Issue with newly installed brake upgrade

[dennis10]

I've recently installed a 340mm MQB platform brake upgrade from a 2019 Golf R on my PQ35 platformed mk5 Golf GTI Edition30, along with new stainless brake lines, Pagid pads, Brembo discs, sliding pins, bolts and rubber boots.

It all went pretty well, I bled the brakes using a pressure bleeder, have a decent pedal and it brakes nicely (have driven about 40miles since the upgrade), but I've got a problem with the drivers side in that it doesn't appear to be sweeping the disc cleanly, only the outside half of the disc seems to be sweeping, with the inside ring still coated in the factory paint covering. Conversely, in the same 40 miles the passenger side has swept itself pretty much clear, although it did look similar to the drivers side for the first 20miles.

I stripped the calipers and pins out again this weekend gone and regreased everything - Does this sound like a caliper piston issue or sliding pin issue? Or anything else? The brakes don't appear seized and from the outside you can see the pistons/pads moving when you press the brake pedal. Or perhaps I just need to bed them in for longer?  I did manage to get the disc to sweep a further cm or so, I've done 100+ miles now, so this was with some heavy braking, but I will add that my mpg does seem down a bit on my normal, initially wasn't sure if this was down to the extra rotational weight of the discs and calipers or something slightly seized.

Thanks in advance

[GVK]

I'm wondering if one of the carriers is bent, putting the pads out of line. Was the brake kit off a salvage car that had been  in an accident?

[GreigC]

Does it look like this? I installed MK7 R calipers to my MK5 GTI and it took well over 800 miles to fully sweep the discs. Now are perfect.

[mjmallia]

They should not take 800 miles to make full contact with the disc........100 miles max to bed in pads and even before then it will be even wear as the pads are tapered at the far edges for fitting, but still give a good 90% disc contact.

That to me is crying out that the caliper, carrier or pads are not mounted correctly, and bet the pads are worn at an angle.........you can see the hot spot on the top edge of the disc where the pad is making most contact.

[GreigC]

I agree…. The images above were roughly 2 weeks after fitting as I sent them to my mechanic… I eventually took the car to the garage and they confirmed all was good. I researched this issue and seems common on MK7 calipers that they take a while to clear the lower portion of the disk. They have been on the car well over a year now and are perfect now.

Brakes both sides today:

[dennis10]

I'm wondering if one of the carriers is bent, putting the pads out of line. Was the brake kit off a salvage car that had been  in an accident?

Thanks GVK - they were from an ebay salvage breaker called Torque Motors, they had 99.7% feedback with 52k items sold, but I guess that is no guarantee.  I don't think they are bent, I checked everything over and lined them up with each other beforehand - resprayed them myself in GTI red and applied decals, so I've spent some time looking at them and they seem perfect.

Does it look like this? I installed MK7 R calipers to my MK5 GTI and it took well over 800 miles to fully sweep the discs. Now are perfect.

Yes pretty much exactly like that - I think the one you have less clean sweep on is the drivers side too?  Which is the same as mine.  Did you notice a dip in mpg when you were waiting for them to break in?  As I've definitely noticed a few mpg less since fitting

[dennis10]

They should not take 800 miles to make full contact with the disc........100 miles max to bed in pads and even before then it will be even wear as the pads are tapered at the far edges for fitting, but still give a good 90% disc contact.

That to me is crying out that the caliper, carrier or pads are not mounted correctly, and bet the pads are worn at an angle.........you can see the hot spot on the top edge of the disc where the pad is making most contact.

I've double checked everything, bought better Pro Slip brake grease that has different grease for pins/pads and clips, cleaned out the carriers and regreased it all and everything moving pretty well.  I fitted myself and after redoing for the second time I realised I did have the pins in the wrong holes - according to internet lore, the one with the rubber bush should be in the top hole both sides, I had the reverse - but I know that people have run the opposite without issues. 

If I had to pick one thing I noticed it was that the drivers side pins (drivers side is the issue) moved less freely in the rubber bellows once fully seated, like the vacuum was sucking the pins in and restricting the movement/release back out - but I redid these pins a couple of times with a clean out and regrease and re-seating and it improved, although not as good as the passenger side.  I've read about that online and there seems to be a diverse opinion on whether to release that vacuum from the rubber boots or not

[GreigC]

Not sure what side was the faster side at going down. Afterwards they were both equal with a small ring like the second image and stayed like that for ages! Then finally cleared fully on both sides.

I can’t say I noticed a difference in MPG at the time. The brakes always felt fine although was disappointed by the performance initially when installed. Now they are bedded in they perform excellent and I’ve had no issues.

[dennis10]

Saw this on a reddit post, do you think this could be the reason?

I suspect the issue is with your caliper piston. They have a slight notch in them so it applies more pressure (or less pressure ) to the leading face , vs the trailing face.

I suspect, since the calipers were rebuilt, the piston was not oriented correctly, and is grabbbing the outer lip more than the inside lip.

This is guessing!

I've attached an article/photo showing orientation, and is based on direction of rotor travel, whether it biases upwards or downwards. Yours seems to be biasing vertically.

This was from a Porsche forum, but can be found in various Mercedes manuals too

Edit : link added https://forums.pelicanparts.com/porsche-911-technical-forum/367970-caliper-pistons-set-way.html

The reddit poster marked that this turned out to be the reason (piston was oriented the wrong way so putting more pressure on the outside edge)  Not sure if this is a thing on mk7 R calipers though?

He also said that he replaced the caliper with a remanufactured one with the piston oriented the right way, and another poster said he could have just twisted the piston round instead of replacing the whole caliper

Reddit post:  https://www.reddit.com/r/AskMechanics/comments/14wqgea/please_help_me_with_these_brakes_new_pads_not/

[GreigC]

Can you post images of your brakes?