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Discussion Starter · #1 ·
So I've had this issue that's turned up about 2 weeks ago where I get a thumping noise as the car is driving. As I speed up it becomes faster.


I thought it might be the tires/wheels but I just switched over to the winter rim/tire set and still the same issue. It's definitely rotational-related by what I can tell.


I checked the front axle-nuts and they were on tight.


The dealer serviced my brakes a few months back and did say that the rear rotors needed replacing and although they are rusty and due I held off 'til later. I'm starting to wonder if maybe they're warped and every time the high spot crosses the brake pad I get the noise.


I searched all over but couldn't find anyone with the same issue before me.


Any ideas??

Thanks
 

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A tire issue was my first suspicion, but since you ruled that out by installing the winter wheels, then your known brake issue is probably the most likely suspect. Does the noise change when you apply the friction brakes? By the way, braking when in Neutral will bypass the regen brakes and give you all friction brakes. So that will help you test them. It is also a good idea to brake that way occasionally to clear the rust since driving on salted roads can cause a lot of that.
 

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Discussion Starter · #3 · (Edited)
Does the noise change when you apply the friction brakes? By the way, braking when in Neutral will bypass the regen brakes and give you all friction brakes. So that will help you test them.
Thank you Barry for the suggestions!!

It does indeed go away when I brake and when I coasted in neutral and applied the brakes I got a definite pulsation indicating a likely warped rotor. It's funny how you don't notice the pulsation when braking in Low but it's very pronounced when the strong regen is taken out of the equation.


Looks like a dealer visit is forthcoming ...
 

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Thank you Barry for the suggestions!!

It does indeed go away when I brake and when I coasted in neutral and applied the brakes I got a definite pulsation indicating a likely warped rotor. It's funny how you don't notice the pulsation when braking in Low but it's very pronounced when the strong regen is taken out of the equation.


Looks like a dealer visit in forthcoming ...
Most likely you didn't feel the pulsation because the friction brakes weren't engaged.
 

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This would be an easy fix. Glad to see you have a direction to go. I hadn't given much thought to braking the vehicle with it in neutral as a test, and as a way to shake some potential dust, rust or dirt off the pads and rotors.
 

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Mine was acting like that and I drove at around 40 MPH and intermittently applied the park brake to shine up the corroded looking rear rotors. Everything is smooth now.
 

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Discussion Starter · #7 ·
Mine was acting like that and I drove at around 40 MPH and intermittently applied the park brake to shine up the corroded looking rear rotors. Everything is smooth now.
Hmmm, if the rotors & pads weren't already 4.5 yrs old I'd consider that ... thanks for the tip. Assume you can just pull up and then back down on the little brake lever thingy on the dash?
 

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Hmmm, if the rotors & pads weren't already 4.5 yrs old I'd consider that ... thanks for the tip. Assume you can just pull up and then back down on the little brake lever thingy on the dash?
The age doesn't matter, just the thickness of the pads. Mine still look new at 115 K miles.
You assume correctly
 

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Mine was acting like that and I drove at around 40 MPH and intermittently applied the park brake to shine up the corroded looking rear rotors. Everything is smooth now.
I've done this with a manual parking brake, pulling up gradually enough to feel friction, then releasing...on...off...on...off...

Do all Volts have the electric parking brake? if so, I'd be concerned that the "full on" effect could lock the wheels, creating a dangerous situation...

But...I agree that the OP should try something like this prior to replacing the rotors. Uneven corrosion could be causing the unusual vibration.
 

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There is no reason to use the parking brake for this purpose, and may be less safe to do so. Above 5 mph, activating the parking brake actually activates brakes at all 4 wheels through the ABS system. It does not isolate the rear brakes like in a typical car. Only below 5 mph will it pull the cables to the rear wheel parking brake. So just use the brake pedal in neutral for this.
 

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There is no reason to use the parking brake for this purpose, and may be less safe to do so. Above 5 mph, activating the parking brake actually activates brakes at all 4 wheels through the ABS system. It does not isolate the rear brakes like in a typical car. Only below 5 mph will it pull the cables to the rear wheel parking brake. So just use the brake pedal in neutral for this.
I agree with this clarification.

Don't know the bias of the ELR braking. For more than a decade, VAG products have found a rear bias safer than front, so rear wheels of VAG products typically show much more brake wear/dust, due to them working so hard.

Anyone know if the ELR is similar? ...simple curiosity...
 

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Discussion Starter · #12 ·
Yeah, my gut instinct tells me to just bake in neutral every now and then as a better option.
 

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I've never heard of anyone needing to replace their brakes on the volt due to wear. It's rust and oxidation from NOT being used that cause it problems.

As far as the ELR, on mine pulling the parking brake makes my car want to fishtail on my dirt road. Not advisable.

I just replaced my OEM tires on my ELR and also had the thumping. The rear tires had some very slight flat spots from hard braking. I'm betting the bias is enough that the fronts do not lock, but the rears will much much sooner in a hard braking event.
 

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Discussion Starter · #14 ·
So just got back from the dealer and figured I'd finalize my post.

It was indeed the rear brakes. I got new rotors and pads and got a brake fluid flush while I was at it ... all good now.

I'll be making a mental note to brake the every now and then in neutral assuming the rear brakes are used more than they otherwise would in Low. Maybe normal Drive will be the same as neutral, not sure ... should be in getting the rear brakes involved more than Low.
 

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Thanks for the update. I should be doing to same as my rotors own the rear, especially the one on the drivers side is horrific. It's gouged and pitted like it's been unused for many years. Pads are fine, the rotors are shot.
 

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Maybe normal Drive will be the same as neutral, not sure ... should be in getting the rear brakes involved more than Low.
No, driving in D will not get the friction brakes involved more than driving in L. When you press the brake pedal in D, the car engages regenerative braking as much as possible before blending in any friction braking. You have to brake in N if you specifically want to engage friction braking and bypass regenerative braking.

A good time to do that is any time you are nearing the place where you will get your next charge and you still have excess charge in the battery. Also exiting a freeway often involves a significant braking event, so that is a good time.
 

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Discussion Starter · #17 ·
Thanks Barry!
 
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