Rubber grommet on rear master cyclinder piston

I have been trying for 3 hours to get that little rubber grommet over the piston to no avail. Secrets??

Brute force with thin pin levers to work on over the piston hump form the outside inward IIRC. Lube with fluid of course.

capehorner said:

I have been trying for 3 hours to get that little rubber grommet over the piston to no avail. Secrets??

Click to expand...

Do you mean the secondary piston cup? It does take some force to expand the cup over the end of the piston however the cup is tough so it can withstand the amount of stretching necessary to get it over the end of the piston. I would normally hold the cup against the end of the piston with my thumb, then insert a thin bladed screwdriver (like an electrical screwdriver) into the hole in the cup and work it over the end of the piston, just make sure it is well lubricated first.

Thank you all for your input. Finally we have lift off. I don't want to do this again. My thumbs and fingers thank you.

matt bowman

It's a brutal game, but the seal is tough and you just have to use plenty of lube and force it on.
JD75

GM makes a rubber conditioner (in a tube) designed to soften up older rubber like weatherstripping and window trim etc. Sure wish I could get another tube of it as time has passed and not available off the shelf. Remember using it for my MK 111 brake rubber cap and it all went SO easy. Blue tube.

There are very few solvents that can soften good rubber and all of them destroy some of the bonds that make the seals so tough so I'd be pensive especially after having experience of one perfect hard brake one instant and absolutely nothing the next instant.

http://en.wikipedia.org/wiki/Natural_rubber
There are two main solvents for rubber: turpentine and naphtha (petroleum). The former has been in use since 1764 when François Fresnau made the discovery. Giovanni Fabbroni is credited with the discovery of naphtha as a rubber solvent in 1779. Because rubber does not dissolve easily, the material is finely divided by shredding prior to its immersion.

Thanks Hobot ,would never use such a product for brake internals, only the outer seal cap that keeps the dirt out. And other non -critical bits.