what gear ratio???

I picked up a 40 merc rear but I can't figure the ratio. 99b stamped on it. No speedo gear to help identify.

 

I'll asume it's a complete rearend with the driveshaft and tube. Mount two tires of equal diameter, put a chalk mark on a tire and directly across a chalk mark on the backing plate. Without rolling the tires make a chalk mark on the driveshaft and a corresponding one on the torque tube bell. Now pick up the torque tube and roll the rearend towards you counting the revolutions the driveshaft makes to roll the tire one complete revolution. Repeat a couple of times to ensure accuracy but the driveshaft revolution count is your gear ratio. Example: a little over 4 revolutions is a 4.11

Make sure you roll the rear tires straight forward as steering the rearend in an arc while counting will alter the result.

Frank

 

fairly certain those were all 3.78. oddball rear end as the driveshaft and pinion were integral

 

Early Mercs were known to have one piece pinion shaft/drive shaft and 3.54 gears. That 99 No. appears to be a model number.

 

There should be a stamp on the boss on the bottom ie. 9-37 or 9-36