Sanding new brake discs

[algas]

Just going to replace the discs and pads, back along it was good practice to slightly sand the discs to help bed in the pads, is this ok to do now or is it not nessesary

 

[jj4091]

I've never heard of it but not a mechanic.

 

[accelerator]

I'm not a mechanic but I've never heard of this being done. I wouldn't be sanding my nice new brake discs!

Modern brake pads have much better performance, so it's not going to be necessary in my opinion.

You should just drive the car and drive carefully until the brakes are bedded in.

 

[Burnerman]

Not desirable at all!
Just remove any preserving oil that may be there.......discs with painted centres don't have that as a rule.
Ensure the hub that they sit on is completely clean, and add a thin layer of ceramic grease if you can.
John

 

[Old Salt]

Discs I fitted recently came with a silvery coating and instructions not to remove it. Just a wipe over after fitting with brake cleaner to remove any greasy finger prints.

 

[Avocet]

I've never done it. As other have said, just de-grease the discs before fitting. Bedding-in the new pads is important though. Pad materials have changed a lot since they banned asbestos. They now have much more metal in them (hence why the discs wear much faster these days). You need to deposit a thin layer of pad material uniformly on to the discs. The replacement pads will often come with instructions on how to do that, but it usually involves a series of decelerations from modest speeds, getting progressively more aggressive but CRUCIALLY, never coming to a complete stop. The problem with coming to a complete stop with hot brakes, is that the pads tend to microscopically "weld" themselves to the disc surface. The car is plenty powerful enough to break that "weld", so you just drive off again as normal, but you then end up (if the brakes were hot enough), with a microscopic patch of pad material on the surface of the disc, and every time it passes between the pads, it's a bit grippier than the rest of the disc surface, and this creates the "warped disc" illusion. In order to minimise the chances of this happening, it's important to bed the pads in according to the instructions, so you get a more uniform layer of pad material deposited over the whole surface of the disc.

 

[mointainwalker]

I've never done it. As other have said, just de-grease the discs before fitting. Bedding-in the new pads is important though. Pad materials have changed a lot since they banned asbestos. They now have much more metal in them (hence why the discs wear much faster these days). You need to deposit a thin layer of pad material uniformly on to the discs. The replacement pads will often come with instructions on how to do that, but it usually involves a series of decelerations from modest speeds, getting progressively more aggressive but CRUCIALLY, never coming to a complete stop. The problem with coming to a complete stop with hot brakes, is that the pads tend to microscopically "weld" themselves to the disc surface. The car is plenty powerful enough to break that "weld", so you just drive off again as normal, but you then end up (if the brakes were hot enough), with a microscopic patch of pad material on the surface of the disc, and every time it passes between the pads, it's a bit grippier than the rest of the disc surface, and this creates the "warped disc" illusion. In order to minimise the chances of this happening, it's important to bed the pads in according to the instructions, so you get a more uniform layer of pad material deposited over the whole surface of the disc.

How often does that happen ? I bought an o.e. set of pads and discs for my Vectra and there was nothing included. I just used them as normal - which for me is never massive braking - which seems roughly to meet the parameters you lay out.

 

[Lower]

I've never done it. As other have said, just de-grease the discs before fitting. Bedding-in the new pads is important though. Pad materials have changed a lot since they banned asbestos. They now have much more metal in them (hence why the discs wear much faster these days). You need to deposit a thin layer of pad material uniformly on to the discs. The replacement pads will often come with instructions on how to do that, but it usually involves a series of decelerations from modest speeds, getting progressively more aggressive but CRUCIALLY, never coming to a complete stop. The problem with coming to a complete stop with hot brakes, is that the pads tend to microscopically "weld" themselves to the disc surface. The car is plenty powerful enough to break that "weld", so you just drive off again as normal, but you then end up (if the brakes were hot enough), with a microscopic patch of pad material on the surface of the disc, and every time it passes between the pads, it's a bit grippier than the rest of the disc surface, and this creates the "warped disc" illusion. In order to minimise the chances of this happening, it's important to bed the pads in according to the instructions, so you get a more uniform layer of pad material deposited over the whole surface of the disc.

That's more of a performance or race pad requirement. Modern conventional brake pads don't need that. You just fit them and drive normally.

