4WD Problems, '92 Crew Cab Dually

Actually, I have two problems with my truck and for which I'd like advice.
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 stop spinning.
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.
LongFisher
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"David W. Walters" wrote

You are just chasing your tail here. Why do "you" think that one wheel turns while the other one doesn't in 4HI?

Normal....you have the heated actuator.....it sometimes takes a while for the front axle to disengage...and often you need to throw it in neutral if the wheels are off the ground.

I don't think that you have any problem at all with the engagement of the front axle....unless you consider the older style of actuator to be a problem.

One hub is spinning because the other side probably has more friction between the front pads and rotors. (for whatever reason). If you pry the spinning wheel's caliper over a bit so that it catches the rotor....you will see the other side start to spin. This is how "differentials" work.
> Fourthly, I saw on the TSB (www.alldata.com) that there are

Go to a dealer with your serial number, they should be able to set you up with the correct wiring harness. If I remember correctly, it's the harness that is different, not the actuator.
Machine your front rotors...though on that vehicle it will be a bit of a bear. Probably best to just buy new rotors.
Ian
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inline... On 26 Nov 2003 07:21:59 -0800, snipped-for-privacy@earthlink.net (David W. Walters) wrote:

sounds like your passenger side caliper is dragging.

your actuator is working fine... the 4wd light is actuated by an independant position switch in the axle that only lights when the axle is engaged, not just when the thermo actuator is receiving power.

yes, they suck... bad design.

I've got the electromechanical one in my '88 K2500... it rocks.

I'm looking at TSB #76-43-01A right now and it says that you're correct for 88-93 8501lbs or heavier trucks... so it looks like you're SOL on that regards.

no, your actuator is working fine, if it didn't engage, neither hub would be spinning.

your 4wd is working fine, you've got an open diff in the front axle and your caliper is dragging sufficiently to keep the passenger side hub from spinning while it's up in the air.

look on the GVWR plate on your driver's side door. a ton dually crew cab should have a gvwr in excess of 10,000 lbs.

yes.
the passenger side hub is *FINE*. your rotors are warped and/or the caliper is dragging. have your rotors turned and/or replaced and all should be well. while you're at it, pop the rear drums of and make sure your shoes are adjusted properly.
HTH, Bret

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Many thanks to Bret, in particular, and to others who also contributed to this thread. I've learned a lot.
I did confirm what Bret and others have said, that the 4wd is working. I jacked up the rear end at the differential so both rear wheels and tires were off the pavement. I used a 3.5 ton floor jack I have which has a set of four, small, metal wheels on it.
Then while the truck was in neutral I slipped it into 4wd and waited until the light came on. Then gently into drive. Of course, the truck began to move solely from the pulling power of the front wheels.
I'll be looking into the brake problem now. As it turns out, my wife (at the time) had an accident in my truck while driving it to work some years back. It was the driver's side front which was hit and one of the repairs done by the insurance arranged shop was the replacement of the rotor on that side, among other repairs. As it looks for all the world that this is the wheel which is generating the pulsations, I think it's likely that the shop put on a rotor which was not a stock rotor, but rather, a knock off. Over time, that rotor developed problems.
I suspect that the problem may be that corrosion has affected the "vanes" portion of the rotor between the braking surfaces such that when the rotor gets hot it does not expand evenly throughout. Rather, I think it warps.
This would argue against just having it resurfaced, right? If this is true then new rotors are needed, right? Perhaps, one can get by with replacing just the one on the driver's side. I expect I'll also reline the brakes during this repair as the old pads, although not worn out, will be easily replaced then.
A couple of questions, though...is there something I should try on the passenger side to ensure that the brake pads are not dragging after the new pads are installed? Also, someone said that with a truck that old the calipers and flexlines leading to them should be replaced. Is that true or is someone just trying to sell me parts and labor for the repairs?
Thanks again.
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