Stock Caliper Has Play?

[kyoo]

Recently did a brake pad job for my E92 M3, and without touching the brake fluid the pedal is now soft until about 1/3rd of the way down. I bled the brakes even though I didn't touch the system, and it's soft.

I think I may have found the reason the pedal is soft - there's a decent amount (1-2mm) of play in the caliper when pressing the pedal. Discovered this as I was doing the brake fluid flush. I don't think there should be ANY play in the caliper, correct?

It almost looks like it wants to twist itself off before physically being able to go further - an exaggeration, but the caliper moves backward when the brake pedal is depressed.

I don't remember having any play in the caliper before removing, and it seems like the only thing that holds the caliper to the caliper bracket (which I didn't remove) are the two slider pins? I've gotten those on pretty tight now, not sure what else it could be. I assume the cover spring doesn't do much in the way of holding the caliper on...

Quick answers appreciated. Not sure what else to tighten since those are the only bits you need to remove to get the caliper off the bracket.

Wondering if the outer retaining spring got weak from the uninstall & reinstall? idk. More play in the fronts than the rears.

[kyoo]

Updating for my own notes. It seems very likely/possible that the cause of the caliper flex & softness in pedal I am feeling is due to worn rubber bushings that the slider pins slot into. I'm not sure how they could have worn in the way that they did after simply removing the pins, but based on the description of what the brass bushings (https://www.ecstuning.com/b-ecs-part...003326ecs02~a/) are intending to fix, it seems to be exactly my issue of twisting/flexing caliper.

I would swap to the kit above if it were legal in stock class, but as it is not, I will try replacing the rubber bushings & oem pins to see if that helps align the caliper better.

[kyoo]

Originally Posted by M3Post

You need to replace the rubber caliper pin bushings with these:
https://www.ecstuning.com/b-ate-part...111157038~oea/

thanks, that's more or less what i figured/found. surprised this doesn't come up, maybe i was particularly rough with the install/uninstall and the rubber bushings went bad. pedal was super stiff before it.

unfortunately those aren't legal in stock class where I run, but if I can get the pedal feel back to what it was before the pad swap with new rubber bushings/pins/clip, i'll be more than happy with it.

[kyoo]

thanks, yea i really would love to use those if i could, but again if i can get back to normal with the rubber bushings that will be great. will find out once i get them installed.

thanks for the input

[kyoo]

I swapped back on the OEM pads to see how they would feel - the pedal was firmer again than it was on the new Ferodos.

I think it may be due to there being less OEM material, and perhaps that makes it easier for the caliper to bite down on it - ie like biting a thin sandwich vs a giant burger. Either that or the compressibility of the OEM pads is really good.

Either way, I think that tells me getting new sliders, bushings, retaining clip will be pointless, feel will wind up the same and it'll just be a waste of money.

[kyoo]

bumping this - any reason why worn OEM pads would exhibit a stiffer pedal than new Ferodo DS2500s?

[kyoo]

Originally Posted by M3Post

Well, I'll play and go out on a limb to speculate that the thinner, worn OEM pads are not as compressible as the new and thicker Ferrodo pads. Brake pad friction material is often suspended in an organic binder (like resin). When brake pads are bedded in (broken in) they often need to out gas as the pad comes up to temperature. Then pad cools, and as the pad material "cures" it often becomes harder than when it is fresh out of the box.

Moreover, since the worn OEM pads are thinner, there is simply less material to compress. Another reason might be that since the OEM caliper is a sliding caliper, the torque moment on the pins and bushings is lower with thinner pads. Again, and because of the trolls out there, this is speculation on my part but is rooted in my own experiences. Just trying to help. That is the what this forum used to be (i.e. a place to provide opinion) before it was taken over by the Trolls and Know-It-All wannabes.

Here's a link to consider:
https://textar-professional.com/text...mpressibility/

that is solid info and educated speculation, all of which I will consider. I appreciate it. It's a little harder to get good info on technical discussions on this forum save for a few guys it seems, which is unfortunate.

thanks, I'll look through the data. I think I've more or less isolated the issue to either the pads or how it grips these pads compared to OEM, etc. Didn't consider the torque moment on the pins/bushings being less on pads with more wear, that is interesting to consider.

[MSY]

Play is normal on stock calipers. I personally a lmk ways found it hard if you are manually bleeding to get right feel but I'm not super patient. Pad size certainly effects feel but you should have no problem with new pads get
Ing a firm feel. I'd bleed a couple more times

[dparm]

Originally Posted by M3Post

Well, I'll play and go out on a limb to speculate that the thinner, worn OEM pads are not as compressible as the new and thicker Ferrodo pads. Brake pad friction material is often suspended in an organic binder (like resin). When brake pads are bedded in (broken in) they often need to out gas as the pad comes up to temperature. Then pad cools, and as the pad material "cures" it often becomes harder than when it is fresh out of the box.

Moreover, since the worn OEM pads are thinner, there is simply less material to compress. Another reason might be that since the OEM caliper is a sliding caliper, the torque moment on the pins and bushings is lower with thinner pads. Again, and because of the trolls out there, this is speculation on my part but is rooted in my own experiences. Just trying to help. That is the what this forum used to be (i.e. a place to provide opinion) before it was taken over by the Trolls and Know-It-All wannabes.

Here's a link to consider:
https://textar-professional.com/text...mpressibility/

Good post. Glad to see some people still want to talk tech. I had said something similar in another thread, namely that the OEM caliper design is going to have a lot of play.

Brake pad friction material density typically goes down as it wears. This is not something people mention. It's usually just "OMG look at that motherfucking coefficient of friction holy fuck" or pad thickness measurements.

