Smoking brakes on one side...help!

[traviswt]

Last night I took my S4 out for its first real drive of the year now that the weather is getting to be reliably decent here in Ohio. I checked my oil, adjusted the air in my tires, and took a short 15-minute drive around town, with a small 5 minute stretch of highway driving in there (just one exit down and back) so that I could open things up a bit and really get it warmed up. As I was returning home and sitting at a red light, I could smell and see a decent amount of smoke coming from my driver’s side with that unmistakable brake smell. When I got home a few minutes later, things were smoking hot and still visibly smoking. The caliper was too hot to touch (and the paint is blistered a bit), the wheel was almost too hot to touch, and I didn’t even attempt to touch the rotor. I took the cap off of my brake fluid reservoir and the reservoir was completely full, all the way up to the cap. I did not check this fluid level before my drive, and I don’t think it was this high previously, but I cannot be certain. I had bled the brakes a year ago and adjusted the reservoir then so maybe the heat of the driver’s side caused the fluid to expand into the reservoir? Im not sure if that’s how it works, just guessing at this point. I should mention that my brakes are still stock.

Some backstory on the car and brakes before I ask my questions, which are below if you want to skip ahead. The car sat most of last year as I needed a new exhaust from the turbos back and was sorting that out. In that time the old brake pads on the driver’s side rusted to the rotor and when I went to move the car, the pad material broke right off of the backing plate. So, I replaced the front brake pads and rotors on both sides (just oem replacement hardware from autozone) in the fall of 2018 and as far as I can recall, when I drove the car to and from the shop that installed the exhaust, there were no braking issues or smoking, but that involved mostly highway driving with minimal hard braking. The car sat in my garage on a trickle charger all winter, so the brakes were not exposed to the elements. I guess what I’m getting at is that they shouldn’t be frozen or locked up.

I should note that when I noticed the very full brake fluid reservoir after returning home, I did what I could to soak up a bunch of brake fluid with paper towels and drop the level a little bit. I was able to roll the car up and down my driveway just by pushing it with it in neutral, so it doesn’t seem like the brakes were dragging or stuck at that time, even when things were still smoking hot.

Questions:
Could the overly full brake fluid reservoir be why the brakes on the driver’s side front were dragging\not fully releasing, or is that a side effect of them, and the brake fluid, getting so hot?

What steps should I take to troubleshoot further?
I plan to remove the brakes on that side and inspect everything, look for evidence that something got stuck and was dragging, check the pads, slide pins, and caliper pistons to make sure they can move freely, etc.

What damage could’ve been done during this extreme heat?
I’m guessing that some damage was probably done to my wheel bearing if it got as hot as everything else. The paint on my caliper has definitely seen better days. I would guess that my brake fluid life has shortened due to the extreme heat as well, if it got that hot. And I would suspect that my pads are probably toast now. What else should I be worried about or check out in greater detail?

Thanks for any help in advance.

[fR3ZNO]

What do you mean by "adjusted the reservoir"?

Was a specific wheel smoking or the whole drivers side? If you have one, a infrared thermometer is a nice tool to diagnose a dragging caliper (go for a short drive and measure temps of the rotor/caliper and compare to the rest of the wheels, one that is hotter than the rest would point to a dragging caliper). Which is what it sounds like from the sound of things. Especially with the car sitting for extended periods of time. But like you said, I would look over the calipers and make sure the slide pins are lubricated and also check the pistons to make sure they are not seized.

Also, yes the pads that got overheated will likely need to be replaced... it is likely that the fluid was boiled and that might explain the overflowing res.

[traviswt]

By adjusted the reservoir I mean that I had made sure that its level was between low and hi after I had bled the brakes. I used a power bleeder and was keeping an eye on the level as I was bleeding. I don't recall there being any issues with the fluid level at the time.

Ill have to look into getting an infrared thermometer, sounds like it could be helpful here.

