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Old 09-29-2008, 09:02 PM   #1
myturn89
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Default Rear Axle Gear Ratio Question

I have a 1989 automatic with GM1 (2.59) rear axle gear ratio.

What can i change this to? 3.54? is that the highest for the automatic? What is the G92 "Rear axle performance ratio"? Below are the codes that I pulled from another thread.....

G44 Rear axle 3,07 ratio
G92 Rear axle performance ratio
GH0 Rear axle 3,54 ratio
GM1 Rear axle 2,59 ratio
GM3 Rear axle 3,45 ratio
GT7 Rear axle 3,33 ratio
GU2 Rear axle 2,73 ratio
GW4 Rear axle 3,31 ratio
HE3 Rear axle 3,07 ratio

Any ideas on cost - both do it yourself and from a shop?
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Old 09-29-2008, 09:24 PM   #2
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As far as I know.....you can change to a 2.73 or a 3.07 by changing the diff itself.....because you have a 2.59 in yours the gear carrier itself limits your selection in aftermarket ratios ,there may be a 3.4X or 3.5X available and I know that there is a 3.75 that will fit your carrier......some other ratios require that you start with a 3.07 carrier
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Old 09-29-2008, 10:18 PM   #3
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I have a 2.59 and it sucks compared to the 3.07 I had in another vette , so now I just bought 3.75 to put in, but I am doing my intake. and probably heads, and cam later! good luck!
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Old 09-30-2008, 01:13 AM   #4
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3.07 is optimum for TPI unless you a doing engine mods to gain more revs=intake / heads / cam
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Old 09-30-2008, 08:31 AM   #5
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3.07 is optimum for TPI unless you a doing engine mods to gain more revs=intake / heads / cam

-Beppe-
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Old 09-30-2008, 08:52 AM   #6
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I recently took out the 2.59 and rplaced it with a 3.07. It makes a huge difference. I race at a 1/8th mile track and it took 1/2 second off my times. Went from low 9's to mid 8 seconds. I paid about $300 for the complete chunk and it took about 5 hours to swap it out.

Last edited by aminnich; 09-30-2008 at 10:47 AM.
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Old 09-30-2008, 10:40 AM   #7
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3.07 is as much as you want in an L98. However the difference might not be worth the expense.

For now I'd go with a higher stall TC, and after driving that for six months decide if you want to go in and change the gearing.

C409: With GM parts, the 2-series (2.59/2.73) case is different from the 3-series case, so you'd have to change that, IF you were using GM parts. However, many companies make the lower gear ratios (3.54s, 3.73s...) with proper ring gears for the 2-series case.
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Old 09-30-2008, 11:14 AM   #8
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Quote:
Originally Posted by pologreen1 View Post
I have a 2.59 and it sucks compared to the 3.07 I had in another vette , so now I just bought 3.75 to put in, but I am doing my intake. and probably heads, and cam later! good luck!
Good to know, I'm looking forward upgrading my 2.59's to 3.45's.
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Old 09-30-2008, 11:33 AM   #9
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Originally Posted by conv90 View Post

-Beppe-
I switched my 2.73 to a 3.07. 2.59s are great for highway gas mileage but they suck around town. i also got a Vigilante TC.
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Old 09-30-2008, 01:05 PM   #10
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Quote:
Originally Posted by myturn89 View Post
I have a 1989 automatic with GM1 (2.59) rear axle gear ratio.

What can i change this to? 3.54? is that the highest for the automatic? What is the G92 "Rear axle performance ratio"? Below are the codes that I pulled from another thread.....

G44 Rear axle 3,07 ratio
G92 Rear axle performance ratio
GH0 Rear axle 3,54 ratio
GM1 Rear axle 2,59 ratio
GM3 Rear axle 3,45 ratio
GT7 Rear axle 3,33 ratio
GU2 Rear axle 2,73 ratio
GW4 Rear axle 3,31 ratio
HE3 Rear axle 3,07 ratio

Any ideas on cost - both do it yourself and from a shop?
3.54 was the ratio for the early 6 speed in 1989 like mine (and maybe a few cars in later years). It's really not suitable for an auto.
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Old 09-30-2008, 06:49 PM   #11
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I can get a 3.75 ratio but what else do I need to do immediately? Do i need to do anything to the ecm, will shifting get all whacked? I understand that it will not be "optimum" at first but other mods are going to be down the road. since i am changing i was thinking of just doing the full upgrade while i am in there......any thoughts ideas??
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Old 09-30-2008, 07:38 PM   #12
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Originally Posted by Kool88vette View Post


