93 240SX Vert shaking at speed

[USC Justice]

OK, at the point of frustration with my project car. It is a 1993 Convertible 240SX. I have done the 5spd manual swap, and swapped in an SR20DET. It has a full BRM exhaust. I have upgraded to the 300ZX TT Brakes. The car is sitting on GAB adjustable struts, and RSR springs. I have changed out the tension control rod inserts with poly kit, as well as upgraded front and rear sway bars to the Godspeed sway bars. I think that's all the relevant things to my problem.

The problem is this: Between 58 and 67MPH (as indicated on the digital speedo and verified by GPS), the entire front half of the car shakes. It is noticeable and unpleasant to say the least. The car was sitting on Rota Subzero wheels with Avon Z rated tires. Thinking that it was a wheel fitment/balance issue I have swapped out to a set of Enkei RP05 wheels wrapped in Kuhmo Solas tires. Tire size is 215-45-17 (don't know if that has any bearing on it, but thought I would mention it too). It does not do this at any other speed, and if accelerating very quickly, then it is not nearly as bad.

I know many will say, simply drive much faster than that and don't worry about it, but unfortunately in both morning and afternoon rush hour, that's about the best I can hope for.

Any thoughts, advice, or ideas as to what to do would be very appreciated.

Thanks,
Donald

[sx moneypit]

If all the parts on the front end are in good shape and the tires are balanced correctly, i would take a good look at the driveshaft and u-joints.