Brake issue - booster or master cylinder?

[IcarusLSC]

I've got a weird issue with my 2014 Chrysler 300 5.7L AWD brakes (BR5 I believe). When I press on the brake at a stop or parking etc and just pressing lightly on them all seems fine, but when I am stopped in gear or not if I press firmly or hard on them they will go to a certain point then a quick 'pop' like there is a hard spot in the master cylinder or brake booster (not normal), then travel slightly more till I can't press anymore (normal). I can feel it in the pedal and hear it but can't figure out where its coming from.

I replaced all the rotors & pads front and rear, front calipers, and flushed all the fluid in May of '23 but that made no difference with this issue.

Anyone have any tips or tricks to try and figure out whats causing it? It only happens when I press firmly on the brakes, but is annoying when it does it as it just feels like something is wrong...

Thanks

 

[XJRiver]

You mention calipers were replaced. There is a left and a right. Were they crossed? I've done it myself. ( never hurry brake jobs )

 

[IcarusLSC]

You mention calipers were replaced. There is a left and a right. Were they crossed? I've done it myself. ( never hurry brake jobs )

I made sure they were correct and the bleed screws were on top as OEM was.

 

[Dave9]

You might check the state of the rear calipers(?) pad slider rails and caliper pins, in case one is sticking, and inspect all wheels' soft lines in case one has collapsed. Were any of the brake pads ears a really tight fit?

Otherwise I would get a helper to be at, to bleed the furthest wheel, while you have your head, hand, and a flashlight under the dash to press the pedal as you would for a typical bleeding procedure, to see if you have the same notchy resistance when the pedal is so much easier to push down and only pushing fluid out that one rear caliper. If it is still notchy then I'd suspect you have a buildup ridge in the master cylinder... but if the pedal is hitting a bag of popcorn under it, or the floor mat, or just binding on its pivot, you'd probably notice that too.

Is it possible that you still have a little air in the system and this is why you are now noticing the pedal being able to travel further past a master cylinder bore ridge (IF it is), than the brake pedal traveled prior to the brake pad and caliper replacements? A ridge usually forms when the master cylinder piston rarely if ever goes past that point, not every time you brake harder... just trying to consider what has changed since the brake jobs were done, or did I misunderstand and this issue was present before ANY of the work was done, had this problem prior to May '23?

 

[IcarusLSC]

Thanks for the great info Dave9. Some good things to think about and look into. I actually don't recall if I could feel the 'notch' while bleeding, so will try to bleed a bit more through it this weekend and let you know. It does sound like it may be a master cylinder issue from your description...

Pads/calipers slide very nice front and rear. I replaced the ss sliders when I did them (Raybestos EHT pads come with new ones, I used Raybestos Element3 coated rotors and RB caliper.) Calipers were nice and 'free moving' and I lubed the pins and sliders with Permatex 80653 Silicone Extreme Lube.