Over the summer I plan on putting in posi and 3.73 gears into my 91 camaro rs with stock 5.0 v8 and 700r4 trans. I have been reading that this upgade will throw off my speedo so I would like to know what is needed to fix this. I know I will have to change the speedo gears but I don't know anthing about them so I don't know which ones to use. I have searched it but can't really find anything helpful. If anyone has done this upgrade will you tell me what you did to adjust the speedo.
Thanks

 

http://www.partshp.com/speedometer_gears.htm

http://www.3rdgenformula.com/91/91speedometer_gears.htm

https://www.thirdgen.org/forums/tran...eter-gear.html

they may help ya

 

long story short, you need a 15 tooth drive gear, and the choice of driven gear depends on your tire size. 245/50R16 needs 44 tooth.

 

How hard is it to change these gears I plan on haveing a shop install my posi and 3.73 gears and I figure if it is not to expensive I'll have them fix the speedo while there at it Plus I have afte market 17" rims will that make that much of a diffrence in the speedo gears?

 

The GM part number for the gray 15 tooth drive gear is 8642620. As for the driven gear, if you're running a 245/45R17, or 275/40R17, or 315/35R17 tire on the rear, then use a dark gray 44 tooth driven gear, GM part number 25513051. If you're running a 255/40R17 on the rear, use a light blue 45 tooth, number 25513052. If you're using a 255/45R17, or a 285/40R17, or a 335/35R17, then it's the purple 43 tooth, number 25513050.

 

thanks for the info it is a big help, is it relly hard to change the gears or I should say does it take a long time to do.

 

Its really easy just pull the tailshaft housing off and switch the gear off the shaft and change the gear in the housing( you may need a new housing if your old gear is 38 and below teeth) the hardest part is taking the tailshaft housing off

 

Not so. In the old days, each driven gear lived in a carrier that sits in the tailshaft housing. There were several different carriers, each serving 3 or 4 different driven gears, and the carriers were aluminum. We won't get into the whys, the OP doesn't need this info.
But these part numbers I gave for the driven gears, they include a new plastic carrier for each driven gear. Unless you're going off-roading on rocky dirt roads, the plastic isn't a problem. The new plastic carriers are almost as difficult to damage as the old aluminum carriers.

 

Thanks, for the info the part number you gave me, where can I find these parts a dealership or do you know of a good website?

 

The part numbers I have are GM part numbers, I always just pay the local GM stealership's asking prices for speedometer gears, let them eat the shipping charges. Otherwise, I'd try www.gmpartsdirect.com

 

Cool, Thanks for the Help, I have 225/55R17 tires what gear would be used for them.