gpseymour

This started happening at the same time the CEL came on (P0136 - apparently O2 sensor, apparently unrelated) on my 2000 E320 4matic. When I brake, as the car gets to near stopping - certainly under 15 MPH - I feel a little "slip" in the brakes. It feels a lot like the sensation of the traction control kicking in during an over-aggressive turn on wet roads, but now it happens every time I stop, even if I'm stopping very gently.

Any ideas? Is there any way this is related to the P0136 code? It started at pretty much exactly the same time, but could just be a coincidence.

kajtek1

Are you sure it is not transmission disengaging?
Observe rpm at that moment.

Paulmurphy

Check front wheel hub ABS rings for a fracture
On the rear check outer drive shaft ABS ring for same thing
Or if you can get diagnostic plugged in on ABS live data it will pick up the bad ABS ring or sensor but only at low speed as you pull up to a stop

gpseymour

Would the transmission disengage several times while stopping? And I feel it in the brake pedal, so it seems unlikely, unless you know something I don't about this (which is possible).

kajtek1

Yes, it does.
With years of driving with 5-speed I did not notice that, but new to us 7-sp coupled to diesel makes quite jerking at low speeds.
So I start paying attention what 5-sp on older car does and to my disbelieve, it is progressively downshifting while you slow down, helping with braking.
Just with different gearing, it is harder to notice on 5 sp than on 7sp.
Just because of that I switched 7sp transmission to C mode, what is not the best when you drive in the mountains.

gpseymour

I've been considering a bluetooth device to gather real-time info. Is there anything specific I should look for or avoid? I'm mostly interested in gathering diagnostic info like this, and would be using my iPhone or iPad.

gpseymour

Okay, after my last post, I went out for a long drive and paid attention to RPM and the slipping feeling. It does, in fact, appear to be sync'd with the downshifts while I'm stopping. So, why would I suddenly be feeling those via the brake pedal.

raymond g-

it's challenging for me to really know what you're experiencing because you're
doing your best to describe a feeling...a sensation using the best words you can
to paint a picture of what the car is actually through.

if it is what I'm envisioning, it may simply be the transmission's synchromesh
failing to match the handoff between gears properly. so, when slowing down,
the transmission normally would downshift during predetermined revs and
smoothly change gears

but in your case, the handoff between gears is done with too great a difference
between speed/revs and you feel jerkiness. is that correct?

try resetting the adaptive transmission and get back to us. (scroll down to
"Transmission, ECU resetting")

if you're very lucky, that may solve the issue. if not (at worse) the tranny may need
to be worked on. i had that done but it was under extended warranty so it was at
no cost. when i brought it back a 3rd time, they replaced the transmission

gpseymour

I'll try the transmission reset for some other reasons, but I doubt it's related to this. It's not really jerky. It's really a sensation felt almost entirely through my foot on the brake pedal. I'm not entirely certain I can detect it other than there, though I can't be sure. What I think I feel otherwise is a slipping feeling, rather than a jerking feeling, but that might be my imagination filling in information based on what my foot feels. I'll ask my wife to ride with me on a drive this week and ask if she feels it.

raymond g-

so when you say that it feels like it is slipping, does that mean that when you
step on the brake, you're not feeling a corresponding and proportionate braking
action...and that the car's forward motion is not arrested?

(still trying to picture this, obviously)

if you had a ball bearing on the floor, when the sensation is felt, what action
are you taking and which direction would the bearing roll?

kajtek1

Don't rule out Placebo effect.
As I said, I drove 5-sp in different cars for over 10 years and never noticed the transmission braking. Now once I am aware it is happening, I feel it all the time.
Funny on latest job I was coming from intersection where after left turn I had like 200 yard to next light that was timed red for me all the time.
So knowing the timing I was simply letting the car roll down the sloppy street. The 5sp transmission would slow down the car till about 8 mph and then disengage, giving sensation of accelerating.

gpseymour

That's what I'm not sure of. I definitely feel something in the brake pedal. Whether I'm feeling anything besides that, or my mind is being tricked by the sensation from the brake pedal, I'm not sure.

The feeling from the brake pedal is a very brief (less than a second), very fast vibration. The closest I can describe is that it's the same sensation I feel in the pedal if the tires are slipping and the ESP kicks in.

raymond g-

i'm not sure how helpful it really is to guess and throw in the presumed sensation of ESP
(vs, for example, ABS), or that the tires are slipping (they're not, as far as I know) at
this point. what is more important is that you describe the observation (frequency,
speed, consistent repeat under X circumstances, kinesthetic feedback etc).

gpseymour

It's not quite that, and you're asking good questions that are making me think more about what it feels like. It's almost like it feels like the brake pedal is slipping a tiny bit - like it just goes a fractional bit lower suddenly. I don't think that's actually happening, though, just what it feels like.

To use the ball bearing, it feels like when I'm stopping the ball bearing would be moving forward steadily (as it would under braking power), then would slow its forward momentum (during the "slipping"), then resume. The pause would be maybe half a second, at most. As I said before, I'm not sure that pause would actually happen, but it feels like it would.

I think this might be entirely in the brake pedal since my wife didn't notice anything from the passenger's seat, but she wasn't trying to feel anything either. I'll get her to pay attention for anything odd next time she's in the car with me.

gpseymour

Something is definitely different, because this sensation from the brake pedal is too pronounced not to have noticed before, but it may be nothing more than a bit of vibration in the pedal. The rest may be entirely, as you suggest, in my head.

gpseymour

I used that example because it's the easiest way I know to describe the sensation. The frequency is about 5 times every time I brake to a stop. It seems to occur roughly at the same time as downshifts (by watching RPM, which I can only do a bit of while stopping, for obvious reasons). It is consistent with every stop, without fail, under every condition I've driven under in the last couple of weeks. And the only kinesthetic feedback I'm certain exists is some sort of vibration in the brake pedal. The rest may be my brain trying to make sense of that input.

gpseymour

Well, my wife has been sick, so we haven't taken a drive together. However, I have confirmed that I can actually hear (not just feel) whatever it is. I hear it as almost a soft groan that lasts just as briefly as the vibration I feel in the brake pedal.

kajtek1

The truth is that with such delicate symptoms we can guess forever with no guarantee to confirm guess this way or the other.
SOP in such case is to eliminate easy things that should be taken care about anyway.
So I would do standard service even if it is not yet due.
-transmission ATF change and pilot bushing replacement. Add TCU washing if you notice traces of leak
-brake fluid flush and pads replacement even if you have them new
-ABS sensors and reluctor rings careful inspection
- you mention O2 sensors, but were they replaced? How old are spark plugs?