>Note: GM-specific stuff follows:
>
>Obviously (I hope), if you slam on the brakes, it is possible to lock the
>front wheels at a deceleration rate that is less than what it would be once
>all the weight transfers forward and gives better grip up front. A problem
>with the ABS on my '94 Z28 and my '89 Z51 Corvette and my '92 GMC Jimmy was
>that once the ABS kicked in, that amount of brake line pressure was the MOST
>you could get until you got off the pedal and the ABS reset. I'm not yet
>clear on what happens with the ABS on my '99 Corvette, except that it makes
>a hideous gravelly noise when it engages.
>
With my Tahoe, maintaining a high degree of consistant braking force near
the limit and the brakes respond well. (as good as possible for 5000 lbs of
truck) Once you exceed available traction and ABS engages, the difference
is staggering. It's literally like lifting completely out of the brakes.
This behavior is duplicated on all surfaces, dry/wet/ice e.t.c..
Whomever said "GM's ABS unit is dumb" is probably close. It does take a
signifigant time to engage/disengage ABS (1 second or so which feels
signifigant.. <g>) But the unit also seems to PULSE quickly enough (or my
foot tells me so) too so I'm not sure it's calculation-speed related. The
line pressure mentioned above certainly sounds like it could be responsible
as the vehicle requires signifigant amounts of pedal pressure before the
brakes are useful in the first place. (much heavier pedal than anything
else I've driven)
Although unlike Kevin's Jimmy, this behavior is evident immediately ABS
engages, regardless of application speed, weight transfer e.t.c. Once
active, ABS kills braking performance in identical fashion.
So if I understand this right, once ABS engages, the unit immediately voids
a signifigant amount (30-40% seems right) of brake line pressure through
attempts modulation or pulsing.. Perhaps the unit is not adapted to the
extra effort required in activating the Tahoe's brakes in the first place??
Sounds like a poorly engineered device the good 'ol Chevy bean-counters
saved a few bux on.. Not suprising..
BTW, Anyone know of any potential problems that might appear by yanking an
ABS fuse?
-Brian (who can't WAIT to park the barge for topless weather..)
>I encourage anyone, especially with GM vehicles, to go do some tests and
>report their findings as well. I think ABS is A Good Thing, but using it to
>fullest extent on course isn't quite as simple (for me, at least) as just
>"nailing the brakes".
>
>KeS
>
-Brian
porterb@mediaone.net
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