Brakes won't fully pressurize

[eman13261]

Okay so I think I figured out the problem. I recently had my calipers repainted and it appears that the shop didn't take the piston seal out. They were painted black so it was difficult to notice the dried paint on them, I have since contacted and yelled at them. My only surprise is that this problem didn't occur immediately after they were painted (partially the reason I didn't include it in my first diagnosis).

Regarding whether the rear disc is stock or not I'm honestly not sure at this point. I originally thought it was but after seeing on a few images of special IIs with rear disc I called it up to being aftermarket. I've included closeups of the rear mc so you can decide for yourself.
I appreciate all the help and I didn't think anyone was slagging my bike

 

[eman13261]

Okay so I think I figured out the problem. I recently had my calipers repainted and it appears that the shop didn't take the piston seal out. They were painted black so it was difficult to notice the dried paint on them, I have since contacted and yelled at them. My only surprise is that this problem didn't occur immediately after they were painted (partially the reason I didn't include it in my first diagnosis).

Regarding whether the rear disc is stock or not I'm honestly not sure at this point. I originally thought it was but after seeing on a few images of special IIs with rear disc I called it up to being aftermarket. I've included closeups of the rear mc so you can decide for yourself.
I appreciate all the help and I didn't think anyone was slagging my bike

 

[Paul Sutton]

Interesting about the paint. Did you find brake fluid leaking where the paint was? What is your plan of action now?

 

[fredintoon]

Hi eman,
judging by your attached photo the rear M/C attachment points sure do have a factory look. So WTF, eh? I dunno neither.
The photo also seems to show that your bike still has the stock M14-ended swingarm through bolt.
2 ways those can go wrong.
If it isn't torqued tight enough to stop the swingarm bearing tube from turning the swingarm won't work right and the bike will handle funny.
If it is torqued tight enough to work right it's M14 threaded end will sooner or later snap off and let the through bolt fall out onto the street.
That's no fun at all. Ask my son about the 100 foot black trail on the street as he rode my XS650 to a stop with it's back wheel locked.
An M16 threaded through bolt can be bought from MikesXS. Or there's a Suzuki through bolt that'll fit but it needs one of it's hex-head flats
ground away to fit the Yamaha's stop block. And the Suzi bolt don't have grease drillings so drill & tap the swingarm cross-tube to insert
a grease nipple. Which is a good idea anyway. The route from the through bolt grease nipples to the outside of the swingarm bearing
tube where it needs to be is seriously convoluted.

 

[eman13261]

After closer examination I found paint on the seal and traces of it in the brake fluid after bleeding. I think that this resulted in an incomplete seal. Definitely not having someone else paint them so i have them soaking in some mek to remove any traces of paint and I'll put new seals in afterwards.

Thanks for the tip fredintoon I'll have to check that out! Luckily I haven't had any handling issues like you described. I did add a grease nipple to the swings when I installed brass bushings

 

[Paul Sutton]

MEK can be quite aggressive. In the paints industry there is an MEK Rub Test. This is where a cured paint film is repeatedly rubbed with MEK to see how long it takes for the film to wear through. You should be able to remove the paint by gently rubbing with a very soft cloth wetted with MEK. It should only take a couple of minutes.

So, was there any sign of brake fluid leaking? There should be if the seal was not working? I just hope the paint is not a red herring.