My brakes work normally except on rare occasions the pedal will go almost to the floor. Once, it happened while hard braking after exiting the freeway. The other time, I was sitting at a railroad track waiting for a train to pass. The pedal very slowly went almost to the floor. After releasing the brakes, and depressing the pedal, they were normal again.
There is no loss of fluid. I recently replaced the front rotors. At that time, I flushed the brakes with a pressure bleeder.

When your front calipers drag on the rotors going down the freeway the heat generated will boil the fluid in both circuits causing total loss of hydraulic pressure. You'd rear-end someone at the toll booth if it wasn't a free way. Next high speed run you make, check the temp at the wheels. You most likely need a new set of front calipers.

Slow sinking of the pedal while at a light is what happens when the master cylinder is scored. It bypasses fluid. Perhaps someone before you bled the brakes with the pedal before you did with a pressure bleeder. Get a new master.
--
Art Benstein near Baltimore

From Rock Auto's newsletter:

I had been planning on replacing all of the brake lines on my Chevy Silverado for some time, but never got around to doing it. But after a weekend of hauling
loads of wood, one of the rear brake lines blew out and forced me to take care of the delayed repair. Since I would be doing all the work anyway, I also decided to replace the front calipers.

I was rushing through the job and not paying much attention. Once I routed all the new lines and put on the new calipers, it was time to bleed everything. But
during the bleeding procedure, I noticed I had a ton of fluid pressure in the rear calipers and almost none in the front. Also, the pedal was not getting firm.

After about an hour of scratching my head and much colorful language, I discovered that I had routed the brake lines through the proportioning valve incorrectly. But, my story does not end there.

I rerouted the brake lines to the valve and tried bleeding the brakes again. My father and I bled the brakes over and over and over, but the pedal was just not
getting firm. I had bled brakes before, but never have I had to bleed them as much as I was. I looked on forums, asked friends who had similar trucks and looked at my brake line routing again; nothing worked. I eventually surmised that it might be the ABS module needing an electronic scan tool to properly bleed. I did not have that type of tool, so I threw in the towel and took the truck to a nearby shop.

The next day I got a call from the mechanic...I could not believe what I had done. I had put the calipers on upside down and on the wrong sides! With the bleeder screws at the bottom of the calipers, no amount of bleeding would have removed the air bubbles from the brake fluid. I had to pay the mechanic $240 to fix my blunder! Do not make the same mistake that I did. Take your time and do not rush a repair.

Trying to order a master this morning. Neither FCP, IPD, nor EEuro offer an ABS master cylinder. A net search came up with parts geek rebuilt for 43.43 + 37 for core. Anyone out there know a source for ABS master cylinder? I suppose a rebuilt would be fine, it might be preferable to the Chinease parts crap shoot I am forced to live with.
Oh brave new world.

We also see the remanufacturing being done in Mexico.

Not only masters, but ABS calipers for the 240 are becoming rare. We see rebuilders using non-ABS cores and modifying them to use one pipe.

See this link about the masters: ABS master cylinder replacement / rebuild kit?
--
Art Benstein near Baltimore

"Did you know actor Raymond Burr had a brother who was a lumberjack? His name was Tim."

Well.... I followed the link. A lot of good info. Could not find new part. I found and bought a Master Cylinder at Oreilly. $115 bucks. Rebuilt in China.
I have to ponder...
Part made in europe.
Put on a car in Sweden
Car sent to USA.
Some years later removed from car. Sent to China.
Rebuilt and sent back to US.
I dont know yet if it is the proper cylinder, as it would not be the first time I bought a part that was not the proper one.
If it IS the right one, I will go back and buy another for a spare.

Lately I took a ABS master cylinder and the front calipers at a U-Pull at a scrap yard. It came from a 1993. I assume it should be the same as what is on my 1991.

Since I do not need it now I took it apart, cleaned and wipe dry. Then air blown and wiped again. The seals looked OK.

I re-assembled carefully with Silglyde lubricant and then secured it in a bench vise. I pushed the piston many times so the lubricant will spread all over inside. I put it in a zip-lock poly bag and hope it will stand good until I need it.

The ABS master cylinder is tricky to take apart. The fluid reservoir has to be pulled outfirst.

Then if you look in the front hole bottom you can see a pin locking the front piston section. When this pin is removed you can carefully remove the triangular lock wire holding the two piston sections. These can pop out and fly all over the place, so use a rag and your hand to let these pistons come out slowly. Make sure you notice how they go back in. There are weird shape parts in there and must go back in the same order.

If the lock pin in the front reservoir hole is not removed the front piston section of the master cylinder does not come out.

I have not taken apart a non-ABS master since a long time but I dont remember having to remove a lock pin as in the ABS type.

I think this pin is a safety device to prevent total loss of pedal presure in case of a brake line leak. It might keep pressure in the second brake line going to the ABS pulse module.

It would be nice to see a drawing of the whole fluid system with the various brake line failures.

Hope that helps and welcome sugestions on a better method to preserve those now so precious parts.

Happy new year everyone.

Mazda3 bug activates emergency brake system for no reason.
35k vehicles are being recalled to fix the issue.

Driver assists can help make our trips much safer, but integrating software decisions into the control of a vehicle could cause serious problems if the system glitches at the wrong time. According to Mazda, a "Incorrect programming" in its Smart Braking System (SBS) can make fourth-generation Mazda3 vehicles to falsely detect an object in their path while driving and automatically apply the brakes while driving. The problem affects 35,390 2019 and 2020 model year cars in the US, but Mazda says it is not aware of any injuries or deaths as a result of the defect.

If the issue occurs, the driver will notice because their car has suddenly stopped, and also as an alarm sounds and a message is displayed on the in-car warning screen. Some Reddit posters report experiencing situations of the system activating while driving with nothing around, and note that while the system can be disabled, it appears to re-enable itself every time the car starts.


https://www.engadget.com/2019/12/25/mazda3-smart-braking-system-recall/