Automotive

Can rusty rotor pass safety test

  • Last Updated:
  • Aug 4th, 2021 2:57 am
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Feb 20, 2015
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My Mother has a relatively new car with almost no mileage on it (barely drives it and doesn't wash it). Her rotors got so rusty it was causing brake issues, she went to the dealer and they charged her to grind them down.

Cars want to be driven and if you are storing your vehicle, make sure it's sqeaky clean before doing it... road salt will rust them pretty easily.

It's usually not a problem, go take it on the expressway and after a few trips it'll all be worn off.
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Sep 22, 2009
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rugerty100 wrote: Driving an EV, I try and brake hard after rainfall and car wash to remove moisture from the brakes.ill my tires?
Why is having an EV relevant in this discussion?
Does your EV have rotors made of gold?
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BDSL wrote: Why is having an EV relevant in this discussion?
Does your EV have rotors made of gold?
How would you know they weren't driving an EV if they didn't tell you?
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Mar 22, 2004
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rugerty100 wrote:
How's the wear on the tires?

Driving an EV, I try and brake hard after rainfall and car wash to remove moisture from the brakes. Otherwise the brakes never get engaged in normal driving and might rust/seize.

At the same time, I don't want to kill my tires. Would routinely hard braking once or twice a week kill my tires?
BDSL wrote:
Why is having an EV relevant in this discussion?
Does your EV have rotors made of gold?
Because EVs have regenerative braking they don't use friction braking as much as a traditional vehicle. The brakes usually end up lasting a lot longer because regenerative braking but can suffer from getting accumulated rust that could potentially cause it to seize.

Anyone who has an EV, to make sure you are using strictly friction brakes, do your hard braking in full neutral to make sure you get the rust off the rotors. If you're doing it in drive, you're not doing it right.
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Sep 4, 2006
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rugerty100 wrote: How's the wear on the tires?

Driving an EV, I try and brake hard after rainfall and car wash to remove moisture from the brakes. Otherwise the brakes never get engaged in normal driving and might rust/seize.

At the same time, I don't want to kill my tires. Would routinely hard braking once or twice a week kill my tires?
Won't hurt the tires. I drive an EV as well. Pop it in neutral before braking, no regen that way!
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jayoldschool wrote: Won't hurt the tires. I drive an EV as well. Pop it in neutral before braking, no regen that way!
Unfortunately the e-Golf still regens in neutral. It doesn't regen when braking in reverse, but I don't feel too comfortable reversing at speed on a public road!

I purchased this car secondhand and had to get the rotors replaced for safety cert even though it was only 3 years old. The brakes rusted and seized, and I don't want that to happen again.
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Apr 5, 2011
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I recently had a safety assessment done on a 2 year old car.

It failed because the inside of rotors was rusting.

If the mechanic is by the book then they will look at the inside of rotor and see how much rust there is.

I was told that this rust happens due to the car sitting for a long time and won't come off with heavy breaking. It is hard to know how honest the mechanic was. But I ended up replacing the rotors.

Your pictures only show the outside part of the rotor. It is hard to know how much rust is present on the inside.
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radeonboy wrote: Because EVs have regenerative braking they don't use friction braking as much as a traditional vehicle. The brakes usually end up lasting a lot longer because regenerative braking but can suffer from getting accumulated rust that could potentially cause it to seize.

Anyone who has an EV, to make sure you are using strictly friction brakes, do your hard braking in full neutral to make sure you get the rust off the rotors. If you're doing it in drive, you're not doing it right.
Regenerative braking doesn't mean it doesn't use traditional friction (pads and rotors) at all. Brake pads and rotors still get consumed...slower. Look at Prius...
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BDSL wrote: Regenerative braking doesn't mean it doesn't use traditional friction (pads and rotors) at all. Brake pads and rotors still get consumed...slower. Look at Prius...
Varies significantly based on the model. Prius has a nice balance.

For my e-Golf, I can touch the rotors after a typical drive and it'll be cold.
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kr0zet wrote: Yes. The rear wheels are responsible for about 25% of your braking, the other 75% is the fronts. That's why the fronts got the rust off more so than the rear. Rusty rotors are not an issue for a safety. They will check the brake performance and the brake pads.
Why are people upvoting this? It’s 100% wrong information.
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BDSL wrote: Regenerative braking doesn't mean it doesn't use traditional friction (pads and rotors) at all. Brake pads and rotors still get consumed...slower. Look at Prius...
Dude I didn't even say "at all". I suggest you go back and re-read what I wrote without skimming...reading things fully without skimming is very important.

