Geez one thing after another these days! So I have no brakes. I swapped over a different master cylinder I had around that I thought worked but the pedal still goes to the floor.

The back story is I put in brand new calipers in the front, new stainless steel brake lines, and switched to DOT-4 fluid for the higher temperature rating. Brakes faded very quickly after that. I don't have any fluid leaking around any of the fittings. I have bled all 4 corners several times and am confident I have no air in the system.

The only variable I can think of is can a brake booster go bad and cause the pedal to goto the floor? Other possibility is both masters are bad.

Without the car running I can get pretty good pressure to build, but once the car is started the pedal goes right to the floor.

 

both masters are bad...

 

….or at the very least, poorly bled. The brake master needs to be bench-bled (see youtube) first or they are an absolute Bee-otch to get all the air out off once mounted…
Know your pain. And: Went thru 2 "new" master cylinders (non-mazda - won't do THAT again!) before I got a solid one.

Stu Aull
80GS
Alaska

 

Thank you for that.
When preparing to remove the 12a, the break master decided on its own to drain out on the floor.