Originally Posted by rainjeep
can the rear axle pinion angle be changed by adding shims only? if so how do you know how big of shims you need? took my transfercase drop spacers out and now i have vibrations, daily summer driver and don't think i need an expensive custom made driveshaft for what i use it for.
With an auto your driveshaft is only 0.75" longer than the example above. I see you have a 4" lift so you will have the same issues with an added 10 degrees on your driveline angle. The maximum angle you should be running with a standard driveshaft is near 15 degrees. You started off with probably about 7 degrees so you are beyond the advisable angle.
You say "drop spacers" have been taken out so i assume the rear of the transfer box is now higher? This will add 1-2 degrees to those angles.
You COULD shim the perches but this may not be advisable, if those shims worked loose you would have a problem. However it is cheap, so assume the perch is 4" long and you need 1/2" difference between front and back to achieve roughly 10 degrees upward pointing, probably a bit more. The closer you are to pointing at the rear of the transfer box the better, it also raises the yoke a bit. Best thing to do is to measure it with a protractor and spirit level and work out what your angles are and where they need to be. How you are going to get the axle to sit squarely on the spring with shims is hard to say, but you will probably think of something.
Better solutions are rotation of the diff housing (more difficult than it sounds as it is not supposed to rotate) and rewelding of the perches.
If you are having vibrations it could be because your joints are worn. Have you checked them for play? With this amount of angle they will not last long and you will need good quality ones (say Spicer) and regular greasing or spend a lot of time under it. With a vice and BFH they are not difficult to chaneg at home.
When my wife first got her 1984 CJ I found a joint which had failed and not been changed. The circular ends of the cross bolt on one were worn about 35% and worn square rather than round. It had near 1/2" of play and it was only a question of time before t broke up or something else cracked. The noise from the exhaust drowned the noise and vibration from the drivetrain.
A custom driveshaft will not by itself change the physics of these large changes in each revolution. You are working the joints pretty hard. However a CV joint installed at the transfer box and a pinion pointed up will allow an angle of up to 30 degrees before it binds. This is pretty extreme.