Hi I'm new to this forum but I'm thinking you guys will have some good ideas to help me figure out my vibration problem. A little background info...I have '63 Buick 215 V8 hooked up to a Borg Warner t35 automatic. This combo is in my '68 Volvo 122. Every thing has worked out pretty well with the swap except I get a oscillating vibration which becomes noticeable about 3000 rpm. I don't think it is in the drive-shaft or rear because it gets worse as rpm gets higher in 2nd then goes away when shifting to 3rd. It then comes back as rpms build up. I had the harmonic balancer rebalanced so it is good. I am now thinking the flex-plate or torque converter might be out of balance. I took off the inspection cover on the bell housing and can see where the ring gear bolts the flex-plate. There are what look like extra bolt holes for balancing. Two of the holes had small bolts with different thickness heads. They looked like balance weights. Is balancing the flex-plate the problem and if so how can I balance it while it is still in the car?