When driving in wet road conditions, I've noticed some odd behavior from my brakes. On dry pavement, a linear push on the brake pedal provides a linear stop- the harder you push the harder you stop, in a smooth and constant fashion. But when wet, in the last second (or last few feet, or last 1 or 2 mph, however you want to word it) of braking they grab really hard, sort of jerking me to a stop. It's like if you were to chart it, dry pavement stops would be a diagonal line while wet pavement stops would be a diagonal line with a sharp exponential curve at the end. This is the only vehicle I've experienced this in... is this normal behavior for the hybrid's very different braking system?

It's not a big deal, more of an annoyance than anything else. I usually just compensate with pedal pressure, but I thought it was worth asking about since I'm more than halfway through my warranty period.

 

Yup, grabby when wet. That describes the behavior of my 2008 AWD model.

 

https://www.greenhybrid.com/wiki/ind...ape_Hybrid_FAQ

Part II: DRIVING THE ESCAPE HYBRID

9. Why is it after it rains, my brakes get all grabby?

Short answer, because you're not using them. Most of your deceleration, outside of stepping hard on the brakes isn't actually braking, it's the regeneration system taking your motion and turning it back into energy to use, which means that your wet brakes don't get a chance to friction dry when you apply light braking pressure (like in a conventional vehicle), which means your brakes are still wet when they are used when stopping. Wet brakes grab hard, hence the grabbyness.

 

I've noticed that mine, in addition to increased grabbyness, also emit a shriek that could challenge any banshee when wet. Luckily, I usually get to park in a garage so it doesn't happen too often. And I leave late enough in the morning that none of my neighbors has threatened bodily harm.

 

The problem is with the composition of the OEM pads. I complained of this to the dealer and got the standard "that's the way they all are" response. I replaced the pads with EBC pads, the rotors with with EBC dimpled/slotted ones and had stainless steel brake lines custom fabricated (they are not yet available on the aftermarket) and the problem disappeared instantly. Merely replacing the pads will take care of your complaint, however. (I always replace al of the above in my vehicles.)

Front: DP71709 or DP61709

Rear: DP61710

 

I suspect that changing the pads may impact the "shriek" noise reported by some. But isn't the grabbiness somewhat imbedded in the brake-by-wire system?

When the FEH brake system is most sensitive to "grabbing" - in the moments during braking just before the vehicle is fully stopped - the computer may be switching over from regen braking in MG1 to hydraulic pad/rotor braking at the wheels. In non-regen systems, the rotors would be wiped dry by then, in the FEH they may still be slightly wet, hence the tendancy to slip and then grab as the hydraulics are applied just before coming to a stop.

Drilled and slotted rotors would probably help channel the water away sooner.

 

Audi (I also think BMW) has a system in place where it detects rain and will auto apply the brakes (without slowing the car down) to dry the brakes in case of an emergency. Very clever.

 

It is a function of cold wet brakes. One of the service trade journals sugestes that you periodicaly do some aggressive braking to clean the pads and rotos. The claim that alot of the prius' rotors were rusting and pitting due to little use.

 

It's the pads. Ford had one brake TSB out calling for replacing the rear pads with a new composition version and machining the rotors.

 

Just as an FYI, I have NOT noticed this on our 07 AWD......and I've paid attention. We get a lot of wet, and sometimes make short, low speed trips that would not dry the brakes with aggresive braking first, and I've waded through some puddles off-road (love to go driving in the wilderness.....). I've never had them grab or squeak, and I can't sense a transition from regen to hydraulic.

Perhaps there are some batches of brake pads that aren't quite like some of the other batches??? Not bad enough to be considered failing, but showing some different characteristics???