Brake pads appear rusty

The pads don't rust. The rotors do. It's not uncommon for the rotors to have a little surface rust after sitting overnight after it rains. This is probably what you're seeing. Not a problem.

 

The Prius rotors are inclined to rust more than most cars. The reason for this is that under normal braking the rotors are not used until the car is below 7 mph. Regen braking does the rest of the work.
It is a good idea to put the car into neutral while moving below 50 mph and use the brakes about once a week. This forces the car to use the rotors to slow the car keeping them clean and shiny, stopping rust build up.

John (Britprius)

 

Surely you must be joking, Britprius.

The Gen II Prius regen is limited by the ability of the traction battery to absorb the energy. It cannot
take advantage of all that energy like a Tesla can.

Unless you decelerate like the Oasis of the Seas, you will be using the friction brakes on a daily
basis.

 

One way to upgrade the look of the brakes is with a caliper cover by companies like MGP. You can also find caliper cover on ebay and Amazon for cheap although many of those sold on the marketplaces will be cheap, plastic imitations that need to glue on unlike MGP caliper covers.

Regardless, the oxidation you describe doesn't sound like it should be a problem and caliper covers are strictly aesthetic despite what the manufacturers may want you to believe.

 

I repeat the Prius under normal braking uses regen down to 7 mph. It then transfers to friction brakes (the rotors). Unless you are on a very long descent when the HV battery does become fully charged (8 green bars on the mfd) when it will then change to friction braking. It will then burn off some of the excess energy in the HV battery by spinning the engine with no fuel injected and no spark, thus lowering the charge. However under normal road conditions (not long downhill sections) the braking is by regen!!!
This is the main reason Prius brake pads can last and have lasted 200,000 miles, 100,000 + is normal.
As a by the way the Prius can regen 100 amps at 200 + volts, "I'll leave you to do the maths" this braking effort is enhanced by the gear ratios between the wheels and the MG's

John (Britprius)

 

So, you're saying if you need to stop from 70 mph to 0 mph on a short exit ramp from the highway you don't use the friction brakes?

Hogwash.

And the main reason the Prius friction brakes last 200K miles is a change in driver behavior when one gets behind the wheel of a Prius. Why not take advantage of free energy? That's why many Prius drivers coast to a stop well ahead of time. And brakes are improving all the time. I managed to get 100K miles on the first set of brakes on my 92 Honda Civic VX. It's not uncommon for Asian cars to top 100K miles if not 150K miles on a set of brakes if driven conservatively.

 

I think you should read my post again. Regen braking stops and normal friction brakes take over below 7 mph. I stand by what I have said. Under normal braking "not an emergency stop, or a situation where the abs or vsc are used, and the battery has the normal charge level of five blue bars" the car will use regen braking on the front wheels only. Given these circumstances the car will use regen braking from 70 mph to 7mph.

Talking of short off ramps is of no use to me being in the UK. How long is short, and are the ramps up or down? Our exit ramps from our motorways are usually up hill and perhaps 300 yds long, but some are downhill.

No figures I produce are going to convince you so I suggest you use an application such as Techstream or the excellent Priidash " Torque maybe capable but since I do not have this or used it I do not know" and record your braking events to check my statements, then come back for further discussion.

John (Britprius)

 

I can confirm Torque works to monitor both regen braking force and friction braking force. Even with a fairly decent application of the brakes (ie, not slamming the brakes to come to a complete stop) most or all of the braking is done by regen until you hit 7mph. Torque will show that there is some SMALL amount of assistance from the friction pads and this does increase above 7mph if you're stopping in a HURRY.

HTC Evo 3D

 

Thanks for the confirmation.

John (Britprius)

 

I've noticed the same using Torque. However, I believe that under most driving conditions, it would be rare to need to put it in neutral and clean the brakes. I try to drive without brakes as much as possible (and stay in the regen range when I have to), but there is always going to be that light that changes right before you get to it, that car that cuts you off, or something else that causes you to have to brake hard fairly regularly. If you need to clean the rotors, I would expect you to be getting great mileage or rarely drive.
I've only done the neutral brake cleaning once in my Prius, and that was after several days of hard rain. The brakes were grabbing hard when they switched to friction. I'm pretty sure it was caused more by sand and debris in the pads from driving through puddles, though, as the rust is always gone after driving.

 

The need to clean the rotors will depend on a number of things:- Do you brake gently or hard, how smooth are the roads you drive on "bumpy roads cause the abs to operate forcing friction brake use" , are you in a wet climate, do you live by the sea, and are your roads salted. All of these will make an impact. Once the rust has established itself on the rotors it rapidly gets worse unless cleaned off.

John (Britprius)

 

Anything that could be sprayed on them to prevent / get rid if the rust?

 

I do not know of any product that could be used on the rotor since the area in question is the braking surface. If light rust can be seen it is easy to remove by braking in neutral occasionally to polish up the surface. This can easily be seen through the front wheel spokes.

John (Britprius)

 

In the UK along with the rest of the world (not the north American continent) we have the dubious advantage of having disc brakes (rotors) front and rear. Because of the natural brake bias of about 70% front 30% rear the rear discs (rotors) rusting is a real problem in damp or wet climates on the rears.

John (Britprius)

 

I suggest you read the following.

Toyota Hybrid System Diagnosis - Course 072, Section 6, Brake System states: "As soon as the accelerator pedal is released, the HV ECU initiates regenerative braking. MG2 is turned by the wheels and used as a generator to recharge the batteries. During this phase of braking, the hydraulic brakes are not used. When more rapid deceleration is required, the hydraulic brakes are activated to provide additional stopping power."

It also states that: The (HV) battery will accept charge up to an instantaneous rate of 20 to 21 KWH. Much of the energy from light braking at high speeds and harder braking at lower speeds can be recovered. Excess energy over the charging limits is wasted as heat in the brakes just as in other cars.

 

Exactly the figure I gave you in post (7). 100 amps x 200 volts = 20 kw. The speed of the car has nothing to do with rapid deceleration you can rapidly decelerate from 5 mph, I quoted normal braking. To quote your own post above "much of the energy from light braking at high speeds and harder braking at lower speeds can be recovered" no system can recover all of the energy because of conversion losses even the Tesla. Again I say check this for yourself with readily and cheaply obtainable equipment and post the results.

John (Britprius)

 

I can see that it's pointless to debate this with you. You won't budge, even a little.

You win.

 

There really is nothing to debate! Your talking about rapid short distance braking and Brit is taking about "normal" braking. Most drivers drive normally.

BTW Brit is very knowledgeable about the Prius!


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