Gears & Axles - new to f-bodies.. been reading but still have some questions.

ok first, my gearing is supposed to be 3.23's but no matter what i do with my programmer i cant get it to read correctly for the speedo, even with accounting for tire size. previous owner said he thinks it was 3.73's but couldnt verify. how can i determine it without removing the cover? also when i give it some throttle i hear a clunk coming from the back part of the car, possibly suspension or rear axle. any ideas? it already has a new spohn eurethane trans mount that i put in last weekend, so its not that.

with my current mods my car (supposedly) ran a 12.7@109 with mods in my signature. if it does in fact have the stock gearing, what kind of time decrease can i expect by going 3.73 or 4.10? its a daily driver that gets about 10 miles a day... rarely gets out on any type of highway, so not concerned much about MPG's. i just wanna make sure my rear is good before putting in a converter and heads and cam swap.

1st thing you have to determine is your current rearend gearing !
driveshaft turns vs axle turns.
rotating the driveshaft 2 3/4 turns to get 1 axle turn = 2.73
3 1/4 turns = 3.23
3 3/4 turns = 3.73

ok. any more input on the other things? my sticker in door jam indicates 3.23, but who knows if someone grabbed a junk yard rear and swapped it out that had 2.73's.

also either way, I want to change out the gears, and refresh everything back there (pinion bearing, axle bearings etc) so is there any recommendations on parts? i came from diesel trucks so i dont know much about what works good on these cars...

if you plan on throwing a cam in or any mods to up the hp i wouldnt waste time and money going into the junk 10 bolt..

doing mild XER273HR-14 cam and LS6 heads. nothing crazy

Stock is crazy enough to pop the 10 bolt. I would just save the 400 bucks and put it toward a 9 inch.

If you have a smart phone, download the SpeedBox app and tell me how many RPMs you turn at 70mph.

I will let you know tomorrow

If you don't already know, after you figure-out what gearing you have, tape measure the tire and wheel to figure-out what number to plug into the tuning software table. Your speedo will be more accurate.

I mention this because I was cruising down the highway with a cop right behind me and my speedo was reading 65, the speed limit, but I got pulled over for speeding. It turned out that the standard 25.66" figure for 17" wheels was way off.

RPM @ 70 mph and tell us the tire/rim size and we could probably make a pretty good guess.

with stock 245 50 16 or 275 40 17's:

3.23's will put you right at 2100rpms@70
3.42's will put you around 2300
3.73's will put you at about 2500

Dont fall into the black hole of belief that lower gears make your car quicker either.

between 2000-2100 rpm's. so according to the info given i have 3.23's, not 3.73's like we were told.

When i had 3.23s I was at 2k @ 68mph. Sounds like that's what ya got OP.

you can find a used 9" in the used parts section for $1800.

I just sold my low mileage S60 for $1900.