Downsizing Rear Calipers from F30 to fit 17" Wheels

[M3SQRD]

Originally Posted by tftimbn

M3SQRD

Alright, here's the comparison. I noticed that if I line up the side tabs, the Audi pad is also taller. You can see in my excellent tracing, the top comparison is by lining up the tops of the pads, and the bottom comparison is by lining up the mounting pads. The Audi pad is longer in the direction we want, but also a few mm in the direction we don't. This does create an issue on the caliper only for the piston side, where the pad does not fully go in due to this.

I see 2 options, 1) trim the top of the pad, or 2) what I would likely prefer to do, is grind down part of the caliper bracket with a die grinder to allow the pad room. You can see the obstruction in the video around the 3:37 mark. I would likely grind up to the visible seam on the caliper. My thoughts are this would likely have to be done even with a custom pad, and at that rate, the size of the pad would be about the same as this Audi pad, and for simplicity sake, we have off-the-shelf replacement parts and a one-time caliper modification.

The pad play opposite of the piston side appears to be the same (granted theres no rotor installed nor is this on a vehicle at the moment, it's pouring rain today and tomorrow).

The piston pad no longer has the springs either. I'm not sure if I would consider this an issue or not. As well, the pad wear sensor is supposed to go on the outer pad, where this outer pad does not have a spot. It may fit on the inner pad, but at this point, I wouldn't lose sleep over trying to get the pad wear sensor in. I'd rather just plug it in and tie it up somewhere and not worry about the idiot light.

The Audi the pad guide and anti-rattle clip are definitely a much tighter fit. Have you tried using an e46 m3 pad? That’s probably the best pad to use and likely only requires grinding the inner radius so it doesn’t hit the rotor hat or perhaps it doesn’t need to be ground at all. The three-legged spring that goes into the caliper is to prevent the pad from rattling; however, the outer pad is going to rattle badly as as clunking when changing directions from fwd-rev or rev-fwd. if you went with a custom pad from Carbotech they add the custom pad to their catalog so in the future you just order pad xyz.

[M3SQRD]

Why not try the e46 M3 rear pad? The pad is the right width at 123 mm, guide geometry is a little different and it has a good radial depth at 59 mm:

[M3SQRD]

Another option is to run the f30 pad that doesn’t fully cover the swept area but is a more aggressive compound compared to the front which will pull the brake bias back toward the rear. Ideally, get to at least 68% front biased (matches the M2C 2NH brake bias.

[tftimbn]

Originally Posted by M3SQRD

Why not try the e46 M3 rear pad? The pad is the right width at 123 mm, guide geometry is a little different and it has a good radial depth at 59 mm:

Hm, that's a pretty good shape lol. Let me see if I can find some locally or I'll order another set on Amazon.

[M3SQRD]

Originally Posted by tftimbn

Hm, that's a pretty good shape lol. Let me see if I can find some locally or I'll order another set on Amazon.

I forgot to mention, this pad will likely overhand the rotor OD based on visually comparing the f30 and e46 M3 pad. Another pad worth checking is the e46 330ci pad.

[tftimbn]

Originally Posted by M3SQRD

I forgot to mention, this pad will likely overhand the rotor OD based on visually comparing the f30 and e46 M3 pad. Another pad worth checking is the e46 330ci pad.

Had a busy week, but here’s the E46 M3 pad. (P/N D683)

https://imgur.com/a/N5CO2Ud

Looks like it’ll still be subject to grinding the caliper bracket, but, doesnt seem to go over the rotor. I’ll likely end up grinding it out tomorrow for a test fit.

What do you think?

[M3SQRD]

Originally Posted by tftimbn

Had a busy week, but here’s the E46 M3 pad. (P/N D683)

View post on imgur.com

Looks like it’ll still be subject to grinding the caliper bracket, but, doesnt seem to go over the rotor. I’ll likely end up grinding it out tomorrow for a test fit.

What do you think?

From the pictures, the pad radial depth looks good but maybe it doesn’t extend to the rotor OR by 1-2 mm. This basically tells you what radial depth is needed. The geometry of the pad guide is very different from the f3x caliper guides. In pics, it wasn’t horrible but with the actual hardware it doesn’t look great. The pad guides help keep the pads from vibrating so opening up the clearance will only make the vibration worse. I assume the caliper bracket is more expensive than your ~$29 pads? If it is, modify the pad, not the caliper, in case you have to compromise and run the first shown radial depth pad.

[tftimbn]

Originally Posted by M3SQRD

From the pictures, the pad radial depth looks good but maybe it doesn’t extend to the rotor OR by 1-2 mm. This basically tells you what radial depth is needed. The geometry of the pad guide is very different from the f3x caliper guides. In pics, it wasn’t horrible but with the actual hardware it doesn’t look great. The pad guides help keep the pads from vibrating so opening up the clearance will only make the vibration worse. I assume the caliper bracket is more expensive than your ~$29 pads? If it is, modify the pad, not the caliper, in case you have to compromise and run the first shown radial depth pad.

I actually only paid $40 each caliper, so I'm not really worried. It looks like if I go the pad route, I'll have to cut into pad material. I'd only be cutting a hair off the top of the bracket where the pad hits, no where near the guides. Surely the pad itself wouldn't recognize a difference as if it was just a smaller pad.

I think this is the route I'm going to take. I'll trim the caliper, use the E46 pads instead of the Audi pads, also because it seems I can retain the brake sensor that way. I do feel more comfortable with this fit as opposed to the Audi pad, because it does have the spring to hold it in the caliper, so that was definitely a good call on your part for suggesting the E46 pads.

Edit: Here's the opposite, F8X calipers on an E46. Quite the machining went in to play here. https://nam3forum.com/forums/forum/m...swap-on-e46-m3