Brakes don't stop well in some areas

Here's more details and discussion:

http://priuschat.com/forums/gen-iii...o-brake-surge-still-there-despite-recall.html

 

The "brakes" will switch from regeneration to hydraulic brakes only, if you go over a bump or if the wheels slip. This causes a loss of braking for about 1/2 second. Many claim the car accelerates (it doesn't, deceleration just stops for 1/2 second).

An important note for all is that although this happens regularly, if you are in a "panic stop" situation the car never goes into regeneration braking and this effect doesn't happen. "Panic stop" is sensed by the car if you hit the brakes quickly and/or hard.
Go ahead and test this if you like, but be warned, the Prius will stop faster than you can imagine, so ensure any passengers are securely belted in and loose items are fastened down in some way.

Learn to brake earlier (it also helps your mileage). You will, like most of us, also learn to anticipate this effect.

I post this after the link to one of the many forum topics on this because it can't be said enough. Braking is kind of important!

 

It's also important to understand that brakes only work as well as the tires. If you have slippery tires, you can't have good brakes. The tires used on a Prius are generally optimized for low rolling resistance, not grip, so this will aggravate the braking issue described above.

Tom

 

hard to believe your just noticing this after 2 years. something must have changed. tire wear, road condition?

 

Sounds to me like your tires are sliding over a smooth surface, like a manhole cover, railroad track or crosswalk stripe when it's wet.

 

I would add that this misnamed 'brake surge' effect, absent during panic braking (Brake Assist), also seems to be absent during ordinary hard braking. It seems to be triggered by bumps only from pure regen braking. But pure regen is possible only with light to moderate braking, varying with speed. I have no evidence, first hand or from stories here in PC, that it ever happens in situations where short braking distance is essential.

Loss of traction from worn tires on slippery surfaces, such as manhole covers and metal plates, is most likely in harder braking. And it is a sign of inadequate tires, not a brake issue.

But OP has not given us enough clues to distinguish between these issues and other possible problems.

 

It is certainly more prevalent during regen braking, but it is also exhibited by other non-hybrid Toyota vehicles. The FJ Cruiser exhibits this behavior while not being hybrid. It does use electrically boosted power brakes similar to those in the Prius, so this may be an ABS reaction in that type of braking system.

Regenerative braking increases the likelihood by braking with only the front tires, and then through a differential, so losing traction on one tire causes a complete loss of braking.

Tom

 

They may have a lot of life, but even so may have lost a lot of grip. There is a big difference between tread and grip. Most low rolling resistance tires use a grit to increase friction. Once this wears away the tires tend to slip.

Tom

 

The Prius, like all new cars, has anti-lock brakes, which automatically release and re-brake whenever a skid condition (such as wet steel) occurs. It may seem a little scary, but ABS is a great safety feature.

 

Check out the treadwear rating on your tires. I've noticed that a lot of OEM tires tend to have very low treadwear ratings under 300. Tires with under 400 treadwear ratings don't tend to last very long.

 

yes as compulsive pointed it is discussed there.

Basically it is inherit evil of dual brake system.. In terms of dealing with it you have to be aware of under what condition the transition from regen-to-friction braking happens, and when you are using regen, give yourself additional space. Also helps to understand what may cause it (wet metal objects and road paint) good luck.

 

Note as pointed out before, this phenomenon also occurs on cars without dual braking systems. ABS brakes alone are enough to cause it, although it is exacerbated by regenerative braking.

Tom

 

I don't think the regenerative braking feature has anything to do with it, although I admit I've never disassembled the braking system. Regenerative braking is a lot like the engine braking you do on a manual transmission car when you downshift; it is totally separate from the friction braking system. I've panic-braked in my Prius, and the friction brakes engage instantly.

All cars with ABS behave oddly when ABS engages: The car makes an odd noise, and the brakes release and re-engage. This is the intended behavior of a car with ABS braking.

 

Regenerative braking is a shortcut into ABS. When braking regeneratively the Prius only uses the front wheels, which are connected to MG2 through a differential. This means the loss of traction for a single front tire forces a switch to friction braking. Because the switch to friction braking was forced by a traction issue, the friction system comes up immediately in ABS mode.

Regenerative braking is not directly related to ABS, but it gets you there faster.

Tom

 

yes as Tom says; problem that it is enough for 1 wheel to slip to have no brakes, where normally it will be one wheel out of 4. I guess Toyota could have put a locking differential, but that would increase costs.

 

And not stated but some of us understand, that the -real- "perceived problem" is that there is a 1/2 second (or so) of braking -release- when the switch from regenerative to friction braking occurs. If this didn't happen nobody would notice. Which is why nobody complains in -other- cars.
An engineering problem to be solved.

And I say again, if 1/2 second puts you in danger you are braking too late.

 

The FJ40 people complain, and they don't have regenerative braking. They do have Toyota electrically assisted ABS brakes.

Tom

 

That would be the FJ Cruiser people. The FJ40 was a 60s design, completely manual.
I have an FJ Cruiser (feel like I'm in an AA meeting ) and don't have a problem, but my 2007 doesn't have the fancy system they have now. Still have anti-lock and also have VSC (which saved me from spinning out and rolling last winter) so I'm not complaining!

I will repeat what I have posted before. When I drive the FJ I think "how 20th century". Pearl is so much more sophisticated - and in this case much better! In everything it does other than ground clearance.