Brake disk hitting caliper?

[Alow]

Has anyone seen this before? The brake disc seems to be hitting the inside of the caliper as it rotates, making a grinding noise as I drive. When I apply the brakes it goes away but when I let go of brakes it comes back. I checked the part number of the disc and it is the correct part number for my 128 according to realoem and what is stamped on the zimmerman box. Bought these from FCPeuro and they say made in germany. To even confuse matters more, I have another set (for the street vs. the track) and that one looks identical but does not hit the caliper.

I am wondering if it's installation error but there is no real way to mess this up.. the screws go where they go..

anyone seen this before? kinda stumped… this is a 128i with bmw performance brakes. it's the rear brakes

[spidertri]

Can you measure the offset distance of the hub face to the disc surface and compare to your rotors that don't hit?

First thing that comes to mind is the rotors from the E90/92 328i that would be 10mm different offset due to the unique rear hubs found on the 128i that stick further out.

[iminhell1]

Calipers are shot. What's happening is when you apply the brakes the bushings around the pins are flexing.
Try replacing the rubbers and pins. Also do a good job bleeding all the old fluid out. Heat is what kills these things. Old fluid does not displace fluid as well as new.

2x 34216869617
2x 34111157041

[Alow]

Thanks for the ideas guys. I did measure the rotors but they are the same offset so that's not it.

The guides for the pins look in good shape, so I didn't think that was the issue but made a mental note to replace them anyway.

I did find the culprit.. after a few tries of different rotors and pads I realized the PFC 08 pads I have are smaller than the OEM. This is why the rotor hits the caliper. With another set of pads (street pads) there is no contact. Turns out bimmerworld has on their website that this pad size (starts with 396) fits the rear of the 128i but it does not! I will give them a call tomorrow.

[spidertri]

That's weird, I've run multiple sets of 396 PFC pads in the rear and never had that issue, both 08s and the Z rated street pads.

Main issue that I've seen with the 396 pad that PFC makes is the clip doesn't actually hold the inner pad against the piston, but besides a rattle sometimes, it has never caused any issues.

Would be interesting to hear what bimmerworld says.

[tracer bullet]

Originally Posted by Alow

Thanks for the ideas guys. I did measure the rotors but they are the same offset so that's not it.

The guides for the pins look in good shape, so I didn't think that was the issue but made a mental note to replace them anyway.

I did find the culprit.. after a few tries of different rotors and pads I realized the PFC 08 pads I have are smaller than the OEM. This is why the rotor hits the caliper. With another set of pads (street pads) there is no contact. Turns out bimmerworld has on their website that this pad size (starts with 396) fits the rear of the 128i but it does not! I will give them a call tomorrow.

Offset perhaps but also overall diameter, one set may be a hair larger than the other.

Not quite seeing how pad size will change this. Agreed w/ Iminhell that there's some deflection going on, and it's probably the sliding part of the caliper that is deflecting. Pads might be wearing unevenly as well, specifically the top getting thinner than the bottom. Maybe their backing material, or the face of the brake piston, or even the inside of the floating part of the caliper is offset or dirty or something along those lines and they were more or less installed at an angle. Those are big chunks of metal but brakes are really strong and can still make them bend / deflect.

Is thos on both sides?

[Thunderguts]

Are you absolutely sure those rotors are the correct diameter? I would measure them and see if they correspond to the box. Deflection is possible, but I'm leaning towards slightly oversize rotors.

[Alow]

Originally Posted by Thunderguts

Are you absolutely sure those rotors are the correct diameter? I would measure them and see if they correspond to the box. Deflection is possible, but I'm leaning towards slightly oversize rotors.

yes, measured them. exactly same size. Also, the same rotors with a different set of pads (oem) do not make contact with caliper.

[Alow]

Originally Posted by tracer bullet

Offset perhaps but also overall diameter, one set may be a hair larger than the other.

Not quite seeing how pad size will change this. Agreed w/ Iminhell that there's some deflection going on, and it's probably the sliding part of the caliper that is deflecting. Pads might be wearing unevenly as well, specifically the top getting thinner than the bottom. Maybe their backing material, or the face of the brake piston, or even the inside of the floating part of the caliper is offset or dirty or something along those lines and they were more or less installed at an angle. Those are big chunks of metal but brakes are really strong and can still make them bend / deflect.

