Advice on car servicing - what do these numbers mean?

[London1986]

Hi all

A friend of mine has had her car serviced at Halfords (I know!)

She has had her front brake pads and discs replaced but she can still hear squealing after driving home.

On a report she has, they have given her the following numbers - https://ibb.co/7JGYB4J

If you can't see the image, the numbers are:

Before service
Front pads - 6mm - 18%
Front discs - 20mm - 0%
Rear shoes - 3mm - 25%
Rear drums - 3mm - 0%

After service
Front pads - 11mm - 41%
Front discs - 21.9mm - 95%
Rear shoes - 4mm - 50%
Rear drums - 232mm - 100%

So few questions...

1. What do the % mean? If the front pads have been replaced, shouldn't they be 100%?
2. Why are the front discs similar mm yet 95% difference?
3. Anything else funny about those numbers?

Interested to hear your thoughts

[E-bmw]

Remaining life/friction material/thickness.

EG.

Front discs.
Minimum thickness 20mm - 0% remaining. 21.9mm 95% of usable thickness remaining

Edited by E-bmw on Thursday 11th January 10:40

[Scrump]

A similar question was asked on here about tyres and the % that Halfords state. It seemed that was the percentage of wear remaining between some average (fictional) starting tread depth and the 1.6mm legal minimum.

I am guessing this something similar with the % being the wear remaining before the minimum thickness is reached. I can’t explain why the new parts aren’t 100%, again I am guessing that the assumed starting thickness isn’t correct.

[London1986]

E-bmw said:

Remaining life/friction material/thickness.

EG.

Front discs.
Minimum thickness 20mm - 0% remaining. 21.9mm 95% of usable thickness remaining

Edited by E-bmw on Thursday 11th January 10:40

Thanks for your response.

I get that, however what throws me a bit is the front brake pads. If they've been replaced and are now 11mm, wouldn't you expect closer to 100% and not 41%?

[London1986]

Scrump said:

A similar question was asked on here about tyres and the % that Halfords state. It seemed that was the percentage of wear remaining between some average (fictional) starting tread depth and the 1.6mm legal minimum.

I am guessing this something similar with the % being the wear remaining before the minimum thickness is reached. I can’t explain why the new parts aren’t 100%, again I am guessing that the assumed starting thickness isn’t correct.

Yeh it does seem very strange. I have of course asked her to go back to them and ask them to explain what these % mean but I thought' id ask here to see if it was anything obvious.

The main concern is why the breaks are still squealing and was wondering whether these numbers would highlight anything useful.

[E-bmw]

London1986 said:

Scrump said:

A similar question was asked on here about tyres and the % that Halfords state. It seemed that was the percentage of wear remaining between some average (fictional) starting tread depth and the 1.6mm legal minimum.

I am guessing this something similar with the % being the wear remaining before the minimum thickness is reached. I can’t explain why the new parts aren’t 100%, again I am guessing that the assumed starting thickness isn’t correct.

Yeh it does seem very strange. I have of course asked her to go back to them and ask them to explain what these % mean but I thought' id ask here to see if it was anything obvious.

The main concern is why the breaks are still squealing and was wondering whether these numbers would highlight anything useful.

I suspect the difference is the way they have measured, which is wrong.

Pads are normally 16/17mm full thickness, but perhaps they have measured just the friction material, which sounds more likely.

Obviously, that means the original calculation was wrong, but hey ho, they aren't real mechanics at Halfrauds are the

The squealing had little, if anything to do with the disc/pad thickness from the start, so unlikely to have changed.

ETA. As below unless the squeal is different & they do just need a bit of use first.

Edited by E-bmw on Thursday 11th January 11:26

[MustangGT]

London1986 said:

Yeh it does seem very strange. I have of course asked her to go back to them and ask them to explain what these % mean but I thought' id ask here to see if it was anything obvious.

The main concern is why the breaks are still squealing and was wondering whether these numbers would highlight anything useful.

Brakes squeal for a number of reasons, one being new brakes need bedding in. A few heavy braking runs will likely do it.

[London1986]

E-bmw said:

I suspect the difference is the way they have measured, which is wrong.

Pads are normally 16/17mm full thickness, but perhaps they have measured just the friction material, which sounds more likely.

Obviously, that means the original calculation was wrong, but hey ho, they aren't real mechanics at Halfrauds are the

The squealing had little, if anything to do with the disc/pad thickness from the start, so unlikely to have changed.

Ahh ok that makes sense.

So is it fair to say you'd take those %s with a pinch of salt?

And the squealing as mentioned above could potentially just be new brake pads/disc needing to be worn in?

[Scrump]

London1986 said:

Ahh ok that makes sense.

So is it fair to say you'd take those %s with a pinch of salt?

And the squealing as mentioned above could potentially just be new brake pads/disc needing to be worn in?

I would ignore the %, they are meaningless and have nothing to do with the squealing.

[E-bmw]

Scrump said:

I would ignore the %, they are meaningless and have nothing to do with the squealing.

^^^^ Wot 'e said.

Just their way of justifying the work done.

[stevieturbo]

Scrump said:

I would ignore the %, they are meaningless and have nothing to do with the squealing.

True, but they should be forced on an explanation, ideally in writing.

[stevemcs]

The rear drums confuse me, new shoes are probably 5mm thick and i have never known a drum to wear out, so how can they go from one figure to another ?