I am trying to make my 82 z28 a little more streetable by downsizing the gear ratio to something a little more gas-pump friendly. The rear end is a gm limited slip 10 bolt out of an 83 firebird. Is there a way to measure the ring gear size without removing it (so I can order a new gear set) ?
I think its a 7.5 with a 3.42 ratio. With a 245 50 r16 tire at 75mph I'm at 2600 rpm.

The trans is a stock 4l60E. I'm sure its in OD and I'm sure the torque converter is locking up.

Any help or opinions would be greatly appreciated.


Thanks
Robert

 

I ran your numbers and you should be turning 2300 rpm at 75 in od, assuming the tire is 26" tall.

3.90 = 2600 in od. But your 4th must be kicking in otherwise your rpm would be 3700.

Consider buying a complete diff with the gear you want, or trade with someone who wants a deeper gear. You will not just have to buy the gears, but pay for the install. And not just anybody can do a r&p job, and do it right. Around here, posi 3rd gen drum diffs can be had for 100-200 hundred bucks.

 

The early third gens have a 7.5" ring gear. Around the mid 80's it was increased to 7 5/8" but is still considered a 7.5". Parts are interchangable.

1982 didn't offer an A4. You don't have a 4L60E unless someone installed it from a later car. The A3 will be a TH200c

 

Thanks guys, I appreciate the info.

P. S
I do have a 4L60E, I did an Lt1/4L60E conversion from a 94 z28 about a year ago