Tell me what you make of this. Maybe like a month ago it started happening, it seems like my brake pedal is getting softer, or spongier? Over time it's taking more pressure on the pedal to get a normal amount of braking. I'm pretty sure it's not the booster. The pedal gets rock hard when the car is not on, and acts normally as it should. I've done the test for the master cylinder, with the car on, If I use a moderate amount of pressure the pedal will go about half way to the floor and then get really hard and I can't press any further. Plus when I get out of the car after a long drive, none of the rotors will be hot like they used to. They're warm but I can keep a finger on them for a few seconds. I haven't touched the brake system in months and never bleed it myself, and the reservoir is full, so I doubt there's air in the lines. Unless something goofy is happening to my MC, I'm guessing it's got something to do with the calipers themselves? But would all 4 calipers start seizing at the same time? Any thoughts? What is happening to my poor car?

 

Maybe you have a bad hose?

 

check your rear calipers.


I've had my brake pedal get soft a couple times. Both times ended up being an issue with the slide pins on my rear calipers seizing in the bore. The caliper would no longer float so as the pad wore away from hitting the pedal, there would be a gap it needed to fill...hence the inscreasing softer pedal over time.

I replaced the caliper $35-40 or so, and problem went away. Happened to me twice actually.

 

how did you validate this? manually try to slide the caliper after compressing the piston?

 

If you diassemble the caliper, you can push/pull the slide pins in by hand. They should move easily.

When one is rusted in place, you will know it

 

Can you spray it with wd40

 

No, you need to take them out and lube them up with a silicon paste or something designed for brake hardware.

 

Nope. You're gonna have to disassemble completely and use silicone-based brake caliper grease to do this job correctly.


That's also assuming they haven't seized complete into the bore of the caliper bracket that you need to replace the bracket.

 

I would bleed all corners first. Then if the problem still exists, I would check the calipers. Seals and all.