Specifically, the drivers side front wheel was smoking...bad. The passengers side rotor was hot but not too hot to touch so it was doing work, but nothing like the drivers side. The rears both felt like the passengers front, hot but not too hot to touch. All 4 rotors had bright metal from where they were wearing, so they all looked like they were doing work. My passengers rear doesnt look to be fully engaging so Ill have to look into that. Both rear calipers are remanufactured OEM as my old rear calipers were having issues.

Thanks for the advice! I havent had a chance to check the reservoir since last night but I will a bit later today, just to see what the fluid level looks like now.

[VR6Bomber]

Caliper seized.
Definitely happens when cars sit for a while.

[Pdaniel8]

Try to spin the wheel by hand, with the wheel of the ground to check or seized caliper.

[traviswt]

Thanks guys, Ill give these tests a shot.

With it being able to roll freely in the driveway when in neutral, would that be a good indication that the caliper had freed up at some point during the drive? What Im worried about is being able to reliably take it out regularly even after I check it out. For example, if its some sort of intermittent issue.

[fR3ZNO]

Thanks guys, Ill give these tests a shot.

With it being able to roll freely in the driveway when in neutral, would that be a good indication that the caliper had freed up at some point during the drive? What Im worried about is being able to reliably take it out regularly even after I check it out. For example, if its some sort of intermittent issue.

Yes, it could have freed up but as soon as you press the brake pedal during a drive it would get stuck again resulting in the same issue.

[traviswt]

So if I do have a caliper that sticks semi-frequently, is that a rebuild or replace scenario? How fixable is something like that?

Or maybe move to a big brake kit like I've been wanting to.

[CELison]

You can find a used caliper cheap or just upgrade. Depends on your budget. HP2s are pretty good as is, but stoptech, 17z, 18z, ect are obviously superior. I have stoptech ST40s in my car. Very happy with them.

[Pdaniel8]

Did you change brake fluid recently?

[traviswt]

You can find a used caliper cheap or just upgrade. Depends on your budget. HP2s are pretty good as is, but stoptech, 17z, 18z, ect are obviously superior. I have stoptech ST40s in my car. Very happy with them.

I was looking at the Stoptech ST40s actually. It seems that any BBK is fairly expensive but the ST40s seem to be a bit more reasonable than some of the other choices without as much modification as 17z,18z,etc need, from what Ive read anyways. Maybe this will be the time for me to do the upgrade.

[CELison]

They're great. Just use the stop tech 2 piece rotors. They're a little pricey to replace (just did it last week), but worth it.

[traviswt]

Did you change brake fluid recently?

I replaced both rear calipers early last year and in doing so I bled those lines with new brake fluid until it ran clear and without air. I did not bleed the front lines though so there will be a little bit of old fluid still mixed in.

[Pdaniel8]

I managed to free up mine from my mk4 (also rear, very common on golf mk4) with new fluid and by moving the caliper piston in and out 5/6 times.

[traviswt]

Whats weird here is that the pistons moved fine when I was changing the pads and rotors last fall. Unless something happened while it was sitting, then I dont see how the caliper could be so stuck. I guess its not impossible but damn.

[james 408]

Yeah stuck caliper. Also those pads are complete garbage and extremely dangerous for spirited driving, but your one-side issue is definately a caliper deal. It's possible I guess air in one line or some binding/pinching, but far less likely.

Edit: at least as an initial cause, sounds like you boiled the fluid maybe too in the process so maybe that's at least a contributor. It's odd you didn't notice any pulling. Like if it's that lopsided, the car should have been fighting you in several different ways.

[Bordom]

Brake line probably collapsed internally.

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[traviswt]

Brake line probably collapsed internally.

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I have stainless steel braided brake lines on all 4 corners which makes this pretty unlikely right?

[traviswt]

I may have sourced a used Stoptech ST40 kit for the front. It needs rebuilding but I can handle that given the lower price that its being sold at. It comes with the hats for 2 piece 332x32mm rotors but no rings. It looks like there are one piece rotors available for this setup which are way more reasonable in price than buying replacement rings. Is there any reason why the two piece rotor hat\ring option is about 4 times the price per side than just a one piece standard 332x32mm rotor? Are they better in some way? It just seems ridiculous to pay a little over $600 for 2 rotor rings which are consumable parts.

Has anyone rebuilt these before? Im told that Ill need new seals (and probably boots), Stoptech brake lines, and then pads and rotors.

[traviswt]

Yeah stuck caliper. Also those pads are complete garbage and extremely dangerous for spirited driving, but your one-side issue is definately a caliper deal. It's possible I guess air in one line or some binding/pinching, but far less likely.

I don't really drive that crazy but I see what you're getting at. At the time, given that I was about to drop almost a grand on having the exhaust replaced, I was looking to just get up and running again and stay stock. A BBK is an upgrade that Im planning (probably now since these issues have popped up) but at the time I just needed the car to be able to drive reliably to the shop and get around town for a while so that I could enjoy it after not having driven it for so long.

[Bordom]

I have stainless steel braided brake lines on all 4 corners which makes this pretty unlikely right?

Less likely but doesnt mean it couldn't happen.

I'd start by inspecting the guide pins first and then the pistons. If you replace those and it still does it, I'd look at the line as suspect next

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[traviswt]

Less likely but doesnt mean it couldn't happen.

I'd start by inspecting the guide pins first and then the pistons. If you replace those and it still does it, I'd look at the line as suspect next

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Thanks for the info. Ill definitely be checking those out.

[CELison]

I may have sourced a used Stoptech ST40 kit for the front. It needs rebuilding but I can handle that given the lower price that its being sold at. It comes with the hats for 2 piece 332x32mm rotors but no rings. It looks like there are one piece rotors available for this setup which are way more reasonable in price than buying replacement rings. Is there any reason why the two piece rotor hat\ring option is about 4 times the price per side than just a one piece standard 332x32mm rotor? Are they better in some way? It just seems ridiculous to pay a little over $600 for 2 rotor rings which are consumable parts.

Has anyone rebuilt these before? Im told that Ill need new seals (and probably boots), Stoptech brake lines, and then pads and rotors.

So I have lightly used rotor rings, OEM stoptech. I'll sell them to you if you're interested. I thought I warped mine but it was just uneven brake pad deposit. So now I have brand new ones on the car and these just sitting around. PM me if you're interested.

[traviswt]

So I have lightly used rotor rings, OEM stoptech. I'll sell them to you if you're interested. I thought I warped mine but it was just uneven brake pad deposit. So now I have brand new ones on the car and these just sitting around. PM me if you're interested.

Ill keep that in mind if I end up grabbing the upgrade. Just doing some pricing negotiations now. Thanks!

[traviswt]

I pulled the trigger and have a set of used Stoptech ST-40 brake calipers coming (which need rebuilt and are currently disassembled), which fit 332x32mm rotors according to the seller, and will come with rotor hats for a 2 piece rotor setup as well. Ill need seals, boots, brake lines, pads and rotors (either rings or one piece rotors).

Can anyone recommend pads for this setup? I dont really know much about this brake system or what to look for when it comes to rotors and pads. I did some research a while back and everyone seems to like this setup, so Im comfortable with that, its just the logistics of getting it going with all the options out there for pads and rotors where Im a bit in the unknown.

CELison, you have a PM incoming about your rings.

[james 408]

anything from hps (low end) to stoptech/HC+ (mid++ tier) to full on track pads. Basically you're trading dust and squeek and cold pressure performance on the low end, for friction/heat capacity on the top end of the spectrum.

street pads top out at 500-800 degrees F. Mid tier 1200+ degrees F, track pads 1600+ degrees F. The only way you get above 1000 degrees is by downhill and/or 100+ MPH.
Friction coefficients from 0.3 on the low end to 0.7 on the high end. Braking force is still limited by tire traction for the most part below 70mph in the dry. But the feel is affected, and above 100mph street pads will melt and lower their friction point will underperform at high speed, whereas track pads will come up to temp and be able to do it repeatedly at twice the friction rate.

BBKs just allow a cheaper street pad an extra 100 degrees of cooling, less flex (feel). Which means, like track pads, they only really stop faster on the track unless you're adjusting brake bias.


Brake bias is adjusted on nonmatching bbks or if you throw track pads on one axle and leave crappers on the other. More front bias will help in the dry straight line, more rear bias will help solve understeer (within the sweetspots). All of this will be tweaked once you hit ABS, but you'll hit abs prematurely without full lockup at a different wheel if you screw up the bias. Front bias setups will struggle in wet/slippery conditions or on crappy tires. ABS won't solve this, especially as real world you're doing things like brush braking ( https://www.youtube.com/watch?v=2oU9OSINyTY ), because triggering abs = slower, and triggering it only on any corner will often trigger the front plowing due to abs biasing to keep the car straight. See electro controlled prop valves under abs system to understand more on that -- ours has a quirk that locks into abs even after you release it... it's a 'feature'. After x seconds of abs, you can't release the brakes and turnin without a delay in response, you have to pre-release, or transition out of abs to liftoff/brush braking early. For the same reason, any ebrakes cannot be combined with anything but a brush brake without abs freaking out (in other words lift brakes first before rotating the car, and then just tap the brakes so they don't go full nazi). Keep in mind, some of this may relate to the recoding they did for the 2001.5 changes, including stability control, and whether you turn traction control off always, but it nevertheless holds on all platforms (give or take the intrusiveness and the presence of a LSD). Believe it or not, wheelspin, odd biases, or absing backwards is really not well sorted at all in just about any modern abs system, it freaks it out. Try abs braking in reverse right after a spin, you've got to ebrake to cut stopping distance in half on every platform I've ever done it on with abs. It's the same reason they say it doesn't work well on ice.

Point being, don't cheap out on the rear pads or mismatch track pads vs streetpads on axles or otherwise screw up the bias :) Friction coeffecient match front and rear axle based on the tire grip levels and conditions. And make sure they're setup in optimal temp ranges for the type of use.

PS there's also the rs4 coding that I have yet to try out, there's very little information on it, but you can back into bias ratios on the platform and surmise what it's trying to do. Flyboy swapped it out, made a marginal change but he only sampled straightline. Would be dope to find a manual on it that shows the different ratio mapping. https://www.apcautotech.com/getmedia...ing-valves.pdf

"Electronic Proportioning: No Tampering Allowed
As a small sidebar to the mechanical proportioning valve discussed here, there is a movement afoot to replace
the proportioning valve function with the hardware performing the ABS function. While this is not yet the
norm, most high-end performance cars already have this feature as standard equipment and one can predict
with reasonable certainty that the trend will continue.
Based on information gathered from the four ABS wheel speed sensors, the Dynamic Rear Proportioning (DRP)
or Electronic Brake force Distribution (EBD) algorithms calculate the front-to-rear slip ratio of the four tires.
Then, given preset thresholds and parameters, the ABS hardware can intervene and modify the brake pressure
going to the rear wheels automatically.
Because DRP and EBD are based on actual wheel slip and not on brake line pressure, this type of rear
proportioning is more flexible and adaptable to modifications one might make to their vehicle. It is also less
expensive, as the OEM can now remove the mechanical proportioning valve from the vehicle and replace its
function with other hardware already on board.
Naturally, the OEM does not want owners fiddling with their front-to-rear proportioning, and as a result there
is no way for the enthusiast to reprogram DRP or EBD to suit their desires. Of course, if the vehicle’s original
front-to-rear bias is in tact in the first place, there is no need to reprogram anyway. "

https://www.audiworld.com/forums/s4-.../#post13242125

[traviswt]

Whoa, that is a lot of information to absorb and was very informative. Thank you!

I only drive my car on the street and Im still on stock K03 turbos, so I dont really hit 100+ mph. I think this means that I can probably get away with a decent street pad, or maybe mid range pad if I want to future proof things a tad. I do have basic cheapo pads in the rear for now, but Ill consider upping those to a better pad in the future so that the bias stays somewhat even. Not sure thats something that Ill notice myself, but hopefully it will positively influence the braking performance.