Rear brakes going before front

Have you been driving this Prius (or any Prius) very long? Do you know about the brake-in-neutral-after-soggy-weather routine?

-Chap

 

How many miles on it?

Do you know if the rear brakes have had previous inspection, where the caliper's been pulled off? They CAN be put back together wrong: caliper piston orientation is important, to prevent drag?

Feel the rear wheels after a good drive, see if they feel hot. Better: chock the front and jack up rear, see how freely they turn. Slight drag is acceptable, due to disk brakes, but they should easily spin a revolution or two, when you let go. More drag is likely indicating the aforementioned misaligned piston.

 

there have been posts about premature rear pad/rotor wear, i think it's salt related, and they get so little use, they stick.

 

Please explain this "routine" for the rear brakes. I, too, just had to replace my rear pads & rotors though the front brakes are fine.

 

The ability of the Prius to slow by regenerating electricity means that it makes so little use of the actual brakes that they don't get the surface rust scrubbed off of them by normal use the same as in a conventional car.

This is a Prius quirk going all the way back to Gen 1. The symptom is, any time the car has been sitting for a while in damp weather (overnight in rain or fog, etc.), you'll get in, start it up, drive off, and think the brakes either sound horrible or feel extra grabby, or both.

That's just surface rust built up on the rotors slightly.The car normally applies the brakes so lightly they just rub the rust and make horrible sounds, instead of clamping harder and rubbing it off.

The solution? For the first couple stops in your commute, shift to neutral first, so the car uses no regen and fully stops with the friction brakes. Usually in just one or two stops like that, the brakes are all cleaned up and silent and non-grabby again.

This is something we should be making sure every newb on PriusChat is finding out, because it's so easy, and very often owners who haven't been told about it will assume their brakes are on their last legs because of the noise and grabbiness—and we've even had at least one case where someone took the car back to the dealer every time, and the dealer took the opportunity to charge for a brake job each time, instead of saying "here, do this, they're fine."

So ... there could be something wrong with the brakes ... but if you didn't know about the couple-stops-in-neutral routine and you haven't tried it, don't read too much into some brake noises before you do.

If you did the work, and actually saw that the rears were badly worn ahead of the fronts, then in your case there may have been something else really going on. I mentioned the stop-in-neutral routine for the original poster, who seemed to be concerned mostly because of hearing brake noise, which is the classic situation for "try a few firm stops in neutral before spending any more worry on it."

-Chap

 

no, but you may want to have a close inspection before doing anything. squealing doesn't necessarily mean worn pads.

 

Many thanks, Chap, for your full explanation of why the rear brakes have this issue and exactly what to do about it! Why don't Prius manuals inform people of this 'side effect' of regen braking & describe how & when to compensate for it by shifting to neutral before pressing the brake pedal, thereby ensuring that the friction brakes are engaged?!!!

It seems that occasionaly doing the stop-in-neutral routine 2-3 times would also be a good prenventive practice when it's humid, after driving in the rain, & in the winter after driving through snow & road salt (once its safe to stop in neutral).

 

i think we are conflating two different issues here. noise from surface rust is one, and premature rear pad/rotor wear is another.

 

Well, I'd be cautious about going that far. Brakes can have lots of issues, and often puzzle #1 when a new poster puts a question on PriusChat is to figure out whether or not that person's issue is the same one described in some existing thread.

The "brakes get noisy/grabby after sitting in damp" is a common issue across all Prius generations, so it is worth knowing about, and probably the first thing to check if somebody comes with a question about noise and/or grabbiness without other data. But there are certainly other things that can also happen to the brakes.

-Chap

 

it's also not just the rear brakes that suffer from moisture/rust.