Should I get new discs?

[smr84]

Hi,

I need new rear pads doing next week but now, having looked at my rear discs I am wondering if I should get them replaced at the same time.

As of January 7th this year both rear discs had 10.65mm (11mm is new and 9mm is minimum)

The discs look quite crumbly and crusty to me.

Is it a big job to replace the discs at the same time as the pads.. should I replace them even though they're 10.65mm, albeit corroded looking?

Here's a pic of one of the discs.

[GreenV8S]

Are the rusty areas actually swept by the pads?

[stevemcs]

Yes, get discs, I bet they will be much worse on the inside face.

[SlimJim16v]

I would change those, but I do it myself so not much extra cost.

[21TonyK]

Based on your figures the discs are just about 20% worn by now. I can't think of anything you replace on a car with 80% life left in/on it. The rusted area is cosmetic only and new discs will look the same in a few months and provide no benefit as rear brakes perform significantly less function than the front.

Personally I'd ask the garage to check them, tidy them up if you don't like rust, and then change them next time the pads are replaced if <10mm.

But then, I'm old enough to remember getting your discs skimmed instead of replacing them.

You could always pop a wheel off and get handly with a file and a bit of paint to tidy them up, but then, they are brakes.

[Gary C]

Nowt wrong with them

Dont replace them, especially with the sort of chocolate none OEM parts by Eurocar parts etc.

Many many more years left on them.

[Smint]

I'd check the rear face of those discs, if they're similar condition to the front face i'd leave them in place, you could always spin the discs whilst holding an old chisel in place to remove the rust then slap some metal paint on.

Before fitting new discs i paint the unswept outer parts including the outside edge, this helps delay rust build up though fair to say i might have a teeny bit of a phobia about rusty brake discs and calipers.

[smr84]

Thanks for the replies. Its 50/50 so far then!

Would the discs, rusty as they are, damage new pads?

As they were 10.65mm 2 months ago, how much life should I expect out of them from now until they do need replacing?

I realise oxidation will lead to rust and am not bothered in the sense of aesthetics as it will happen to new discs not long after new but thought with that rusty lip it might damage new pads?

[Smint]

smr84 said:

Thanks for the replies. Its 50/50 so far then!

Would the discs, rusty as they are, damage new pads?

As they were 10.65mm 2 months ago, how much life should I expect out of them from now until they do need replacing?

I realise oxidation will lead to rust and am not bothered in the sense of aesthetics as it will happen to new discs not long after new but thought with that rusty lip it might damage new pads?

Looks like the present pad friction material doesn't contact the rusted sections, but you'll confirm that one way or the other by the wear ridges in the old pads.

Course if new discs are cheap as chips and you're DIYing it then you could change them, if it were mine i'd let the present discs see the next set of pads out, the only proviso being you might get an advisory for rusty discs on the next MOT...hint dab of paint :-)

[Gary C]

smr84 said:

Thanks for the replies. Its 50/50 so far then!

Would the discs, rusty as they are, damage new pads?

As they were 10.65mm 2 months ago, how much life should I expect out of them from now until they do need replacing?

I realise oxidation will lead to rust and am not bothered in the sense of aesthetics as it will happen to new discs not long after new but thought with that rusty lip it might damage new pads?

Well, how many miles did it take to get to 10.65 ?

Seriously, there is nothing wrong with them the shiny bit is where the pads sit, the rusty bit is where they dont. Any new disks will be in the same condition after one winter.

The rusty bit wont damage the new pads as that is not where they contact the disk as thats why they are not shiny. Its all perfectly normal. Have a look at almost any car a couple of years old to see similar.

The disk can wear 3mm before the manufacture reccomends replacement, and any solid disk can actually wear much more than that.

Edited by Gary C on Saturday 15th March 20:32

[GreenV8S]

smr84 said:

Thanks for the replies. Its 50/50 so far then!

Would the discs, rusty as they are, damage new pads?

Are the rusty areas actually swept by the pads?

If they are, the discs need replacing. If they aren't, they don't.

[E-bmw]

GreenV8S said:

smr84 said:

Thanks for the replies. Its 50/50 so far then!

Would the discs, rusty as they are, damage new pads?

Are the rusty areas actually swept by the pads?

If they are, the discs need replacing. If they aren't, they don't.

^^^^ Wot 'e said.

All day, every day.

Especially as the inner surface is almost always worse that the outer.

On top of that if the car is a keeper why not just do the job once & then you know.

[Pit Pony]

Smint said:

I'd check the rear face of those discs, if they're similar condition to the front face i'd leave them in place, you could always spin the discs whilst holding an old chisel in place to remove the rust then slap some metal paint on.

Before fitting new discs i paint the unswept outer parts including the outside edge, this helps delay rust build up though fair to say i might have a teeny bit of a phobia about rusty brake discs and calipers.

Chisel ? bd file !!!! (Or flapper disc on angle grinder)

[CrgT16]

Check manufacturers recommended spec it feels you when you need to replace them.

For me it depends on the car, the use of said car and how deep the war is. If the rusted areas create a reasonable “wall” that I might think the pads will not move freely I just replace them. Then again I probably replace discs every other pad change. 1 disc per 2 pads.

[Pit Pony]

CrgT16 said:

Check manufacturers recommended spec it feels you when you need to replace them.

For me it depends on the car, the use of said car and how deep the war is. If the rusted areas create a reasonable “wall” that I might think the pads will not move freely I just replace them. Then again I probably replace discs every other pad change. 1 disc per 2 pads.

Remove the wall, with a file.

[steveo3002]

look at the inside face before deciding ,theyre often way worse

if thats as bad as it gets in the pic you can knock that rusty lip off with a grinder

[CrgT16]

Pit Pony said:

Remove the wall, with a file.

Have done so many times but sometimes I just change them. Depends on use and car. More forgiving on a car to go to the shops than a car that needs high speed deceleration often. The manufactures recommendation for change is conservative. There is more life to the elements than stated but they need to cover their back. On the other hand discs can be had cheap for common cars so a replacement is not that onerous.

[paul_c123]

Unless something else weird has happened to the discs, I'd just go off the recommended thickness and change them if they're nearly at, or under, the minimum in the specs.