correcting pinion angle after lowering rear

[1969burb]

I'm hoping someone can point me in the right direction. I have lowered the rear of my burb 5 1/2 inches in the back. (4 inch lowered springs and 1 1/2 blocks.) (1/2 ton with trailing arms) I have a vibration at 35-45 mph that wasn't there before and I assume it is a pinion angle problem. I know this can be corrected with shims, but how do I determine how many degrees I need to correct it?

[pjmoreland]

Instead of trying to calculate the amount of angle correction, it might be better to measure the angle of your transmission output, and the angle of your rear axle input to see how far off they are from each other. You could either have a driveshaft shop measure the angles for you, or you could buy one of those cheap level angle measurement tools from a place like Sears or Home Depot and measure it yourself.

[taylorde]

I know that when I bought my crossmember from cpp it was ajusted already for a 4" drop in the rear. the trailing arms were moved from the bottom to the top

[1969burb]

I will go ahead and measure mine, anyone else had these vibration issues? what degree shims did you use to correct it?

[shifty]

i lowered my '03 GMC Sierra and I had to use these little pinion shims from Sir Michael's. they were 2º of adjustment in the angle per kit, one shim per side. i think it was 2º specificallly for a 2/4 drop, but obviously the drivetrain is a little different between the two trucks.

the vibration you describe is something i hear about when people lower without adjusting pinion angle.