Re: 5kQ ABS: the rat with no splines

[QSHIPQ@aol.com]

In a message dated 97-02-12 14:10:22 EST, you write:

<< Well, the ABS OFF light on the '88 5kCSQW stays on all the time.  I 
 tried locking and unlocking the diffs and pressing the ABS OFF switch.
 When I do these things I can hear a relay clicking, but the light stays
 on.  I haven't had a chance to dig into it yet, but I looked through 
 Bentley, which said that the first thing to do was to check out a few 
 fuses and relays.  It also sounds like one of the first tests is to 
 see if the brake modulators work under hard stops even though the light 
 is on.  Have any of my esteemed colleagues had to deal with a similar 
 problem?  If so, what did you find as the source?  Bentley suggests 
 using some big electronic monitoring tool that gets inserted in-line 
 with the connector on the ECU ... does anyone know if this has any-
 thing more than what I could get by probing wires with a DMM?
  >>
Chances are you have a sensor out of alignment.  The sensor caps are cheap
(like .80 ea) and are a good idea, since yours are prolly history...  These
keep the sensor tips from getting eaten when pushing them towards the
driveshaft....  The ABS defaults to off, does a self ck continuously while
driving...  You can hook up a DMM to the sensor outputs, raise the car and
spin the wheel, you get a square wave (A/C) from the sensor...  The actual
value is irrelevent, matching them is...  Basically, you want to get the same
reading from all sensors spinning the wheel aprox the same speed by hand....
 

The sensors too far from the driveshaft will give you what I refer to as
pedal "boing", this is a groaning/spring sound just as you come up to a
stop....  The sensors too close will give instant abs pedal kick in...  Too
far out tends to shut off ABS quicker than too close....  If you can't get
the light to go out at all, you might have a fault in the center Diff lox
switch, or one of the sensors is now just bad.  Worn or crudded driveshaft
splines can do it too, but you don't get as much corrosion where you are
steve.  There is an inspection/water drain at the bottom of each strut, you
can sometimes get a brass bottle brush in there, tho pulling the driveshaft
out is easier, and about a 20min job per....

First ck for proper sensor output, then ck the diff lox switch, then the
driveshafts.  Rarely does that abs box go bad, but you could be the first....
 I know, based on your choice of diffs, that the actuator is prolly
working....  If you can't get the light to go out at all (for 10 feet or
about 20 seconds), chances are something basic is wrong...  Sensors out of
alignment usually allow the light to come on till the first brake app or
20-30 seconds, whichever comes first...  

Good luck

HTH