ejin4499 Posted December 19, 2010 Share Posted December 19, 2010 I am doing a auto to manual swap with (for the project truck) non-stock size tires and was wondering how I figure out how many teeth need to be on the speedo gear in order for the gague to be within 5-10 mph at 70 mph. I think the gear from the manual will be off because of the different rear differential and the gear from the auto will be wrong because of the different gears in the manual transsmision all of wich happens before we even get to the tire size. thanks for any links regards already searched +speedo +speedo +calibration +speedo +gear Link to comment Share on other sites More sharing options...
ejin4499 Posted December 21, 2010 Author Share Posted December 21, 2010 http://www.rodandcustommagazine.com/techarticles/0801rc_mechanica_speedometer_calibration/index.html While its not an answer it does give some really good info and may lead to an answer Link to comment Share on other sites More sharing options...
ejin4499 Posted December 21, 2010 Author Share Posted December 21, 2010 anyone know if the fs5r30a had a magneticaly drive speedo or a gear driven speedo? Link to comment Share on other sites More sharing options...
GrimGreg Posted December 22, 2010 Share Posted December 22, 2010 There are only 4 speedo gears available from Nissan, 17, 18, 19 & 20 tooth. http://www.courtesyparts.com/kb_search_result.php?keywords=[32703M]+\(WD21&cPath=5572_5573_5640_5657 Link to comment Share on other sites More sharing options...
ejin4499 Posted December 22, 2010 Author Share Posted December 22, 2010 There are only 4 speedo gears available from Nissan, 17, 18, 19 & 20 tooth. http://www.courtesyparts.com/kb_search_result.php?keywords=[32703M]+\(WD21&cPath=5572_5573_5640_5657 Ok Ill go with that. How do I figure out wich one would be the closest to the right one? Link to comment Share on other sites More sharing options...
MY1PATH Posted December 22, 2010 Share Posted December 22, 2010 If you have 4.3 gears and 31's you need 17 If you have 4.6 gears and 31's you need 18 If you have 4.3 gears and 30's you need 18 If you have 4.6 gears and 30's you need 19 If you have 4.3 gears and 235's you need 19 If you have 4.6 gears and 235's you need 20 That should get you pretty damn close... Link to comment Share on other sites More sharing options...
sewebster Posted December 22, 2010 Share Posted December 22, 2010 If you have 4.3 gears and 31's you need 17 If you have 4.6 gears and 31's you need 18 If you have 4.3 gears and 30's you need 18 If you have 4.6 gears and 30's you need 19 If you have 4.3 gears and 235's you need 19 If you have 4.6 gears and 235's you need 20 That should get you pretty damn close... So, I think my truck came from the factory with 235s, and now I have 31s. The circumference ratio of these two tire sizes is 1.073 (235s are 28.9" in diameter). But the speedo gear ratio is apparently 19/17 (4.3 gears). 19/17=1.118. So instead of the speedo reading 7.3% too low, now it would read 4.5% too high (if I got the 17 tooth)? Seems like if I switched to the 18 tooth instead I could get it to read 1.7% too low, which would be closer... Am I doing something wrong in my math? Link to comment Share on other sites More sharing options...
MY1PATH Posted December 22, 2010 Share Posted December 22, 2010 Just pull a 17 and 18 from a JY and see what does you better. My 31's are actually 30.5 the 17 a little high and the 18 was a little low. Some 31's are 31.5"... Don't forget the gear that drives the speedo gear is a worm gear(Like large screw threads) so you don't have the exact number of teeth per rotation because it will vary by the diameter of the speedo gear not just the number of teeth. Link to comment Share on other sites More sharing options...
sewebster Posted December 23, 2010 Share Posted December 23, 2010 Just pull a 17 and 18 from a JY and see what does you better. My 31's are actually 30.5 the 17 a little high and the 18 was a little low. Some 31's are 31.5"... Don't forget the gear that drives the speedo gear is a worm gear(Like large screw threads) so you don't have the exact number of teeth per rotation because it will vary by the diameter of the speedo gear not just the number of teeth. Cool. Do you have to drain your tranny fluid to do the swap? Is it just a simple pull out the connector and switch gears thing? Link to comment Share on other sites More sharing options...
MY1PATH Posted December 23, 2010 Share Posted December 23, 2010 (edited) have a rag handy as you will get some drip. The speedo gear Is above the fill level but the t-case pumps oil up to the speedo gear when you are driving and the internal molding keeps about ~1oz of it there when you are stopped. Edited December 23, 2010 by MY1PATH Link to comment Share on other sites More sharing options...
wilson Posted January 1, 2011 Share Posted January 1, 2011 I just replaced my stock 20 tooth gear with an 18 tooth. as I suspected, the speedo now doesnt work. how can you change gear sizes without changing the spacing between axles the gears spin on? or am I missing the trick to get the gears to engage? Link to comment Share on other sites More sharing options...
wilson Posted January 4, 2011 Share Posted January 4, 2011 nobody? Link to comment Share on other sites More sharing options...
MY1PATH Posted January 4, 2011 Share Posted January 4, 2011 I have not done this with the electonic units yet but with the mechanical ones the shaft is offcenter the 20 tooth gears are pretty close to center but the 17t is offset noticeably. But you also change the whole module not just the gear on the end... Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now