Regen vs Mechanical Braking

[Tech429]

As the title suggests...

I've read that on these hybrids the regenerative braking is used down to about 7mph where the Mech braking takes over.  This is fine but then I also read that this will cause the Mech braking not to be used very often and therefore can and will cause rust and other build up on the discs.  And this is an issue as it can cause scraping sounds when braking at 7mph and under.  I have noticed a scraping sound when in low speed (like in a car park and just reversing out and/or setting off) when applying the (Mech) brakes.  But this is obviously the discs causing this when braking at low speed.

So many drivers have been asking if it is possible to disengage the Regen braking (which it isn't) or to reduce it (which apparently only Tesla have this setting option).

So how does one clean the build up on the discs when the Regen brakes are used 80%+ time?  In normal ICE cars you can clear the discs by going down hill and applying the brakes to clear the build up etc.  But on these Hybrids how can this be done unless you are going downhill 7mph or less?

Someone suggested going into N for a very short while and brake - would this only use Mech brakes or would it still use Regen?

Just wondering if anyone has an idea on this - or even to discuss?

[tfc]

My car stays outside over night and when its been raining the brake disc's get wet and have rust on them which is understandable, by the time I've drove to the top of the road about 250 metres and come to a stop at the junction the disc's are wiped clean and all the rust stains have gone.

You could try and find a quite bit of road or car park where there is no one about and do about 10mph and  gently apply the brakes  a couple of times with your left foot only for a couple seconds  and release,  then see if the noise is still there when you come to a stop.

 

[Tech429]

2 minutes ago, tfc said:

My car stays outside over night and when its been raining the brake disc's get wet and have rust on them which is understandable, by the time I've drove to the top of the road about 250 metres and come to a stop at the junction the disc's are wiped clean and all the rust stains have gone.

You could try and find a quite bit of road or car park where there is no one about and do about 10mph and  gently apply the brakes  a couple of times with your left foot only for a couple seconds  and release,  then see if the noise is still there when you come to a stop.

 

Mine is left outside too and i do try to use the brakes lightly but even after a few miles the brakes are scrapy.

Perhaps i'll wait until better weather.

[Woofwoof]

If you brake hard it will use the mechanics brakes or put it into neutral  where it will not generate electricity

[Jackx1]

I’m experiencing the same rubbing sound on my brakes. Tried to clean them up with some heavy braking as suggested on here but still do it regardless. Discs look in OK condition, car has only 13,000 miles.

[Yugguy1970]

Stupid question time

Is it scraping or is it the low speed audio warning?

[kisslee]

Hello.

I have noticed that while driving in reverse, the mechanical brakes always apply. If I drive forward and apply the brakes, I can't hear any scraping but as soon as I go in reverse the scraping starts - to be clear, this only happens after conditions that are described by others (rainfall, long perionds of not driving the car)

So maybe try driving in reverse and gently applying the brakes, but to be 100% sure, go for a longer drive.

 

BR

[TonyHSD]

Well, tell me about it 

My hybrid is 13 years old with only 240000 miles. The car has almost everything original except the brakes. I had total of two sets changed discs + pads and not because been worn out but because of rust. And the problem it’s not only the surface rust but also stuck slider pins and rusty pistons that does not return. This is what happens last week to me and I do service my brakes at least once a year. Front left wheel the piston got stuck, causing brake dragging and overheating. I fixed it and now all good but I need to go all other 3 corners. And my car gets properly used every week 600-1000 miles on average. 
The problem because of the regenerative braking Evs and  hybrids brakes are always cold. You can’t always reduce regenerative braking, it’s just not possible.  
All you can is use the brakes more progressively when coming off the motorways and safe to do so. The reality is that if the discs didn’t clean after few days they will need dismantling and physical cleaning, lubricating the slider pins with silicone grease. Diy or trusting mechanic. 
Here how looks overheated discs 

 

Usually typical temperature of the discs on these cars even after hours of driving should be as low as 18C° winter and as high as 44C° summer and after heavy use. Anything outside these numbers , any rust, scratches, or red dust means it is time for brake service. And recent cars also suffer this fate, 2020, 2021 even 2022 can be ready for cleaning, that bad can be the brakes in uk  👍

 

[Woofwoof]

I noticed scoring on my disks after 8 months, like a circle etched into my disks, what does that mean?

