The 510 sedan uses an IRS rear end with a solidly mounted R-160 differential with a 3.70 ratio. Automatic cars used a 3.90 ratio. The estate car or wagon used a solid H-190AL differential with leaf springs and 3.70 ratio with the standard and 3.889 with the automatic. The Differential from the 521 will swap in if the wagon side gears are used and will give a 4.375 ratio.