Let's establish the axiom of this issue:

If the pavement is perfectly smooth, and I step on the brake firmly, even hard, 30-40-50-60 mph, I feel NO pulsing, especially at the steering wheel --- a smooth, confident braking experience.

So, I feel safe in assuming the issue is not rotor runout, or other pad vs. rotor issues. Tires not worn. And the car is, otherwise, a beautiful ride, at 20-40-60-80-100+mph.

HOWEVER, if the pavement has a very minor "washboard", which is not really apparent during normal driving, which the you can just barely feel, and maybe not at all, and which you can just barely see in the right light, IF you step on the brake (or if cruise control does so on a downhill), you get a very strong pulsing, BUMBUMBUMBUMBUM . . . felt in the body and also in the steering wheel pulsing right and left 1/8-1/4 inch.

(This kind of almost invisible washboard is common with new asphalt applications, where the paving machine does not do a perfect job and leaves this patterned uneven surface that is almost never noticed, and is then carried on to older pavement in SOME cases.)

FURTHER, this whole thing just showed up overnight --- it may have taken a week, I don't know, but suddenly I found my self saying, What the hell this????!!

So, the issue has TWO required elements; braking PLUS unevenness in the pavement. NOT ROTOR RUNOUT or other typical pulsing brake issues, because the issue does not arise with smooth pavement, even with light, medium or hard braking.

(2011 E550, with all the stuff, including Airmatic. 51,000 miles. Last wheel removal, May 1, 46,000 miles, for LF TPMS replacement. Last brake job, Jan 9, 43,000 mi, incl. rotors + rear air suspension bellows.)

What is your best guess?

Lug bolts?

Struts/Shocks?

Other front suspension parts?

Brakes?

Aliens?

Thanks for suggesting . . .

 

I had a similar issue a few years ago with a Honda. Same thing - strong pulsing on braking on uneven pavement, everything fine on smooth pavement.

Turned out to be lug nuts that weren't tightened during a rotation.

You can always do the old school test.

Grab each wheel and try to move it in and out. Any noises?

Move the steering wheel back and forth while standing still. Any noises?

 

Thanks,

Just ripped the wrench out of the trunk. All the lug bolts are tight, as best I can tell. If torqued correctly, I have no way to tell.

 

My guess is the shocks.

 

Lift the front tires clear and grab them at opposite sides and give them a healthy shake test....top to bottom and front to back. Hear or feel anything?

 

If the tires on your car are the originals, they might be the culprit, even though they don't look worn. At 50,000 miles, I had a similar problem almost 6 months ago. It went away after I change all 4 tires.