Is thos on both sides?

From what I can see, if the pad isn't tall enough, the caliper is too close to the rotor. Once the clip that holds the two pieces of the caliper together is in, the caliper gets pushed into the rotor.

Also, the rotor made contact when driving. When brakes were applied, the contact would actually stop. Thus, I don't think it's the bushings/guides of the pins in the caliper.

Haven't called bimmerworld yet unfortunately haven't had a chance.

[Thunderguts]

Okay, so then the difference in pad thickness must be mis-aligning the caliper when you reattach it. Odd, but what else could it be?

[tracer bullet]

Originally Posted by Alow

From what I can see, if the pad isn't tall enough, the caliper is too close to the rotor. Once the clip that holds the two pieces of the caliper together is in, the caliper gets pushed into the rotor.

OK, so - you could be right, but - I'm not following.

I can't think of a way the pads are involved. The caliper is directly bolted into place, and in a roundabout way so is the rotor. If those two are contacting, then either 1) The rotor is too big, 2) the caliper is flexing, or 3) both.

The pads just go along for a ride on the pins. I'm not seeing them driving anything.

That said, there could be something else that is flexing, or loose, but I can't think of what since they're all more or less connected to athe same pretty huge chunk of metal.

[iminhell1]

The pin/bushing sets the clearance to the rotor.

There are 2 things that would change that clearance (using correct parts),
a) Rotor moving, enlarged bolt/hub; under braking the rotor could be 'pulled' to the caliper

b) Caliper flexing, either worn parts or seized parts; that caliper 'floats', when either the pins or the piston are seized there is uneven pressure applied to the pads, pulling the caliper uneven over time (uneven ware on a pad, taper)

Other than those 2 things, I don't know of anything else that would cause this. A larger or smaller pad plays no part that I can think of.


The only outlier to this situation would be a bad wheel bearing. But I assume you'd notice far more than just some rotor rubbing if a bearing was that bad.

[Alow]

Originally Posted by Thunderguts

Okay, so then the difference in pad thickness must be mis-aligning the caliper when you reattach it. Odd, but what else could it be?

My thoughts exactly. Although it isn't the pad thickness but rather the height and shape of the ears of the pad. Those play a part in how close the caliper is to the rotor once you attach the retaining clip; as the clip pulls the floating caliper into the rotor.

I did call bimmerworld today and showed them these pictures and they are also stumped. They asked for more detailed pictures of the pad on the rotor by itself, the other pads, etc. I will update this thread too when I take them.

[spidertri]

Have you run these PFC pads before? Or is this a brand new set?

[Thunderguts]

I guess swap out the rear pads for something high performance in the stock size. I have the rear performance brakes with ATE rotors, but I've only ever had Hawk HPS on them.

[tracer bullet]

Originally Posted by Alow

Although it isn't the pad thickness but rather the height and shape of the ears of the pad. Those play a part in how close the caliper is to the rotor once you attach the retaining clip; as the clip pulls the floating caliper into the rotor.

You may be right but I'm not seeing it. Rotor position is dictated by where it bolts to the hub. Caliper position is dictated by where it's bolted in the back (the knuckle I guess you'd call it). The pins guide the pads. The clip keeps them from rattling.

I feel like your caliper mounting is an issue. It's flexing, or loose, or installed at an angle - rust or debris between it and the knuckle perhaps? If it were my car I would unbolt it and inspect those surfaces.

Again you may be right. I just don't see it though. Definitely intrigued however.

[spidertri]

So I was looking at this last night while changing from my 08s to my Z rated rear pads. I do see what Alow is talking about with the 396 pad shape and the potential for the caliper to come into contact with the rotor.

When the pad is installed, since the ears on the outer pad aren't identical to the OE 128i pad shape, they allow ~1/4" fore-aft movement of the pad itself when the caliper is properly bolted in place and the spring clip installed.

