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Discussion Starter #1
Hi, for several years I've had uneven wear on the outer face of a front brake rotor on my E46 330i, yet each year it passes the annual MOT brake test.

The wear on the inside face of the rotor is as you would expect but the wear on the outside face is minimal.

Has anyone seen similar before ?

Should I replace the Calliper sliding pins or rebuild the calliper with a new piston, seals and pins.

thanks
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Wow can't believe that passes MOT.
At the very least new pads mate. You're only using ~30% of that pad. Given you're not using all of it, I suspect that the center would get very hot?

I'd likely replace the rubber bits for the pins and thoroughly clean the pins of any gunk.
 

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OP I would definitely replace both pads and rotor.

I'm trying to think of how that could happen and why, over time, it wouldn't wear evenly as the pad beds.

It does seem like your guidepins are frozen and it's not allowing the outside pad to be pulled in. You're losing a third of your braking on that corner.

Use a wire wheel to clean up all the carbon...and brake cleaner...and clean the hub and inside the wheel too so everything fits clean and tight. ...and grease the guidepins (is my opinion...some don't...many have strong opinions on it either way)...but I agree with Don you should replace the bushings. I put my guidepins in my electric drill gently and used fine sandpaper to clean them up while spinning. Like 600 grit or something.

Surprised you've gone so long like this, but glad you're going to fix it!
 

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Even better: Put your 7mm Allen on a 3/8 electric driver. Grab it with Steel Wool (medium) and spin a couple of turns. BAM it's clean and shiny. Real fast too.
 

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Discussion Starter #5
thanks guys, not sure I can buy just the rubber bushings, I think they come with new pins as a kit. The rotor has been like that for at least 3 years and every MOT I ask the guy about it and he replies, well it passed the brake efficiency test, and I have to say the car doesn't pull to one side even under real hard braking.

Possibly the rotor is distorted in the middle, if it wasn't maybe it is now, although I think the previous rotor was worn similarly when I replaced it years ago.

The brake on that wheel works and it isn't seeping fluid so the piston and seal must be OK. So I'll concentrate on the sliding pins and rubber bushings and try again with a new rotor and pads.
 

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thanks guys, not sure I can buy just the rubber bushings, I think they come with new pins as a kit. The rotor has been like that for at least 3 years and every MOT I ask the guy about it and he replies, well it passed the brake efficiency test, and I have to say the car doesn't pull to one side even under real hard braking.

Possibly the rotor is distorted in the middle, if it wasn't maybe it is now, although I think the previous rotor was worn similarly when I replaced it years ago.

The brake on that wheel works and it isn't seeping fluid so the piston and seal must be OK. So I'll concentrate on the sliding pins and rubber bushings and try again with a new rotor and pads.

Those bushings are absolutely available, I change them out on every rotor and pad change. For as for as cheap as they are (about 8 bucks for the OE maker ATE) and makes sure the caliper moves as it should I'd say it's a no-brainer. I'm also on ceramics, so really long intervals between brake jobs makes it worth it.

34216869617
 

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IMHO I cannot see how pins could result such wearing. I assume you do not drive much, as you have same rotor for 3 years. Means you didn't remove pads yet? What I see is that pad barely touches dick on both outer and inner side of a disk, and wears in a middle. My guess is you have some hard item (stone, metal piece) stuck some way in between disk and pad and stays there till now, grinding disk in a middle. take pads off and get a picture. My money is on that
 

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If the pins bind, it will indeed result in less 'cleaning' of the outer face of the rotor.

In a corrosive environment, something like that eventually happens. Doesn't do it in a
dry, polite climate, only in damp salty ones. In Western NYS, we'd get rotors looking like
that pretty regularly, since the sliders would rust to the calipers. They DO move, they just don't
move correctly.

Me, I'd replace bushings, pins, rotors and buy a nice set of stock (Textar, Jurid, etc) pads, you
know, the kind that make lots of dust? Because they tend to scour the rotors far better than low- dust pads.
Actually, I'd put new seals in the calipers too, because they usually need it.

t
overachiever.
 

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I don't think this is caused by pins, pistons, or seals at all. Something's amiss with the brake pad. I'd bet it's either defectively built with a convex surface, or there is rust under the pad material from the backing plate rusting - likely from the spot in the center where the backing plate has holes through it to grip/attach the friction material. As it ages and water intrusion continues, the rust continues to swell and maintains the contact only of the center portion of the deforming/lifting friction material. Replace pads in full sets on an axle and so that's my thought - replace all the pads and clean and lube the caliper bits as normal.
 

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If the pins bind, it will indeed result in less 'cleaning' of the outer face of the rotor.

In a corrosive environment, something like that eventually happens. Doesn't do it in a
dry, polite climate, only in damp salty ones. In Western NYS, we'd get rotors looking like
that pretty regularly, since the sliders would rust to the calipers. They DO move, they just don't
move correctly.

Me, I'd replace bushings, pins, rotors and buy a nice set of stock (Textar, Jurid, etc) pads, you
know, the kind that make lots of dust? Because they tend to scour the rotors far better than low- dust pads.
Actually, I'd put new seals in the calipers too, because they usually need it.

t
overachiever.
Photo of pad would show the reason.
pads replaced will solve the problem. disk skimming would possibly be required too.
 

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Discussion Starter #11
If I remember the previous disk on the same wheel was exactly like that, uneven wear. I replaced the rotor, fitted new pads and greased the pins. And now the same again on the same wheel on the same face.
The MOT tester said he's seen it before, its because we live near the coast. Strange that it's only on the one wheel tho.

I have ordered new bushings & pins as a kit and will check if the pads are flat, I bet they aren't in which case I'll renew them. The disk is probably toast so will replace that too. Then lets see if the new disk goes the same way !

I'll post photos on here how I get on.
 

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Curious as to what brand pads you had installed last go round?
Is it possible you drive very little and use very little brake causing the oxidation buildup NOT to wear away?
 

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Discussion Starter #13
Curious as to what brand pads you had installed last go round?
Is it possible you drive very little and use very little brake causing the oxidation buildup NOT to wear away?
Yes only about 5000 miles a year these days, sorry can't remember what brand the pads are
 

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Discussion Starter #14
I think we have a solution and it's a combination of the suggestions we've had.

The pins were stuck and did not move freely in the bushings. So I cleaned them up with the drill method and they are nice and shiny now. Even then they didn't slide easily at all in the bushing but once I had greased them and pushed / rotated them through a few times the grease took effect and they slide great now.

Secondly, as you can see, the brake material has started to delaminate from the metal disk pad. Along with the wear pattern it's time for a new set and a rotor to go with it.

So there we have it folks, a caliper not sliding smoothly and a deformed brake pad !!

20200630_142344.jpg 20200630_143005.jpg 20200630_142210.jpg

So did the sticking caliper cause the brake pad to deform or was it ingress of water and dirt through lack of use ?
 

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Taking a victory lap!!
 
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