I switched my 2.73 to a 3.07. 2.59s are great for highway gas mileage but they suck around town. i also got a Vigilante TC.
Quick question...did you find a noticable difference going from 2.73 to 3.07? I have a 1990 Vert with the 2.73 and have been contemplating a gear swap but not too severe....Im curious about the 3.07's ..need your imput.
thanks
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Old 09-30-2008, 08:27 PM   #13
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Quote:
Originally Posted by myturn89 View Post
what else do I need to do immediately? Do i need to do anything to the ecm, will shifting get all whacked?
Need to install correct speedo gears in trans so ECM sees correct road speed for calc.
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Old 09-30-2008, 11:36 PM   #14
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Quote:
Originally Posted by UNCLEBILL View Post
Quick question...did you find a noticable difference going from 2.73 to 3.07? I have a 1990 Vert with the 2.73 and have been contemplating a gear swap but not too severe....Im curious about the 3.07's ..need your imput.
thanks
I noticed a major improvement in acceleration around town. I have to be careful now or I'll spin the wheels real easy. That's the way I like it.

I guess the 2.73s and OD are good for mileage while crusing at speeds above 70 mph. I hardly used OD with the 2.73s because the freeways here are too congested and it's always stop and go traffic. At 65 mph in OD the engine would lug up hills.

I think I probably lost some freeway mileage but I really haven't noticed anything. I'm glad I did the swap.

I picked up a used 3.07 pumpkin in the C4 parts for sale/wanted section and I had it rebuild before I installed it.

I had to change my speedo gear. That part was about $11.00 and takes 10 minutes to change.

Last edited by Kool88vette; 09-30-2008 at 11:41 PM.
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Old 10-01-2008, 12:24 AM   #15
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I would DEFINATLY stick with the stock stall converter if it's going to be a driver for you.
If you're "ALL ABOUT THE STRIP" then different story... Problem is that you'll "always" be under the lock up for normal driving...

P.S. I have the 3.07's and they work very well !!!
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Old 10-01-2008, 05:30 AM   #16
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Quote:
Originally Posted by Kool88vette View Post
I noticed a major improvement in acceleration around town. I have to be careful now or I'll spin the wheels real easy. That's the way I like it.

I guess the 2.73s and OD are good for mileage while crusing at speeds above 70 mph. I hardly used OD with the 2.73s because the freeways here are too congested and it's always stop and go traffic. At 65 mph in OD the engine would lug up hills.

I think I probably lost some freeway mileage but I really haven't noticed anything. I'm glad I did the swap.

I picked up a used 3.07 pumpkin in the C4 parts for sale/wanted section and I had it rebuild before I installed it.

I had to change my speedo gear. That part was about $11.00 and takes 10 minutes to change.
Thanks for the reply.It sounds like this would be the best setup for my needs. I noticed the same lugging going up hills in OD also.
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Old 10-01-2008, 07:53 AM   #17
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Quote:
Originally Posted by Kool88vette View Post
I noticed a major improvement in acceleration around town. I have to be careful now or I'll spin the wheels real easy. That's the way I like it
I'd be willing to bet your improvement in acceleration is more due to the TC than the gear change.

I'd imagine the 2.59s are a real dog in LT1 cars, but truthfully they're really not that bad in a L98. I noticed a much bigger improvement in my car (91 A4) when changing to a 2500 stall converter than I did when I changed to a 3.07.
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Old 10-05-2008, 04:40 PM   #18
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i am thinking of just going to a 3.54 upgrade - i am getting conflicting responses? I have an 89 automatic convertible, is this a total waste of time or will i know a substantial improvement in performance off the line?
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Old 10-05-2008, 05:07 PM   #19
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Quote:
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i am thinking of just going to a 3.54 upgrade - i am getting conflicting responses? I have an 89 automatic convertible, is this a total waste of time or will i know a substantial improvement in performance off the line?
from what I found out and experienced, the 3.07 is the stock performance gear in l98's and it is performcance compared to the 2.59, 2.73. I also drove a fairly stock 88 ( long time ago)stick with 3.55 and then drove my mustang home and it felt like a grand am. anyone who has put high performance gears in their c4 did it for a reason and like it. If they don't its because of rpms, gas milage, or excessive torque. All things I appriciate! good luck!!
P.S. If I had stick I would get 4.11's but thats me and I can be excessive!
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Old 10-05-2008, 07:47 PM   #20
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Quote:
Originally Posted by myturn89 View Post
i am thinking of just going to a 3.54 upgrade - i am getting conflicting responses? I have an 89 automatic convertible, is this a total waste of time or will i know a substantial improvement in performance off the line?
It really depends on what you're doing with the car. If you're looking for a stoplight warrior around town then I'd say you'd be fine with the 3.54s. If you're interested in ETs at the track, your best off with 3.07s on a stock motored L98. A steeper gear ratio might get you a slightly better 60' time, but you'll lose all the time and then some on the top end

I've had a 2.59, a 3.07 and a 3.33 in my car and I regret going to the 3.33. The 3.07 was the best all around performer, at least in terms of 1/4 mile.
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