[daryl rsv4]

I had my calipers powder coated last week, so we reinstalled them and bled each caliper twice and still getting a soft pedal.

Powder coater pressure tested each piston before return and all was good.

Should we bleed again?

[daryl rsv4]

I’m trying to post a picture to show rust marks on the rotor to show the pads are not making full contact.

What app are you guys using to post pics on mobile? Thanks!

[Watsey]

Pictures of the callipers and the pads would be useful.

There’s a long list of things to check :

• Sufficient fluid in the master cylinder reservoir.
• Did you seal the brake pipes/hoses when the callipers were removed from the car ? If not, could the fluid have drained all the way back to the master cylinder and/or ABS pump thereby causing an air lock ?
• Have you checked that the pistons are extending fully, and that the pads are moving freely into full contact with the rotors ?
• When you bleed each caliper it’s good practice to use a rubber mallet to bang each caliper do as to dislodge any air bubbles such they are evacuated by the fluid.

Are you experiencing soft pedal but good braking performance, or has braking been reduced as well ?

[daryl rsv4]

Yes, master cylinder was topped off

We used brake line clamps while the calipers were off

We have not, I only went by the powder coater saying all pistons were pressure tested

Good to know

Braking performance is the same, I just have to put the pedal between 1/2 way and the floor. When I hit the brake initially, let off slightly (not all the way) and hit the brake again, the pedal is back to normal if that makes sense.

Appreciate your response.

[Billfitz]

Originally Posted by daryl rsv4

I’m trying to post a picture to show rust marks on the rotor to show the pads are not making full contact.

If you mean the thin bands of rust at the rotor edge and near the hub that's normal.
You post photos using a photo hosting website, or your own website if you have one.

[daryl rsv4]

Originally Posted by Billfitz

If you mean the thin bands of rust at the rotor edge and near the hub that's normal.
You post photos using a photo hosting website, or your own website if you have one.

No, not the thin bands on the rotor, I’m talking the contact areas on the rotor where the pad makes contact.

Yes, I know that. I am asking what app are people using to get the url for a picture. This is the only forum I know where you have to add the url.

I used to use tiny pic to post pics on here, but they went under years ago.

[casualDIYer]

Not making contact with the rotor seems like an odd problem. The pistons exert a significant force so if something is resisting that force, it must be significant.

How new are the pads? Do you have any old pads? The idea here is with either worn pads or by removing the caliper you want to test how well the pads will slide along the caliper pins without the use of the piston. There are two flat spots, top and bottom, roughly 10-15mm wide that keep the brake pad from moving up and down but do not hinder it's motion in and out with respect to the rotor as it slides back and forth along the caliper pins either when the brake is pressed or when it is released. There should be no binding. The pads cannot get stuck. Keep in mind, the top may bind while the bottom remains free and visa-versa. This will cause the pad to touch the rotor at an angle.

I think this possibility is remote since the powder coating people should know about these flat spots (4 in total, 2 left, 2 right) and avoid coating them but there is always a 'new guy' who rushes and makes an error.

If there is no binding of the pads along the length of travel of the caliper pins, look into using ISTA to bleed the brakes. ISTA has a procedure to activate ABS and shake out any stubborn bubbles a normal bleed would not be able to free up.

Good luck

[johnung]

A common issue that results in a soft brake pedal is to bleed brakes, but fail to follow the ISTA procedure which makes sure to vibrate off all of the air bubbles clinging internally to brake components.

Video by FaRKle!
https://youtu.be/o7XsCMqZXw0?si=we1BEosPHoWaK3El

[Watsey]

Originally Posted by daryl rsv4

No, not the thin bands on the rotor, I’m talking the contact areas on the rotor where the pad makes contact.

Yes, I know that. I am asking what app are people using to get the url for a picture. This is the only forum I know where you have to add the url.

I used to use tiny pic to post pics on here, but they went under years ago.

You can attach photos directly using the Bimmerpost App - well, definitely using the iOS version.

[daryl rsv4]

Here’s a pic of what I was explaining with the rotor. This was with driving about 10 miles after the 2nd bleed.

[Watsey]

That just looks like normal/common scoring of the discs.

Have you allowed enough time for ghee new pads to mate to the discs, and/or properly bedded them ?

A new flat pad being pressed against an uneven disc surface will initially result in reduced braking performance untill the surfaces have fully mated.

[daryl rsv4]

Originally Posted by Watsey

That just looks like normal/common scoring of the discs.

Have you allowed enough time for ghee new pads to mate to the discs, and/or properly bedded them ?

A new flat pad being pressed against an uneven disc surface will initially result in reduced braking performance by Neil the surfaces have fully mated.

We used the same pads & rotors because there was plenty of meat left. Look closer at the rotor, pads are definitely not making full contact.

[daryl rsv4]

Look where I circled.

[daryl rsv4]

Originally Posted by johnung

A common issue that results in a soft brake pedal is to bleed brakes, but fail to follow the ISTA procedure which makes sure to vibrate off all of the air bubbles clinging internally to brake components.

Video by FaRKle!
https://youtu.be/o7XsCMqZXw0?si=we1BEosPHoWaK3El

We’ll be working on the brakes again this morning and we’ll give this a try. Thanks for posting!

[HighlandPete]

Originally Posted by daryl rsv4

Look where I circled.

Are you sure the pads were put back in the original positions?

Look as if they could have been mismatched and are having to bed in to a different disc friction face.

[Watsey]

Bearing in mind that the BMW MPerformance calibers are 6-pot units, and that the outer pistons align with the wider radius of the swept area, I'd check that these outer pistons are extending correctly.

[daryl rsv4]

Originally Posted by HighlandPete

Are you sure the pads were put back in the original positions?

Look as if they could have been mismatched and are having to bed in to a different disc friction face.

Good point, I’ll check that when we pull the wheels off. Pretty sure we did, but I’ll definitely check. Thanks!

[daryl rsv4]

Originally Posted by Watsey

Bearing in mind that the BMW MPerformance calibers are 6-pot units, and that the outer pistons align with the wider radius of the swept area, I'd check that these outer pistons are extending correctly.

Definitely will, thanks.

[casualDIYer]

Is there any sound of scraping, like the rotor is making contact with something, when you drive?

[shawnhayes]

Originally Posted by Watsey

Bearing in mind that the BMW MPerformance calibers are 6-pot units, and that the outer pistons align with the wider radius of the swept area, I'd check that these outer pistons are extending correctly.

These are clearly not 6 piston calipers. They are 4 pistons. Your advice is sound, but it’s very unlikely that a stuck piston could cause this uneven wear.

Shawn

[Billfitz]

Originally Posted by daryl rsv4

Look where I circled.

Those rotors were scored before the pads were changed. They should have been refinished before putting on the new pads. Over time the new pads and rotors will break in to each other, but they'll never be perfect. I'd pull the rotors and refinish them to flat.

[HighlandPete]

Originally Posted by Billfitz

Those rotors were scored before the pads were changed. They should have been refinished before putting on the new pads. Over time the new pads and rotors will break in to each other, but they'll never be perfect. I'd pull the rotors and refinish them to flat.

OP says he has used the same parts...

Originally Posted by daryl rsv4

We used the same pads & rotors because there was plenty of meat left. Look closer at the rotor, pads are definitely not making full contact.

I'd second what you say, if it was new pads on old rotors. It is why I suggested the pads were put back in different positions. Now trying to bed pads to different friction faces.