ABS

The only time I have ever heard of a problem like this was on a 5 series.

That had different profile tyres on it, ( one was different to the other three !!)  which led to a slightly different circumfererance.

This led to a "following error" within the cpu going out of range with increased speed.

I dont know, but imagine you are sensing on the hubs, possibly wheel bearings.

Are they both absolutely identical ?

And more importantly, do they match up to the rears ?

Dave

I cant see how the springs will matter.

I'm not sure what its sensing on, but the effect will be four pulse trains going back to a micro.

You have at least one of these trains going out of synch, either too fast, or too slow, it wont be much, and the "error" will increase with speed.

If you actually had a sensor problem ( a missing pulse train ), as soon as you went above the "base" speed,( normally 10 - 20 mph ), the system would error.

If you have access to a scope ( maybe someone at work ?), you could scope the sensor , with the car in the air, spinning the wheels at a known speed, ( use a drill with a rubber wheel in it, onto the tyre tread ).

You could then look at the "mark space ratio" of the trace, and see the offending "wheel".

This wouldnt work on cars with different sized wheels on the front and back ( like some 911s etc ) , as the difference will be dealt with mathmatically back at the micro.

I wonder if you could look in the manual and see what its sensing on ?

If its ferrous and exposed, and therefore corroded, that could cause a problem, just carefully clean it up, being careful to preserve the spacings.

Was it ok before you changed all the stuff at the front ?