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Discussion Starter · #1 ·
I don't think it got mentioned over here yet, but those
of you somewhat handy with electronics and are tired
of waiting on Coastal can build your own wheel brake
pressure monitor right now. Full details at
http://techno-fandom.org/~hobbit/cars/bp/ and I'll
be happy to answer further questions about it.
.
If you're New England local, come to the Altwheels festival
[ http://altwheels.org/ ] to natter about this and lots of other
mods. My "naked Prius" should be out on the lawn someplace.
.
_H*
 

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Interesting quote:
"A braking request that exceeds the regeneration limit clearly begins bringing in the rear brakes first, to avoid front-end dive and balance out the vehicle, before applying pressure to the "big guns" up front if needed."

Most cars use the rears very little because they will just skid as they are lightly loaded. Perhaps the rear battery weight helps in the Prius?

Hmmm, makes me a little less happy with the rear drums if they are the first to be used...
 

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KTPhil, don't worry!

The braking effect on the front wheels is the sum of regen and the front disks. The braking effect on the rear wheels is only from the rear drums. The order of application is: regen, rear drums, front disks. So by the time the rear drums are applied, there is already a fair amount of braking on the front wheels. The application of rear drums and front disks is engineered to keep the correct balance between front and rear wheel braking effects.
 

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I'm not worrying about skidding (the ABS will see to that). I'm questioning the conventional wisdom that the rear drums see only the lightest of duty (and therefore that discs add little), but this link states that the rears are used first.
 

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Hydraulic braking is in addition to, not in place of, regeneratve braking therefore there is still braking action on the front wheels when the rear brakes begin to be applied. Applying hydraulic pressure to the rear first simply maintains the correct proportion of front to rear braking effort.
 

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That is not what the article says. It says that rear brake application precedes front brake application.

Yes, there is regen via the fronts, but I am speaking about BRAKING, using brake pads or shoes. If the rear sheos are applied before the front pads, then we can expect more rear brake wear (and perhaps fade?) relative to the front, at least in comparison to a conventional car.
 

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Discussion Starter · #7 ·
Well, maybe I should clarify that. If braking is
*solely* used, such as when you throw it in Neutral and
then use the brakes [i.e. no regen], then the fronts definitely
get heavier use than the rears.
.
The rundown means to say that if you *exceed* the limit
of regen and have to start bringing in wheel braking to help,
that the rears are brought in before the fronts. The fronts are
brought in soon [where "soon" means a request for even more
braking power] after that, so it's not like you're
screaming along about to lock up the rear end.
Regen will provide just about the only stopping torque up to
about 100 amps of battery-charge current, and that's all
you get, but even that's a fair amount of force
applied to the front wheels.
.
The braking ECU also looks at the *rate* of pedal
application, and if it detects what it thinks is a
panic stop [very fast movement] it brings in the physical brakes
right away regardless [with emphasis on the fronts]. The
regen-then-rear dance only happens under light braking.
.
I could have gone on at much more length in the article, but at
that point I'd pretty much be rewriting the service manual...
.
_H*
 

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Hmm, let's see: The front brake pads will last much longer than in a conventional car. The rear brake pads will last much longer than in a conventional car, but not to as large a proportion as the front pads. Gee, that's a reason to worry!

Oh wait, but that's only if you mostly brake at just the right pressure to slightly exceed the full regen capacity.

WHY IS THERE PANIC?

Oh yeah, fade. Let's try again.

The front pads will take longer to fade than in a conventional car. The rear pads will take longer to fade than in a conventional car, but not by as big a proportion. Darn those Toyota engineers and their foolish attempts to maintain correct balance in the braking system! Fire the lot of them!

Meanwhile, I will be glad we have regenerative braking and won't complain that it doesn't benefit the rear brakes to the same extent as it does the front brakes.
 

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You missed my point. It's not a value judgement on the setup, and it's not about which wheels do the work. It's about what brake surfaces are seeing wear.

It's the surprising fact that the rear brakes are used more than expected. The practical effect is that if you brake lightly on a regular basis (as we should for good mileage), you can't expect that the rear brakes will not see wear. I've changed my own brakes for 30 years on front and rear drive, front and rear engined, and the Prius is the exception to the rules about relative wear.

Nobody is "worried" about it, nobody's "complaining" (your words, not mine). It's just a fact of car maintenance that an owner/mechanic like myself should be aware of, and not just asume that the rears don't need to be checked as often as the fronts(which is a pain for drums vs. discs).
 

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With more surface area on drum shoes than bisc pads, the drums should last longer. However, lining material varies, as does lining thickness, so I don't think there is any one answer.

From a maintenance standpoint, discs are easire to replace, and easier to inspect, due to the more open mechanical design.
 

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Past 78k miles in 2001 Prius, and having looked, neither front nor rear friction pads are anywhere near needing replacement. Drive happy, everybody; you chose well.

DAS
 
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