Ludicrously basic question - Gen 2 brakes

[Chasnotdave]

I've got an 05 Prius Gen 2 and I noticed the rear disks are, like, really rusty. Braking seems OK but then I tend to be a bit of a cruiser anyhow so might not've really pushed them hard enough to notice recently.

Anyhow, it made me realise, I don't really know how the braking system works on my car - in fact most cars.

So I'm gonna ask. I'm assuming all four brakes should operate when braking, right (sorry, told you it was a ludicrous question!)? And it's just the rear brakes only work on the handbrake, right?

Well, the handbrake works because i can see the scouring on the disks when I've moved against a lightly-applied handbrake. But it seems like the footbrake isn't working the rear brakes because after I get back from a drive, they're still rusty.

In which case - anyone got any ideas what's broken, please?

Oh, and Hi. New bloke on the forum - even thought I'm on my second Gen 2. Should have got here earlier really :)

[Catlover]

Welcome to the forum.

When you brake there is a transfer of weight to the front of the car, the front gets heavier and the back gets lighter. Consequently the manufacturer, in recognition of this, makes the front brakes work harder and the rear brakes lighter. If they didn't do this, and make braking even for example, the back brakes would lock up, which wouldn't be good for you the driver.

I would suggest, to keep the rear brakes in good order, that you occasionally, and only when it is safe to do so and you are travelling in a straight line on a well made road, is brake heavily, not necessarily to a halt but hard. Not too hard such that your brakes lock, that is not what you want, but heavily such that all four brakes really work.

The problem is if you brake light all the time the back brakes could start to seize such that they not working efficiently as manufactured to do, meaning in an emergency you will not stop within the distance the car was made to, and your car could fail an MOT, where the test measures the efficiency of all four brakes individually.

Park your car overnight in the open and if it rains your brakes will have some rust  which will rub off as you drive and brake, but if you leave rust the disc can get pitted in time, and as I said, start to seize due to lack of movement. So it is critically important to keep things moving.

Of course, most hybrid owners are in it for more miles to the gallon, and we anticipate traffic ahead and tend not to use brakes heavily, hence I say find a straight piece of well tarmacked road and brake hard only when safe ie no other road users around.   Joe

[Chasnotdave]

Thanks for the advice Joe - yep, guess my steadier approach to driving has had its consequences. I'll bear that in mind - I guess it's a bit like making sure you use the air con from time to time to keep it working and draining properly. I'll try and find somewhere a bit deserted and start stepping on the brakes a bit - see if that frees things off.

[Harters]

Also, you could try putting the car in neutral, when its safe to do so as thats stops regen braking, then try some braking as Catlover suggests.  Once you have done that a few times put the car back into drive and carry on your way

[Chasnotdave]

Yeah, that seems to have worked. Took it out to a deserted b-road and did a few emergency stops and i can see the shine coming back onto the disks so they must be working. Phew! Guess I'll have to dig out that inner boy racer in me from time to time. Thanks chaps

[Catlover]

I forgot to mention before.  I bought my Gen3 2 weeks ago, privately. The previous owner had rear discs and pads fitted mid Jan this year........ must have suffered corroded and/or seized rear discs. All my benefit.

[Dancing Badger]

When braking gently the car uses regenerative braking - you can easily see this on your hybrid indicator on the dash which will show recharging under braking. In this state, the retardation is only at the front wheels, and the mechanical brakes (ie the pads and discs) are not being used at all, the car is being slowed by the electrical resistance of the motor generators. At low speeds (under 7 mph I think) the mechanical brakes come into use. This is often not enough to keep the brake discs clean of the surface rust which affects the discs on all cars.

When you brake hard, then the mechanical brakes come into use - and work on all four wheels, although biased towards the front as Catlover explained.  The parking brake operates only on the rear wheels. So you can effectively clean the discs by braking hard as you've now discovered. However, as Harters says, when you select neutral the car does not regenerate at all, and when you brake in neutral the car uses only the mechanical brakes. This is a more comfortable and arguably kinder way to keep your brakes clean. I do this regularly on the way to work - there's a gentle downhill about 100 yards long leading to a give way and I simply select neutral and brake gently down this hill, select drive at the bottom and drive on normally. I do it about once a week, it seems to do the trick. Brake pads wear much slower on hybrids than on conventional cars due to them not being used much in this setup, but the risk is that they can end up needing work doing through lack of use - rusty discs, seized calipers, that kind of thing. Incidentally you can't (well, at least I can't) feel any difference at all whether the braking is regenerative or mechanical, which I think is rather impressive engineering.

[PeteB]

1 hour ago, Dancing Badger said:

... Incidentally you can't (well, at least I can't) feel any difference at all whether the braking is regenerative or mechanical, which I think is rather impressive engineering.

When the Gen 1 Prius was the only model available there was a US company (Coastal Tech) that made a number of aids for the car, including one that showed a couple of extra dash lights - red for friction brakes active, green for ICE off (there was no EV indicator or button on the Gen 1).

[QuantumFireball]

Hybrid Assistant (Android app) can tell you if you're using friction brakes (brake icon goes red). I can hear the disc brakes at lower speeds.

One thing to watch out for is the slider pins on the rear calipers can seize, which can lead to uneven wear and noise. One of my rear discs had significant corrosion that wouldn't go away because the pads were not coming into contact properly - after replacing one seized pin and lubricating the rest, they're looking a lot better now (and no noise). Probably worth lubricating them every 2 years or so. I haven't check the pins on the front brakes as they seem to be working OK.

[Sooty]

Another way to clean/ operate the rear brakes is to reverse quite fast in a safe area and brake. This way the weight of the car is transferred to the rear and the rear brakes will apply harder.

Also Regen braking does not work in reverse as far as I know.

HTH

[kithmo]

4 hours ago, Sooty said:

Another way to clean/ operate the rear brakes is to reverse quite fast in a safe area and brake. This way the weight of the car is transferred to the rear and the rear brakes will apply harder.

Also Regen braking does not work in reverse as far as I know.

HTH

I think you're right there Bruce, I've never had a problem with brake discs rusting and my car stands on my drive for 2 or 3 days at a time out in all weathers. I reverse about 30ft down my drive each time I use the car, with my foot slightly on the brake, which probably cleans the discs.

[Chasnotdave]

On 21/02/2018 at 9:11 PM, Dancing Badger said:

The parking brake operates only on the rear wheels.

In that case, I guess another way to get the rear brakes working would be to drive forwards but brake to a halt using the parking brake a few times? In fact, I could probably apply it gently to a point where it's braking a little and cleaning the disks but the ratchet doesn't grab enough to make it so I've got to stop then disengage the brake. 

[kithmo]

Not sure if the parking brake actuates the brake pads on the Gen 2, I seem to remember reading somewhere that the brake disc has a built in, smaller, drum brake with shoes for the parking brake, or was it a dream ?  

[YarisHybrid2016]

On 2/23/2018 at 7:46 PM, kithmo said:

Not sure if the parking brake actuates the brake pads on the Gen 2, I seem to remember reading somewhere that the brake disc has a built in, smaller, drum brake with shoes for the parking brake, or was it a dream ?  

Anyone know what the Yaris has? Does it use the main brakes or does it too have brakes and shoes? I thought I knew, but now I'm doubting myself...