How To: Bench bleed a brake master cylinder

How to bench bleed in several easy steps (previously posted by Mike):

Bench bleeding basically gets all the little air pockets out of the master cylinder before you install it. It can also remove a bunch of fine particles of debris that may be left over from assembly/re-manufacturing, etc.

Tools you will need:

1. Bench Vise
2. Screw Driver
3. Brake fluid reservoir cup
4. Brake fluid catch cup (may or may not come with fittings, depends on where you buy it. If not, not really important...just use a big gulp cup...do not use a super big gulp cup...that would just be silly).

Supplies:

Brake fluid
Muscles



1. Open the package your new MC comes in. Unwrap and discard packaging.

2. Place your MC in the vise. Tighten vise. Make sure you still have access to the outlets.

3. Install your stock fluid reservoir. This is so you can put brake fluid in...duh.

4. Once you have installed the reservoir, place your catch cup reservoir under the outlets.

5. Fill the fluid reservoir.

6. Take your long screw driver, and push the plunger located in the back of the reservoir so it acts as a brake pedal being pushed. You should see a crap load of bubbles and some fluid. Keep refilling your fluid and keep using your screw driver til all you get is pure fluid.

7. Install your MC.

8. Buy Mike a box of popsicles.

Where would you like said Popsicles sent?

Thank you!

Mmmmm, bacon

I will add to this thread since everyone coming here will be changing a master cylinder.

If your resivore is as dirty as mine, how to clean. The design doesn't lead to cleaning very well. I really wanted to spray brake clean in there, but I've had a bad experince with brake clean and plastic. So I first put some diesel in it and swished it all around. Then I put gas in it and did the same. Finally, I did the same with #4 brake fluid. I dumped it out and I looked pretty clean.

About the bleeding, I found that if you held your thumb and finger tight on the outlet holes, the process goes quicker. What happens is your digits become "one way" valves. You can still see the bubbles, but no air goes back in the cylinder between pushes.

Quote:

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Originally Posted by Helirich

I will add to this thread since everyone coming here will be changing a master cylinder.

If your resivore is as dirty as mine, how to clean. The design doesn't lead to cleaning very well. I really wanted to spray brake clean in there, but I've had a bad experince with brake clean and plastic. So I first put some diesel in it and swished it all around. Then I put gas in it and did the same. Finally, I did the same with #4 brake fluid. I dumped it out and I looked pretty clean.

About the bleeding, I found that if you held your thumb and finger tight on the outlet holes, the process goes quicker. What happens is your digits become "one way" valves. You can still see the bubbles, but no air goes back in the cylinder between pushes.

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The correct way would be to attach hoses to the output ports of the MC and then place the other end of the hoses back into the reservoir. that way when you press the MC bore in, you can still see the bubbles and when you release the bore, no air will be drawn in. Also, you won't waste brake fluid.