speedometer error

[wally stokes]

I got my overdrive working and went down the hiway to try it out. The tackometer read 3200 and my speedometer read 100 .We were keeping up with traffic so i think about 60 to 70, so were is the problem in the speedometer,the angle drive is new

 

[curtis]

Assume your tyres and wheels are standard and that the diff hasn't been changed?
Or are you saying it was alright before and now the overdrive works it isn't

Curtis

 

[john_j]

...or are you saying you have fitted an overdrive and now the reading is wrong?
It might also help if we knew what your car is!

 

[wally stokes]

the car is a 59 BN4 the overdrive came with the car. The tranny and overdrive had been rebuilt and the car has just been put on the road recently and was getting the overdrive working.The wheels and tires are the proper size as for as the diff goes I only assume it is the proper one, I do not know how to tell if it is. The rest of the car came in box's so it is possible that the speedo was switched but all the other guages are the rite ones.

 

[Dave Russell]

Hi Wally,
It's a little hard to tell where the error is. It could be in the tachometer or the speedometer. The axle ratio is stamped into the upper front part of the alum. near the mounting flange. The marking should be something like 41/10. the ratio is 41 divided by 10 which is a 4.1 to 1 ratio which should be standard for your car with overdrive.

Also your car should have a 28% overdrive which translates to a .78 ratio. (1/1.28 = .78) A 28% speed increase or a 22% rpm reduction. The OD % ratio is the first two digits of the serial number on the OD identification tag. Eg. 28/1308/002857 or similar. At a true 3200 rpm in fourth gear I would expect about 58 mph. In fourth overdrive at 3200 rpm, I would expect about 72 mph. At 100 mph in overdrive fourth, I would expect about 4400 rpm.

As far as I know the angle drive ratios were the same at 2.5 to 1, and your speedometer should be marked 1325 in very small numbers on the face. This is it's designed cable revolutions per mile.
D