What should I do?

Dealer did not comment when it went in for service.

[APS]

14 hours ago, Tech429 said:

So how does one clean the build up on the discs when the Regen brakes are used 80%+ time?  In normal ICE cars you can clear the discs by going down hill and applying the brakes to clear the build up etc.  But on these Hybrids how can this be done unless you are going downhill 7mph or less?

 

The regen and mechanical braking effort is blended - Yes, if you never brake harder than what the regen can provide, then the mechanical brakes don't really do much. You can easily track this by looking at the power meter (if you have one) this will show 'negative' for when you regenerate (coasting or braking). When it bottoms out i.e. you are regenerating as much as possible, any further braking effort is handled by the mechanical breaks.

The simple answer is to make sure you use your brakes. Brake beyond that regen region. You can certainly do the same as you suggest, go down a hill or break from high speeds. This will exercise and put some heat in your brakes. 

[APS]

17 minutes ago, Woofwoof said:

I noticed scoring on my disks after 8 months, like a circle etched into my disks, what does that mean?

What should I do?

Dealer did not comment when it went in for service.

A small rock or some other foreign object has lodged itself at the leading edge of the brake pad and scored the disc. 

Fairly common, not usually a problem unless really severe. Garage and MOTs may make a note, but are mostly interested in checking the overall wear and that the thickness of the disc is not below the minimum.

[Woofwoof]

It’s on a few of my disks at the same spots

prob at a catching point in the pads?

can I remove it without causing damage?

[TonyHSD]

1 hour ago, Woofwoof said:

It’s on a few of my disks at the same spots

prob at a catching point in the pads?

can I remove it without causing damage?

Any pictures will be good 👍 

[APS]

1 hour ago, Woofwoof said:

can I remove it without causing damage?

Yes, you can remove the pads and have a look. Whatever caused the scoring is probably ground to dust since long. So you are unlikely to see anything. The pads will shape to the grove in the discs so from a braking capability point of view it won't make any difference. Replace the discs once the pads are worn.   

[Woofwoof]

12 minutes ago, APS said:

Yes, you can remove the pads and have a look. Whatever caused the scoring is probably ground to dust since long. So you are unlikely to see anything. The pads will shape to the grove in the discs so from a braking capability point of view it won't make any difference. Replace the discs once the pads are worn.   

I'll prob be replacing the car before the discs need replacing.
I'm assuming the pads will last at least 40,000 miles ~ 4 years which I am not expecting to own the car for that long.

[TonyHSD]

17 hours ago, Woofwoof said:

I'll prob be replacing the car before the discs need replacing.
I'm assuming the pads will last at least 40,000 miles ~ 4 years which I am not expecting to own the car for that long.

These cars wear off the rear pads and discs first then the front.
It will vary between the different ownerships but roughly around after 40-50k miles the rears will be wearing thin and noted on your service check list and recommend replacing. The longer journeys you do the longer the pads will last, I am on 104000 miles since last change in 2020 and rears will need change soon, the fronts are very little worn. In better climate environment the brakes can last the lifetime of the car with only maintenance once in a while, in USA a Prius phev was shown with original brakes at 314000 miles. 👍

[Yugguy1970]

Anything Corolla sized or above can't rely purely on regen braking, too heavy.  In the RAV I have to brake really lightly to keep it in the charging/regen zone, also braking sharpish from any high speed uses mechanical.

[AndrueC]

I rarely use my brakes in the first place. Typically only for actually bringing the vehicle to a final halt. My old driving instructor told me that brakes are for stopping and for correcting your mistakes.

I prefer to lift off in good time and let the car slow under engine braking (recharging for hybrids). There's rarely any need for me to use the brakes above 10 mph.