 

[Harry Bloomfield]

That's more of a performance or race pad requirement. Modern conventional brake pads don't need that. You just fit them and drive normally.

It, the judder, can and does happen on conventional brakes, during normal use - it has happened to me. The simple fix, is to get the disc really hot through heavy braking, from speed, do it several times, without actually coming to a complete stop. That cleans up the disc, and puts an end to the judder.

Coming to a hard braking stop, with disc hot, and pads resting on a single place of the disc, causes the brake judder.

 

[Munroast]

That's more of a performance or race pad requirement. Modern conventional brake pads don't need that. You just fit them and drive normally.

every thing needs 'Run In' pads and disks will last longer and perform better if you are gentle with them at first, of course they will work just fine if you drive like a looney from day one, but they will be better if you bed them in gently.

with most surface that are to be in contact. Even finely machined or polished parts aren’t perfectly smooth; they have tiny high spots, At first, only those high spots touch, meaning the real contact area is much smaller than it looks. That creates very high pressure and frictional heating at those spots.

then if these high spots tear out you have hollows and new high spots

A proper running-in period means the parts will mate more closely, reducing friction, vibration, and wear over their lifetime. So yes, drive slowly and brake gently for a while

 

[Lower]

It, the judder, can and does happen on conventional brakes, during normal use - it has happened to me. The simple fix, is to get the disc really hot through heavy braking, from speed, do it several times, without actually coming to a complete stop. That cleans up the disc, and puts an end to the judder.

Coming to a hard braking stop, with disc hot, and pads resting on a single place of the disc, causes the brake judder.

I agree. I used to do a lot of track days and put significant effort into finding a disc/pad combination that wouldn't end up with really nasty judder from uneven pad deposition or the pad falling apart because it was overheated before it had gassed off properly. Proper performance pads have a specified bed in process that does work and then ensuring that the breaks were cooled before coming to a standstill prevents the localised deposition problem that so many people think is warped discs.

But conventional OEM quality brake pads are designed to not need a specific bed in process and from fitment.

 

[Mottie]

Ensure the hub that they sit on is completely clean, and add a thin layer of ceramic grease if you can.

That’s between the disc and the hub, not the disc and the pad…..

 

[foxhole]

It, the judder, can and does happen on conventional brakes, during normal use - it has happened to me. The simple fix, is to get the disc really hot through heavy braking, from speed, do it several times, without actually coming to a complete stop. That cleans up the disc, and puts an end to the judder.

Coming to a hard braking stop, with disc hot, and pads resting on a single place of the disc, causes the brake judder.

Isn’t judder due to ABS kicking in after harsh braking .?

 

[Harry Bloomfield]

Isn’t judder due to ABS kicking in after harsh braking .?

No, that judder through the pedal, is to warn you the ABS is having to operate, due to one or more wheels slipping on the surface. This judder, tends to appear most at certain speeds, when braking, and not felt so much through the pedal.

I had a Scorp, many years ago, which developed the judder. It always appear, when slowing down to enter a slip road off the motorway. It was so bad, I was on the point of replacing the front discs, when I happened across the explanation and the fix - up to 70 on a quiet road, brake hard almost to a stop, without actually stopping, repeat once more, and the judder just disappears. I've used the fix since then, on other cars, and each time it has worked.

It's caused by braking hard, coming to a full stop, with the disc hot, and the pad pressed hard against the hot disc. Let it roll to a gentle stop, use the handbrake.

 

[foxhole]

No, that judder through the pedal, is to warn you the ABS is having to operate, due to one or more wheels slipping on the surface. This judder, tends to appear most at certain speeds, when braking, and not felt so much through the pedal.

I had a Scorp, many years ago, which developed the judder. It always appear, when slowing down to enter a slip road off the motorway. It was so bad, I was on the point of replacing the front discs, when I happened across the explanation and the fix - up to 70 on a quiet road, brake hard almost to a stop, without actually stopping, repeat once more, and the judder just disappears. I've used the fix since then, on other cars, and each time it has worked.

It's caused by braking hard, coming to a full stop, with the disc hot, and the pad pressed hard against the hot disc. Let it roll to a gentle stop, use the handbrake.

Oh , I only use brakes to stop , not adjust speed , was taught that was careless driving .