Low Speed Braking Issue: Feature or Problem?

[X5M-ISH]

Happy Day Light Savings Time, friends.


Ever since I have had my 2006 4.8is, there is this 'thing' that the brakes do at low speeds which drives me up an f'ing wall. No other car (or other BMW's I have owned) do this.


During low speed braking, say under 25 mph, the pedal feel pulsates. This pulsating is extremely uniform. Also, this only happens during partial braking as in partial depression of the brake pedal. Like a throbbing feel; weak, firm, weak, firm, weak, firm several times a second.


Since owning, I have done an entire brake overhaul: rotors, pads, brake fluid flush, INPA ABS pump activation...there are zero bubbles in the brake lines; all of this did not change the pulsation. I vaguely remember coming across a thread where e53's have this brake assist feature to compensate for trailer weight or the e53 being pig'ish that loosely describes what my 4.8is is experiencing along with a place in INPA or BMW Scanner to disable it. Unfortunately I cannot find the thread. Please enlighten me if the ABS pump may be showing signs of wearing out or if true, a way to disable this stupid feature (if it is in fact one). Mahalo!

[Clockwork]

I have never heard of or experienced this uniform vibration in the brake pedal.
Sorry. You sure it's not worn bushings in the steering/suspension department?

Sent from my Pixel 3 using Tapatalk

[EODguy]

I get that on mine, but only when the ABS is cycling and I've really stomped on the binders.

Not sure if a future failing booster can trigger the ABS because of a vacuum problem or an adjustment issue in pedal travel.

Sorry but that's just my WAG....

Sent from my SM-A730F using Tapatalk

[Attacking Mid]

I put new pads/rotors on mine and didn't have time to do a proper pad bedding-in. Mine do the same thing. I don't know if there's anything short of having the rotors lightly turned and properly bedding-in the pads that would help. I'll probably just live with it.

AM.

[Ohsoslow]

I had similar thing with mine, turned out to be lower control arms though.

[X5M-ISH]

I forgot to add that the entire front suspension was rebuilt in late August. Every suspension arm, ball joint, bushing and tie rod was replaced with the alignment done shortly after. I suppose I'll either bleed the brakes again or perform a bit more analysis on the ABS unit and look for issues. Either way, this pulsating is annoying.

[X5M-ISH]

An update simply to log this for future searchers:
I had a suspicion that the front left wheel was bent and took the wheel in today to have that checked out. Low and behold, there is a slight lateral wobble to it - maybe 3 to 5 mm. From what I understand, a wobble or bent wheel will cause the ABS/Speed sensor in the hub to misread the wheel speed as it rotates around the hub. This in turn tells the ABS computer to do its thing for that caliper OR that end of the vehicle. Being that this pulsating thing was a front end issue, the fact that the wheel is bent makes sense.


The snow wheel-and-tire setup has been mounted for a few days now and the problem has all but gone away. In the near future, driving around with INPA running will tell me in real-time what the ABS wheel sensors are measuring, loosely utilizing points from this thread here: https://xoutpost.com/bmw-sav-forums/...-question.html . From what I understand, the sensors are crazy sensitive and with minute adjustments using data from INPA anyone can get the ABS system back in check AS WELL AS saving time, effort and cash over replacing the sensor(s) outright.