Dialing in speedometer

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Moparmadness408

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So I have a 1967 Plymouth valiant that I just did an engine swap in, and when my speedo says I’m doing 80 I’m actually doing 60 mph. It has the 727 torqueflite with 27 inch diameter rear tires and a 3.55 gear set in the rear end. What amount of teeth of speedometer pinion do I need?
 
Whatever number you have in there times 80/60. But if you want to be more accurate. note your odometer when you pass a mile marker, drive 10 miles note your odo at the tenth marker. divide the difference by 10 and multiply that times the number on your current gear and that is the new gear number. Or you could just find the chart.
 
Speedo table

speedo chart.JPG
 
I found one of those digital speeding signs and It was reading 38 and my speedo was a little above the 35 mark.
Good enough
 
OP did not read the service manual. Chrysler products have always been the easiest to deal with speedo wise because there is no mainshaft gear to be changed. The speedo gear housing is eccentric to accomodate different diameter gears. It's in the service manual. Download them for free at MyMopar. No, I don't work there
 
I use my GPS to check my speedometer. You can also install an app called Waze for your phone.
 
Last edited by a moderator:
rear gear X 10 to get speedo tooth count. pretty close (35 tooth) with stock tires.
 
I forgot to mention I am using an aftermarket mechanical speedometer. When the speedometer cable is turning 1k rpm the speedometer registers 60 mph. Are the factory speedos calibrated the same way? If not what’s the number of teeth on the output shaft gear?
 
trapster said:
Speedo table

View attachment 1715561113
Click to expand...

Just want to make sure I get this right.

I have a 3.23 rear axle I believe and curently have 195/75R14 tires, the diameter would be 25.5”. I will be putting on 205/75R14, with a diameter off 26”.

According to this chart I should go with a 33 tooth gear, is that correct?

Edit: In the transmission section of my manual it says “7*14 - 3.23:1 - 6 cyl - No. of drive teeth 7 - 18 tooth - Dark purple” was there a change at some point and am I looking for a different measurement?
 
chinze57 said:
Just want to make sure I get this right.

I have a 3.23 rear axle I believe and curently have 195/75R14 tires, the diameter would be 25.5”. I will be putting on 205/75R14, with a diameter off 26”.

According to this chart I should go with a 33 tooth gear, is that correct?

Edit: In the transmission section of my manual it says “7*14 - 3.23:1 - 6 cyl - No. of drive teeth 7 - 18 tooth - Dark purple” was there a change at some point and am I looking for a different measurement?
Click to expand...
Yes you would need a 33 tooth speedometer pinion.
 
Ok so I did trapsters suggestion and multiplied 26(the current one in the vehicle) by 80, then divided by 60 and got 34. So if everything reads correctly after that, then that means the factory speedos will register 60 mph when the cable is turning at 1k rpms as well as the aftermarket one I got.
 
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