Q: I was told I need to shim my axle after I lower my full size Chevy truck. What does the shim do and which one should I use? Amy – Sycamore, IL
A: This is a common question. Depending on how low you dropped your truck a pinion shim may or may not be needed. What you’re doing when you lower the back of your truck is moving the axel up to bring the truck down. As the axle is moved up, the front of the axle where the pinion gear connects to the drive shaft needs to be lowered to prevent the U-joint and drive shaft from binding and causing a vibration. This is where the shim comes in.
The shim is tapered and is installed between the axle and the leaf spring. The thick end of the shim faces the rear of the truck and will rotate the axle, bringing the pinion angle down. The shims come in different sizes from 2 degrees to 6 degrees. Not all trucks will need to be shimmed. Test-drive the truck and feel for any vibrations. If you feel a vibration from the rear of the truck start off with a 2 degree shim and work up to the larger size until the vibration goes away.
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