Brake and Clutch Fluid

[Spyglass]

The Mityvac MV8000 arrived so I thought I would tackle the brake and clutch systems today.

The previous owner had the bike for 15 years but rarely used it, and it basically sat since 2019.


This is the clutch side. The fluid looked OK, but there was some sediment evident. The gasket was in good shape, and no evidence of leaks or corrosion on the paint. The boot was a bit ratty, but I don't think I'll worry about that. It has the common handle wobble, but I'll try to address that with a thin washer.

Here is the brake reservoir.



A wonderful brown jelly mess. The diaphragm is intact but covered in residue and corrosion from the underside of the cap. There is corrosion and paint peeling by the cylinder, which I assume is caused by a leak which I hadn't noticed.

So...it looks like a front brake diaphragm, cylinder kit, much cleaning and paint are in my future. I'll just flush the clutch side well as it appears to be in fairly good shape.

I never got to the rear brake

 

[Fire-medic]

Take a good look for corrosion not just oxidation, on the brake master cyl interior. If the bore is bad and using wet-or-dry fine sandpaper 220, 320, 400 won't clean it up sufficiently, you will need a new master cyl.

 

[Spyglass]

Here's what the rear reservoir looked like, and I have one plugged-up bleed screw.

 

[Spyglass]

I replaced those two assemblies with a used set from http://www.MorleysMuscle.com and replaced all the bleed screws with Goodridge SB8125 speed bleeders.

The front and back brakes were easy to bleed and now have nice clear fluid.

The clutch on the other hand has been a 2-hour episode and still is not bleeding.

I've tried pumping the clutch handle only, using the MityVac only, a combination of both, and there continues to be foamy fluid the comes out.



It's definitely the new brake fluid, as I have been slowly filling the MityVac reservoir, but only foam and bubbles.

The clutch worked before I changed the assembly (because it was leaking).

Am I missing something obvious here?

Thanks.

 

[Spyglass]

I've tied the clutch handle back overnight in case the air can find it's way to the top, and I'm on the hunt tomorrow for a syringe to push from the bottom.

Amazing what you find when you do a search on the forum

 

[Fire-medic]

I have more than one Mighty Vac and the reverse flush with a syringe works most effectively & most quickly for me

 

[barber1303]

I just did the clutch on my '85, flushing both push and vacuum with a syringe, and I STILL needed several sessions with the clutch lever zip tied overnight to get all the bubbles out. I'm wondering whether air gets trapped in the master cylinder due to the mounting angle on the handlebars such that running fluid through the circuit doesn't catch it.

 

[Spyglass]

So...the solution ended up presenting itself once I noticed the threads around the bleed screw were allowing a bad seal. This occurred with both the OEM screw and the speed bleeder.

I borrowed a friend's MityVac that went both ways (so should have spent the extra $30 it seems ) and noticed the fluid dripping down on the floor when I tried to force fluid up through the system.

I put a half-width of teflon tape around the top of the screw and it suddenly became an easy job.

 

[Yvonne Blaz]

CONGRADULATIONS ! YOU HAD ME ON THE EDGE OF MY SEAT & I JUST LOVE A SUCCESS STORY