11-10-2020, 10:51 AM
Hi Nick
I can’t help with the take off pulley and drive but i have been through a PA speedometer rebuild recently and learned quite a lot. According to Mike Flannery https://www.magnetic-speedometer-repair.com he can’t recalibrate these mechanical speedos so some form of gearbox on the drive may be necessary. Alternatively, in your case, the right combination of pulleys on the take off.
Firstly I would suggest checking the speedometer revolutions per mile. I found that by using an electric drill I could determine the revs / minute to mph relationship on the speedo. I calibrated my drill using a strobe rev counter app on my phone. Then checked what the output from the speedo drive was. This meant counting the turns of the drive to distance covered whilst pushing the car over a short distance. Then you can determine the gearbox ratio (or correct pulley size).
Carefully checking everything I found that the odometer was reading correctly (Using gps) but the speed under by about 5 to 10 mph. This indicated that I had the right gear ratios but that the speedometer governor was out. Bearing in mind Mike’s advice I’ve decided to live with that and use a speedometer app on the phone to record speed. I am now pretty good at looking at the speedo and mentally correcting for true speed
.
Cheers
Howard
I can’t help with the take off pulley and drive but i have been through a PA speedometer rebuild recently and learned quite a lot. According to Mike Flannery https://www.magnetic-speedometer-repair.com he can’t recalibrate these mechanical speedos so some form of gearbox on the drive may be necessary. Alternatively, in your case, the right combination of pulleys on the take off.
Firstly I would suggest checking the speedometer revolutions per mile. I found that by using an electric drill I could determine the revs / minute to mph relationship on the speedo. I calibrated my drill using a strobe rev counter app on my phone. Then checked what the output from the speedo drive was. This meant counting the turns of the drive to distance covered whilst pushing the car over a short distance. Then you can determine the gearbox ratio (or correct pulley size).
Carefully checking everything I found that the odometer was reading correctly (Using gps) but the speed under by about 5 to 10 mph. This indicated that I had the right gear ratios but that the speedometer governor was out. Bearing in mind Mike’s advice I’ve decided to live with that and use a speedometer app on the phone to record speed. I am now pretty good at looking at the speedo and mentally correcting for true speed
.Cheers
Howard