Bedding in brake pads to old rotors, myth or legend?

[Submariner1]

OK in an attempt to get rid of brake squeal I changed the front pads.
I have driven around now for 730 miles with very gentle braking. Avoiding holding the brakes on after Braking for say 300 miles; and since then just pretty tame/moderate braking.

So is it time to use a bedding in process?
Partly spurred on due to feeling very slight brake judder, braking down from high speed. But it could have been the M4s poor surface, as not noticed it before or since changing the pads. (I also need to re-torque the bolts as I set them to 140 Nm and the locking bolt to 130 Nm not the 150 Nm in the manual.)

Wow what a lot of conflicting advice, ranging from:-
- 3 moderate stops from 30mph to 15mph, and then 3 fairly hard stops from 60 mph to 10mph
To
- 20 stops from high speed (100mph) to 15 mph.

The only consistency in these advisory practices is
- dont stop completely
- always imediately get back up to speed to cool them off for 3 mins to 1 mile (again conflicting advice)
- never sit with your foot on the brake after a stop, where the pad is in contact with the disk.

As I have Brembo front calipers, I looked on their site. Ironically the only thing I could see was

"A brief running-in period is always needed
Brake discs and brake pads are the heart of the braking system and their perfect working efficiency is reflected in the active safety of the vehicle. However, a brief period of running-in is needed (approximately 300 km) from when the brake discs and brake pads are replaced. During this period, the driver should make brief, soft braking movements to allow the surfaces of the brake pads in contact with the brake discs to align correctly. A poor running-in period could cause the components to wear down irregularly and compromise the performance of the braking system."

Note no suggestion of Pad material transfer or any kind of hard braking!

On the other hand I did see this advice, which seemed to have a fair bit of logic.

"How to Bed in Brakes

1. From 60mph, gently apply the brakes a couple of times to bring them up to operating temperature. This prevents you from thermally shocking the rotors and pads in the next steps.
   
   
2. Make eight to ten near-stops from 60mph to about 20 mph. Do it HARD by pressing the brakes firmly, but do not lock the wheels or engage ABS. At the end of each slowdown, immediately accelerate back to 60mph, then apply the brakes again. DO NOT COME TO A COMPLETE STOP! If you stop completely, with your foot on the brake pedal, pad material will be imprinted onto the hot rotors, which could lead to vibration and uneven braking.
   
   
3. The brakes may begin to fade after the 7th or 8th near-stop. This fade will stabilize, but not completely go away until the brakes have fully cooled. A strong smell from the brakes, and even some smoke, is normal.
   
   
4. After the last near-stop, accelerate back up to speed and cruise for a few minutes, using the brakes as little as possible to allow them to cool down. Try not to become trapped in traffic or come to a complete stop while the brakes are still hot.
   
   
5. If full race pads, are being used, add four near-stops from 80 to 20 mph.
   

After the break-in cycle, there should be a slight blue tint and a light gray film on each rotor face. The blue tint tells you the rotor has reached break-in temperature and the gray film is pad material starting to transfer onto the rotor face. This is what you are looking for. The best braking occurs when there is an even layer of of pad material deposited across the rotors. This minimizes squealing, increases braking torque, and maximizes pad and rotor life.

After the first break in cycle shown above, the brakes may still not be fully broken in. A second bed-in cycle, AFTER the brakes have cooled down fully from the first cycle, may be necessary before the brakes really start to perform well. This is especially true if you have installed new pads on old rotors, since the pads need some usage to conform to the rotor wear pattern. If you've just installed a big brake kit, pedal travel may not feel as firm as you expected. After the second bedding cycle, the pedal will become noticeably firmer. If necessary, bleed the brakes to improve pedal firmness"

So in summary for my new pads and old rotors, thats 8-10 hard stops from 60-20mph. Cooled in between, then a long cool down and an additional 8-10 hard stops from 60-20mph.
Obviously gently warming the brake rotors first, never coming to a stop, or activating ABS lockup, and cooling them down between stops.

With hindsight I do wish I had changed the front rotors, as I may keep the car another year ( yeah like it that much )

 

[L John]

I always drive normally with no hard driving until they're bedded in but braking a bit earlier due to the reduced braking. You can feel the reduced braking when they're first fitted and once you're happy braking feels normal just get back to your usual driving.

The real issue is if a disk is worn more towards the inner or outer, the pads need to contact a larger area before hard braking but other than that I don't think there's any need to be changing driving too much during the initial bedding in.
If you over heat brakes they can glaze and a small contact area will cause more heat. If you don't drive like a lunatic and your disks are in decent condition I don't see any real problem.

 

[Submariner1]

I always drive normally with no hard driving until they're bedded in but braking a bit earlier due to the reduced braking. You can feel the reduced braking when they're first fitted and once you're happy braking feels normal just get back to your usual driving.

The real issue is if a disk is worn more towards the inner or outer, the pads need to contact a larger area before hard braking but other than that I don't think there's any need to be changing driving too much during the initial bedding in.
If you over heat brakes they can glaze and a small contact area will cause more heat. If you don't drive like a lunatic and your disks are in decent condition I don't see any real problem.

