Replacing brake M.C.; best bleeding technique?
 

Hey everyone,


I'm replacing my brake master cylinder with an OEM one, and I've seen a few different methods to do the bleeding. one is to bench bleed, then install on the car. Another is to just bleed it on the car by loosening and tightening the flare nuts. Just curious what method folks here have found is better.


I've also been battling a spongy brake petal despite several attempts to fully bleed my system, and wondering if you guys have any tricks for the RX8. I've usually done "assistant" method to bleeding brakes: having them pump and hold, open and close bleeder screws, repeat.


But I've been researching and there are (at least?) five ways to bleed brakes:
1. Assistant
2. Pressure (at the master cylinder reservoir)
3. Vacuum (at the calipers)
4. Gravity
5. Speed bleeders (bleeder valves with check valves)


The gravity method seems interesting, because many folks have said that method gave them the best results (it also happens to be very simple and easy, if not quick).


I bleed farthest to closest to the master cylinder. But should i also be finishing by bleeding at the master cylinder?


Any comments or recommendations would be appreciated.

I don't have a comment for master cylinder bleeding but I will say that speed bleeders make the rest of the job hella easy. That said, I think MrPockets is in love with his Motive Power Bleeder.

Bench bleed, then use a Motive power bleeder as an air pump. It's faster if you equip the line on the Motive with lossless quick-disconnect fittings so you can top up the master cylinder without having to re-pressurize the Motive.

JV

^ This.

Emphasis mine. Do not put fluid in the Motive bleeder or you're going to have a bad time.

i mostly use vacuum bleed at home because i have air compressor. gravity bleed at the track, just to do a quick bleed. if there's any air in caliper from fluid boil, it would be at the top, so it doesnt take much bleed them out with gravity bleed. if you got air inside the line or abs pump, you'll need a way to push the fluid faster to move the air with it. you can also remove the caliper from the knuckle and hold them high with the lines straight to make sure no air is trapped on high spot of the line.

or maybe the brake kit you're using has higher piston surface area and require more fluid to push them, so you have more pedal travel?

yeah. got the new MC in. Not too hard to bleed. Just installed dry, filled, pumped the pedal a bunch until some feel came, and then did the "pump bleed" with an assistant.