Pinion angle at transmission mount
 

My 72' El Camino had worn air shocks so I replaced them with conventional shocks, I also installed
HD rear coil springs so it would have a slight forward rake. This isn't a Drag car or daily driver, just something for weekend use (Plus the Hot-Rod Power tour). Anyway, after I finished I took it out for a ride and there was a vibration coming from the driveshaft/Rear-End (Pinion angle). I had the same vibration with my 39'Ford Coupe when I built it, years ago. That was and easy fix because all I had to do was find the right angle and use (3 degree) wedges over the leaf springs, but coil spring suspension is a bit more complex. I hate to spend the money on rear adjustable control arms so instead I took a ride to the local parts store to see if I could find a shorter height transmission mount to lesson the angle, but no luck & I don't know of anyone who makes them either. Before going for the adjustable control arms I was thinking of raising the motor mounts with a plate or washers which is another cheap fix...
Anyone run into this problem with a coil spring rear suspension?
PS: This is a completely stock 1972 El Camino with a 350, a/t & 12 bolt rear-end. It has all the smog stuff still on the car including the air cleaner.
It sat in a garage on jack-stands for 25 years and is in great condition.

The first thing I would check would be to see if the drive shaft is straight,
and being that it has set for a long time I would look at the U joints. A bad
U joint will cause a vibration. Usually if the pinon angle for example is 3
degrees down, the transmission should be 3 degrees up or vise versa. Hope this
helps.

I drove the car w/o a problem before I changed the springs. The u-joints are good, I had the driveshaft out when I pulled the trans to replace the front (& rear) seal.
I'll try shimming the motor mounts next, no big deal because I have to lift the engine in order to pull the oil pan & replace the dried out rear main seal (Front seal too).
I bought this El Camino because I owned a 71' when I was a kid, it was a SS454 4spd., it was my daily driver from 1973 - 1984... Stupid me, I sold it to buy the new body styled 1978.

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