Dual Master Cylinder Reinstall

[crankin]

After a two year rebuild I am trying to bleed my brakes but with now luck. I removed both brake lines from the Dual Master Cylinder and pressed the brake pedal. Should I immediately see fluid squirt out or do I need to prime the master cylinder?

I have pumped the brakes for about 10 minutes but get just a little spit of fluid here and there…maybe every 30 pumps a get a harder spit as if fluid is building up…then nothing.

What do i need to do? I am just worried that the master cylinder has went bad.

[amcordo]

After a two year rebuild I am trying to bleed my brakes but with now luck. I removed both brake lines from the Dual Master Cylinder and pressed the brake pedal. Should I immediately see fluid squirt out or do I need to prime the master cylinder?

I have pumped the brakes for about 10 minutes but get just a little spit of fluid here and there…maybe every 30 pumps a get a harder spit as if fluid is building up…then nothing.

What do i need to do? I am just worried that the master cylinder has went bad.



I just did this. You need to prime it before installing it. Fill it with your favorite brake juice, then depress the plunger using a screwdriver. BEFORE releasing the plunger cover both holes either with some sort of plug like a screw or with a third and fourth set of hands. Then let the plunger go. Stop covering the two holes and repeat. Make sure you do this at an angle (plunger down ish at 45 degrees, then the opposite end down at 45) to get all air bubbles out. After liquid is shooting out like it owns the place quickly install.

You can also use a bench clamp or quick grip to hold it to something which can make it a one person job. Or do what I did and wedge it between the front bumper and wing and spray corrosive brake fluid all over my paint.

[SafeAirOne]

I have pumped the brakes for about 10 minutes but get just a little spit of fluid here and there…maybe every 30 pumps a get a harder spit as if fluid is building up…then nothing.

That doesn't sound right. Presumably the reservoir is full... Is the piston returning after each pump? You might try bench bleeding it first, just to make sure it's not an air issue.

Bench bleeding (http://autorepair.about.com/od/fixityourself/ss/MC_bench-bleed.htm)

[EDIT:] amcordo types faster than I do...

[amcordo]

[EDIT:] amcordo types faster than I do...


True but your post is probably more professional/accurate.

[crankin]

Wow. Its the little things that I should have known that make me feel stupid. Thanks Guys!

[SafeAirOne]

Wow. Its the little things that I should have known that make me feel stupid. Thanks Guys!

Well, bench bleeding only MIGHT be the answer. I've never had to do it on my single-circuit 109 though.

[crankin]

It’s a dual line system and the piston doesn't seem to return fully...I sprayed some liquid wrench down the piston and can get to return and compress ever so often. I am thinking that the master cylinder piston is sticking. Is this something that a rebuild kit can fix? Or do I need to spend the cash on a new one?

[gudjeon]

I would get a rebuild kit for two reasons:
It may help you find the source of where it is hanging up.
And,
it has been contaminated if you put in a penetrating solvent. Brakes seals do not like anything but brake fluid. Any other oil or solvent will break down the rubber components. It may work initially, but will break down over time.

I used to rebuild old Euclid, industrial and auto brake fluid components and all we ever used was plain old Vaseline Jelly for assembly. It never harmed the rubber components and dissolved away with the brake fluid, which needs to be bled anyway. Lubed seals being installed have less tendency to twist and tear.:thumb-up: