Hi all, I replaced my front pads and rotors w/OEM parts less than 1,000 miles ago due to age, and pulsation in the brake pedal. Car is a 2015 S550 w 44K miles. The car felt noticeably better, but still had slight pulsation, so I replaced the rear pads and rotors (OEM rotors, and Brembo pads) as well. Pulsation was roughly the same, which is pointing me back to the fronts, plus the steering wheel shutters upon braking.

So, I'm trying to figure out how I could have pulsation in the fronts w less than 1,000 miles. My research pointed to cleaning/lightly sanding the front rotors (w Scotch Brite pad) for any potential brake pad material transferred to the rotors causing run-out in the case of improper bedding etc... No luck after taking apart again and sanding/cleaning.

Here's what I'm narrowing in on - since putting the fronts on, which were very smooth upon install, I've had the car in the shop for tires, wheel refinishing- basically, the wheels were on and off the car a few times. Any chance improper installation/torqueing of the lug bolts could cause such premature failure of my rotors? I know how critical this is, it's just hard to believe the rotors could have gotten out of round so quickly. Just brainstorming before an impulsive repurchase and redo of the entire fronts...

Few other facts - front pads that I replaced were all worn evenly, no sign of drag etc. I've used the Distronic cruise right after installing the front pads on a fairly long trip, pulsation on the new pads seemed to have started after this trip (I know the Distronic cruise applies brakes variably).

I've never had this happen with how many 4-corner brake jobs I've done in my time, including my SL.

Thanks in advance for any thoughts...

 

The only thought - if it's pulsating, then something isn't straight.

Go to a shop where they not only change rotors but also know how to operate a rotor runout/warp gauge and ask them to use it... even on new rotors - I have seen more than once wrapped brake rotors (not to mention the hub can also be at culprit, and this would get verified during the same procedure).

 

Even handling the Rotors while taking them out of the Packaging is very specific as to not grab them from the Hub. Must be printed in the box for a reason....

 

Thanks guys. Will work on checking the runout next. Will check the rotor face and the hub for trueness.

 

Any suggestions as to how to remove the brake pad retaining pin? This is the one in the caliper w the 13mm bolt in back that needs to be removed to slide the pads out without removing the caliper. It's seems completely frozen. I've sprayed it up etc. do not want to tap on it too much in fear of breaking the caliper.

Anyone deal with these frozen suckers before?? --Thanks --

 

Back off the 13mm bolt, leaving it in place, and then give it a tap from behind the caliper to get it started.
Or, take the bolt out entirely, find a parallel punch that fits inside the thread, insert it and give that a tap, it should pop out!
Mine were tight when I did the pads, but once I figured out what I needed to do they acquiesced!

 

Put car on lift.
remove wheels and tires
put a dial indicator on a magnetic base and attach to inner fender.
set dial indicator to the face of the rotor (the part that is attached to the hub)
rotate rotor to verify it is round to 0.002"
Do the above for all 4 wheels.
If this fails, fix the appropriate corner until the rotor face runs true.
If this passes, the problem is not in the rotors, wheel bearings or suspension.

Once the rotor face is true with the hub, then check the rotor braking surface itself.
If this is out of round, the rotor itself is the problem.

If none of the rotors measures out or round, then do the same thing for the inner face of the wheel then the outer face of the wheel.
Here you want to measure the radial runout then the lateral runout.
You could have a bent wheel.

 

Thank you! I've tried tapping the bolt but have not tried a punch. That's a good idea.

 

Thanks for this great information. About a week ago I was actually able to check the runout on the rotors and hub. Rotors were out .003-.004 at 180 degrees on the rotor. Clear sign of an issue.

I then carefully checked the runout on the hubs and they were very true. Gauge didn't move beyond .0005.

So I dove in and replaced OEM front rotors again and new pads and hardware including new caliper bolts. I cleaned the hub w wire brush, cleaned and lubed all other contact surfaces, torqued down the caliper bolts, rotor retaining bolt and wheels to spec.

Car returned to perfection. Which tells me the rear brakes that I recently did are good.

200 miles on new fronts and problem has returned!! This time I hear and feel a tapping from the calipers that gets worse the harder I apply brakes. which is causing a pulsating sensation as well and I'm sure will mess up the new rotors soon.

Clearly there's an issue that I cannot seem to diagnose. Could be caliper or brake line, or suspension drivetrain etc ... I'm not sure how to diagnose those properly.

One item maybe worth noting- prior owner replaced front wheel and tire. I did notice the caliper was scorned on top - the wheel must have compressed and hit the caliper. Other than the finish being gouged I don't see other damage. Wonder if the spindle could have bent now that I'm thinking about it... when I removed the pads that came with the car all looked even and the car had slight pulsation which made me change all the brakes in first place. But nothing that I thought was more than a car a 44k miles and worn brakes.

I've got 25 plus years doing brakes on car and trucks and this one is really thrown me for a loop. There's probably some added complexity w fixed calipers, but I've done this job on my SL which years later is still perfect.

I have a great Indy I use for unique situations so will probably take it by while all the consumable brake hardware is brand new still.

Good point on the wheels. I had them checked a while back and my wheel shop made one slight adjustment and they are straight now.

In the meantime if you guys have any other thoughts please let me know! This shouldn't be this hard for a problem to find given how quick it's come back within 200 miles. Visually all looks good. Bolts are tight etc. If I try anything else I may put the stock brake pad pins back on. The ones I used were not oem. I went with powerstop z23 pads which had great reviews on here. I did go 500 miles and there's barely a trace of brake dust fyi. Thanks all.

 

Torques with lube or without lube ? Analog torque wrench or digital torque wrench ? And how much TQ ? Antiseize ?

TIme to see if the calipers are parallel with the rotors. This also has a 0.002" spec. Adjustable parallels are used to measure caliper-to-rotor clearances with a micrometer:: top-outside must equal top-inside must equal bottom-outside must equal bottom-inside. Do not measure piston to rotor, measure inside of caliper to rotor. If this is wrong the flange holding the caliper to the hub is probably bent. You can use shim stock to fix--a dealer would replace.

A bent spindle would show up on the rotor concentricity checks.

The only added complexity in fixed calipers is getting the caliper centered on and parallel with the rotor (above)

Good luck.

 

Thank you again. I'm not familiar w adjustable parallels so will research that.

 

I had a similar situation. I replace my pads and rotors and went on a 1500mile trip only to have my brakes shutter shortly thereafter.
I replaced the rotors again and it’s been the smoothest ride since then.
I took advantage of FCPEuro.com return policy on free replacement parts.

 

Yep- I came across them for my most recent purchase (second time buying rotors in 2 months! ) Have you driven a considerable amount on the new rotors?

 

Hers a quick pic- 500 miles now on these pads and the side that went through the broken wheel trauma has this debris on the brake pad. Drivers side does not have this. Sharing as maybe it's an additional clue as to what's going on. It almost looks like the material the new rotors come with?

 

Looks like something got wedged between the rotor and pad. Maybe just removing the pad and debris may fix your issue

 

Here's to hoping. Will break it down in the AM and see what the deal is.

 

Update - removed debris and it was not between the surface of the rotor and pad so highly unlikely that was the issue. Everything else seems aligned. Pads have the appropriate movement against the anti-rattle clip, nothing seems tight etc.

 

Oh, by the way, the holes drilled in those rotors are not properly chamfered.

 

As in improperly milled? I'm not sure. They're oem out of the box.

 

Any "good" machinist would have a 45º chamfer at least 1mm wide at the corner of the hole--otherwise you get stress risers in the metal.

 

From here you have a bent spindle. That caliper is not making contact with the front of the rotor.
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Could also be a bad caliper but with the wheel tire history likely the spindle.

 

Thanks guys. Amazing how to the eye, all looks true. Pads line up perfectly on the rotor, cut in the new rotor perfectly, as does caliper appear true.

I'm trying to wrap my head around this. So, if the spindle is off, it's throwing the caliper off from properly/evenly applying the brakes, correct?

Would an alignment machine help to identify the issue? Traditional alignment adjustments probably would not cause uneven brake engagement since the whole spindle moves together any adjustment. FYI Tires wear evenly, and car tracks perfectly.

If spindle is bent where it mounts the the caliper, I wonder if the only way to verify is to measure the clearances on the caliper via the parallel check mentioned above.

The spindle is massive, I would think the caliper would bend before the spindle. But who knows.

I'm taking the car to my indy next week who will check this all out.

 

A slightly bent spindle would not be appreciable with alignment equipment or to the naked eye.
From your picture which you say has 200 miles I see a rotor that has NOT been engaged by the caliper on the outer side, the machining traces are still visible.

Do check caliper piston engament and movement but most likely you have a bent spindle from that impact that broke a wheel.

It is extremely unlikely the caliper or its mounting points are bent, when you break a wheel the force goes tire>wheel>hub>spindle>frame & subframe. The caliper is not part of the absorbing the impact.

 

Thanks for further explaining. Although, the pads must have engaged some degree to wear off the gray that comes on the new rotors, no? But perhaps they're not engaging as much as they should. Also, it takes very little force to wear that gray off. You can almost take it off w your finger nail...