of clear hose capped off with a plug and tiewrapped to the frame).