05 HCH brake problem

No insult taken. I don't know what "regen braking transition to hydraulic" means; could you explain that? I'm an electrical engineer, so I'm not an idiot, but I really don't know much about cars.

The thing is, the brakes feel fine until I hit a bump. Then it feels like the brakes release completely; something tells me that shouldn't be happening.

Great, then it should be easy from engineer to engineer ... ;)

Your HCH has two main sub-systems that are responsible for inducing a loss of momentum and eventually a stopping action on the vehicle.

The first and most important is the hydraulic system that is found in most cars nowadays. When we press on the brake pedal, added pressure is induced into the brake fluid which then activates the disc callipers and drum shoes on each of the four wheels, thus causing the vehicle to slow down via good-old friction mechanics.

Now the second subsystem is the regenerative braking system that is an integral and essential part of your hybrid vehicle. It uses the IMA electic motor that literally becomes a high density generator to produce electricity that is fed back to the battery array.

To make this two system setup work together, the vehicle's IMA has a regenerative algorithm that behaves cooperatively with the normal hybraulic braking system. In other words, the regenerative system works either exclusively or along side the hydaulic system to help slow the car down.

However given what I just said, there are transition points between the two systems that change the brake pedal feel as well as the braking effectiveness. These transitions are the result of speed change and rate of change as well as pedal pressure changes and which may take take some getting used to ...particularly for folks who have not driven hybrids before.

I was basically infering on these attributes & behaviors in the previous email.

Now, you said the brakes feel fine until you hit a bump... then they "release". Well, I find that pretty very suspicious if not scary and my approach would be to have another dealership look into the problem. It is obvious that your first contact was not fruitfull and sadly, that's is an all too common occurrence at least until the smaller dealership technicians have more experience servicing hybrid vehicles.

Cheers;

MSantos

You also have ABS (anti-lock brake system) involved.
If a wheel has traction loss and the ABS module see`s a wheel speed difference it can and will cause this type of feel.
I have felt this same action with my 2007 HCH-II and it is a normal condition.
You`ll be wasting time and money trying to fix a normal operation of your brake control systems and in the end have the same results.:eek:

Now, 2 years later, i have just seen this post because I just experienced brake problems with my 2004 HCH.

I too have always felt that weird "release of the brakes" when going over bumps or really bumpy/pot-holey roads. But people have told me it's the ABS. So you're not alone in this experience.

However, this other unfortunate thing just happened to me, and I'd like to know if this has happened to anyone else. I was at a stop, on an off ramp from a freeway, sitting in traffic, waiting for my turn. I was in 1st gear, with my left foot on the clutch and my right on the brake. I lifted my foot from the brake, just enough to let it roll forward a little and then pressed it again to stop, but the brake would NOT depress. It was a "hard brake" and would not press in to stop the car - I kept rolling forward. And I know I wasn't pushing the wrong peddle because my left foot was already in on the clutch and the gas would've surged me forward.

Has anyone with a manual HCH ever experienced a hard brake like that? I would really appreciate some help on this...