Well my iroc just got towed to my house yesterday and i was liking at the rpo codes and my car has the j65 g80 posi disc 9 bolt 2.77 rear. The car is beggin for some gears do i have to change the differential when i swap 2.77 to 3.45 or is it a direct swap. Also were can i find a set of 3.45 gears?

 

3.45 9 bolt gears are EXTREMELY rare. Also if you come by some you will need a 3 series carrier. The only 9 bolt gears that are still re made are borg warner 3.70's. Good luck.

 

Do you have a link on who makes 3 series carriers and 3.70 gears?

 

Try Randys ring and pinion.


Or

http://www.gearsareus.com/GearsAreUs...ff/gearsgm.htm

 

randys has the posi , installation kit, and 2.77-3.45 gears
us gear has 3.70

Should i get 3.70 or 3.45 like i planned?

 

3.45 gears will keep the car right in its powerband. Since you are using tpi you dont want to over rev the car since it makes its power down low. 3.70's may work "ok" if you completely max out your tpi setup.

 

I have an 89 iroc which came with a 2.77 9 bolt posi. First I bought a complete 9 bolt rear off ebay with a 3.70 gear. It was great off the line -mostly tire smoke though! Regular driving it sucked cause the 1-2 shift occured in about 2 car lengths. It was like driving a car with 2.77's cause the trans was always in a higher gear. At the track (1/8 mi) it only picked up about 2 tenths. I then bought a 3.27 set and it seems perfect for my 5.7l (239 rwhp) /700 r4 combo. Much better around town and my et's were down by another 3 tenths! (read: 2.77 to 3.27 lowered et's by a half a second in my car!) I've heard the tpi motors perform best when "loaded" with numerically lower gear ratios. I would like to know how a 3.45 set would feel but as has already been said- they're pretty hard to find. Also, there isn't any aftermarket gearset for a 2 series carrier that I am aware of. Three series are out there and you will definatly have to have one. The used three series I bought is looser (?) than my stock one- and everyone knows "happiness is... A tight posi!" The aftermarket 3 series posi runs close to a grand! Which brings up an interesting point. 9 bolts bring a premium on ebay. (I sold all my "old" stuff and it paid for all my gear-swappin) For the price of changing around the limited selection of 9 bolt stuff you can build a bitchin 10 bolt and have more choices. I really hated to take a 9 bolt out of my car cause it is supposed to be a little stronger- it's "special"- and it's what came in my car- bla bla bla. But in retrospect, I think the 10 bolt woulda been a better choice- specially now that I'm thinking five speed and might like to try a 3.45 or a ??? and I need a better posi so I can so donuts again and... Just some thoughts...take it for what ya paid...