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Discussion Starter · #1 ·
Car was parked in garage for 3 days, not driven. This morning, on "Reverse" out from garage the Car wouldn't move, so a little pedal and there was a loud "THUD" as if the car was gripped on by "something" and released reluctantly. Driving the car on alley way the "thudding" continued as it was moving. 1) Checked tired pressure - all good 2) Checked no puncture 3) No error lights whatsoever on dashboard. The thudding sound continued next 10 miles while I have hazard lights on not wanting to drive over 40 mph. As it goes from 20-45 the road noises mask the "thudding" sound.

The "thud": It sounds like a kid attaching a Card on the bicycle wheels

Not wanting to "risk" anything running/rubbing against who-knows-what and making it worst, I went ahead and got it towed to the Dealership (10 miles away). Of course the Service Dept. calls me and said "we didn't hear anything" - REALLY ????

Has anyone experienced any of these ????
841
 

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A potential factor is that most of the day to day braking is regen braking, meaning your car may not use the physical brake rotors very often. They can get a little bit (or lot) of rust building up on the rotors, which is absolutely normal; on a non-EV car your brakes scrub off every time you use the car. For the XC40, I believe that setting "Park" is engaging the brake pads a'la parking brake on non-EV cars, so you could have a little rust form around the pad with a bit of a ridge.

If this happens in the future, you can probably do a little aggressive braking once or twice to scrub the pads. @SeattleCat describes this in some other posts. Here in Sacramento, rain is a foreign concept, so I haven't run into this (yet).

This is all conjecture, though, just a possible reason.
 

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Discussion Starter · #3 ·
A potential factor is that most of the day to day braking is regen braking, meaning your car may not use the physical brake rotors very often. They can get a little bit (or lot) of rust building up on the rotors, which is absolutely normal; on a non-EV car your brakes scrub off every time you use the car. For the XC40, I believe that setting "Park" is engaging the brake pads a'la parking brake on non-EV cars, so you could have a little rust form around the pad with a bit of a ridge.

If this happens in the future, you can probably do a little aggressive braking once or twice to scrub the pads. @SeattleCat describes this in some other posts. Here in Sacramento, rain is a foreign concept, so I haven't run into this (yet).

This is all conjecture, though, just a possible reason.
You are awesome ! I'm going to print this message and bring to Dealership with me - heading there in an hour to hear what they have to say. It was way too loud continuously for over 10 miles for my comfort.
 

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Agree with last post. If you either wash the car or drive in heavy rain then park it before the brakes dry, this will happen. Since the parking brake sets automatically and the rotors will rust (as with all cars unless they have ceramic rotors) and then the brake pad will "stick" to it until you drive some. I have had this happen on many vehicles that have the parking brake set automatically.
 

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Seems like a good option to add would be a way to disable regen entirely for sake of cleaning the brake pads without having to brake harder than regen does. @SeattleCat mentioned something similar, but I was thinking a button somewhere or even better, if the car could detect this somehow, then turn on this mode for a couple braking cycles then back off again.

I absolutely love one-pedal driving, and I believe that with OPD off, 'braking' still uses regen up until you need more stopping power, then the rotors/pads do the work. But that means stomping pretty hard on the brakes. So... you'd think there'd be a more-automatic way to manage this situation. I do not know what other EVs do about this, if anything.
 

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Discussion Starter · #6 ·
Seems like a good option to add would be a way to disable regen entirely for sake of cleaning the brake pads without having to brake harder than regen does. @SeattleCat mentioned something similar, but I was thinking a button somewhere or even better, if the car could detect this somehow, then turn on this mode for a couple braking cycles then back off again.

I absolutely love one-pedal driving, and I believe that with OPD off, 'braking' still uses regen up until you need more stopping power, then the rotors/pads do the work. But that means stomping pretty hard on the brakes. So... you'd think there'd be a more-automatic way to manage this situation. I do not know what other EVs do about this, if anything.
I have YET to use OPD -- and Yes, it was raining all last week then the Car didn't move for 3 days in garage. I'm absolutely surprised how loud the thudding sounds were ! And for over 10 miles of driving...... I just couldn't risk anything "wrong" with it ! Have never experienced anything like that before so it was super concerning.

Thank you all for your feedback, will take it to Dealer with me for sure
 

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There is a huge common misconception. Opd does not switch regenerative breaking on and off what it does is change how the accelerator pedal works.

Whether OPD is on or off the first n amount of deceleration whether it is from pressing the break pedal or from letting up on opd will be regenerative.

