Braking issues when driven hard. 2015 Q70

[JucoQ70]

Hey Guys. I just purchased a 2015 Q70 about a month ago... The car is a dream to drive and I’m planning some mods in the near future.. I’m writing to see if anyone has had these issues and what was done to rectify them.. Braking was fine until one night I decided to really get after it and see what the car can do.. (the Dealership replaced the pads and the rotors was cut according to the maintenance records they gave me). So I’m at about 80-90mph on the freeway and I start to brake. Now I can smell
The pads heating up and thought that was normal
Since they were new pads. So I take a good brake and the pedal goes all the way to floor!!!!!! It comes back up and I experience braking power again but all the way home until
The rotors cooled braking power wasn’t what it should be. Once again this weekend I was driving hard and the same issue returned. I have a service appt with Infiniti in the morning. Any ideas what I’m looking at? I checked the master cylinder. It doesn’t look
To be leaking and the brake fluid level has stayed the same so I don’t think I’m losing fluid. I’m thinking it’s the brake booster!!!

[EdBwoy]

Humor me, what color is this car?
And how many miles does it have at the moment?
The problem sounds sort of familiar.

[JucoQ70]

Silver. And I bought it with 46,092. It’s at 46541 at the moment

[emm3seven]

Your description sounds to me like the classic symptoms of boiling brake fluid (old fluid that has absorbed too much water). I’d start with a full brake fluid flush, as your fluid is likely old.

Typical brake fluid is hygroscopic, and over time it will absorb water. The water in the brake fluid will convert to steam if your calipers get too hot. Steam, being a gas, is unfortunately easily compressible and will interfere with the normal hydraulic behavior of brakes.

By all means ask a dealer, but if you don’t know when the last time your brake fluid was changed, do a full flush/replace with new fluid.

[JucoQ70]

Your description sounds to me like the classic symptoms of boiling brake fluid (old fluid that has absorbed too much water). I’d start with a full brake fluid flush, as your fluid is likely old.

Typical brake fluid is hygroscopic, and over time it will absorb water. The water in the brake fluid will convert to steam if your calipers get too hot. Steam, being a gas, is unfortunately easily compressible and will interfere with the normal hydraulic behavior of brakes.

By all means ask a dealer, but if you don’t know when the last time your brake fluid was changed, do a full flush/replace with new fluid.

The fluid looks brand spanking new. I was at the dealer to day for the issue and they said they couldn’t find anything other than the rear rotors being heat glazed and recommended changing them... I was gonna replace everything (rotors,pads,bleed all lines and whatever is in the cylinder).

[macgiver]

yeah but maybe the dealer removed fluid in the m/cyl down enough and poured in new fliud - for I do that with a Turkey baster to start with fresh fluid before my complete bleed process . Difference is the "stealership" wants you to "think fluid looks good" so they can steer you to more high dollar repairs - when they end up doing and / or knowing that suggested full flush IS all you need?? You'll probably see several likely unnecessary things on that final bill. They know these things , have seen it all and GETCHA when they can
The man is right about simply asking ONLY for the specific job of "full flush and bleed out all bleeders , and all wheels" . Do only this FIRST and assess that outcome!

p.s. Also NEVER give background like we've heard from you to a mechanic doing SPECIFIC work only - for the truly dishonest dealer/shop will still make stuff up / screw you , especially hearing you have "problem" and ESPECIALLY if the category is brakes they always use scare tactics with brakes. You simply state " just bought new "used" car , time for full brake flush/bleed" and so you NEED TO GO SOMEWHERE ELSE !

[EdBwoy]

Silver. And I bought it with 46,092. It’s at 46541 at the moment

Good. At least it's not this blue nightmare -help-2015-q70-intermittent-brake-malfun ... 05098.html


I also recommend at minimum bleeding your brake system as maybe the system was opened and improperly filled during the brake service. A flush might not be necessary, but it isn't a bad idea if done correctly.

...

For future reference, here are some handy tips on troubleshooting brake issues:
https://m.roadkillcustoms.com/test-power-brake-booster/

[satown210]

Are you sure the pedal is going to the floor? If so that is a hydraulic issue. Whether it's boiling fluid, bad master etc. FWIW a bad master cylinder isn't only bad sometimes. Your issue sounds like heat. Sounds like you have brake fade. People think the pedal is going to the floor but it really isn't. The brakes are overheating and not gripping so you press harder until you are near the floor.

[JucoQ70]

Are you sure the pedal is going to the floor? If so that is a hydraulic issue. Whether it's boiling fluid, bad master etc. FWIW a bad master cylinder isn't only bad sometimes. Your issue sounds like heat. Sounds like you have brake fade. People think the pedal is going to the floor but it really isn't. The brakes are overheating and not gripping so you press harder until you are near the floor.

I’m kinda thinking that’s what happening. Coming from owning a Maxima. I’ve never had this issue and it startled me.. dealership told me it could
Be brake fade. I’m just gonna replace everything and bleed out the lines

[satown210]

Just replace them with quality stuff. Most brake pads from local auto parts are junk. On my old Infiniti, the previous owner put Duralast Gold on it. Autozone's premium stuff. Exiting the highway at 75mph by time I was down to 35mph there was severe fade. Absolute dangerous junk. Right now I am running EBC Green Stuff pads and rotors. Took them about 1000 miles to bed in and stop making noise. So far so good.