1979-1993 & 94 Conv [Subscribe to Daily Digest] |
I went through a longish period in the DC/MD/VA area with my 84 900T where I had a vibration over 55 mph that drove me nuts. Several tire merchants, from the old NTW (now NTB), Merchants, and Kelly Tire, Firestone, etc., all balanced the tires/wheels and no go.
I finally took the car to Autothority in Fairfax where the shop super was a Saab aficianado (go figure--but he also told me if I ever wanted to buy a Porsche bring it to him and they'd inspect/advise me on it) and brought a floor jack and the tire/wheels to him one by one. EVERY ONE OF THEM WAS OFF BY AN OZ OR MORE! One assembly was balanced so badly that it had less imbalance with no weights on it than with the alleged balance. It was 26 grams out of balance with no weights on it at all. There were something like 2.5 ounces (75 gms) of weight on it.
The foreman also showed me how his Hunter balancer had an override button hidden on the panel...that the panel also could be shifted to read either oz or grams...he preferred grams. Most balancers only read to the nearest 1/4 or 1/2 oz....an oz is 30 grams!!! And if the total imbalance is under an oz many balancers read 0.0! The override button displays the exact imbalance down to a tenth of a gram (although how accurate that is on an absolute scale is another issue).
Tire balancing is as much an art as technique...if your tires don't balance or have too much weight (more than 3 oz is considered a defective tire...don't accept it or return it to Tire Rack or wherever you got it) you should ask the technician to remount the tire turned 90 degrees on the wheel and see if that reduces the amount of weight.
Road load balancing is becoming more available...Hunter makes a balancer with a roller that puts about 500-700 lbf on the tire while it's imbalance is being read...generally results in a better balance/ride. Look around for it.
Last thought...as a general rule, tire imbalance gets worse with speed rather than peaks/resonates at one speed....I'd look real hard for a bent rim with an imbalance vibration at 45-55 mph or even possibly a loose/failed engine/trans mount. As I recall, Ford had such a vibration problem that ALLDATA notes involves a motor mount replacment and probably a mass damper addition.
posted by 140.32...
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