I had a terrible shake that two tire shops spin balancing machines failed to balance out a few years back, so on a trip down into Mexico, I stopped once again for balancing. The guys there used an old electric motor with a pulley on it to spin the rears (front drive car), and they used the car's engine to spin the fronts. Within 15 minutes, they had all 4 balanced and no more shake (and charged me only a couple bucks to do it). Really makes a believer out of me for balancing as installed on the vehicle, instead of on a balancing machine. They didn't even have one of those clip on gizmos to move the weights around while the wheel is spinning, they did it by eye sight, feel, and trying the weights here and there until the shake was gone.
Since then, and since I mostly install my own tires anyway, (I have an old Coates tire machine, and I really hate for anyone else to even touch my machines), I first bubble balance them, then spin them and play with the weights until no more shake. Sure, it's old school, but it works really well, in fact much better than a spin balancer, since it takes all the rotating parts into account (brakes, axles, etc.)! If you have an open diff., give it a try.
Chock the car really well, and I mean REALLY WELL, then jack up one rear wheel, and spin it up with the engine. Increase and decrease speeds slowly so the car doesn't try to fly off the chocks. Find the RPM with the worst shake (you will be amazed at how bad things can get to shaking). If your eyes are really good, you may be able to see the heavy spot without any aid as the tire moves up and down, (or I imagine you can use a strobe to stop the wheel in motion). Even if you have no idea where to put the weight or how much, add some weight to one side of the wheel. Try it again, see if it's worse or better, if worse, apply the weight to the opposite side. When it improves, add a second weight 1/4 way away from that one, and try again. By moving things around, you will very shortly start improving the shake a bunch. Using heavier and lighter weights and moving them around carefully, you can soon figure out what it needs. Often you can control all the shake by adding weights to only one side of the wheel, sometimes you have to go to the other side of the wheel after getting the first side as good as you can. Wheels that need stickon weights make it a pain to do all this... If you are careful and methodical, in 15 or 20 minutes, your problem of shake will be gone.
Going to run up over 100 mph? Don't do any of this, find a shop that can spin them on the vehicle for you. Spinning that much weight can be dangerous at those speeds! Remember, when spinning with the engine and one wheel is on the ground, at 30mph on the speedo the spinning tire is really going 60mph! And, NEVER stand in front of or behind a car with a wheel spinning like that...
Just what I do... certainly not for everyone, and especially not for the panzies...
Corley
