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RT Jul 6th, 06, 8:54 AM Can anyone tell me what effect does changing the driven speedo gear have on the speedometer? I used the calculator on a speedometer website to find that I need a 19 tooth driven gear. I have a 22 tooth gear that is causing my speedometer to read quite a bit higher than actual speed. Will the smaller gear slow the speedo down? It seems to me that a smaller driven gear would raise the speedometer reading ?? Thanks, Rich DZAUTO Jul 6th, 06, 9:35 AM For the DRIVEN speedo gear, fewer teeth will make the speedo read faster and more teeth will make the speedo slower. GENERALLY speaking, a change of just one tooth on the driven gear will result in about 3mph change in your speedo. Driven speedo gears range from 17 to 25 teeth. Also, there are 2 sizes of driven gears, which must be matched to the drive gear that is on the main shaft inside the tranny. The small gears are 17-22 teeth and the big gears are 22-25 teeth (YES, there is a big and a small 22 teeth gear). The big 22 teeth gear is green. The gray 22 teeth gear is small. What color is your 22 teeth gear? By big and small gears, I mean the outside diameter. The difference is only about 1/16in. Wally Jul 6th, 06, 11:41 AM Driven gears with GM part numbers and yes they can be had no matter what your local dealer says. L22T green nylon 3860345 L23T black nylon 3860346 L24T yellow nylon 3860347 L25T orange nylon 3860348 NOTE: these FOUR (4) gears used with 1.76" outside diameter circle gears. L17T purple nylon 3987917 L18T brown nylon 3987918 L19T natural nylon 3987919 L20T blue nylon 3987920 L21T red nylon 3987921 L22T silver nylon 3987922 NOTE: these SIX (6) gears used with 1.84" outside diameter circle gears. RT Jul 6th, 06, 1:11 PM DZauto, the 22 tooth gear is grey. (or silver, going by Wally's part # list) Maybe both gears need to be changed? More info: 3.55 rear, P22570r14 tires. Thanks, Rich RT Jul 7th, 06, 9:24 AM I just checked and realized I was wrong about the rear end ratio. It's 3.36. Rich DZAUTO Jul 7th, 06, 11:47 AM Rich, Most (but not all) Muncies have an 8tooth speedo drive gear on the main shaft. GENERALLY, with an 8tooth drive gear in the tranny and a 3.36 rear gear ratio, either a 20 or 21tooth driven gear would be used. BUUUUUUUUUUUT, if your driven gear is already a 22tooth gear (and your speedo is too fast), when you drop down to a 20 or 21tooth gear, then your speedo will read even faster! RT Jul 7th, 06, 4:50 PM DZAuto, that's what I'm thinking, but if I'm doing this right, the calculator on the website I mentioned, http://www.tciauto.com/tech_info/speedo_gears.htm says that my driven gear should be 18.4 (or 18) teeth! I counted the teeth (through the hole in the case) on my red/pink drive gear and it is 7 teeth and the revs/mile of the BF Goodrich radial T/A's is 785. Thanks, Rich | ||