[kyoo]

ferodos feel even worse after an autocross, damn. I don't know how, but it feels like air. will start flushing liters through to see if there's an improvement. will also replace the oem hardware to see if that helps at all. pads started squeaking during normal driving too, until I press the pedal. definitely seems like something is off. I may swap in oem pads again to see if the pedal is still stiff with them, but I've ran ferodos on my evo 9 before with no mushiness in pedal

[dparm]

Originally Posted by kyoo

ferodos feel even worse after an autocross, damn. I don't know how, but it feels like air. will start flushing liters through to see if there's an improvement. will also replace the oem hardware to see if that helps at all. pads started squeaking during normal driving too, until I press the pedal. definitely seems like something is off. I may swap in oem pads again to see if the pedal is still stiff with them, but I've ran ferodos on my evo 9 before with no mushiness in pedal

The DS2500 is going to have a more linear pedal feel that a typical street pad. It's not terribly grabby. And I don't think autocross is really going to put much heat into the brakes.

A little bit of squealing right as you come to a stop is not unheard of on that pad. Try re-bedding:
https://www.zeckhausen.com/catalog/i...Path=6446_6443

[kyoo]

Originally Posted by dparm

The DS2500 is going to have a more linear pedal feel that a typical street pad. It's not terribly grabby. And I don't think autocross is really going to put much heat into the brakes.

A little bit of squealing right as you come to a stop is not unheard of on that pad. Try re-bedding:
https://www.zeckhausen.com/catalog/i...Path=6446_6443

i understand the first part, but the mushy pedal is not that. my 07 corolla's pedal is firmer than my m3 though, and that is unusual. I will try re-bedding, but I'm otherwise baffled. the feel is identical to having air in the lines, so like I said I will re-attempt bleeding as well.

[Richbot]

This may call for a dealer-bleed? The dealer biannual fluid change procedure runs the ABS/DSC pump, not that expensive, get a loaner and autocross it instead that weekend. That left front is RIGHT under it, maybe 24" of line before you're in the pump, maybe got a bubble up in there somehow? Wouldn't explain why the Ferodos seem to feel worse than stock just swapping back and forth, but...

Have you done any ABS stops with the new pads on the car? Just curious (and curious if you can even trigger lockup). DON'T DO ANYTHING UNSAFE THO

[kyoo]

Originally Posted by Richbot

This may call for a dealer-bleed? The dealer biannual fluid change procedure runs the ABS pump IIRC, not that expensive, get a loaner and autocross it instead that weekend. That left front is RIGHT under it, maybe 18-24" of line before you're in the pump, maybe got a bubble up in there somehow?

Have you done any ABS stops with the new pads on the car? Just curious (and curious if you can even trigger lockup). DON'T DO ANYTHING UNSAFE THO

yes, have triggered abs. thinking about doing some bleed-abs-bleeds during the process. it's grabbing, it's just that the first full third of the pedal is total mush. again I realize different pads have different compressibility, but this is beyond the range of normal

[Richbot]

Well I guess another question presents itself then, do you think ABS was pulsing the fronts at all, or just the rears?

[kyoo]

good question, i've no idea. after revamping all of my brakes on the evo, I don't think pedal feel should be very complicated. minor differences in pedal feel between pads & things you can do to help it, but otherwise it can only be a handful of things, especially as i've been narrowing things down in my investigation.

fwiw, here's my autox run. not particularly fast by any means but continuing to get used to the car.

[dparm]

Any competent indie BMW shop should have the computers to cycle the ABS pump. Just tell them you want the brakes bled properly.

[sgreer78]

Sam, Dave has a tool that can cycle ABS pumps if you decide that's what you want to do. I still think there's some issue with your rotors and those Ferodo's not getting along. Before I do my pads I'm going to have my lips turned down.

[dparm]

To be clear, are you saying there is a lot of pedal travel before the brakes start to work?

Or are you saying that pushing harder on the pedal doesn't seem to stop the car any harder?

[kyoo]

Originally Posted by dparm

To be clear, are you saying there is a lot of pedal travel before the brakes start to work?

Or are you saying that pushing harder on the pedal doesn't seem to stop the car any harder?

there is a lot of pedal travel before the brakes start to work, yes. hard to gauge exactly how much, but a significant amount more than oem pads. oem pads started working, felt like, almost as soon as you touched the pedal. these pads, 1/3rd down before feeling the brakes engaging.

seems like air but weird that it started right after the oem pad switch - I want to retry the oem pads one more time, but getting tired of swapping pads in and out.

sean, will reach out - as far as I understood, was some kind of special tool bmw used, but I should be able to get that fluid out after activating abs and bleeding a few times also. in CA for work this week, will investigate more this weekend.

as far as ideas go, I'm not sure what else it could be, or what in the pad or caliper could really cause such a difference in feel except air in the lines. bizarre, don't want to keep obsessing about it but the difference is so stark that I really just want to know what it is/what happened

[dparm]

If the first X inches of pedal travel have no resistance and there is no braking happening, that sounds like air in the lines. When that happens, if you pump the brakes a few times, does the pedal firm up?

[kyoo]

Originally Posted by dparm

If the first X inches of pedal travel have no resistance and there is no braking happening, that sounds like air in the lines. When that happens, if you pump the brakes a few times, does the pedal firm up?

have bled, but will bleed again more. yes, a double pump makes the pedal feel like it used to feel, "catching" at higher up on the pedal - this is exactly the symptom of brakes with air, I agree. it does feel like air in the lines, but I have also had a misaligned shim feel exactly the same. no shims in this case, but trying not to rule out any weird possibilities. I should try out a different pad too, if it gets to that.

appreciate the continued input.