Lowered the front springs 1 in and installed new rear axle and rear springs and noticed a vibration above 45 mph which increased with car speed. Vibration was from the rear and went through the back of my seat. Bought an magnetic angle finder from harbor freight and with full weight on the wheels the driveshaft was angled down from front to back 3 degrees. Detached the u joint and placed a flat piece of steel across the front of the pinion and the angle finder on the steel and the pinion was angled down 2 degrees from back to front. Which meant I had to angle up the pinion 5 degress to get it in line with the driveshaft. Purchased 2 aluminum pinion shims on line which was 4 degrees angled. Basically it is just a wedge with a hole in the center. Had to also purchase new longer U bolts at a local spring auto shop. $10 ea. Also need a longer center spring bolt.Take the old one to spring shop to get correct size. Jack up rear axle and put jack stands under the rear frame rails. Lower rear of car to put all the weight on the frame rails so axle will hang. Loosen the u bolts, slowly raise up the axle until you see it separate from the spring. Put c clamps on each side of the center spring bolt to hold together the spring leafs then remove the center spring bolt.Put washers or steel spacer 1/4 in. to raise up the head of the new longer center bolt and put bolt thru the spring and tighten. The head of the center bolt has to be raised up to accomodate the shim and still fit thru the center of the spring perch. In my case the thick part of the shim is at the front to raise up the front of the pinion. Shim fits between spring perch and spring. Lower the axle onto the shims and align the spring perch with the center bolt. Install new U bolts and bolt down. Whole procedure cost about $75. I went to a local speed shop for this work and was told they do not put in shims but would have to remove and reweld the spring perches in a new position for $600. no thanks. Vibration is 95% improved.