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Grabing brakes on 07" Prius

I have an 2007 Toyota Prius and in the morings, especially if it is humid or moist outside, my brakes grab badly during the first couple of stops…it’s bad enough to make somebody run into the back of me. When it happens, you will also hear a screeching noise coming from the (sounds like ) rear brake, passenger side. I have taken the car to the local garage twice and they found nothing wrong. I have taken it to the local Toyota dealer 3 times and likewise, they found nothing wrong either.

have them check to see if the brake callipers are sticking, or if the brake pads are glazed.

I had this issue with my 86 Buick Park Ave way back. It had front disc but rear drum brakes and the one wheel would lock up first thing in the morning after it had been in the rain the night before. It was very unsafe. I finally just replaced the brake shoes that looked perfectly fine and that did it. I suspect you may just have to replace the pads and is probably a reasonably cheap thing to do at this point. I spose it could be caliper too but guess I’d replace the pads first. That new the caliper should never have been removed so doubt the hose could have gotten twisted or kinked.

How hard are you pressing the pedal, and is it sinking to the floor when you do it? I ask because Priuses (Priii?) have a 2 stage braking system. In the first stage, a generator scrubs off kinetic energy and dumps it into the battery. Only in the second stage do the actual brakes come in to play, and that stage only happens when you press the pedal harder.

So, it’s not necessarily a problem with the actual brakes. It could also be the brake controller, which is the computer that decides how much braking force is required, and from which system (regenerative or friction brakes or both) that braking force comes from. It’s possible that the brake controller is engaging the friction brakes when it shouldn’t, which would cause this problem.

It could also be the pedal sensor - if the sensor is borked and thinks you’re pressing a lot harder on the brakes than you are, then it tells the brake controller to apply more braking force than it should.

What you may need to do is leave it overnight at the garage (and it may have to be the dealership for this one, since they’re more likely to have proper diagnostic equipment for a hybrid) when it’s humid, and have them drive it while it’s hooked up to a datalogger.