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ORIGINAL: Stewart

I know I'm ressurecting an old thread but I want to know what some of you all think. I'm getting bad vibration from my driveshaft after my 4.10 gears were installed at about 85 plus. I guess with the higher ration the driveshaft when spinning for 85mph is more like 120 plus with stock gears. Now when I bring this issue up with the dealer, they will of course not know about my gear swap unles they drive the car or open up the rear end which wont happen. But this is what I'm wondering about, on one hand since the car is limited at 120 as long as the vibration would have happened with stock gears before this then Ford would have to warranty the shaft am I right on that? It doesn't make sense to me that since US roads only go up to 75 that they can use that as a warranty cut off, what if I have my own little track I want to run around at 115, I don't see how Ford would be able to hide bhind the 75mph speed limit. A more likely issue is that if they find out about the gears they will try to use them as an excuse, but if you look at the brochures for the cars one of the advantages they list for the solid rear axle is the ease of swapping out gears, so if they are condoning or at least using something like that as a selling point, something such as increase driveshaft speed should be a reasonable thing to cover whether new gears are in or not. Does any of that sounds reasonable? I just want to figure out how I'm going to bring this up with the dealership, Ideally I'll get the newly designed driveshafts under warranty.