I used the calculator in the equation section tech central on the thirdgen.org page. Based on tire size, RPM, 1:1 3rd gear, and MPH, I got a calculated gears of 3.48. Is that a realistic Gear/Ration?

PS.
I know it's a posi.

 

Don't know about the math but do know how I checked mine.

Both back wheels off of the ground turn tire one complete revolution and count number of turns drive shaft makes,, this is a rough way to check gear ratio.

 

Well, according to www.thirdgen.org , your car came stock with 2.73 gears...unless someone did a gearswap, you have 2.73's and your math is off. They make 3.42 gears, they are popular so if a gear swap was done, its likely that you have 3.42's. Try the method that PearlPurple suggested though, that's a pretty accurate way to tell as well.

 

Well my tires measured 13" from the ground to the center of the hub (radius), I left the Trans in 3rd (D), @ 1800 RPM I was going approximately 40MPH.

At this site: http://www.thirdgen.org/newdesign/te...ulations.shtml
that gives me a calculated G/Ratio of 3.48...

I having the front wheel bearings replaced tomorrow so when I get it up on the lift I will use pearlpurple method and see what I get.

Thanks

 

Check your RPO codes

GU2 - 2.73
GU4 - 3.08
GU5 - 3.23
GU6 - 3.42
GW6 - 3.27
GM3 - 3.45
GT4 - 3.73
G80 - posi
G92 - performance

Performance means you got the optioned gears. You most likely have 2.73's, there was no such 3.48 gear.

 

I found the codes and mine are GU2, and G80 = 2.73 Posi.
I guess that calculator dosen't that great, or my speedometer or tack are off.

Thanks

 

It usually helps to do it in OD of .7 not 3rd. I used .7 going 65 at 1750 RPM with 12" tire radius, came out to 2.74XX, so it is fairly close.

 

Yeah something like your tach must be off...welcome to my world

 

You may have the 3.45 9 bolt in there.
Always do speed/calibration in 3rd on a auto or 4th on a manual using the 1:1 ratio (some 6 speed imports have 5th as the 1:1 but that has nothing to do with us at the moment).

If you don't know the history of the car, then the RPO codes just gives you a general idea of the car.
If someone looked up my codes, it would list a 3.23 Posi drum 10 bolt, but the car now has a 4.10 posi disc 10 bolt in it.

 

Yesterday while the car was on the rack having the front wheel bearings replaced, I did the the tire to driveshaft method and the driveshaft rotated app. 2 3/4 turns to 1 of the tire.

So I sure I must have 2.73 gears.
Thanks for all the replies.

 

THE HISTORY OF THE 3RD GEN ON "Hawks THIRD GEN PARTS"
GOOD LUCK!

 

I Have A 1989 Iroc Z28. I Did About Everything I Know Of But It Still Is Over Heating I Need Some Help!

 

My way of testing is to put the car in the gear that's a 1:1 ratio and drive at 70 mph. Your tach will tell you your axle ratio. 2.73 gears = 2700......3.23 = 3200 etc.

 

76 miles an hour...

If all else fails, take the axle cover off and count the number of gears, then divide ring by pinion. That will tell you forsure.

 

Take the cover off and checked the MFG stamped gear ratio on the OD of the ring gear. No need to count the gear teeth.