Rear pinion shims? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevybill · 09-08-2005, 03:18 PM

I have 3 inch drop coil springs on my truck rear.

Do I need to buy some rear pinion shims for alignment of the pinion angle?
If so, which degree thickness do I need?

Thanks guys

chevybill · 09-09-2005, 08:42 AM

ttt

**pjmoreland** · 09-09-2005, 11:27 AM

I don't remember exactly how long the trailing arms are in the rear suspension, but they are somewhere around 5 feet (60 inches) long. As you lower the suspension, the input to the differential lowers in the front, so you can add shims to raise the differential input back up.

Here's the equation you would use to calculate the angle of the required shims:

shim angle = arctan(drop/trailing arm length)

shim angle = arctan(3inches/60inches)

shim angle = 2.86 degrees

Assuming the trailing arms are 5 feet long, then maybe a 3 degree shim would be good. If you don't experience any driveshaft vibrations after lowering you suspension, then the shims may not be necessary.

09-08-2005, 03:18 PM	#1
chevybill Senior Member Join Date: Oct 2004 Location: calhoun city ms Posts: 940	Rear pinion shims? I have 3 inch drop coil springs on my truck rear. Do I need to buy some rear pinion shims for alignment of the pinion angle? If so, which degree thickness do I need? Thanks guys __________________ ongoing 1970 c 10 lwb 1994 z-28 few mods.-owned since new 1978 vette silver/grey 25th anniv. paint

09-09-2005, 08:42 AM	#2
chevybill Senior Member Join Date: Oct 2004 Location: calhoun city ms Posts: 940	ttt __________________ ongoing 1970 c 10 lwb 1994 z-28 few mods.-owned since new 1978 vette silver/grey 25th anniv. paint

09-09-2005, 11:27 AM	#3
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 6,052	I don't remember exactly how long the trailing arms are in the rear suspension, but they are somewhere around 5 feet (60 inches) long. As you lower the suspension, the input to the differential lowers in the front, so you can add shims to raise the differential input back up. Here's the equation you would use to calculate the angle of the required shims: shim angle = arctan(drop/trailing arm length) shim angle = arctan(3inches/60inches) shim angle = 2.86 degrees Assuming the trailing arms are 5 feet long, then maybe a 3 degree shim would be good. If you don't experience any driveshaft vibrations after lowering you suspension, then the shims may not be necessary. Last edited by pjmoreland; 09-09-2005 at 11:28 AM.



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