Actually, I have two problems with my truck and for which I'd like
The first is that when I brake I feel a pulsation in the truck and
brake pedal. The pulsation is not apparent when the brakes are not
applied. And, the pulsation only occurs after several miles of
driving with regular stops. The pulsation goes away if I drive
highway speeds for 20 minutes or more without using the brakes and
returns after using the brakes for a few stops. I assume the problem
is with a brake component getting warm or hot from braking and
becoming warped. More on this in another post, but, I think the
pulsation is coming from the driver's front brake.
A more immediate problem was discovered while in the process of trying
to identify which wheel was causing the pulsation. I put the truck on
stands so all 4 wheels were off the ground removed the front wheels,
put it into 2wd and pressed the accelerator and brakes at the same
time so as to warm up whatever component appeared to "warp" under
heating. In 2wd, no pulsation (although one rear wheel seemed to
engage a bit sooner than the other).
I then applied the emergency brake and no pulsation. So, I don't
think it's the rears at all.
I then put the truck in 4wd high and allowed the brakes to drag
against while the accelerator was depressed. After a short while, I
felt the pulsation. AHAH, I said. It must be the front disc brakes
which are pulsing.
Then I noticed that with 4wd-hi on only the driver's side hub (wheels
were removed) was spinning (perhaps more evidence that this was the
offending wheel?). The passenger side front hub did not spin when the
truck was in 4wd-hi or low. Rather, it seemed to want to start
spinning (to engage) but would only start to spin and then stop (even
though the brakes were not applied and the other hub and the rear
wheels [wheels still mounted in rear] was spinning freely).
Also, when I took it out of 4wd-hi the driver's side hub continued to
spin for some time. I had to put the truck into 4wd-lo and then take
it out of 4wd-lo and back into 2wd for the front, driver's side hub to
By the way, the 4wd light comes on on the floorboard display when the
4wd is engaged (either hi or lo) and after about 15 - 20 seconds.
So, I seem to have a problem with the engagement of the front axle.
I've read that there are some problems with the stock, heat-activate
actuator. And, I've read the TSB's on replacing the heat-activated
with electro-mechanical ones that engage and disengage immediately.
I've also read that the electro-mechanical actuator is only
recommended as a replacement for the heat-activated actuator if the
GVW is not 8500# or above.
So, here's my questions.
Firstly, are the symptoms I describe above consistent with a problem
with the 4wd actuator? Please consider in your responses the fact
that one hub spins in 4wd but the other does not.
Secondly, does the spinning of one hub and not the other suggest that
the actuator is working but that there is another problem with the 4wd
unrelated to the actuator (I guess that's just another, more explicit
way to ask the same question as above).
Thirdly, how do I determine what the GVW is for my truck so as to
order the right wiring harness and actuator if replacement of the
actuator is required?
Fourthly, I saw on the TSB (www.alldata.com) that there are
replacement actuators specific for certain axles. Where can I obtain
the axle number for my front drive axle? Is it on the axle?
Lastly, if anyone has any thoughts about the braking induced
pulsations I'd be interested in hearing them. While we had the truck
on stands and when the braking had adequately heated the brakes to
cause pulsation I believe I noticed a bit more runout in the brake
disc than when it was cold. But I considered the test a bit of a
failure as the passenger side hub would not spin in 4wd.
Many thanks, and, sorry for the long post. I just wanted to be as
specific as possible about the symptoms of the problems.