ZS MK UK Replacement rear discs and pads

[decrep]

It's quite likely all you need to do is use the brake pads on them for a change, and wear the surface rust off. Too much regen, mixed with water can quickly lead to a rusty looking disk.
Seems MG UK are aware of this, and try and get you to fork out unnecessarily.
There's no regen in neutral, reverse or at 100% charge. find a quiet hill and just brake gently until the squealing stops.

 

[Lovemyev]

This condition is the negative side of utilising the Regen facility on all EV’s.
Braking using the footbrake is a 80 - 20 ish condition, about 80% of the braking is conducted by the front brakes and the remaining 20% is done by the rear brakes.
Therefore the rear brakes never really display the same level of use / wear that the front pads and discs do.
Add strong Regen into the mix on an EV and the rear brake have almost nothing to do at all.
This lack of use allows rust to form that then develops into deep pitting into the face of the disc’s.
It hasn’t taken long for both dealers and MOT testers to lock onto this premature corrosion problem and it is offered them an opportunity to take some much needed lost revenue from EV owners.
Service time for EV’s have become more of a “Health Check” than replacing engine oil / filters etc etc.
They are NEVER going to let this work opportunity pass them by tbh.
There no real solution to preventing this condition or it repeating itself again unfortunately.
Turning the Regen to its lowest setting will help prevent the decline speed of the rust forming, but most of us like this feature so it’s a battle between head / heart and ultimately your wallet .
I tried once a week, to remember to lower the Regen to its lower setting to help with the rust, but it’s not a cure .
On the ZS EV the car defaults to normal Regen and that became my “Go To” setting.
Our S5 on the other hand, it defaults to LOW Regen on start up, this may help a little in the battle of surface rust forming .
Our ZS EV had covered about 28,000 miles in the three and a half years of ownership.
It passed its first ( independent ) MOT with no problems at all and nothing was reported by dealership on any of the 3 annual service inspections it had.
There was “pitting” clearly evident on the surface face of the discs on the rears, so I expected it would get picked up at some time in the near future.
I think owners would complain less, if the price to replace this items at the dealership, was not so expensive !.
The is nothing really special about this discs or pads, very basic standard stuff.
Now third party replacement parts are available at a highly discounted price point.

 

[Andy L]

Trying to find "third party" disks seems to be a minefield ,even though I have the part numbers from MG and put these in ebay I get a match and then further into the listings it states not compatible with epb versions! They then go on to describe them as 280mm dia but Grok is adamant they are 260mm and Grok has matched the dimensions to an mg database. Going to have to take off a wheel and check for myself I think unless anyone on here has the actual size?

Oh and as for using regen 1 and using the brakes more I have done that quite often and after 43k miles the pads show 40% wear and corrosion has still occurred. In comparison the fronts are still showing 10mm pad thickness and minimal wear on the discs.

 

[Lovemyev]

Oh and as for using regen 1 and using the brakes more I have done that quite often and after 43k miles the pads show 40% wear and corrosion has still occurred

Yeah - I did say this above, more use of the footbrake ( less regen) helps slow the progress of deterioration, but it will not prevent the inevitable unfortunately.
The pads would have very little wear under normal conditions, but wear is accelerated because the contact brake surface of the discs to pad material is SO rough ( caused by the pitting and corrosion) that it cuts the material like a cheese grater.
I did upload the info on part number compatibility on another thread.
Removing the rear wheel and measuring will be the best option.
If my memory serves me correctly, the Gen1 and Gen2 models use the same brake disc.
The part number at MG will change IF there is a price change ( I have seen this with other items ).
Some discs are listed as 5 hole and others at 10 hole.
Pretty sure the ZS EV are 5 hole versions tbh.
Here is an example of some of the Borg & Beck discs available.
A lot less expensive than the dealer parts.

 

[Andy L]

Yeah - I did say this above, more use of the footbrake ( less regen) helps slow the progress of deterioration, but it will not prevent the inevitable unfortunately.
The pads would have very little wear under normal conditions, but wear is accelerated because the contact brake surface of the discs to pad material is SO rough ( caused by the pitting and corrosion) that it cuts the material like a cheese grater.
I did upload the info on part number compatibility on another thread.
Removing the rear wheel and measuring will be the best option.
If my memory serves me correctly, the Gen1 and Gen2 models use the same brake disc.
The part number at MG will change IF there is a price change ( I have seen this with other items ).
Some discs are listed as 5 hole and others at 10 hole.
Pretty sure the ZS EV are 5 hole versions tbh.
Here is an example of some of the Borg & Beck discs available.
A lot less expensive than the dealer parts.


