Guys! I finally nailed the problem!!! OUT OF BALANCE DRUMS!! Or I should say, really bad manufacturing QC.
Let me tell my story to guys who will definitively understand this relief.
I went today to my local Pep Boys joint and asked the service manager that I wanted to balance my truck's rear drums. You should have seen his face... SO, I then told him, never mind, just make a shop order for regular wheel balance.
After a brief wait, I then told the technician to take out the drums and to put them on the balancing machine spindle and to select STATIC mode. You should have seen his face also! "How am I going to fasten it to the wheel balancer?" he said. Don't worry, the brake drum hole id the same as the one on the wheel!!
Then he said: "How are we going to attach any weights to it?" Don't worry I have an idea, I said.
Well, all the technicians at the service bay were kind of skeptically looking at this crazy guy doing this experiment.
Ok, the procedure just went smoothly, he dialed in the drum width (4") and the separation with a special lever attached to the machine which lets it know how far away the rotating mass is. (This I am guessing but anyway, the machine nees this info/input).
When we rolled the first drum we got a whopping
12.5 oz of unbalance!! So, after cleaning the surface area of the drum with a wire brush, we attached 4 ea. 3 oz. lead weight strips distributed between the outer edge and inner edge. Thes are the kind they use for mag wheels. I have attached a photo.
You may know that by now I was getting excited. The technician also was surprised. Then, after attaching 12 oz. at the first location we ran the machine again. This time she asked for .75 oz on another location. This is good.
We installed .75 oz and ran her again. The result was a balance drum indicating 0.00 weight needed.
Then, we mounted the other side drum. Spinned her again and...BANG!!
18.0 ounces off!!! Now everybody at the service bay was paying attention.
We installed 6 ea. 3 oz. weight strips after cleaning up the area with wire brush. Around went the machine spindle again and stopped asking for 0.5 oz. on another angular location. Nice. One last go around and we got a 0.00 reading.
Mounted everything back on the truck and took it for road test. Unbelievable...total bliss... I do not have the words to describe the satisfaction of finally getting rid of an elusive problem.
My lesson: Even if I ever buy a new set of drums, I will ask them to be checked for balance; right out of the box, before installing them on my truck.
I may have to improve the weight attachment to the drum since I do not trust these lead strips using adhesive for fitting. I am almost certain that they will eventually fall out due to corrosion under the first lead strip which is holding all the other ones on top of it. So, I have to get creative and eventually improve this. But I already know were the monster is.
This may not be the case for othe SS fellow members with wheel hop. But I have shared my story as an example of what can go wrong and how elusive it can be. These drums are about 11 inches diameter and fairly heavy. I realize now what has been to have 30 ounces of hidden unbalance banging away on my rear axle. Now I have new tires, new wheels, new shocks...well, peace does not come easy or free all the time.
Good luck with your testing.