Jump to content
The MT-07 Forum

Rear master cylinder not working


Recommended Posts

Hey guys. I recently replaced the the pads on my rear break. But made a few mistakes and broke a few things. Long story short bought new parts and installed everything. 

So here begins the problem. I pumped the breaks without noticing that the pads weren't in and I pumped the piston all the way and oil spilled. Ipused it back in and now the master cylinder isn't pumping any oil. Literally no responsive. Does anyone have any idea as what I could do to fix the problem. 


I hope I gave all the information. If you any more just ask so I know what I'm missing and I can answer. 


Thank you in advance 

Link to comment
Share on other sites

It undoubtedly needs to be refilled and bled. 

First. Carefully and methodically retrace all your work to insure the installation has been completed correctly. Assume nothing, recheck everything. Are you sure the piston seal was not damaged when you replaced the piston in its bore? If not check it. 

Second. Make sure the rear master cylinder is full of fresh fluid. Then bleed the rear brake thuroughly until fresh, clean fluid comes out and no air bubbles appear. 


A couple of notes are in order here. One of the most common problems is people getting too eager and missing an obvious step before proceeding. They then waste time, money and effort redoing something over and over until they or usually someone else notices the omission. Don't make any assumptions and jump ahead. Recheck your work. Are the piston(s) reinstalled correctly? Is there sufficient fluid in the resivoir? Lines connected properly? Bleeder in place and  functioning? Pads in correctly?

Since the integrity of the brake system was compromised when the piston popped out letting air in, you may have to conduct a more involved bleeding proceedure that includes bleeding the caliper and backward to the line and the master cylinder. If you are not comfortable doing this enlist the help of a buddy that has done it before.

It's not hard, take your time, use the manual and/or help and good luck.

Link to comment
Share on other sites

After further review I see this has occurred before? Or this a continuation or corrective step in that same issue. How did you correct this the last time it happened?

Let's get this damn thing fixed. PM me if you want a walk thru.

Where do you live? Don't make me come over there, lol.

Link to comment
Share on other sites

One and only guess I have is that you put a bunch of air in the master cylinder when you pumped the piston out of the caliper body. So, you have to put the piston back in place and then bleed the trapped air out.

I'd start the bleeding process by using some kind of syringe filled with brake fluid and push the fluid through the loosened caliper bleed screw, up the brake line, and into the fluid reservoir. Be careful not to overfill the reservoir when doing this. That will go a long way toward getting enough air out so you can start the final bleeding in the normal direction from master cylinder to caliper and removing the remaining air via the caliper bleed screw.

By the way, what parts did you break while changing your brake pads?

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.