So if you have not breaked at over (I think it approx 0.5G) then you have not deployed the break pads.

And I total agree we need a button to switch off the regenerative for 30-60-180 seconds is my suggestion.

In theory the car cycles regenerative breaking off every now and then ( read this in a software update I think) we do know vw does this.

For now we have to break aggressively when we can find a safe place to do it without cops watching.

Another note. Doing aggressive breaking to fix something in the break system only makes sense if the thing wrong is the rusty discs. It happened to me the noise and Grinde but I also got out and visualized the rust before doing the breaking :) and again after to see it was all gone :)

Good luck in break land.
 

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Discussion Starter · #10 ·
There is a huge common misconception. Opd does not switch regenerative breaking on and off what it does is change how the accelerator pedal works.

Whether OPD is on or off the first n amount of deceleration whether it is from pressing the break pedal or from letting up on opd will be regenerative.

So if you have not breaked at over (I think it approx 0.5G) then you have not deployed the break pads.

And I total agree we need a button to switch off the regenerative for 30-60-180 seconds is my suggestion.

In theory the car cycles regenerative breaking off every now and then ( read this in a software update I think) we do know vw does this.

For now we have to break aggressively when we can find a safe place to do it without cops watching.

Another note. Doing aggressive breaking to fix something in the break system only makes sense if the thing wrong is the rusty discs. It happened to me the noise and Grinde but I also got out and visualized the rust before doing the breaking :) and again after to see it was all gone :)

Good luck in break land.
Thanks for the explanation -- I'm just totally shocked at how loud the "thudding" sound is continually as the wheels turn -- it shouldn't be soo aggressive in our usual braking habits to help "clean"/"clear" the rusts and/or eliminate the pads from sticking to the rotors !

Mind blowing -- I'm sure the Service Dept may now make fun of me when I show up, and they're like "nothing wrong with your car" !
 

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There are other issues alas that can cause it.

If the plastic shoe that originally covered the brakes is not removed perfectly it can also result in the same sound.

I am sure there are other things as well.

Why I added the visualization and a reasoning as to what just happened to my car that would cause it. My breaks got crappy after I had the ceramic hydrophobic glass treatment done and they washed the car. Amazing how fast the discs get rusty.

It is hard not to react to bad break sounds. Back In the day ( as in the modern day for non Evs ) grinds break sounds = breaks probably heading to fail. So I doubt they will laugh at you. They may or may not even know about the rust issue.

I hope all the Volvo service departments are as good as my local one.
 

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I posted earlier about a grinding sound from front left wheel on my two week old P8 which another poster thought could be from rust on the brakes. My P8 is now at the dealer’s for this. Their initial view pending some more disassembly is that there was an improperly seated seal during manufacture where the axle connects to the inverter. I am very worried that this may have damaged some important components and I may face further problems after this repair. I would appreciate your thoughts on this. Also whether I should demand a new vehicle.
 

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As to the damage bristle that sounds stressful. Good news is the car is under warrantee. But still I would be upset as well if it happened to Margo (our p8)

Please let us know what happens and hopefully it is nothing bad. Fingers crossed.
 

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As to the damage bristle that sounds stressful. Good news is the car is under warrantee. But still I would be upset as well if it happened to Margo (our p8)

Please let us know what happens and hopefully it is nothing bad. Fingers crossed.
Thanks. I'm waiting on more news from the dealer.
 

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Discussion Starter · #18 ·
Thanks. I'm waiting on more news from the dealer.
I’m showing this post to my sales guy RIGHT NOW as in don’t swipe it under the rug. There are issues here so dont paint a broad brush stroke to conclude “ok” - it’s NOT ok for a brand new car
 

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I’m showing this post to my sales guy RIGHT NOW as in don’t swipe it under the rug. There are issues here so dont paint a broad brush stroke to conclude “ok” - it’s NOT ok for a brand new car
Hey MMK -- I'm wondering if you have the same issue as mine. This started with a bit of grinding when using OPD and releasing the accelerator. It steadily got worse until it was doing it when not in OPD and using the brake pedal. Though mostly at low to moderate speeds and not during highway driving. I've just gotten a text from my dealer's service department that they are ordering a new axle for my P8. I'm trying to get him by phone to discuss further.
 

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According to the owner's manual, if you press and hold the 'P' (Park) button while moving the P8 will do emergency braking using the foot brakes (read: friction brakes).

I've not tried this, but it suggests you could find a safe stretch of road, accelerate to a reasonable speed, then 'hit the brakes', thereby excersizing the friction brakes and scraping them clean.
 
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