Screeching when reversing - not using brakes

[MattyS]

I've started to get a really annoying screeching noise when reversing. I do not think it's brakes because when I apply the brakes it stops. There is no problem in how the car moves though. Any ideas?

 

[Jomarkh]

When you reverse do you have your foot slightly on the brakes?
My MG5 does it.
It is just surface rust and soon clears off.

 

[MattyS]

When you reverse do you have your foot slightly on the brakes?
My MG5 does it.
It is just surface rust and soon clears off.

No I do not. Hovering over the brakes but not on the pedal. Also, it's just in reverse not going forward.

 

[Alb]

Did you have a nervous passenger in the car with you at the time?

 

[Kithmo]

It's probably a stone trapped behind the dust shield.

 

[T1 Terry]

I've started to get a really annoying screeching noise when reversing. I do not think it's brakes because when I apply the brakes it stops. There no problem in how the car moves though. Any ideas?

When you apply the brakes, you apply some pressure between the pad and the disc and this stops the high frequency vibrate the edge of the pad picking up on the disc creates .... and the squeal stops. To prove if this is right or wrong, flush around the brake pads with the hose, then try it and see if it squeals ....

T1 Terry

 

[decrep]

I do not think it's brakes because when I apply the brakes it stops.

Interesting, are you saying, lightly applying brakes, so car is still reversing, stops the noise?

I think that means it is the brakes, but I'm not sure why.

 

[JohnV6]

Could be rusty discs. Try driving with KERS at 1 and braking hard.
It also could be the discs squealing which would require either anti squeal shims or anti squeal compound.

http://www.gomog.com/allmorgan/BrakeSqueal.html

 

[MattyS]

Thank you everyone. just so I'm absolutely clear here, it could still be a brake noise despite me not touching the brakes when it's happening?

 

[dsimpkins]

Yes, my daughter had this with her car recently. Turned out one of the brake pad retaining clips with rubbing the edge of the brake disc which caused a horrible squeal without touching the brakes. Only does it when it's really cold, and once the brakes warm up it stops.

I just removed the pads, adjusted the clips, and noise gone.

 

[Muffler]

99% of the time this caused by mild build-up of surface corrosion on the brake discs because application of physical braking rarely occurs in normal driving, over the car using regenerative braking from the motor to slow even when pressing the brake pedal firmly. Exceptions are when the battery is at full charge or under hard emergency braking. Both my 4 and 5 occasionally squeal when reversing on the drive - solution as others have noted, is to find a quiet stretch of road and do a few hard stops. In my instance, I live at the top of a long winding hill and regularly doing a few acceleration / hard braking cycles as I descend mostly keeps this at bay.

If above doesn’t work then checking the clips most likely will.

 

[T1 Terry]

99% of the time this caused by mild build-up of surface corrosion on the brake discs because application of physical braking rarely occurs in normal driving, over the car using regenerative braking from the motor to slow even when pressing the brake pedal firmly. Exceptions are when the battery is at full charge or under hard emergency braking. Both my 4 and 5 occasionally squeal when reversing on the drive - solution as others have noted, is to find a quiet stretch of road and do a few hard stops. In my instance, I live at the top of a long winding hill and regularly doing a few acceleration / hard braking cycles as I descend mostly keeps this at bay.

If above doesn’t work then checking the clips most likely will.

The Toyota Prius uses all regen braking, except for the last 16km/h, that could be why they don't suffer the problem, but more likely, the pads have a 45% chamfer each end and a cut out section half distance of the pad material end to end ..... brake squeal isn't a new problem, it's been a problem since disc brakes were first used .... they just do it going forward and backward when very light braking and this is the reason discs are skimmed to take that work hardened face off the surface and this helps to stop the severe temps created between pad and disc that forms the dust.

T1 Terry

 

[decrep]

Thank you everyone. just so I'm absolutely clear here, it could still be a brake noise despite me not touching the brakes when it's happening?

Yes absolutely, the fact the noise disappears when you touch the brake pedal, indicates it's the brakes.
Some body mentioned on an earlier thread, it could be down to the pad trailing edge.

the pad front edge is normally chamfered to prevent the disc pulling the pad into it, but the trailing edge often isn't. Chamfering the trailing edge will probably fix the problem.
But as others have said build up of corrosion on the disks is probably partly to blame.
It's well worth trying to clear the corrosion and see what happens.
As also mentioned, in normal use disk corrosion is very common with EVs, as the friction brakes hardly get used, it's all mainly regen that does the slowing.

AND NOTE, unlike what some others have said. The regen setting has little to no bearing on this. The regen setting only affects how the accelerator pedal works, the amount of actual regen remains the same.
So there are 3 ways to activate the friction brakes to clear the corrosion.
IN reverse, there's no regen.
at 100% charge there's no regen, but starts kicking in soon after, so you need to use the brakes a lot before it gets down to 95%
In neutral fairly obviously there's no regen, find a quiet hill and go down it on the brakes.

Apparently you can also activate accelerator and brake simultaneously, but I'm not game to try this, if you use too much pressure I'm worried it could damage something.

listen to the brake noise doing this, there should be a difference, (quieter), when corrosion is cleared