Front Disc replacements

mcbutler · Post by **mcbutler** » Sun Jul 05, 2020 11:43 am

Hi Guys,

During my recent MOT my indy informed me that the inside of my front discs on the outer edge of the rotor contact surface were badly pitted for about 15% of the contact area.
So, having looked I decided that they are not safe and have ordered some grooved replacements.
I talked to several suppliers about their products, to my local indy and several 'tuning shops' in the UK and also via the web.

One piece of advice that came up over and over again was this;

When fitting new discs it is better to refit the old pads (unless damaged) initially as the disc will bed more quickly!

So, new discs with old pads - new pads with used discs is apparently a good rule to follow!

Just knowledge from a few pros to add to our collective mind

Silverstar · Post by **Silverstar** » Sun Jul 05, 2020 12:18 pm

So what happens when the car is brand new? it has new discs and new pads.

Jasonn · Post by **Jasonn** » Sun Jul 05, 2020 1:14 pm

I've always done both (when I did my own work on cars) and my local indy is the same.

Seems strange putting old crud back, only to take it off in a couple of months time - might as well do both and just drive gently for 500 miles.

Probably using old pads for those who aren't patient enough to let them bed in properly

mcbutler · Post by **mcbutler** » Sun Jul 05, 2020 5:14 pm

Silverstar wrote: ↑Sun Jul 05, 2020 12:18 pm So what happens when the car is brand new? it has new discs and new pads.

Well obviously!

mcbutler · Post by **mcbutler** » Sun Jul 05, 2020 5:16 pm

Jasonn wrote: ↑Sun Jul 05, 2020 1:14 pm I've always done both (when I did my own work on cars) and my local indy is the same.

Seems strange putting old crud back, only to take it off in a couple of months time - might as well do both and just drive gently for 500 miles.

Probably using old pads for those who aren't patient enough to let them bed in properly

I dont think its about being patient for them to bed in, its more about safety. Anything that can speed up the process to full brake efficiency has to be a good thing. So long as the old pads are not worn/damaged they are still viable and just as (if not more) efficient than the new ones!
The main reason people dont do it apparently is because they are using a garage so they end up paying 2 X labour! I can understand that.

Silverstar · Post by **Silverstar** » Sun Jul 05, 2020 9:49 pm

mcbutler wrote: ↑Sun Jul 05, 2020 5:16 pm The main reason people dont do it apparently is because they are using a garage so they end up paying 2 X labour! I can understand that.

Why would you pay twice the labour? you have to remove the pads to remove the discs. In all my years in the motor trade with access to many workshops I have never heard of this method of changing brakes. I guess you learn something new every day.

Smartbear · Post by **Smartbear** » Sun Jul 05, 2020 10:01 pm

I don’t like the sound of this very much, the pads wear together with the discs & if used pads are paired with new discs the braking surfaces won’t be a good match with each other.
Better to wear new pads to new discs as a pair imho
Rob

mcbutler · Post by **mcbutler** » Sun Jul 05, 2020 10:23 pm

Smartbear wrote: ↑Sun Jul 05, 2020 10:01 pm I don’t like the sound of this very much, the pads wear together with the discs & if used pads are paired with new discs the braking surfaces won’t be a good match with each other.
Better to wear new pads to new discs as a pair imho
Rob

My initial thoughts as well but if you consider it an old pad will wear to the disc as fast as a new one. And later when you fit new pads to your old disc, well that is exactly the same thing as old pads to a new disc!!! I noted that EBC redstuff pads (bought some) have a special ‘wearing in layer’.

mcbutler · Post by **mcbutler** » Mon Jul 06, 2020 7:49 am

Silverstar wrote: ↑Sun Jul 05, 2020 9:49 pm
mcbutler wrote: ↑Sun Jul 05, 2020 5:16 pm The main reason people dont do it apparently is because they are using a garage so they end up paying 2 X labour! I can understand that.
Why would you pay twice the labour? you have to remove the pads to remove the discs. In all my years in the motor trade with access to many workshops I have never heard of this method of changing brakes. I guess you learn something new every day.

You pay labour to change your discs and replace old pads to get faster bedding in, later on you return and pay labour again to have old pads removed and new ones installed. Unless your'e a DIY guy like me.

Rockhopper · Post by **Rockhopper** » Mon Jul 06, 2020 8:40 am

Changing pads and disks is an easy DIY job, even if you have to buy all the tools needed it'll still work out cheaper that paying a garage plus you learn about how your car works.

obewan · Post by **obewan** » Mon Jul 06, 2020 9:16 am

When I bought my car 4 years ago, there was a 'ring' on the outer edge on both front discs about 20mm wide.
I replaced both discs and pads.
All was fine at first but over time the rings have re-appeared. 1 about 10mm, the other 20mm.
A Google check seems to point to a fairly common issue. As does peering at the dics of many parked cars

I've just had the brake calipers off to paint them and spent some time getting them prepped and cleaning anti-squeal clips, slide pins etc

A couple of weeks later and the rings are starting to clear

Nictrix · Post by **Nictrix** » Mon Jul 06, 2020 9:50 am

obewan wrote: ↑Mon Jul 06, 2020 9:16 am When I bought my car 4 years ago, there was a 'ring' on the outer edge on both front discs about 20mm wide.
I replaced both discs and pads.
All was fine at first but over time the rings have re-appeared. 1 about 10mm, the other 20mm.
A Google check seems to point to a fairly common issue. As does peering at the dics of many parked cars
I've just had the brake calipers off to paint them and spent some time getting them prepped and cleaning anti-squeal clips, slide pins etc

A couple of weeks later and the rings are starting to clear

This could be because the pads are not a uniform size and with the shape of the pad some of the disc gets more wear than other bits.
Ideally the pad should be largest at the outside of the disc and tapers thinner towards the centre. Some pads are shaped like this but others have strange profiles that must add to grooves on a disc.

mcbutler · Post by **mcbutler** » Mon Jul 06, 2020 3:30 pm

Rockhopper wrote: ↑Mon Jul 06, 2020 8:40 am Changing pads and disks is an easy DIY job, even if you have to buy all the tools needed it'll still work out cheaper that paying a garage plus you learn about how your car works.

So long as you get it right of course

mcbutler · Post by **mcbutler** » Mon Jul 06, 2020 3:40 pm

obewan wrote: ↑Mon Jul 06, 2020 9:16 am When I bought my car 4 years ago, there was a 'ring' on the outer edge on both front discs about 20mm wide.
I replaced both discs and pads.
All was fine at first but over time the rings have re-appeared. 1 about 10mm, the other 20mm.
A Google check seems to point to a fairly common issue. As does peering at the dics of many parked cars
I've just had the brake calipers off to paint them and spent some time getting them prepped and cleaning anti-squeal clips, slide pins etc

A couple of weeks later and the rings are starting to clear

Rings a couple of mm wide on the disc are completely normal. OEM and cheaper pads use a lot of iron in their makeup to remove heat from the pad. If you get a 'small excess concentration of iron' in the pad it will create a ring until it wears away. It is the iron particles coming off the pad (and disc) when hot thats forms the permanent stain ing on alloy wheels.

Silverstar · Post by **Silverstar** » Mon Jul 06, 2020 5:20 pm

I think even if I was to change the brakes myself I would still change both the pads and discs at the same time, it just way less hassle than having to keep taking the car apart with the only trade off being maybe a slightly longer bedding in time, even that I suspect would be quite negligible.

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