Laurel caynon causes my brake to smoke.

have you tried b mode?

 

I've been to LA and driven there (not in the Prius) but it's like what 1000ft elevation? Didn't look very big.

I do more than that daily in the Prius up and down. Brakes never smoke. I've been down Pikes Peak (14K to 7K feet, 7K feet drop), brakes never smoked. If you ride them they will get hot at the mandatory brake check points. But put the Prius in B mode and allow the engine to brake you and even Pikes Peak is no problem.

Sounds like you may have another issue, like sticky brakes, that are just more prevalent during longer descents.

 

When I descended Pikes Peak (only from Devil's Garden, as the summit section was snowed in), the traffic ahead was going too slow for me to get anywhere near enough B-mode engine braking. The slow-going leaders were downshifted to reasonable gears for their vehicles, but it was slower than I needed to make good use of B. The distance between switchbacks was too short to safely pass them, so I was stuck riding the friction brakes too.

 

How many miles on your Prius? When was the last brake inspection? Last brake pin lubrication?

 

Please check the caliper sliding (brake pins) bolts. If they are stuck and cannot move, this can create major braking issues.

 

The pivot pins need to be cleaned and lubricated, the front rotors and pads replaced, the rear drums inspected, and above 12mph the brakes shouldn't be doing anything, so, is the traction battery getting the charge above 12mph?
I would think the Toyota techstream would be a good place to start, to find any problem, ie: the brakes shouldn't be taking the load, but they do need work.

 

Lack of competent, routine maintenance.

That's scary you are even asking that question.

Routine maintenance, from a competent shop or a competent DIYer, would prevent this.

 

There are raised contact points on the drum backing plate that require lubrication, for the drum shoe to move freely.

Normal, "Gentle" braking, w/ gentle slowing, yeah, hydraulic brakes won't kick in until speed falls below 7MPH, IIRC.

Harder and Panic braking, hydraulic brakes complement regenerative braking immediately.

 

Questions about the interplay of friction and regen braking at different speeds and driving conditions are very common on PriusChat, often making the answers seem simpler than they really are. There was another post last year that goes into it in more depth; it includes explanation of the Toyota graphs below.




As for why the brakes might be dragging, it's true that a brake caliper is mechanically pretty simple, it has to glom on when you brake and let go when you don't, and it just has to be inspected carefully for why it isn't doing that. There's no rocket science, but there are subtleties.

We talk a lot about the two little slide pins, often forgetting there's another large sliding component there—the piston—that had also better be sliding easily, or you'll be making plenty of heat. And there are two different things to check about the piston: first, that it simply moves easily inward and outward, and second, that it pulls back in by about 0.3 mm on its own when the pressure pushing it out is released. That pulling back is done by the internal rubber seal, and can stop happening if the seal gets aged/glassy. (In a badly rebuilt caliper, it may not pull back right from the get-go; test before installing!)

Starting with Gen 2, the front caliper pistons are also made of a phenolic resin instead of metal, which Toyota chooses because of several advantages, but there is a disadvantage in very rare cases where the material can swell, and then the piston binds in the caliper and needs to be replaced.

When I say "very rare", I mean I have only seen one case on PriusChat ever where swelling of the piston turned out to be the issue. There's one other thread where somebody heard about that possibility, and got sort of fixated on it, saying all kinds of disparaging "plastic is for kids' toys, I'll buy real pistons aftermarket" kind of stuff, only to finally figure out there was a ridge in his caliper bore and it wasn't piston swelling after all. As I said, the swelling seems to be really rare, and require pretty special driving and environmental conditions.

That's a good thread to look at anyway, though, because it does tell a pretty good story of just carefully examining things and going through the possibilities until the problem is found.

-Chap

 

Toyota recommends a full brake inspection every 30K miles or 36 months, whichever comes first. Look in your Schedule Maintenance Guide to verify.

 

No. The underlying cause needs to be resolved.

The cross drilled rotors are probably more expensive than the factory vented rotor. Also cross drilled and slotted rotors will wear out the pads faster, b/c the cross drilled holes or slots, will act like a grater to the cheese (brake pad).

Cars leave the factory with brake components that are matched for the cars weight, power, and original vehicle driving characteristics (econo commuter, semi-performance, performance, etc), for the least amount of cost. Manufactures could equip every car w/ vented and cross drilled rotors, and oversized brake calipers and oversized brake pads, but this will increase the purchase price of the car and brake maintenance. Even a lowly Toyota Yaris could have this extreme brake set-up, but it would be overkill.

If the factory car were modified for performance: intense engine modification or replacement, turbo/super charger, suspension, exhaust, transmission, bigger/wider tires, etc, increased stopping power via larger upgraded rotors (slotted and/or cross drilled), upgraded calipers, larger pads, and usu an upgraded brake master cylinder. Recall the Mazda Miata enthusiasts who do an extreme engine swap of the lowly 4cyl Mazda engine with a Ford Mustang 5.0L engine, Chevy Corvette 5.7L engine, or a turbocharged RX-7 engine, in addition to a suspension, transmission, and intake and exhaust overhaul. The original factory brakes would be insufficient for such a performance modified car. These extreme enthusiasts know it, and correctly upgrade the brake components too.

Now if you modify the Prius like those Miata enthusiasts, you would want to upgrade the factory Prius brake system somehow. You don't drive a Prius to set any typical performance metric: 0-60MPH, 1/4 mile, track lap time, etc. You drive a Prius to set MPG records.

Get the brakes fixed and all will be well. Use B mode on "steep" descents, to minimize the potential of overheating the brakes.

 

get out the way!

 

Yes, mid-40's to high-40's on a Gen-2 with a good battery is normal for "drive it like you stole it" mode. With the range you're getting, I'd be pocketing a little bit of money when you can to replace the inevitable. That MPG is within the battery-is-about-to-fail range.