Rearend gearing

[csm85c93]

I have 2.56 in it now, stock. What I want to know is what gear would be equal to my driving in drive now, when I'm in overdrive with the new gear. I've tried to ask some people and I think they where confused. Another way to say it is I want the RPM when I'm in drive now to be my overdrive RPM. Hopefully that doesn't screw up anyone. Thanks for all the Help.

[dxrflyboy]

It depends on your overdrive gear ratio. Divide your present gear ratio by the overdrive ratio. Example: If your overdrive is .7:1, divide the 2.56 by .7 (2.56/.7=3.66). The closest ratio would probably be a 3.73 in this case.

[wako29]

3.73s are a pretty big jump. I dunno how a Caprice will act to it, but I know that F-bodys way diferently when they go to 3.73s, and they have like 2.8s stock. Expect to see a huge change in acceleration

[csm85c93]

Thanks for all the help. I'm kind of leaning towards 3.42. Does anyone think that would be a noticable difference? Also, how big of a difference in accleration is it from 3.42, meaning noticable at all? Again thanks alot for the help.

[CD Smalley]

Well I have 2.56s in my 86 and 3.42s in my 89. Now the 89 does have a L05 vs the LG4 of the 86. But the 89 pulls ALOT harder. It just does everything with less effort than the 86. I don't think it's all in the gears, but they certainly help.

[wako29]

you will notice a huge difference by going with the 3.42s.

[SR20DETpower]

my brother had 3:73's on his Impala, it is probably the fastest thing you can do to your car, you will notice a nice improvement for just one part.

on those Lt1's with the computer retuned it will actually go faster then the stock 155mph speed limiter, people say it goes to about 158 or so now. So it doesn't kill your top end, actually it improves it, and your first gear where they are real dogs is helped out a lot.

[caprice84]

How bad does a jump from 2:70's to 3:42's affect gas milage? I was thinkin new gears, but I heard they kill your milage.

[quaddriver]

Id check your ratios again

look up the rpo code

when you exceed 3.23 on that carrier, you need a different carrier to get to 3.42

[dxrflyboy]

Originally Posted by caprice84

How bad does a jump from 2:70's to 3:42's affect gas milage? I was thinkin new gears, but I heard they kill your milage.

Without adding an overdrive, gearing your car down will hurt your highway gas mileage. I couldn't give you any exact figures, but I can give you an example.

I used to own a '76 Impala 8-passenger wagon with a 350 and 2.93 or 3.08 gears. I never broke 15 mpg on the highway even though I kept it under 70 most of the time. I just bought a '71 Kingswood Estate with a 402 big block and an unknown gear ratio, although I know it's geared much higher than 3.08, since it moves out slow and upshifts at higher speeds than the '76 did. Even with the bigger engine, the highway mileage is well above 15. At some point, I plan to add an overdrive transmission and 3.55 gears. I will be restoring the car first, so it will be a while before I can make the mods and track the mileage.

Dan

[csm85c93]

Are you sure about changeing the carrier? I sure hope your wrong for my sake. I guess I'll have to check up on the myself or find a junk car with a 3.42 or something. If I change my whole rearend to a 8.5, what else would I need to do? New driveshaft, Different springs and shock, Control arms?

[fed92sled]

I highly support the use of 3:73s. My car pulls like a mofo off the line and will lay the smack down on most any mustang. Im running a LT1 w/ exhausts and i love it. The 3:73s make a big difference. The only downfall is that your speedometer will read too high. Go to pcmforless.com and get your pcm reprogrammed and it will fix it right up.

[burnM]

You have an LT1 in that Caprice? You sure it's not just a 5 ltr?

[fed92sled]

I have a 1992 9c1 with the 5.0 (form which fed92sled was created) and a 1994 9c1 with the 5.7. The 92 is for sale by the way.

[caprice84]

I wasn't sure about the carrier. Any tips on a good ratio with the overdrive? Let me know.