Ideas on pulsing raspy brake noise?

Well, brake work is a very generic term. Can you change the rotors and pads just like any other car? Yes! Can you turn the drum and replace the shoes just like any other car? Yes.

I'm guessing your problem is a warped rotor or a rusty one. You might try going down a secluded road at about 40 mph and hitting the brakes hard. Or if that scares you, back up with the brakes lightly applied (use two feet, one on the brake, one on the gas). In reverse, the regenerative braking system is disabled so all braking is done by friction. Doing this will get rid of the rust on your rotor if that's your problem. If not, take off the wheels and look at your pads. My pads on my 01 were so old, they literally fell apart one day. Yours might have done the same.

 

You could drive about 40 mph, then put the car in neutral and stop. At least in the gen 2, it turns off the regen and uses just the pads and rotors to stop

 

Ah yes, I forgot about the neutral thing and yes, that applies to the Gen I as well.

 

If you carry that roughish rotor into your friendly neighborhood Carquest or similar shop, along with its brother from the other side, they'll probably stick both of 'em on a lathe for you and hand you back two smooth flat rotors for about $30. The only reason they couldn't do that would be if they're so heavily worn that the lathe would cut them thinner than the minimum thickness, which is highly unlikely on a Prius because it makes such little use of the brakes. Or if they're especially badly warped. They can tell you that before putting them on the lathe.

You'll naturally want new flat brake pads to press on your newly flat rotors.

If yours are at all like mine were, you might find that the inner surface (the one that's hard to see without taking the rotor off) has a strange wear pattern where only about the middle 2/3 of the pad was touching.

-Chap

 

Don't rule out wheel bearings.

Bob Wilson

 

ABS kicking in?

 

The most enduring lesson I learned from my own left front bearing going last year was how completely unable I was to diagnose it with the car in the air. With mine, the only symptom I was having was a noise (growl or hum), and only in real driving conditions with the weight of the car on it. I must have jacked up the car half a dozen times over as many months ... because the noise kept getting more noticeable, so I kept thinking "all right, by now it must be bad enough that I'll be able to tell which one it is with the car up." Nope.

I was also surprised that I couldn't pick out the bad one by temperature either ... I was sure it would have to be measurably warmer after driving some distance, but it wasn't.

The one thing that finally nailed the diagnosis for me was a wireless stethoscope I could listen to inside the car while driving ... setting it up took a bit of time, but once I was rolling down the road comparing the pickup channels, I had my culprit within, like, five seconds.

Four years ago when my right rear went, it did eventually get bad enough that I could tell which one had the problem by spinning the hub while jacked up ... that one felt noticeably "notchy".

-Chap

 

Rotors and pads tend to develop a shiny "glazed" surface over time, with different frictional characteristics. If you have a rotor resurfaced, it won't have that, and you don't want to start clamping on it with old glazed pads. IF there is absolutely nothing wrong with the pads (they are thick, and totally flat, well bonded, etc.), you can deglaze them with 150-grit sandpaper by hand (don't breathe the dust), but that'll take longer than just putting new ones in.

If you do just one side, you'll have differences in friction between sides while braking. IF there's absolutely nothing wrong with the pads and rotors on the other side, except for glazing, the 150-grit hand sanding works for rotors as well as for pads (learned from an old 1984 Ford shop manual, so it's official) ... but takes a fair bit of patience. You have to take the rotors and pads out anyway to do it.

Chances are that the "IF they are perfect" qualifier does not apply to you given the age of your car. I'm guessing you might find, as I did, that the inner pads and inner rotor surfaces are meeting in a narrow track and the pads are no longer flat but stepped at the edges. You definitely don't want to re-use those or they will start right away at wearing your newly-surfaced rotors into the same shape again.

I would urge just surfacing both rotors and changing all four pads ... you won't regret it.

I've also read reports of some pads having thick linings left, but the bond failing between the lining and the metal, just because of age/environment and not wear, with the lining being ejected from the brake. It has never happened to me, but I think there are reports in this forum. Maybe the Prius is one of the few cars where pads last long enough for that other weird stuff to happen, just because they wear so slowly.

When I first bought my car (used, at 126,000) I measured the pad thickness, and again the next year and the year after that, and was able to plot the wear and see that they would probably hit the minimum thickness in 2017. That was cool, but I ended up changing them last year anyway because of the narrow-inner-track, stepped-wear issue (which I had not noticed before because I was only measuring the visible edges) and it's kind of nice to know I did.

-Chap

 

Yes, please do both sides and replace the pads. You will not regret it.

 

There's a differential sitting between the two drive axles, which means the average of the two wheel rotation speeds must be the same as the transaxle final drive speed. Being in Park locks the transaxle, so the only way either wheel can spin is if the opposite wheel is spinning the same speed in the opposite direction (so they average to zero, since the tranny is locked). That's what you're doing if you spin one wheel by hand while they are both off the ground.

-Chap