speedo gear change to make accurate

[easyrider]

I have had the speedo calibrated and when I installed dash assy. the speedo is off 15 or so mph ( too fast). I don't understand why it wouldn't be the same gear(at trans) with my using the same transmission and same engine and same rear end and same dash assy. . I did use 225/70-14 instead of the orginal size that came on the car, but I don't see how that would up my speedo 15 miles per hour at 45mph. Any help?
I have a 318 cu. in. wide block engine / auto trans.. Does anyone know what the standard rear end gear would be for this combination?
Thanks in advance for any help you can give!

 

[tallhair]

I have had the speedo calibrated and when I installed dash assy. the speedo is off 15 or so mph ( too fast). I don't understand why it wouldn't be the same gear(at trans) with my using the same transmission and same engine and same rear end and same dash assy. . I did use 225/70-14 instead of the orginal size that came on the car, but I don't see how that would up my speedo 15 miles per hour at 45mph. Any help?
I have a 318 cu. in. wide block engine / auto trans.. Does anyone know what the standard rear end gear would be for this combination?
Thanks in advance for any help you can give!

what was the previous tire diameter when the speedo was correct was it significantly different? If so that would affect it. another option is perhaps the calibration is off possibly because they used a different rear diameter tire in the equation?

 

[lewtot184]

probably a '741 case with 2.76 gears. a 17 tooth speedo pinion in the tranny would be correct for this gear ratio. maybe you need to check the gear ratio?

 

[696pack]

Mopar Speedometer Pinion Numbers
Tire Overall Diameter
Also Some Excel Worksheets, that figure the seedometer for you

For Auto Trans - AUTOMATICchart.xls

Manual Trans - 4SPEEDchart.xls

AXLE RATIO 24" 26" 28" 30"
2.76 2538930 2538928 2538926 2538924
2.94 2538932 2538930 2538928 2538926
3.21 2538935 2538933 2838931 2838929
3.55 2538939 2538936 2538933 2538931
3.91 2538943 2538940 2538937 2538935
4.10 2538945 2538942 2538939 2538936
4.30 2538944 2538941 2538938
4.56 2538945 2538943 2538940

Please note: these numbers are for the standard style pinion gear
also last two numbers are the number of teeth, 2538945 = 45 teeth

 

[lewtot184]

Mopar Speedometer Pinion Numbers
Tire Overall Diameter
Also Some Excel Worksheets, that figure the seedometer for you

For Auto Trans - AUTOMATICchart.xls

Manual Trans - 4SPEEDchart.xls

AXLE RATIO 24" 26" 28" 30"
2.76 2538930 2538928 2538926 2538924
2.94 2538932 2538930 2538928 2538926
3.21 2538935 2538933 2838931 2838929
3.55 2538939 2538936 2538933 2538931
3.91 2538943 2538940 2538937 2538935
4.10 2538945 2538942 2538939 2538936
4.30 2538944 2538941 2538938
4.56 2538945 2538943 2538940

Please note: these numbers are for the standard style pinion gear
also last two numbers are the number of teeth, 2538945 = 45 teeth

looks like the OP has a 65 plymouth. 65 and earlier have different speedo pinions and cables.

- - - Updated - - -

65 should look like this.

 

[tallhair]

Mopar Speedometer Pinion Numbers Tire Overall Diameter
Also Some Excel Worksheets, that figure the seedometer for you

For Auto Trans - AUTOMATICchart.xls

Manual Trans - 4SPEEDchart.xls

AXLE RATIO 24" 26" 28" 30"
2.76 2538930 2538928 2538926 2538924
2.94 2538932 2538930 2538928 2538926
3.21 2538935 2538933 2838931 2838929
3.55 2538939 2538936 2538933 2538931
3.91 2538943 2538940 2538937 2538935
4.10 2538945 2538942 2538939 2538936
4.30 2538944 2538941 2538938
4.56 2538945 2538943 2538940

Please note: these numbers are for the standard style pinion gear
also last two numbers are the number of teeth, 2538945 = 45 teeth

696 do you have a link for these handy? thanks

 

[easyrider]

how many teeth are on your gear?

 

[696pack]

696 do you have a link for these handy? thanks

Here is one for you:

http://www.bigblockdart.com/techpages/speedtire.shtml