abs coming in too early is this normal?

[bullyd]

every time i put any real pressure on my brake pedal my abs takes over, is this a characteristic of the e34 or is something wrong? there is no way my tyres were skidding, ive tryed it in various situations and the abs is cutting in way before the traction could possibly be lost! comments greatly appreiciated

[zygoteer]

ABS works by essentially comparing the relative rotational speeds of the wheels.
If some tyres are 'significantly' more worn than others then the effective rolling diameters of the tyres could make the rotational speed differences be beyond the control threshold making the system cut-in.

A more sensitive scenario could occur on a car using staggered wheels having slightly different tyre diameters front to rear.

[Jon K]

it would help too to know the situation this happened. Mine activate, but i was on 1/4" of ice on Kumhos

[bullyd]

ABS works by essentially comparing the relative rotational speeds of the wheels.
If some tyres are 'significantly' more worn than others then the effective rolling diameters of the tyres could make the rotational speed differences be beyond the control threshold making the system cut-in.

A more sensitive scenario could occur on a car using staggered wheels having slightly different tyre diameters front to rear.

im running 245 45 17 rear and 225 45 17 front,all bridgestone potenzas 'bout 3-4mm tread on rear 4-5mm on front

[bullyd]

it would help too to know the situation this happened. Mine activate, but i was on 1/4" of ice on Kumhos

tryed it in the dry under moderate braking , wet under less than moderate braking and abs cuts in, trust me there is no way im losing traction,

[Elekta]

I crashed at a 30 mph panic breaking situation...I sure wish the abs would not have kicked in b/c for sure my new rubber would have stopped me on their own.

abs is hard to work for us older folks because we just push harder when it engages when we should be releasing....would rather have skidding feedback frankly as my pumping the breaks might have prevented my bender.

in the paint shop today btw....it's been too long

[zygoteer]

... from your info ...
Front 225/45-17 has a rolling diameter of approximately 634 mm worn about 4 mm = 630 mm
Rear 245/45-17 has a rolling diameter of approximately 652 mm worn about 6 mm = 646 mm
(assumes approximately 9 mm 'new' tread depth - it varies between brands/models etc.)
Therefore difference = approx 2.5%
From what I know in the past, about Teves systems, this doesn't seem to be an excessive difference and would probably not cause your problem.

On this basis, I would look at the wheel sensors for a problem - if a sensor is missing pulses (symptomatic of a 'bad' sensor or dirt on the reluctors), or a sensor is picking electrical noise (usually caused by frayed wiring and/or bad connections) to give spurious pulses, then it would explain what you say.
Most sensors can be statically checked by measuring the electrical resistance with a DVM.

Uunfortunately it is my experience that getting sensors out to clean etc. can be a real problem - corrosion can make it such that extracting it will damage the sensor, so you end up fitting a new sensor anyway

[ScD]

I crashed at a 30 mph panic breaking situation...I sure wish the abs would not have kicked in b/c for sure my new rubber would have stopped me on their own.

abs is hard to work for us older folks because we just push harder when it engages when we should be releasing....would rather have skidding feedback frankly as my pumping the breaks might have prevented my bender.

If your ABS is working properly, it will stop you a lot quicker than any pumping of the breaks by a person. The most effective way to emergency stop in an ABS car is to stand on the stop pedal, nothing more.

[bullyd]

[QUOTE=zygoteer]... ]Most sensors can be statically checked by measuring the electrical resistance with a DVM. QUOTE]
whats the resistance meant to be? whats the threshold?

[632 Regal]

Wham! 245 45 17 rear and 225 45 17 front... I believe this is your problem.