Master cylinder refurbish - R100GS

[Posh Pete]

Afternoon all. It looks like the MC for the old GS is in need of a refresh. I simply can't get enough pressure in the line (so far) despite several bleeds and tying the lever back overnight to purge any air.

Yup, I know I might have to bite the bullet if the MC bore is fecked. It also looks from the attached schematic as if only two screws are involved - one attaching the reservour to the MC and the other attaching the MC to the twistgrip assembly?

So ... any tips for the job? TIA.

 

[johnnyboy]

Have you tried back bleeding the system?

 

[Posh Pete]

Have you tried back bleeding the system?

Nope. I usually manage ok using the old fashioned method and an overnight purge. It's never had fantastic pressure, pulling quite far back before getting resistance.

 

[johnnyboy]

Nope. I usually manage ok using the old fashioned method and an overnight purge. It's never had fantastic pressure, pulling quite far back before getting resistance.

Try back bleeding then. It's a more positive way of pushing the fluid/air up to the reservoir. Back bleeding is also old fashioned

 

[barny]

If the M/c is shot it could be an opertunity to fit a smaller one to improve feel. I think motobins do 13-12 & 11mm ones.

 

[Gelandestrasse]

To answer your question, 2 x screws #18 and undoing the brake pipe gland bolt (after removing the hand guard - take the mirror off) puts the master cylinder on the bench. You don't need to remove the reservoir. But you may need to remove the throttle cover (#9).

Your symptom (lack of pressure) may not be the master cylinder; there are other reasons, for example, corroded pads not moving, a collapsed rubber brake pipe, a blockage somewhere (in the brake line, in the reservoir, in the bleed nipple, etc). Does the lever go to the handlebar when you pull it?