Speedo Drive Gears
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Post by: john.p.clegg » Mon Mar 22, 2010 7:08 am
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john.p.clegg - Coveted Fifth Gear
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Post by: dusty » Mon Mar 22, 2010 11:04 am
Thanks John, but I have a black one (23 teeth I think) and a white one (22 teeth)
According to a spreadsheet I found on here I need one with 26 teeth to suit a 4.11 diff, no idea what colour that would be though...
Cheers
Jon
According to a spreadsheet I found on here I need one with 26 teeth to suit a 4.11 diff, no idea what colour that would be though...
Cheers
Jon
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dusty - Third Gear
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- Joined: 07 Mar 2007
Post by: msd1107 » Mon Mar 22, 2010 4:51 pm
Dusty,
You may have trouble sourcing a 26 tooth gear. The commonly available ones are 23, 24, and 25. Early Elans or +2s running a 3.55 differential with 165-13 tires (speedometer with 1000 TPM) have the same problem. They need a 22 tooth gear. The later cars went to a 980 TPM speedometer to get around this.
It may be worthwhile to call around to vendors of the high ratio differentials to see if they have any clue.
The way to correct this is to send your speedometer into a shop that rebuilds and calibrates Smiths speedometers.
If you are running 155-13 tires you will need a 20/53 (1050 TPM) (stock is 20/50) pair to match a 25 tooth transmission drive gear, 20/55 (1094 TPM) for a 24 tooth gear, and 20/57 (1142 TPM) for a 23 tooth gear.
For 165-13 tires, this changes to 20/51 (1022 TPM) for 25 tooth, 20/53 (1065 TPM) for 24 tooth, and 20/56 (1111 TPM) for 23 tooth.
If your tires are different, go back to the spreadsheet, enter your tire size, and enter 7 in cell B11, 25 (or what ever you have) in cell C11 and read the speedometer tooth number in cell Q46.
The help text at the start of the spreadsheet starting at line 616 explains all of this.
The rebuild people have a complicated procedure to follow for them to calibrate the speedometer, but the spreadsheet takes all guess work and imprecision out of the process. Hopefully, if you tell them what you want, they can do it.
David
1968 36/7988
You may have trouble sourcing a 26 tooth gear. The commonly available ones are 23, 24, and 25. Early Elans or +2s running a 3.55 differential with 165-13 tires (speedometer with 1000 TPM) have the same problem. They need a 22 tooth gear. The later cars went to a 980 TPM speedometer to get around this.
It may be worthwhile to call around to vendors of the high ratio differentials to see if they have any clue.
The way to correct this is to send your speedometer into a shop that rebuilds and calibrates Smiths speedometers.
If you are running 155-13 tires you will need a 20/53 (1050 TPM) (stock is 20/50) pair to match a 25 tooth transmission drive gear, 20/55 (1094 TPM) for a 24 tooth gear, and 20/57 (1142 TPM) for a 23 tooth gear.
For 165-13 tires, this changes to 20/51 (1022 TPM) for 25 tooth, 20/53 (1065 TPM) for 24 tooth, and 20/56 (1111 TPM) for 23 tooth.
If your tires are different, go back to the spreadsheet, enter your tire size, and enter 7 in cell B11, 25 (or what ever you have) in cell C11 and read the speedometer tooth number in cell Q46.
The help text at the start of the spreadsheet starting at line 616 explains all of this.
The rebuild people have a complicated procedure to follow for them to calibrate the speedometer, but the spreadsheet takes all guess work and imprecision out of the process. Hopefully, if you tell them what you want, they can do it.
David
1968 36/7988
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msd1107 - Fourth Gear
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- Joined: 24 Sep 2003
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