1985 FJ1100 Clutch Master Cylinder seal installation

[THD]

I'm new and hoping somebody is willing to reply to what I fear is an old question.  I'm replacing the seals in the clutch master cylinder.  The seal that fits on the end of the piston is easy enough but it is not obvious to me how to install the other seal located in the "center" of the piston.  It is located between to large diameter "discs" that are machined into the piston.  Getting the seal to it's installed location would require it be stretched over one of those disc's and they are roughly twice the diameter of the seal's inner diameter.  I fear stretching the seal that much would ruin it. 

[balky1]

I'm new and hoping somebody is willing to reply to what I fear is an old question.  I'm replacing the seals in the clutch master cylinder.  The seal that fits on the end of the piston is easy enough but it is not obvious to me how to install the other seal located in the "center" of the piston.  It is located between to large diameter "discs" that are machined into the piston.  Getting the seal to it's installed location would require it be stretched over one of those disc's and they are roughly twice the diameter of the seal's inner diameter.  I fear stretching the seal that much would ruin it.  

I actually never done it, but if I were you, I would soak the seal in question in hot water and then stretch it over. Lubricate those discs with some brake fluid.

Waaaait, now when reading carefully, this reminds me somewhat on the slave cylinder piston seals. Are you sure it is the master in question and not the slave? Master is on the handlebar.

[THD]

Definitely clutch master cylinder. 

[FJmonkey]

I warmed/softened the seal with water that was just boiling. The heat will not hurt the seal but it will make it easier to fit over the shaft with a touch of brake fluid.

[balky1]

Definitely clutch master cylinder. 

Ahhh yes. Well, Monkey confirmed my assumption.

[FJmonkey]

Make sure the open part of the cup of seal is facing the fluid it needs to push. Imagine that the fluid fills the cup and makes it seal better. The harder you pull the lever the more the cup expands into the bore.

[THD]

Okay, so it turns out those little seals are very stretchy little buggers.  Made sure the seal is warm, some brake fluid for lubrication and bingo, on she goes.  I don't know what they are made of but it is a pretty impressive material. It also helps to have some sort of tool to hook and pull the seal 'cause it is small and slippery my fingers had a difficult time keeping a grip.  I used a dental tool with a smooth curve on the business end. Be sure to not scratch any of the piston's critical surfaces and if you use a pointy tool like I did, keep the sharp bit away from the seal. If you are still uneasy, taking the old seal off the old piston will demonstrate how resilient the material is and put your mind at ease.