jamesinc
I'm getting pedal shudder randomly when braking, especially at slow speeds. It's not rotor warp shudder, this feels like the ABS system is operating. Has anyone heard of this happening? It roughly coincides with ABS MODULE reporting failed RF speed sensor. I am imagining a scenario where the system momentarily believes the RF wheel is not moving and so activates ABS.
VolvoDeger
What car we talking?
jamesinc
VolvoDeger;126002 wroteWhat car we talking?
96 850R
VolvoDeger
Does this resonate through the whole car and when pedal lifted slightly it goes away, is this intermittent as well ?.
jamesinc
Just pedal. Lifting slightly does make it go away. It is intermittent, I haven't managed to reproduce the issue on demand.
Spac
jamesinc;7959 wroteI am imagining a scenario where the system momentarily believes the RF wheel is not moving and so activates ABS.
I see nothing that contradicts this hypothesis.
Would definitely be where I would start looking.
jamesinc
Well the ABS/TRACS lights have been coming and going lately. OBD reports missing/faulty RF sensor. Brains trust suspects faulty module solder. I'll check that and backprobe the RF sensor at the same time. The only reason I brought this up in a separate thread is that it wasn't a symptom initially.
VolvoDeger
O.k this sensation is coming from the rear brakes and it will stay whilst foot on the pedal at the same pressure, when pressure changed it will go away it creates when mostly under light to moderate braking for a length of distance such as approaching a corner at the same speed until stopped. With this said there was shims to stop this but never had any luck so I now just change discs and pads as a set and clean all components.
Abs has nothing to do with this as when abs works all it does pump pressure away from wheel circuit.
I hope this helps you out as it's a horrible resonance through the car............
AlexS
I would start with cleaning the ABS speed sensors and sensor rings as they get a buildup of metal filings from wearing brake rotors over time. The symptoms you describe usually occur when the speed sensors are dirty and you're driving under 10-15kph. Remove each speed sensor and clean the sensor with a rag and brake cleaner and the
sensor ring itself with brake cleaner.
jamesinc
Cleaning the sensors and rings is easy and seems like a sensible place to start, I'll try that first.
jamesinc
VolvoDeger;126020 wroteO.k this sensation is coming from the rear brakes and it will stay whilst foot on the pedal at the same pressure, when pressure changed it will go away it creates when mostly under light to moderate braking for a length of distance such as approaching a corner at the same speed until stopped. With this said there was shims to stop this but never had any luck so I now just change discs and pads as a set and clean all components.
Abs has nothing to do with this as when abs works all it does pump pressure away from wheel circuit.
I hope this helps you out as it's a horrible resonance through the car............
Honestly it doesn't resonate through the car, it's just in the pedal. Brake shudder I will recognise immediately, it's not that. Given the ABS warnings and given that it does sound/feel like the RF wheel, I'm gonna put rear brake issues further down the list, though I will check them anyway as I think the rotors must be approaching EOL anyway.
I'll follow this list, and stop when the problem goes away:
- Clean all four ABS sensors and check rear brake condition (fronts are a fairly new 302mm setup)
- Backprobe RF sensor and wiring to look for other faults
- Reflow ABS module solder joints
- Replace rear brakes/pads
Ex850R
Bugger, I have now got these issues!
After my GPS took me bush, well, a truck ruined dirt track,, I turned back when faced with the big mud puddle...
Its awd so I gunned it and bam, off I went, no wheels pin yay!
Sometime later on the tarmac I got a grinding weird noise from the abs area... The tracs and abs lights are on now...
Will pull codes, maybe I will swap in known good abs unit.
Julian
My car infrequently gets a VERY severe vibration under braking, although the last few weeks it has become much more frequent. I today pulled my abs fuse and it didn't stop it. It is also definitely not warped discs as it is not every time.
It usually happens when braking downhill at low speeds and more frequently in hot weather. It really shakes the whole car but will stop if I let off the brakes a couple of times.
Perhaps one of the brake calipers getting stuck?
VolvoDeger
Is it a 850 or v70 as i have already explained the cause but shot down in flames, done so many of these issues as it shakes the whole car. I shouldn't say shakes the whole car but resonates through the vehicle from the back
jamesinc
Jules is describing something different to me and hasn't mentioned an ABS/TRACS light being on. I'm not shooting you down, I'm saying the symptoms you describe do not match the symptoms I experienced, in particular the ABS fault being reported by the computer. I also (see my comment above) still included your idea on my checklist, so I really don't see what the issue is.
timbo
Sometimes on the later models a loose driveshaft bolt will cause wheel speed sensor codes. I would add checking the driveshaft nut and wheel bearing to your list
jamesinc
I did do the driveshafts less than a year ago, I'll check that also.
jamesinc
I also noticed this morning, I had it happen right at the top of the pedal. I was going about 60km/h, touched the pedal, got a lot of resistance (think like no brake booster assistance) and the usual vibration through the pedal. Again it's really only coming through the pedal, the rest of the car does not vibrate or resonate noticeably.
egads
Booster check valve?
ilduceglider
Thanks Guys. My 940ABS sensor and sensor rings looked just the same as Alex's photo above with metal fragments stuck to the magnetic probe, brushed everything clean with an old soft paint brush and my pulsing braking has disappeared. Recommended
Cheers Peter