I always put permatex silicone extreme brake parts lubricant on the outer pad where the ears of the caliper contact it and this keeps it in place and I don't get any rattles or pad movement. I am also running brass caliper bushings at all 4 corners, so I have less movement of the caliper itself.

Anyway, it seems to me, that if the stock rubber caliper bushings were in bad shape, installing the spring clip would put enough force on it to twist the caliper and pull the outside end closer to the rotor than the inner side. I can't imagine fresh rubber caliper bushings having enough play to have that happen, but it seems feasible that it is a potential issue.

OP did you ever get a response from Bimmerworld? Seems like they might have enough pull with PFC to get the pad shapes updated.

[Alow]

Originally Posted by spidertri

So I was looking at this last night while changing from my 08s to my Z rated rear pads. I do see what Alow is talking about with the 396 pad shape and the potential for the caliper to come into contact with the rotor.

When the pad is installed, since the ears on the outer pad aren't identical to the OE 128i pad shape, they allow ~1/4" fore-aft movement of the pad itself when the caliper is properly bolted in place and the spring clip installed.

I always put permatex silicone extreme brake parts lubricant on the outer pad where the ears of the caliper contact it and this keeps it in place and I don't get any rattles or pad movement. I am also running brass caliper bushings at all 4 corners, so I have less movement of the caliper itself.

Anyway, it seems to me, that if the stock rubber caliper bushings were in bad shape, installing the spring clip would put enough force on it to twist the caliper and pull the outside end closer to the rotor than the inner side. I can't imagine fresh rubber caliper bushings having enough play to have that happen, but it seems feasible that it is a potential issue.

OP did you ever get a response from Bimmerworld? Seems like they might have enough pull with PFC to get the pad shapes updated.

Thanks for pinging me. I forgot to update this thread.

Bimmerworld thinks because I have the BMW performance brakes that these pads don't fit my rear calipers and recommended I go with something else like carbotech. I don't know if that's accurate because the only difference i can tell between these and the original brakes in the rears is a larger piston… and other pads made for the stock calipers (like carbotech) work just fine…. but I went back and forth with them enough times that I decided to just accept my issue. From now on i'll just use carbotech in the rear.

I did recently buy the brass guides and metal pins and plan to install them sometime soon. I don't know if it will make a difference or not but I will definitely try.

[Thunderguts]

Originally Posted by Alow

Bimmerworld thinks because I have the BMW performance brakes that these pads don't fit my rear calipers and recommended I go with something else like carbotech. I don't know if that's accurate because the only difference i can tell between these and the original brakes in the rears is a larger piston… and other pads made for the stock calipers (like carbotech) work just fine…. but I went back and forth with them enough times that I decided to just accept my issue. From now on i'll just use carbotech in the rear.

Nah, that's not it. The Performance BBK uses the same rear pad size as a stock 128i. RealOEM confirms it. I have the BBK and I'm using the Hawk HPS for a standard 128i in the rear.

[spidertri]

Originally Posted by Thunderguts

Nah, that's not it. The Performance BBK uses the same rear pad size as a stock 128i. RealOEM confirms it. I have the BBK and I'm using the Hawk HPS for a standard 128i in the rear.

Yeah, this is exactly correct. I'm running the 42mm rear caliper from a 328 which is the same as the performance brake caliper.

The 396 pad shape isn't ideal for the rears and I don't think PFC sees the market for creating a pad specific for our cars. So if you want to run PFC you have to put up with the compromise.

[Alow]

Originally Posted by spidertri

Yeah, this is exactly correct. I'm running the 42mm rear caliper from a 328 which is the same as the performance brake caliper.

The 396 pad shape isn't ideal for the rears and I don't think PFC sees the market for creating a pad specific for our cars. So if you want to run PFC you have to put up with the compromise.

I think you are right. That's what it comes down to.

[Alow]

To circle back on this thread… i did replace the caliper bushings for the brass kit from bimmerworld. the installation instructions say to not install the retaining clip. with those two changes, the PFC pads seem to fit without the disc hitting the caliper like it was before. I tested it just by rotating the disc while on jack stands.

I haven't done a track day yet, but that seems to be the solution.