Replace brake discs at the same time as pads?

[Tom_G]

Hello all,

 

My local independent garage has advised I need new brake pads all round (not surprised as they have done 35k and I sometimes drive enthusiastically) and front discs only due to corrosion, but that rear discs are ok for now although 75% worn.

 

If I do the pads and front discs will I have to do the rear pads again when I do the rear discs even if the pads are only half worn by that point? Would it be better to just do the lot now?

 

Thanks in advance.

 

 

[KenONeill]

Just now, Tom_G said:

will I have to do the rear pads again when I do the rear discs even if the pads are only half worn by that point?

Yes. Worn pads won't bed to brand new discs.

[RaymondReddington]

5 hours ago, KenONeill said:

Yes. Worn pads won't bed to brand new discs.

Can’t say I’ve ever had an issue. 

[J.R.]

Sure they will, they will just take slighty longer.

 

That said most of us would fit new pads with new discs.

[Tom_G]

Not wanting to have to buy another set of pads prematurely I have asked my garage to offer an alternative quote for rear discs as well as pads, so if it's not much more I think I'll just do the discs anyway.

[SurreyJohn]

Do you mean rear pads are 75% worn, as rear discs 75% worn seems wrong

 

There is a high likelihood that the fronts and rear pads have not worn the same, whilst there is some convenience in getting them all done together, there is a good chance one set (front or back) can be deferred 6-9 months if you want to spread your repair cost.   But you really need pads to be measured vs new size, and ignore the corrosion statement unless they clarify if it is surface (which is normal), or discs are much thinner than should be

 

 

[Tom_G]

7 hours ago, SurreyJohn said:

Do you mean rear pads are 75% worn, as rear discs 75% worn seems wrong

 

There is a high likelihood that the fronts and rear pads have not worn the same, whilst there is some convenience in getting them all done together, there is a good chance one set (front or back) can be deferred 6-9 months if you want to spread your repair cost.   But you really need pads to be measured vs new size, and ignore the corrosion statement unless they clarify if it is surface (which is normal), or discs are much thinner than should be

 

 

 

Discs. Although now I'm questioning whether it was 75% worn, or 75% left as I remember being slightly confused at the time by the initial number and the garage's clarification.

 

Disc surface looks fine on the outside face, although the edge of the disc looks a bit corroded. Going to pop one front and one rear wheel off tomorrow to examine properly and also take my own measurements of pads/discs because I'm not sure the discs should be "75% worn out" already either.

 

Maybe I'm also a bit unsure because something is intermittently making a strange whine since my service last week, which I think is the DSG as it had its first oil change. But I'll make a separate post about that when I get the audio recordings of the whine off my dash-cam.

 

[J.R.]

It will be "worn" and it will be BS.

 

My chauffeur friend generally did his own maintenance but had the servicing done by the selling dealer during the warranty, on collecting the vehicle the invoice said "front & rear brake pads 75% worn" he asked to speak to the service manager and complained that it could not be true as he had recently replaced them himself, "ah but how many miles have you driven since?" was the response, he scratched his head & said well I did them last night & it took me 20 minutes to walk home after dropping the car off this morning so it would be between one and two miles 😳

[bmbmdmb]

By time pads are worn the discs will not be far behind. I think it false economy. I read that new pads should always be fitted to new discs. The suggestion indicated was that friction material is transferred from new pads to disc and a more even surface contact occurs preventing hot spots and avoiding possible warping of discs during bedding in of the discs. 

 

Hearsay (I'm not old enough to remember) but prior to 2001 brake discs contained asbestos, they lasted longer apparently and the suggestion to me was that you could get two sets of pads out of the discs. 

 

If old pads were used there might be noise as the whole area would not be in contact until bedded in. However the two surfaces would not be a vertical face on contact. 

 

I think using old pads is not ideal.

 

Having said this I had a Mazda 3 in family. It failed on pads. They replaced pads only, 500 miles on I changed discs and used 'old pads'. No issues. The caliper carrier bolts were seized and I got that nice job. The discs had rust on back and needed changing.

Edited 2 May, 2022 by bmbmdmb

[aubrey]

You need to confirm that 75%,  35k is not that much for rear discs. I can understand the front but not the rear needing replacement at 35K.   You can normally feel the ridge on the outside of the disc to see how much wear, that's checkable with the wheels on with many alloys .  My bet is they are 25% worn and still have 75% service left. If that is the case then they would not need replacing now.   I've had garages badly overestimate wear, not sure if they are trying to get work.  But I've been told pads need changing when there was loads of material left. Hence best to always check yourself.

[Tom_G]

Thanks all for the useful observations, apologies for the delay getting back to everyone but I had to procure some tools to be able to take the wheels off and measure the pads in order to make my own checks.

 

The rear discs do appear to be about 25% worn, a rough measurement suggests 0.5mm wear on each side and the maximum appears to be 2mm each side (original thickness 14mm, minimum thickness 10mm).

 

 

However, I was disappointed to find the rear pads look to have 6mm left:

 

 

 

The front pads have roughly the same:

 

 

 

I measured the front discs and they are original thickness 25mm, minimum 22mm, and wear is about 0.75-1mm each side, so about 60-70% thickness remaining, however I have no idea if the garage is correct in their assertion the front discs need to be replaced due to corrosion or not:

 

 

I'm probably going to take the car asap for it's MOT which is due in four weeks to a local independent MOT Test only place and see whether they fail the discs, I don't personally think the pads need doing at this stage.

[J.R.]

They are taking you for a pigeon, it's very rare to see discs in such good condition, I dont even need to see the rear of them behind the dustshield to know they are in perfect condition, the garage certainly wont have done.

 

Tell them "nice try but you have now lost a customer".

 

No way in a million years would any of those discs fail an MOT.

[Tom_G]

Just now, J.R. said:

They are taking you for a pigeon, it's very rare to see discs in such good condition, I dont even need to see the rear of them behind the dustshield to know they are in perfect condition, the garage certainly wont have done.

 

Tell them "nice try but you have now lost a customer".

 

No way in a million years would any of those discs fail an MOT.

Thanks, I thought so. This isn't even a main dealer so I was hoping they'd at least be honest! I'll start asking around for a new garage for next year's service...