"don't use friction braking as much as a traditional vehicle."
Last edited by radeonboy on Aug 3rd, 2021 9:03 pm, edited 1 time in total.
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xjesterxx wrote: Why are people upvoting this? It’s 100% wrong information.
What part is incorrect?

Front vs Rear Brakes
FRONT BRAKE DESIGN — HOT STUFF
Back to physics for a moment, to further understand why the front brakes need to handle so much more heat. When you’re moving forward and you hit the brakes, the center of gravity of the vehicle effectively shifts forward, putting more weight and more momentum on the front tires. The front tires therefore gain more traction, and they can take more braking force to stop the car. Because the front brakes generate up to 75 percent of the vehicle’s stopping force, they generate much more heat, over 500°F in heavy braking.

Therefore heavy braking by the OP removed more of the surface rust from the front rotors than the rear...

As for the second part of my statement you think that a mechanic is going to look at a rotor and say, "well thats rusty, FAIL." or perhaps they are going to measure the thickness of the pads to see if they pass then measure the thickness of the rotor to see if it passes?

Will My Car Pass A Safety Inspection Ontario
Based on Ontario guidelines, if your brake-shoe lining is 1.6 millimetres or less, you’ll have to get them replaced so your car can pass a safety inspection.

At 1.6 mm, we recommend talking to us about your brake replacement options. It’s better to get them replaced while you’re here than find out in 6 weeks you need to make another appointment.
Also:
MTO Inspection Guidelines - PDF
Page 28
Note:
Surface rust and corrosion is normal on
metal lines and fittings, and is not cause
for rejection.
BUT
- heavy rust, corrosion or scaling is
present on any metal line or fitting that
reduces or increases the thickness or
compromises the structural integrity of
the material
The OP's pictures DO NOT show this at all...
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cba123 wrote: I just had the brakes on my FIL car replaced. Would these have passed or failed getting a safety certificate? The front side looked ok, but the back side had grooves as shown in the photos.
Looks like a fail to me. Grooves look deep.
Replacement was the right move.

But according to some rfd posters here, it would be a pass if you didn't have a picture of the bad side. Or according to some, brake hard until it smoothens out.
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cba123 wrote: I just had the brakes on my FIL car replaced. Would these have passed or failed getting a safety certificate? The front side looked ok, but the back side had grooves as shown in the photos.
Those are done.
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If your car has the e-brake controlling the rears then partially engage it while driving at low speed for a couple blocks. Check how much effect that has.
Make sure you are only partially engaging it and work your way up from one click. If you don't do this very carefully you could cause lots of damage very quickly.
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Quentin5 wrote: If your car has the e-brake controlling the rears then partially engage it while driving at low speed for a few blocks. Check how much effect that has.
Make sure you are only partially engaging it and work your way up from one click. If you don't do this very carefully you could cause lots of damage very quickly.
Depending on the vehicle. For some vehicles, the e-brake does not use the pads. It uses shoes inside the rotor.
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kr0zet wrote: What part is incorrect?

Front vs Rear Brakes



Therefore heavy braking by the OP removed more of the surface rust from the front rotors than the rear...

As for the second part of my statement you think that a mechanic is going to look at a rotor and say, "well thats rusty, FAIL." or perhaps they are going to measure the thickness of the pads to see if they pass then measure the thickness of the rotor to see if it passes?

Will My Car Pass A Safety Inspection Ontario


Also:
MTO Inspection Guidelines - PDF
Page 28


BUT


The OP's pictures DO NOT show this at all...
OP’s pictures aside you stated that rust is not a concern for safety, which is simply incorrect.

Only 25% of the surface of the rotor can be corroded, any more does not pass safety.

Excessive corrosion can also interfere with your ABS system in an emergency braking situation.

To say that rust is irrelevant for safety is a false statement.
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Two posters have mentioned the requirement for no more than 25% of the radial width of the rotor can be corroded for a pass in Ontario. I've had to swap in new rotors to get a pass in the past where the outboard sides of the rotors looked great but the inboard sides were a fail and it was for this reason. If there is a side of the rotor that is susceptible to rust jacking, in my experience it's the inboard one - especially common among cars that are not driven much.

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