Pretty much what I have always done.
Except on one loan 270 cdi company car, just drove it like a bat out of hell from the day the discs and pads were changed (bluntly work load was crazy) appointment on Monday in Leeds 10.00am, Appointment on Tuesday In Methyr Tidfil 10.00am, first flight to Asterdam up at 5.30 on Wednesday. Etc.
Must have got that glazing as after about 3,000 miles when you braked you got seriously awful judder if you
Braked down from high speed to zero, the last 20mph to 0mph was BAD!
All my fault. Think its the only time I ever abused a car. But it was a Freebie hanging around until the 2 year lease was up.

Just wanted to avoid that shudder scenario at all costs. Oddly enough the discs looks super smooth?

 

[Yugguy]

I've always done similar to this:

- 3 moderate stops from 30mph to 15mph, and then 3 fairly hard stops from 60 mph to 10mph

The key thing IMO is not hold completely, so you are not pressing hot brakes against the disk while stationary.

This is why it's also not a good idea to hold the car on the brakes against D for too long.

 

[John Laidlaw]

I'm with LJohn - same procedure- I've bedded in new pads on older discs a couple of months ago and it worked out fine doing it like this

 

[Naraic]

You've driven 730 miles with these pads...if they ain't bedded in now they never will be. Or, have I missed something?

 

[L John]

You've driven 730 miles with these pads...if they ain't bedded in now they never will be. Or, have I missed something?

Just another 20K to bed them in fully, then change for new pads and start again.

 

[Submariner1]

You've driven 730 miles with these pads...if they ain't bedded in now they never will be. Or, have I missed something?

Not done any hard braking as some proceedures advise.

 

[EmilysDad]

Not done any hard braking as some proceedures advise.

They'll be bedded in by now ...... don't worry & just drive it.

 

[L John]

As Emilys Dad, too late to do a different bedding in procedure now, they're bedded in already.

 

[AMGeed]

You are about 730 miles late with this thread.
Just drive it and enjoy it and stop analysing everything.

 

[Botus]

You've driven 730 miles with these pads...if they ain't bedded in now they never will be. Or, have I missed something?

Indeed. For Submarina1, std practice is 100 miles "normal driving" (gentle), avoid (if possible) an emergency stop, build up from there to usual usage.... (much the same with tyres, although I think they need 200 myself)

that said, mad ex had 5 brand new cars (same brand every 6 month) and drove each one like she stole it, from the first minute she got hold of them. As in ABS job up to a roundabout with 20 miles on the clock, she became very proficient at turning off the hazards (activated with the ESP cutting in) with one hand and continuing four wheel drifting with the other... brakes never complained once. the 18" alloys used to suffer.

 

[stwat]

 

[Submariner1]

Thanks, seems like the consensus is I have got what I have got

TBH before I looked up the pads invoice ... Without any major trips i really thought I had only done about 200 miles!
Amazing how just pottering around they clock up.

Oh well, when I change the discs next time, I will be more diligent.

 

[Frosty149]

I have recently replaced discs and pads to the front of my recently purchased workhorse,
The old kit was so worn it was downright dangerous.
I found the all new setup was grabby to start and then 'vague' - a quick roughen of the disk faces with emery took off the shine and the brakes are now as expected.
I did flush the surface with brake cleaner and was light footed for a couple of hundred miles but the faces of the discs looked too polished, hopefully the scuff-up approach will last...

 

[Submariner1]

I have recently replaced discs and pads to the front of my recently purchased workhorse,
The old kit was so worn it was downright dangerous.
I found the all new setup was grabby to start and then 'vague' - a quick roughen of the disk faces with emery took off the shine and the brakes are now as expected.
I did flush the surface with brake cleaner and was light footed for a couple of hundred miles but the faces of the discs looked too polished, hopefully the scuff-up approach will last...

Glad to hear it worked ... did you use MB stuff?
Read somewhere one disc mfg now comes with a coating one is supposed to leave on during running in think it was MB.

 

[Droverunner]

>>>drove each one like she stole it........ brakes never complained once.

My long and varied experience with discs is that their condition is best kept by very hard use but not abuse... not the longest life but the best performance throughout that slightly shorter life.

 

[Frosty149]

Glad to hear it worked ... did you use MB stuff?
Read somewhere one disc mfg now comes with a coating one is supposed to leave on during running in think it was MB.

Not MB Sub, an inferior manufacturer (French?!)
I did choose better than cheapies though (disks and pads).

 

[Submariner1]

Not MB Sub, an inferior manufacturer (French?!)
I did choose better than cheapies though (disks and pads).

Just wondered as if I remember correctly Malcolm used Zimmerman. Discs and he was very pleased with them.
Atm our dealer is doing such good prices, there is very little in the difference.

 

[LostKiwi]

Yes Malcolm did use Zimmerman and said they were OEM. I've used Zimmerman in the past with no problems.