ive just got my '35 roadster back on the road and noticed today it was reading 25mph when I was really sitting at 30mph. the car has a rebuilt rear axle using 3.54 gears and has 6.50 rear tyres. im currently using an 18 tooth gear but this is obviously wrong - do I need 19 or 20 tooth gear?
speed reading error
- Thread starter weemark
- Start date
drolston
Well-known member
A 19 or 20 tooth gear will turn slower than your 18 tooth gear, making the speedometer even slower. You can get a 17 tooth gear from Model A parts house. Because of the approximately .05" smaller diameter gear, it might not engage the drive gear on the drive shaft unless you find a 17 turtle (speedo gear housing) to go with it, or modify your housing by grinding down the mating surface. The change from 18 tooth to 17 tooth would raise your 25 mph indication to about 27 mph.
JM 35 Sedan
Well-known member
A 17 tooth nylon gear is available from Brattons Antique Auto. Should fit in your existing turtle and work okay. I know of several folks who have used this gear and no modifications were required on the #18 housing.