Same question for a 3.23 gear ratio? Don't they go by color and teeth count? Available at a tranny shop if you know the right one?
Guys, You didn't give year model(s) and my only parts book just covers back to '82, but I randomly picked a "drive gear"(in the tranny) #8634965 and a"driven gear" #25524925 (blue). Both these show to be available thru gmpartsdirect.com In the end (for best accuracy) you'll also need to know tire diameter of course. HTH Mickey
One more thing and I'll leave you alone :grin: Speedometer Gear Formula Number of Driven Teeth = (Number of Drive Teeth x Axle Ratio x Tire Revolutions per Mile*) / 1001 I know...you want this too. *Tire Revolutions per Mile Formula (TRPM) TRPM = 20168 / Tire Diameter (in inches) Have some fun Mickey
jeff do you need the plastic pinion gear for the speedometer for a turbo 400 ? if that what you need, let me know, i have a few nos one and may be able to help. henry white
Jeff, Go to your favorite GM parts counter. It is one of the following gears. You need to figure which one you need using this formula. 20168 divided by tire diameter in inches. Multiply the result by the axle ratio, and then by the # of drive teeth on the output shaft(16-18 teeth). divide by 1001, and round off to the nearest whole # 40 teeth-1362048 (black) 41 teeth-1362195 (yellow) 42 teeth-1362049 (green) 43 teeth-1362196 (purple) 44 teeth-9780470 (gray) 45 teeth-1372313 (light blue) Sleeve 40-45 1362293 Drive gears 16- 8623311 17- 8623312 18- 8623313
Here is some useful info I found on the gnttype.org web site, hopefully the formatting will hold. If not, you can go NOTE: Each tire's section width is based on a particular rim size and construction. Compensate for differences. Increase section width .2 inches for every .5 inch increase in rim width. For example, if the tire's section width is 9.14" on a 6.5" rim and is to be mounted on a 7" rim, the section width would be 9.34". Section width (sidewall flex) will vary by construction. ANY variance will affect calculations! Radius - Diameter - Circumference To compute the diameter of a P-Metric tire, multiply the section width by the aspect ratio (as a percentage). If necessary, divide this number by 25.4 to convert millimeters to inches. For example, a 215/65 equates to a tire height of 5.5019685 inches (215 x .65) divided by 25.4. Multiplying this by 2 for the top and bottom sidewall height and adding the rim size will get the overall tire diameter. For example, if the tire is on a 15 inch rim, it is approximately 26 inches ((5.5 x 2) + 15). The radius is half of the diameter. Multiplying the diameter by pi (3.1415927...) will get the circumference. Tire Revolutions Per Mile To compute the number of tire revolutions per mile, divide 20,168 by the diameter. 20168 -------------------------------------- = Tire Revs/Mile (Tire Heigth X 2) + Rim Size For a 215/65R15: 20168 ---------------------- = 775 (5.5" X 2) + 15 For a 255/60R15: 20168 ------------------- = 747 (6" X 2) + 15 Speed By dividing the original tire revolutions by the new tire revolutions and multiplying by the indicated speed on the speedometer, we arrive at the new actual speed. (Orig. Tire Revs/Mile) ------------------------------- X Indicated Speed = Actual Speed (New Tire Revs/Mile) Using the above tire sizes: (775) -------- X 60 mph = 62 mph (747) Rear Axle Ratio Changing tire diameters will also change the effective rear axle gear ratio. Divide the new tire revolutions by the original tire revolutions and multiply by the original axle ratio. For example, a turbo Buick that had 215/65s and a rear axle ratio of 3.42 (what else?) and moved to a 255/60 will net an effective ratio of 3.30. (New Tire Revs/Mile) ---------------------------- X Orig. Axle Ratio = Effect. Axle Ratio (Orig.Tire Revs/Mile) (747) -------- X 3.42 ratio = 3.30 ratio (775) As you can see, this will theoretically raise the top speed of the vehicle but hurt its acceleration. To regain the original effective ratio with the new tires, a 3.55 ratio is required. (Orig.Tire Revs/Mile) ------------------------------ X Orig. Axle Ratio = Equiv. Axle Ratio (New Tire Revs/Mile) (775) --------- X 3.42 ratio = 3.55 ratio (747) Maximum Speed To calculate the maximum speed of a vehicle, take: Overall Tire Diameter X Achieved Engine RPM (redline) ----------------------------------------------------------------------------- = Max Speed Differential Ratio X Top Gear Ratio X 336 26" X 5250 --------------------------- = 177 mph 3.42 X 0.67 X 336 This differs from actual speed. A stock turbo-Buick's actual top speed is in the 152 to 162 mph range. The aerodynamics on these cars are nothing to write home about. here
3:42 speedometer gear Has anyone figured out the correct gear for a 3:42 ratio? I have 255-60-R-15s on my GS455 and a 3:42 posi and like to know what speedometer gear to use in my Muncie, Thanks AL
Re: 3:42 speedometer gear I have 255/60 -15 BF Goodrich Radial T/A's on my 70 GS, 3.42 gears, and a 17 tooth drive gear on the output shaft of my ST -400. The 255/60 is 27.1" in diameter. 20168 divided by 27.1=744.2. 744.2 X 3.42 X 17 =43267.8. 43267.8 divided by 1001=43.2 I have a 43 tooth driven gear which is purple, and GM part # 1362196. You need to find out how many teeth are on your drive gear. Pull the speedo sleeve out, rotate the driveshaft with the trans in neutral, and count the teeth. If it's 17 teeth, use the purple gear, if not figure out which gear you need, look at my post, get the part # and order it from GM
Keep in mind - A radical change in driven gear (the one the cable slips into) will require a different carrier hub (piece you take out to change the gear) in the transmission. The gear sizes are cast into the hub. Some carriers are hard to find. The drive gear on the transmission tailshaft came in (2) styles - a pressed on steel gear and a snap in place nylon. Removing the steel gears is REALLY tough sometimes. Just finding a shop with the right tool is hard. Change to the nylon gear if you have to take the steel gear off.
GEEZ!!!ou: I didn't know it would be so complicated. I never look at the speedo anyway (because of the gauges on the column I can only see between 30 and 50 MPH anyway). If I ever get the hankerin' to stuff myself up uder my Z-frame and count my teeth, I'll revert back to this thread. Thanks for the input everyone.
I always just went to the GM parts counter Told them the model yr, trans, rear gear, and tire size. I don't ever recall having any problems....But it was 20 yrs ago since I needed one.
Re: I always just went to the GM parts counter Wish it was that easy. If you have the numbers matching trans, you can look in a chassis manual and get the drive gear tooth count. The 70-72 BB had a 16 tooth drive gear. Did not have a 67 manual to look up my 67 BT trans, had to lie on my back and count. It was worth it though.
