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Car Forum / Pontiac / Pontiac Firebird / July 2005Speedo gear help
Hey, I replaced the rims on my '85 Camaro which had 14" with 15" off an '83 T/A. It now has 215/65/15's.. which is a fairly common size.. but since I have chnaged the rims.. my speedo ioff a little. With talking to Dennis.. there is a little gear that you can replace to sync it back up. But what do I need to know to get the right gear? Rear end? Wheel size? Then how easily is it replaced? Thanks. -Geno 1985 Blue Camaro 2.8L auto w/T-tops (aka "Tazmaro") 1988 Blue Firebird Formula 5.0L auto w/T-tops 1985 Brown Firebird 5.7L (360) 5-speed NO T-tops > Hey, > [quoted text clipped - 9 lines] > 1988 Blue Firebird Formula 5.0L auto w/T-tops > 1985 Brown Firebird 5.7L (360) 5-speed NO T-tops It's really easy to replace. BUT, if it happens that your combo requires that the drive gear needs to be replaced, then you'll have to do some additional work that isn't as easy. I swapped from 2.73's to 3.23's and just swapped out the driven gear. All you have to do is remove the speed sensor and change the gear. You'll need to calculate the overall diameter difference. If you can find out what gears you have in the tranny, then you can find a combination that will suit your new tires. -Bruce Here's a tech article to change the gear: http://www.thirdgen.org/newdesign/tech/speedogear.shtml Here are the GM part numbers for all the gears. Part No. Teeth Color Sleeve* 25513042 35 Orange 25007338 25513043 36 White 25007338 25513044 37 Red 25007338 25513045 38 Blue 25007338 25513046 39 Brown 25007338 25513047 40 Black 25007339 25513048 41 Yello 25007339 25513049 42 Green 25007339 25513050 43 Purple 25007339 25513051 44 Dk Gray 25007339 25513052 45 Lt Blue 25007339 *Some applications may use Sleeve No. 25007224 or 10456092 in place of 25007338, or 25007308 or 1045089 in place of 25007339. Red Drive Gear Combinations With drive gear number 8640517, (red, 17 teeth) the following combinations apply: Axle Tire Dia. Driven Gear Ratio (Nominal) (Tooth Count) 2.59 26.0 35 25.7 36 2.73 26.0 37 25.7 38 2.87 26.0 39 3.07 26.0 42 3.31 26.0 45 Gray Drive Gear Combinations With drive gear number 8642620, (gray, 15 teeth) the following combinations apply: Axle Tire Dia. Driven Gear Ratio (Nominal) (Tooth Count) 3.33 25.7 40 3.45 25.7 41 3.54 26.0 42 25.7 43 Lower ratio (higher numerically) rear or smaller diameter tire requires higher driven gear tooth count. Increasing or decreasing driven gear tooth count by one will usually accommodate a 1/4" to 1/2" change in tire diameter. Ok.. I know I have a 3.42 rear end.. my tire size in inches lookes like 26".. I have a stock size 215/65/15 (I know lots of 3rd gens have this size) I just don't know how to find out how many teeth either gear has or what I need. So is that enough info for you to tell me more? Thanks. -Geno 1985 Blue Camaro 2.8L auto w/T-tops (aka "Tazmaro") 1988 Blue Firebird Formula 5.0L auto w/T-tops 1985 Brown Firebird 5.7L (360) 5-speed NO T-tops > Ok.. I know I have a 3.42 rear end.. my tire size in inches lookes like > 26".. I have a stock size 215/65/15 (I know lots of 3rd gens have this [quoted text clipped - 5 lines] > 1988 Blue Firebird Formula 5.0L auto w/T-tops > 1985 Brown Firebird 5.7L (360) 5-speed NO T-tops 26.18" to be exact. This isn't enough info because I don't know what gear you have in the tranny.. You'll need to take it out to find out; count the teeth or figure out what color they are. > Hey, > [quoted text clipped - 9 lines] > 1988 Blue Firebird Formula 5.0L auto w/T-tops > 1985 Brown Firebird 5.7L (360) 5-speed NO T-top Here's an online calculator in HTML to help you figure what tooth gear to change to as well as a source for the different gears. This is helpful if you have changed to a setup that the factory never used. You will need to know your tire diameter and what your rear gearset ratio is to use it. Such as 25.5", 26.8"... and 3.07 to 1 or 3.27 to 1.... Calculator: http://www.bgsoflex.com/speedo1.html Source for all kinds of 700R4 parts and speedo gears: http://transmissionhead.com/ (oh, yeah. it's a BIG page) AW |
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