UPDATE:Alright, basically what is happening now is i'm close, but not close enough; When i used driven gear #3987918--18 tooth "brown" gear, i was actually doing 63 with the needle at 60 and the odometer reads 1/10 more than one mile. i then tried #3987917--the 17 tooth "purple" gear and i'm doing basically 58mph with the needle at 60 and the odometer is still about 1/10 over one mile.
Normally, either of the above would be good enough for me. But i'm trying to figure out my gas mileage so i need something precise
and since i really don't have time to further mess with it, i think i'm going to go with one of those electronic speedometers---either from autometer or cyberdyne. These can be calibrated
exactly.The #3987918
is the stock driven gear for 235/75 15's and 2.56 rear according to the dealer. But i think what's happening is my tires are off brand and thus are different from everyone elses 235/75 in size. Either that or my speedo is slightly out of whack.
So, in case anyone is interested, the stock speedo gears for a TH-350 and 2.56 rear equipped GM vehicle are:
a)With 195/75 15's
drive gear (on output shaft)----#6261785 "purple" 10 tooth
driven gear -------------------# 3987920 "blue" 20 tooth
b) With 235/75 15's
drive gear---------------------#6261785 "purple" 10 tooth
driven gear--------------------#3987918 "brown" 18 tooth
These are the stock gears as they came from the factory. Again, it's not working for me because i suspect that my tires are "funny."
So what did i/we learn?
1)The GM dealer is an excellent resource for not only knowledge of the different part combinations, but the actual parts and prices; If you've switched to a different size tire and/or rear gear that was available on one of these cars, the dealer knows exactly which gears are the right ones. Also, they were cheap--about $5 per gear. Try buying one from summit or tci etc. You'll probably pay at least $20 after all is said and done.
2) Don't get into a rush and get all hasty. Think about what needs to be done and ask
a lot of questions; i was getting ready to take the driveshaft out and the tailhousing off and Mr. Vile stepped in and questioned the situation. On top of that, i still have no idea how i would get the drive gear off the output shaft if it had gone that far.
3) Custom Deluxes (as opposed to Silverados) apparently did come with "small" car tires. i think the silverados had 215/75 15's as standard. But the deluxes were an entry-level 1/2 ton pickup with fullsize car drivetrain. We have to remember that the S-10 had only been out for a year and until those sales picked up, the custom deluxe was still filling the role of the light 1/2 ton pickup? i guess?
Actually, one of the members had a setup that illustrates these smaller tires. i think it looked rather nice actually:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=7156.0i think i may start another thread strictly on speedo calibration, because we we're getting slightly off the original topic.
1