[fred88]

I remember going to an Institute of Advanced Motorists sampler once and the instructor said that he would often see how far he could get without using his brakes. He obviously qualified that statement but it was years ago and I can't remember how, but he clearly thought it was good driving. An interesting point  but I would have thought that it some circumstances it could be frustrating  for other drivers.

[AndrueC]

7 minutes ago, fred88 said:

An interesting point  but I would have thought that it some circumstances it could be frustrating  for other drivers.

In most cases it works out faster. You can maintain a higher average speed. Whereas someone reliant on brakes comes to an almost stop at roundabouts I can moderate my speed and the extra time afforded by my increased slowing distance means I can spot a gap and be across the roundabout before the braker has got going again.

I'm sure (kind of hope, lol) that it's frustrating but it's a frustration resulting from ignorance rather than because it's slower.

It's also safer. If a typical driver encounters something unexpected they may be unable to do anything about it because they are already using close to the maximum braking force available to them. I on the other hand still have most of my braking force in reserve so can always significantly increase the rate at which I'm slowing.

It also saves a lot of fuel. Even our hybrids can't reclaim all the energy being lost so by reducing brake usage we reduce fuel consumption.

Lastly it reduces wear and tear. In over 30 years of motoring with cars typically doing 30k under my ownership I've never had to replace any brake components.

[TonyHSD]

Agreed with last two comments. I usually drive like Andrue says and often get dirty looks by all other drivers even some swearing at me and throwing water bottles etc. Same for acceleration too. Especially on Toyota hybrids where they go up the speed in very linear way the rest of the  drivers are going wild and furious., and I am not a slow driver at all, just sensible, but it seems like these days sensible drivers are very small amount and the majority are like zombies. And you can see the news , every day something has happened and tons of examples of poor driving. 👍

[Bernard Foy]

When I bought my first car (heap of scrap) all those years ago I as an old guy for advice on driving. His reply was “drive as though a glass of water is sitting on the bonnet and try not to spill it” 👏. In other words do everything smoothly.

[fred88]

Remembered a bit more about that IAM guy I mentioned above. Apparently some of his warning lights (faulty bulb?) didn't go out until he hit the brake pedal. If I remember correctly a large part of one of his commutes used to be on the A303 in Somerset. If he managed to get on it without touching the brakes and with a bit of care approaching the odd roundabout, he could get an impressive number ber of miles on the clock with the warning lights still on. Oh, and he was an ex police car driver. 

 

[Cyker]

That smooth speed change style is key to getting good mpg too.

I find if people can see there's a traffic jam ahead they're more resigned and less likely to e.g. tailgate, and more understanding if you leave a bigger gap (And also start to do it too!  ). The slower more even speed change also means you're less likely to be involved in a collision than if you are following the queue for the reasons many mention above, i.e. you have more braking headroom, and buffer space.

I have to be especially careful with the Mk4 to not trigger the AEB!  

People do get more annoyed if you don't keep up and e.g. miss a light change that you and several cars should have been able to get through, but the Mk4's so responsive I can usually drop any tailgating SUVs fairly easily when the road ahead clears  

 

[Don Mac]

39 minutes ago, fred88 said:

Remembered a bit more about that IAM guy I mentioned above. Apparently some of his warning lights (faulty bulb?) didn't go out until he hit the brake pedal. If I remember correctly a large part of one of his commutes used to be on the A303 in Somerset. If he managed to get on it without touching the brakes and with a bit of care approaching the odd roundabout, he could get an impressive number ber of miles on the clock with the warning lights still on. Oh, and he was an ex police car driver. 

 

Did he also use phrases like "Lift your vision" and "a good drive should be boring"? (Americans might say something like "slow is smooth, smooth is fast") I have met police drivers who took pride in never having to stop on "blue light" drives through heavy traffic.

It's all about planning ahead. If you look up & anticipate what is coming you can (almost always) avoid having to make any sharp changes to speed or direction, and you can also hold on to your momentum/speed into roundabouts etc. (like Andrue said).

I imagine that a good proportion of the people on this forum (well, me at least) are attracted to Toyota hybrids because they are so well suited to this style of driving.