Mike sez:
>Ok you 4x4's out there, I have a ? for you, when on a downslope, on
>dirt/gravel, do you have any brakeing problems, with the anti-locks
>releaseing the brakes, as you are trying to apply them? I have a
>4x2, and will be on some nasty dirt roads this spring, and wonder
>if I should pull the ABS fuse, and have "brakes when I want them"
Try it, you´ll like it!
IMHO, a limit-of-traction loose downslope is what four-wheel ABS was MADE
for. You can creep down (the trick to avoiding body and vitals damage)
slower than anyone else. Gearing down is the usual approach, but it doesn´t
help you retain directional control. With ABS, the brake on each wheel lets
go when it locks up and stops rotating.
Using ABS is a bit of a challenge if you´ve got a lot of conventional
experience, because you have to just stomp on the brake and hold it. The
only downside (at least of the Kelsey-Hayes unit on my ´93, maybe they´ve
got better) is that it takes a moment or two for the ABS computer to start
working. Once it does, it will keep you on the straight and narrow. One
caveat: On really long slopes (maybe 300 yards in my experience) you´ll run
out of pedal travel, and the ABS will shut off, giving you normal brakes.
You want to avoid pumping the brakes, but if you have a section of trail
where it´s easy to lift for a moment, do so so the brake master cylinder
can recycle.
The ABS works by releasing pulses of brake fluid from the locked up
wheel(s). The ABS valve body has a set of fast-acting solenoids connected
to brake fluid valves. Under sustained ABS engagement,the fluid volume
provided by the master cylinder is allowed past the valves. If the ABS
didn´t kick out of engagement, you would have NO brake pressure, and no
brakes at all. Instead, the computer also tracks either master cylinder
travel or fluid volume, and disengages itself. The Dakota system isn´t
really four-channel, it´s really three-channel; there´s only one sensor
(the same as the standard rear-only ABS) for the rear axle. If either
slips, the ABS computer releases both rears.
All makes for lots of little parts. It´s a good idea (I think) to change
the fluid about twice as often as a regular brake system. Russell, the
folks who make the stainless-steel braided brake lines for motorcycles and
race cars, has come out with brake bleeder nipples with little check valves
in them. I have them for the rear, and I´m waiting on the front ones.
They´re supposed to let you do a one-man brake bleed. I´ll tell how they
work when I put them on (I´ll do all four at once).
ABS is also great on dirt and gravel roads. I drive at least ten miles an
hour faster than I would without ABS. Still gotta be careful, since it
won´t create traction where there isn´t any, but you can go where you turn
the wheel. Works even on washboard roads.
Enjoy!
Jim
´93 4x4 CC V8
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:11:51 EDT