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Rear Brake Disc Corrosion

2.3K views 9 replies 6 participants last post by  The Aviator  
#1 ·
As my car was nearing 2 years old I booked it into my local Mazda dealership for service. The car had only done 10,700 miles. I have to admit booking it in with some reluctance as my dealings with this dealership has not been trouble-free, however I was given 2 years of free servicing from them at no extra charge when I bought the car, so in the car went.

So the service went OK, but not without the same communication issues found in my past dealings - the service department being almost unreachible by phone - ringing out before Reception taking the call back and having to take a note to either pass info on or ask for a call-back. Late on in the afternoon I got a call back to tell me the car was ready to collect. When I got there I was told the car was ready to drive away, but they found something during the EVHC (vehicle health check) was associated with the rear brakes and the work was advisory, however the report was not yet available but they would send it to me. As I was in a hurry I took the keys and went without further questions. Later on the health check came through and it was reported that the rear discs were corroded and replacement was advised, along with the brake pads (usual procedure). They gave costs for the replacements either with genuine Mazda parts or parts sourced elsewhere. Initially my feelings were of suprise as the car was less than 2 years old and had covered so few miles (though the car had never been left for any time without being driven). Suprise was replaced with irritation when the situation sank in but I took a couple of days to think things over before acting. It also gave me time to check out the rear discs myself and there does seem to be some corrosion there. Whether it's enough to require replacement is another question (I'm no mechanic). My reasoning behind my irritation was that though I accept that brake discs do wear out and are looked upon as consumable, however I would expect this would be over a far longer time scale and/or far higher mileage. Fair wear and tear if you like. For a car with such few miles under it's hood and being so young I fail to see how you could classify rear brake disk replacement as being due to "fair wear and tear". Brake discs should last far longer than this IMO. My view is the root cause is sub standard parts.

So today I went back down to the dealer (from my experience, phoning them is just too much hassle) and was told brake discs and pads do not come under warranty and they have never replaced any under warranty. I explained the above reasoning and my view that it should be a warranty replacement issue. They effectively brushed me off and told me to deal directly with Mazda. I did not leave before getting a phone number for Mazda. When I got home I called Mazda UK and was not told what the dealer told me, the person taking the call agreed that this did seem far too soon for brake discs to need replacement, however the person dealing with me was no expert and she would raise a case with the appropriate department and someone would get back to me within a week. So I guess I will wait and see what their response is.

My car drives well, and the parking brake seems to release and engage without issue. Hill hold also seems to work smoothly and general braking appears good and progressive.

I've seen the thread below on this forum but it was never stated if the work was completed under warranty or if the member paid for the work to be done, the mileage is almost double what my car has done as well.


I would have thought even 20K miles is a bit early for a rear disk to need replacing but I don't know if that was down to disc wear or corrosion.

I'll keep everyone updated on the progress but would appreciate any feedback on whether you consider warranty replacement in my circumstances reasonable or not, or if members have similar storys to tell on the rear brakes.
 
#10 ·
I had a similar mention as well. It particularly applies to vehicle, which are often driven underloaded, i.e. only the driver or the driver with just a front passenger and hardly any load in the boot. In these cases, the front brakes are sufficient to do all required work for stopping the vehicle and the rear ones are underused. This is, of course, applicable to normal drivers, not "boy races".
I had a similar mention as well. It particularly applies to vehicle, which are often driven underloaded, i.e. only the driver or the driver with just a front passenger and hardly any load in the boot. In these cases, the front brakes are sufficient to do all required work for stopping the vehicle and the rear ones are underused. This is, of course, applicable to normal drivers, not "boy races".
Agree, regarding 'Normal' drivers. I just don't
drive on my brakes.
Interesting, this must be a common problem as there are about five CX-30 owners near where I live (like me retired, low mileage) and all have corrosion on the rear disks similar to mine (amazing what you see and learn when out walking the dog).
Booked in for 3rd service early October so see what the dealer says and whether they try to get more money out of me. I estimate, to change the rear disks and pads myself, it would cost around £150. Did the wife's fronts on her Mazda 2 last February and that cost £ 130 for aftermarket OEM standard parts from the local motor factors. On hols soon so a job for a fine day next month i think.
 
#7 · (Edited)
Thanks all for your replies. Mazda UK got back to me and basically told me they were washing their hands of it. Not covered by warranty and implied it was fair wear and tear.

Now I have had 3 VW Golfs before the Mazda and 2 Seats before that and NEVER had any issues with brake corrosion within the first 2 years. Similar annual mileage as well. Where I now and previously stayed is not close to the sea and although I don't cover a huge amount of annual miles I drive my car regularly and quite enthusiastically where the road conditions permit.

I am going to take the car for a good run down a few local twisty roads I know and give the brakes a good try out (gradually upping the braking to see what happens). So far I have found that braking hard in a straight line is stable and progressive and they seem as strong as they've ever been. Perhaps the corrosion will clear up, we will see.

I have to say I am somewhat disappointed by Mazda's response and will take it into consideration when looking for my next car, probably next year.
 
#8 ·
To be honest most manufacturers would have the same attitude. Just experienced an issue very similar on my CX-30 rear disks / rotors at the 1st MOT (Three years, 10,700 miles). The MOT inspector issued an advisory for pitting to the rear disks. He mentioned it was due to the low mileage. Having looked on line seems to be a common problem.
 
#6 ·
I have an older Subaru as well as as a new CX-30. I have noticed with the Subaru that when i am out of town traveling and the Subaru remains unused for a week or two, the disc brakes make a slight grinding noise until i drive the car for a while. As OldFart below mentions I attribute this to a light coat of rust that disappears quickly with use.
 
#5 ·
I had a similar MOT advice after 3 years, but no requirements to replace disks or pads at the rear. If you leave in the coastal UK areas the corrosion is bound to happen faster than inland. What contributes to it is a low mileage and amount of time you drive with not fully loaded car. If it is just you and a front seat passenger with no load in the boot, then the front brakes take the load under braking and the surface rust remains on the rear brakes. My car is parked outside all year round and this contributes to the rust issue as well.
 
#4 ·
I have the same thing on my Mazda on the rears. There are rings where the pad no long touches the rotor surface.

I ordered new rotors and Ebc green pads and corksports ss brake lines.

I then painted all the rotors with high temp paint and will have them installed once the pads come in stock. This should avoid this rusting issue from Happening again.

I will also say the brakes are pretty weak on the highway when the car is loaded with people. This is why opted to upgrade the pads and lines to help.
 
#3 ·
Fairly deeply pitted and you can see that the shiny area where the brake pads bite has been reduced, more-so on the rear left side. I've been standing on the brakes a bit harder over the last couple of days and there isn't any improvement to my eyes.

I think there is a chance that Mazda will ask the dealer to send photos of the discs if they are considering warranty replacement, so if the dealer has accurately described the issue and that the discs do need to be replaced then hopefully the process will be smooth and speedy. If the dealer hasn't accurately described the condition of the brake discs, well i guess that's a different story...