Your front drive shaft is much longer and can a little more of an angle without
vibes. I don't agree with don't use shims up front. I was told not to use
anything more then 4 degrees up front. I'm running 4 deg shims up front with
problems. The shop that aligns my rig also does Big Rigs so
they know what they are doing and have the right size cam bolts to do it
Shims are sold in sizes up to 12 deg. They are not the best solution to
correcting your pinion angle but is acceptable. My rear is out 12 degrees as
of now. I will be upgrading to an explorer 8.8 and don't want to take the time
to grind and re weld perches on an axle I will only be keeping another 4
weeks. I put a double T-Case drop and 4 deg shims in my rear temporarily to
correct pinion angle until I do my axle swap.
When I had my 4" spring lift I ran 4 degree shims for many years
I now have a 5" BDS lift / 1" shackle / 1"body / flatty front and trimmed rear
fender flairs. I just had it aligned and it drives straight as an arrow.
Everyone beats up aluminum shims and I ran a set of 4 deg shims now for
over three years. I just inspected them when I re installed them when I went
from my 4" RC lift to my 5" BDS lift and they were in great condition.