View attachment 40929

They can wait until the summer now ,thanks for the info though.

 

[decrep]

There no real solution to preventing this condition or it repeating itself again unfortunately.
Turning the Regen to its lowest setting will help prevent the decline speed of the rust forming, but most of us

I disagree here, there's a misconception, that the "regen level" set affects the amount of friction brake use.
This seems logical, but it's incorrect.
Regen level setting only affects how the regen is engaged, either from the accelerator pedal or the brake pedal. Level one makes the accelerator less sensitive. The brake pedal then engages regen.
You can check this by looking at the power meter in level 1 while braking, The power meter will go to about -27 before the friction brakes kick in as well.

The only time regen isn't operating is at full charge, in reverse or in neutral.
If you want to keep your discs clean, you need to do some braking in the above modes. a quiet hill comes in handy.

 

[Lovemyev]

Of coarse you are fully entitled to your opinion here, and I fully respect that.
Surely, anything that is used to decrease the actual road speed of the car, other than applying the friction brakes, has therefore reduced the use of the normal friction brake use on the car ?..
This naturally means that less contact of the friction pad material against the brake disc surface, has to be the result ?.
If you were driving a ICE vehicle and not an EV and you observe an upcoming situation ahead, that required you to maintain your current road speed with no increases.
This could be a downhill monitored speed limit area etc.
The down hill decline section is very steep, so to maintain your speed, you firstly remove your foot from the accelerator pedal.
No foot brake is required at this point, but as the decline increases, the car continues to gain more momentum,
You could reduce your speed by down shifting the gearbox of course, which utilises engine braking to then slow down the cars progress, avoiding the use of the footbrake.
But now as the speed continues to increase, you have no other option other than to use the friction footbrake to correct the ever increasing road speed.
Similar situation in an EV now, but as you start to lift your foot away from the “Go” pedal, even in low Regen mode, the cars actual speed is very easily maintained.
As the decline increases even more, the Regen alone is now holding back the car from Increasing its actual speed any further.
This is being achieved purely by retardation by the motor.
As a result of controlled road speed, no friction braking has become necessary and the braking system has had no work to perform at this point.
Only when the Regen has been maxed out and the speed is still increasing, do you now have to consider using the friction brakes.
This is much much later than it would be in an ICE powered car.
This is a repetitive daily situation on
all EV’s and therefore necessitates less use of the friction brakes.
Lack of use means that rust is allowed to build up much quicker on a EV than it would on the ICE counter part.
Rust then progress to deep pitting, dislodged scale embeds itself into the brake pad fiction material and this causes the deep scoring of the brake disc faces, when the brakes are applied.
Replacing the discs and pads will cure the problem instantly, but be assured in the knowledge, that this condition is extremely likely to raise its ugly head again at some point in the future.
It’s an unfortunate and indicative and well documented problem on all EV’s.
As a long retired tech myself, I have forgotten just how many discs and pads I have replaced in my time.
The stark difference in EV’s is the premature necessary replacement of these discs, not down to the high milage covered etc,
In fact it’s the complete opposite really, exasperated by the braking power of Regen and therefore general lack of use !.

 

[decrep]

No argument at all,
All I'm trying to point out, is that there is something you can do about it.
Every now and then use the friction brakes to clear the oxidization.

The only thing I'm not clear on is if the ZS is the same as the MG4.

With our MG4 in level 1, the brake pedal uses as much regen as the accelerator in level 3.

You can test this by watching the power meter in level 1 when you activate the brake pedal.

I strongly suspect, you'll see the power meter display negative numbers, indicating the amount of regen.
My point here is, that selecting level 1 doesn't help clear the rust.

The brake pedal has to be used when there is no regen.
This can be done on a hill in reverse or in neutral, or after a full charge, between 95 & 100%.

Doing this exercise every so often will keep the disks clean.
A bit of a chore remembering to do it, but that's the price of an EV, either pay for disk and pad replacement regularly, or keep the disks clean.
Your choice.
I'm just trying to correct the misinformation, that there's nothing you can do about it.