Braking sensation when coasting

[supton]

I kinda like fuel cutoff, save on gas and the brakes. On a regular commute (like I have), I learn when to let off and coast for an optimal speed for the exit/turn/whatever. If traffic behind me isn't piling up, then i'm bothering no-one, and saving a few pennies each time.

If mpg is good then I wonder if there is no issue here. Van has some large amount of wind drag; you might just have to keep a bit of throttle to "coast" in the old school way. Our hybrid is that way, "coasting" is actually light regeneration.

 

[turboseize]

It is entirely possible that this is a combination of several effects - one or more sticky brake calipers (or clogged brake hoses), plus the effects of deceleration fuel shut-off (which sometimes is only implemented above certain rpms, and with modern systems they may even factor in driving style and previous load... so it may not always appear consistent to the driver).
I would surely have a very good look at the brake calipers and at the brake hoses.
Sometimes, when brake calipers get stuck, they become stuck intermittently.
A slightly stuck brake saddle might not even be noticeable while driving, but you should surely be able to feel it by the temperature. Get the car to out-of-town-speed, drive a few km at a constant speed, then gently pull over, stop and check the rims with the back of your hand. A really stuck brake will make the rim hot enough that you can burn yourself - and a burn inside the palms makes the hand useless, as you can't grip anything, while a burn on the back is only a bit annoying.
If you have a seizing brake caliper, don't ignore it. Not only will it eat through brakes, or even affect braking performance an handling in an emergency maneuver, the heat generated by the constant rubbing will also drastically shorten the life of the wheel bearing.


In 20 years of driving cheap, old cars, I've made it a habit to check rims and tyres at every stop. You can also detect a slow air leak on a tyre this way - the tyre losing air will be warmer than the others. (You have to keep in mind the influence of sun and weight distribution. If you were driving 100km with the summer sun to the right side of your vehicle, of course the right side tyres will be warmer than their counterparts on the other side. And in a FWD car, front right in this situation will be warmer than every other tyre. Now if front right was hot and all the other tyres were lukewarm, that would still mean something. Or if front left or rear left were the warmest... that would definitely be worth a closer look.)

 

[John105]

It is entirely possible that this is a combination of several effects - one or more sticky brake calipers (or clogged brake hoses), plus the effects of deceleration fuel shut-off (which sometimes is only implemented above certain rpms, and with modern systems they may even factor in driving style and previous load... so it may not always appear consistent to the driver).
I would surely have a very good look at the brake calipers and at the brake hoses.
Sometimes, when brake calipers get stuck, they become stuck intermittently.
A slightly stuck brake saddle might not even be noticeable while driving, but you should surely be able to feel it by the temperature. Get the car to out-of-town-speed, drive a few km at a constant speed, then gently pull over, stop and check the rims with the back of your hand. A really stuck brake will make the rim hot enough that you can burn yourself - and a burn inside the palms makes the hand useless, as you can't grip anything, while a burn on the back is only a bit annoying.
If you have a seizing brake caliper, don't ignore it. Not only will it eat through brakes, or even affect braking performance an handling in an emergency maneuver, the heat generated by the constant rubbing will also drastically shorten the life of the wheel bearing.


In 20 years of driving cheap, old cars, I've made it a habit to check rims and tyres at every stop. You can also detect a slow air leak on a tyre this way - the tyre losing air will be warmer than the others. (You have to keep in mind the influence of sun and weight distribution. If you were driving 100km with the summer sun to the right side of your vehicle, of course the right side tyres will be warmer than their counterparts on the other side. And in a FWD car, front right in this situation will be warmer than every other tyre. Now if front right was hot and all the other tyres were lukewarm, that would still mean something. Or if front left or rear left were the warmest... that would definitely be worth a closer look.)

I learned about the brake hose around 2015, when my car was 17 years old. I confirmed it the expensive way. Replaced the front right caliper, and the new caliper too was grabbing and not releasing. People online said to envision an artery that is clogged and allows flow one way. Fluid is pushed to the caliper, but because of damage inside the hose, it cannot flow back properly. That was a Raybestos coated caliper. When I junked the car this year, that caliper looked new, while everything else rusted around it....

 

[camrydriver111]

There is a way to test.

Jack up the wheel, spin the tire, apply the brakes, spin the tire again.

If there is resistance, open the bleeder screw. If the resistance is gone, its the brake hose. If the resistance is still there, then it's the caliper.

Unless you want to go scorched earth and do all hoses and calipers.

From the temperatures its obvious that something is causing it to stick.

 

[ARCOgraphite]

Update. I drove it with the eco mode turned off and the braking sensation when coasting hasn’t occurred. I’ll continue to watch it. However, check engine light came on this morning. Attached is the message. I plan on scanning it when I get home today to see if it provides a specific code.

View attachment 181487

So it definitely only appears to be at high speeds 60+ mph

See video. Essentially took foot off gas when I was over 60mph and the vehicle felt like it was starting to brake / lose speed quickly, I put my foot back on the gas and RPM spiked.

You could also have a bad wheel bearing and the rotor isn't running || to the pads when on the ground.

Also, a stuck EGR-closed may cause more braking as it is akin to a controlled vacuum leak when open - though EGR should not be open at closed throttle IMO.

May just be engine braking - I know my CUV does this off throttle but usually when proceeding downhill.

Did you pop the trans in N during a coast?

Time a 60 to 40 MPH whilst slowing off throttle travelling on level ground in N and then in D

good luck, Ken

 

[notharry]

I think it is odd. In an age where we are trying to maximize fuel economy, manufacturers are keeping the transmission engaged when decelerating. If they allowed the automatic transmission to free wheel and not slow the vehicle by downshifting, it would save so much on fuel. Sure drivability will require reengagement quickly but isn't that what clutches and sprag's do all day long? My F150 Cuts the fuel injection on a algorithm on decelerating as mentioned is normal in some vehicles but and as it downshifts, effectively slows the vehicle significantly. I can see this on the TOW/HAUL mode available on these vehicles and yes it does downshift earlier thus slowing down which is awesome when towing a 10,000 lb trailer, yes? I do understand that its still not without some losses but should be close to putting the trans in neutral manually. Yes Wind resistance plays a big roll in vans and trucks.

 

[turboseize]

As most drivers are incapable of foresight and planning, your proposal would lead to nothing. People don't coast, they rush towards the stop sign or red light and then slam on the brakes...
Also, when driving in hilly terrain, you'll spend a lot of time engine-braking anyways. Whithout dfco, you'd be wasting lots of fuel in this scenario.
So deceleration fuel cut-off in general is a good idea.
And in manual this gives you just another lever to play with. Sometimes the grade is steep enough that you can keep your speed while staying in gear (with dfco, that is with zero fuel consumption!), sometimes this would slow you down, so you're better off putting the car in neutral and coasting (consuming fuel to idle the engine).

If I recall correctly, BMW had implemented this into some of their automatic cars in eco-mode. I have heard rumours that the computer would also use data from the navigation system to determine whether to coast in neutral or stay in gear, but I'm not sure if that is actually true.

 

[alcyon]

My 2022 mazda cx-8 feels like that too especially at very low speeds. I think its a modern vehicle gearbox programming issue or the "generator" that runs the ac when the engine stops.