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-   -   When do brake discs require replacement? (https://www.team-bhp.com/forum/technical-stuff/233862-when-do-brake-discs-require-replacement-4.html)

On most cars the front brakes (and thus pads) are larger than the ones at the rear. Most of your braking/stopping force is generated by the front brakes. Usually the front pads and discs, even though larger than the ones at the rear, do wear out earlier, because they provide most of the stopping power. Nothing to do with position towards the ABS. ABS has no influence on brake wear. It is only activated during very hard braking and that should be a rare occurrence.

On cars which have a front / rear seperated brake line circuits rather than diagnolly operated circuits you are also likely to find a brake pressure balancer device. It ensure that the hydraulic pressure to the rear brakes is less than going to the front brake. This is to prevent the rear wheels locking up under heavy braking. But if anything that also puts more demand on the front brakes again and thus more wear than on the rear.

Jeroen

I've had exact same experience as OP with my 2019 Honda Amaze 1.2 iVTEC. The car has barely run 25,000km and the Service Engineer at the Authorized Service Center near my locality told me I needed to replace both front brake pads as well as brake disks and charged me around Rs. 9000 for replacing a pair of pads and a pair of disks. When I asked him why the disks were getting worn out so fast, he said it depends on the driving style and the disks had grooves on them so they had to be replaced. He also added that they could have been shimmed if the car was a City and added that the Amaze comes with pretty thin discs from the factory.

To be fair, I did complain about brakes not feeling up to the mark when I handed over the car for its scheduled 30000km / 3rd-year service. But the explanations given by the Service Engineer do not seem satisfactory to me.

How would a driving style change cause grooves on the brake disk? After all, the driver is only ever interacting with the brake pedal. Ideally, the disk should have worn evenly, if everything was working as designed, right?

I am not an expert on this subject matter, I shall attach a few images of the replaced pads and disks. I would like some advice from the community on this.

Basis the pictures the Brake Pads needed to be changed. They seem to be wearing rather thin.
The rotors appear to have become grooved. This is because they seem to have borne the brunt of hard braking and/ or plenty of stop start city driving. Also in our operating conditions oftentimes little stones and debris gets trapped in there and creates these grooves. If the rotors indeed are also worn down it is worth changing. Skimming the rotors is an option yes, but it is only a temporary one. And yes, the condition and wear of your brakes definitely has a bearing on your driving style too.

Hello Folks, my Ciaz has been taken to the service centre this morning. Says the disks need to be replaced as it is rusted. I can see there is rust, and I always have a noise when I move the vehicle after a while, but it goes away after a couple of KMs. I had raised this complaint earlier, and the SAs have said this is normal. This time they say it needs to be replaced. I have attached some pics. Please can you suggest if the disks need to be replaced? The vehicle has done only about 25K KMs, and it is a little over 4 years old. Braking works absolutely fine, and I am a sedate driver.

That rust is normal. All brake discs have rust in that area since that is exposed to elements and not scrubbed by the pads.

Unless you have brake judder when braking at high speeds or if the disc has reduced below the minimum thickness, which is unlikely since the car has run 25k only, you will need to get the discs skimmed or replaced.

For noise, get the brake pads surface scrubbed with some emery paper and the brake discs scrubbed with some soap water and scotch brite and the noise will most likely go away.

Bottom line- Do not replace the discs. From the pics, I can see that the brake pads still have some life left and can run for another 5k to 7k kms. Just get them scrubbed.

Brake disc/ rotor is made of cast iron. So, it is very natural that it will rust. Also, if you park your car with wet discs (brake pad contact area), it will also show rust build up in a matter of 2 days. That rust get scrubbed in a short time when you drive the car again and apply the brakes, however, the area which doesn't come in contact with the brake pads will rust.

Your car has done only 25K and I don't see why either the disc or the pads would need a change this soon.

Regards,
Saket

Sagarpadaki is spot on!

Just one additional thought though. The only way to tell whether disks need replacing based on wear is to measure the actual thickness of the disks using a suitable caliber and comparing the actual thickness to the manufacturer recommended minimum thickness. The latter is mentioned in the workshop manual. Now here is the thing, you will be very surprised to the minimum thickness. It is much more than most people are likely to believe. So whereas these disks look fine, they might actually be on or near the minimum. Most of the Internet will tell you manufacturers keep the minimum value high to sell more parts.

I can’t comment on that, but it is fair to assume on something as critical manufacturer will build in a good safety margin, of course.

There is a solid technical reason behind it as well. A Disk ability to absorb heat is a function of the total amount/volume of material. So on a simple solid disk it’s surface times it’s thickness. Remember surface area is pi time radius squared! So for each mm wear you loose a significant amount of material!

The main problem that can occur when the disk becomes too thin is the brakes start fading. Which typically happens under heavy, prolonged braking.

When replacing disks always replace pads too!

I recently checked the four disks on my Mercedes and the front disks on my wife’s Ford Fiesta. They looked absolutely fine. But when I checked the actual thickness against the minimum mentioned in the workshop manuals, it means I will be replacing all of them.

Morale of all of this: nothing to worry about immediately, but don’t get fooled by looking at disks only. You ought to measure them and check against manufacturer minimum values.

Jeroen

Thanks Jeroen, makes absolute sense. I shall hunt around for the workshop manual and get this checked.

Thank you for such quick responses guys! :thumbs up

The SA has been pushing for a lot of other things as well. Like signing up for extended warranty, when I still have about 9 months left of my original extended warranty (no pun intended rl: ). battery warning, when there was none and so on! I guess it is just their normal routine to rake in the moolah. But was quite concerned about the disk brakes. Thank you again folks!

Hello Friends,

Need your expert advise regarding front Discs of my 2016 Verna Fluidic 4S petrol 1.6 VTVT automatic which has only done 5200 kms in these 8 years.
As you can see due to frequent non usage front discs have developed a lot of rust and groove marks on the non rusted area.
I am planning to go for service soon so should i get them replaced or it possible to skim / Lathe them with out structurally compromising them ?
There is absolutely no problems with the brakes - no grinding no squealing and they work perfectly.

Thank you.

Get them skimmed at a lathe. The outer area of the disc is not in contact with the pad when braking. Hence that discolored groove. Braking would have reduced due to that.

Most likely, the pads will have uneven wear.

He says "discs"... so, is the problem on one side or both the front discs. If it is on both sides, is it possible that smaller size brake pads are fitted?

Both Sides. Discs and Pads are stock that came with the car.

Best way to confirm this issue is to check a couple of other cars at the workshop, to confirm whether it is a common issue for this model.

Why don't you post this query on the official review thread of Verna and wait for other owners to respond?

To me, from the pics, it looks like the area where contact is there has no grooves and the area where contact isn't there (the outer 1/3rd of the disc) also doesn't have grooves either - eliminating some physical object (like a small piece of rock) to be the reason for this. Highly likely that incorrect size pads are fitted to the caliper. Does this have rear disc brakes as well ? If yes, high chance that someone at factory/A.S.S fitted the rear pads instead of the front ones, into the front caliper. Is this present on one front wheel or both front wheels ?

Present on both the front wheels. Rear brakes are drum brakes.