So I bought a 929 MC from Ray and finally got around to installing it. Install went smoothly. Reused the banjo line and made the required flare line myself. Bench bled the heck out of it. Then I bled three of the four corners using the speedbleeders I have installed. The fourth corner I had to swap to a standard bleeder and bleed with a mityvac since there was too much air in the line to actuate the speedbleeder. Final result? - mushy pedal. I originally assumed that I just needed to bleed again, then I noticed something weird. While my friend was testing out the pedal feel, I noticed that when he pressed down on the brake that brake fluid was squirting up from the MC into reservoir through the front connection between the two. Now I'm assuming there should be some sort of check valve stopping the MC from pressurizing the reservoir and that I need to replace the MC again. Any other thoughts? Any other reasons this could be happening other than just a bad MC?

 

When the seal moves past the reservoir hole it should not push fluid in to the reservoir .that is when the pressure builds .When you release the break some fluir may return to the tank .Exchange the unit for another or take it apart for inspection . I have been running a 929 MC for several years .I modified mine to go in without making new lines or bending any lines .

 

Yeah this is basically a geyser when you push down on the pedal for most of the travel.

 

Sorry for my poor spelling .

 

I,m bumping this cause I am having the same exact problem? What was the solution?

 

Were these new or rebuilt units? I went through 2 autozone rebuilt units and they both did the same thing you are describing. The third rebuilt unit from advanced worked perfectly, very solid pedal. I knew I was taking a risk with rebuilt units, but I had no idea it would be so bad. It was very frustrating trying to troubleshoot.

 

It is rebuilt. That is all they list from Mazdacomp. I might just order one from Mazdacomp or put my original one back. I bought it from a guy on the forum that never installed it so I am not sure where he got it from. Thanks for the info.

 

You did bench bleed the MC, correct?

 

Yes and the entire system has been bleed a ton. Weird thing that is leading me to think it is the master is when I bleed the fronts, if I pump fairly fast, the pedal slowly gets lower and lower. If I wait a few seconds between pumps, it feels fine. When I bleed the rear, it feels fine. I am using speedbleeders. I noticed the small fountain of fluid going into the reservoir as well.

 

Yeah I got a new unit and everything was perfect. I got mine from Ray.

 

Thanks, I am going to try replacing it and see what happens.

 

I agree,..... parts store units are a hit & miss. I have been through quite a few slaves and masters over the years.

Did you notice a increase in stopping power or pedal feel from this mod?
When it's working properly of course. I have been considering it, but wasn't sure if it was necessary.

 

I got a bad one from Mazda. It happens.

 

I got an increase in pedal feel but the problem is I'm not sure if my original one was going out or not.

 

Same here, but I am also unaware of how good my old master cylinder was. My dad has a stock CYM and his pedal feels similar to my 929 unit with ABS removed.

 

I hear ya.... my brakes are feeling vague... Though I haven't started with the usual - new fluid, pads, braided lines...

We'll see how it feels after this. This mod does look beneficial.

I installed a JDM Type-R 1" bore MC on my Civic after doing a GSR brake conversion, and it was a big improvement. I imagine the FD could use some more juice as well, considering the size of the stock MC