I've had 4°, NAPA bought, shims in my front axles for over 20 years and it has never been a problem but has been one hell of an improvement when 33" tires went on. Steering returns to center when completing a turn and it goes nice and straight down the road no matter how many ruts and grooves there might be. I installed them back on the front axle now that I have rebuilt the entire Jeep and switched to 32" tires instead. Didn't want to discard a good thing when I had it and will always keep them because of the improvement they made. The only thing I bought was new centering bolts of longer length so the wedges stay bolted to the spring packs of the new Black Diamond lift kit.
1984 CJ-7 Renegade