Transmissions and Drivetrain Need help with your trans? Problems with your axle?

Any source for a 3:08 gearset for a 9 bolt?

Old 04-16-2019, 02:30 PM
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Any source for a 3:08 gearset for a 9 bolt?

My Iroc has a 3:42 5 spd. The 400 sbc has over 500ft/lbs the car buzzes down the hwy too much it's not a drag racer. Normal sources dont have a 3:08 for this rearend. Anyone know of one? thanks
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Old 04-16-2019, 03:16 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Anything other than 3.70 will be a used set. You'll probably have to get used gears from Australia.

GD
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Old 04-16-2019, 06:17 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

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Old 04-17-2019, 12:30 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

A complete used 2.73 peg leg drum 10-bolt should be an easy find. Put a want-ad on craigslist and I'll bet the offers blow up your inbox. Don't gut a good gear set just because it doesn't match YOUR combo. Starving kids in Kansas dream of doing burnouts and can't find a good gear ratio for a 9-bolt. Just sayin.
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Old 04-17-2019, 03:50 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by Drew View Post
A complete used 2.73 peg leg drum 10-bolt should be an easy find. Put a want-ad on craigslist and I'll bet the offers blow up your inbox. Don't gut a good gear set just because it doesn't match YOUR combo. Starving kids in Kansas dream of doing burnouts and can't find a good gear ratio for a 9-bolt. Just sayin.

lol
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Old 04-18-2019, 10:09 AM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Do you have a 3.45 9 bolt in your car now? If you do, it would just be easier to get a complete 9 bolt axle with the gear ratio you need and swap it in, then sell your rear for more money than the one you're buying because the 3.45 is a more desirable ratio. So much so that I would want the pumpkin from your axle with the gears and ship it the the USA because setting up used gears SUCKS.
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Old 04-18-2019, 03:05 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by scooter View Post
Do you have a 3.45 9 bolt in your car now? If you do, it would just be easier to get a complete 9 bolt axle with the gear ratio you need and swap it in, then sell your rear for more money than the one you're buying because the 3.45 is a more desirable ratio. So much so that I would want the pumpkin from your axle with the gears and ship it the the USA because setting up used gears SUCKS.
It's a 3:42 sorry....but anyway as far as I know the 9 bolt only came with a 3:42 in a third Gen
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Old 04-18-2019, 03:10 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by Dscott View Post
It's a 3:42 sorry....but anyway as far as I know the 9 bolt only came with a 3:42 in a third Gen
9 bolts came with 2.77, 3.27 and 3.45 gears in 3rd gens. If you have a 3.42, you have a 10 bolt.
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Old 04-18-2019, 03:41 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by chazman View Post
9 bolts came with 2.77, 3.27 and 3.45 gears in 3rd gens. If you have a 3.42, you have a 10 bolt.
3:42 or 3:45 whatever it is. It has stock 4 wh disc and 9 bolts on the cover....I counted. With the stock Iroc wheels and 245 50 16s at 75 mph in 5th Im at 2750 rpm Id like to be around 2000.
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Old 04-18-2019, 06:53 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

I'll trade you for a 2.77 9 bolt out of my parts Trans Am. You pay shipping.

GD
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Old 04-19-2019, 12:08 AM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by GeneralDisorder View Post
I'll trade you for a 2.77 9 bolt out of my parts Trans Am. You pay shipping.

GD
Hmmmm....That seems a little tall but isnt there a chart somewhere where you could calculate rpm?

And Id pay for your stuff to be shipped to me....and youd pay for my stuff to be shipped to you.
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Old 04-19-2019, 06:54 AM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Probably, but if money or honor is changing hands, pop the cover and look for the stamp on the ring gear.





Pics are of a 10-bolt, but the 9-bolts are marked the same way ??:?? divide the two numbers, round to the closest, that's your ratio. Likewise you can count the teeth on the ring and pinion gears and that'll give you the numbers stamped in the ring gear. Sometimes you'll see the ratio stamped as the regular published ratio.

9-bolts are a bit goofy. The ratios are a bit different for GM, 2.77 instead of 2.73 in the 10 bolt, 3.27 v 3.23, 3.45 v 3.42, 3.70 v 3.73. I've heard there is a 3.08 9-bolt gearset that GM used but never had one in hand, same with the 9-bolt with drum brakes.

Generally speaking, a TPI has enough grunt from idle to pull 2.77 gears. A lot more were built with 2.77 gears than 3.27, 3.45, or 3.70 gears.
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Old 04-19-2019, 09:51 AM
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Re: Any source for a 3:08 gearset for a 9 bolt?

You can play around with this one:

https://www.randysworldwide.com/calculators/rpm/

Your tire height is 25.6"

I did and 2.77 won't even get you to 2000 RPM. About 2200 is where you will be from where you are now..... the 2.77 is the highest gear available for the 9 bolt that I'm aware of so if you wanted even taller to get to 2000 in 5th you would probably have to go to an auxiliary over-drive like a Gear Vendors..... though I don't think anyone offers anything that works with the torque arm.

I can pull the cover of course. But it's a 2.77. My daily is the same car, same year. Both have the same 2.77 diff in them. With Delco-Morain iron rear disc's. The 9 bolt diffs have a metal tag with the ratio and the LSD information.

GD

Last edited by GeneralDisorder; 04-19-2019 at 11:49 AM.
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Old 04-20-2019, 12:16 AM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by GeneralDisorder View Post
You can play around with this one:

https://www.randysworldwide.com/calculators/rpm/

Your tire height is 25.6"

I did and 2.77 won't even get you to 2000 RPM. About 2200 is where you will be from where you are now..... the 2.77 is the highest gear available for the 9 bolt that I'm aware of so if you wanted even taller to get to 2000 in 5th you would probably have to go to an auxiliary over-drive like a Gear Vendors..... though I don't think anyone offers anything that works with the torque arm.

I can pull the cover of course. But it's a 2.77. My daily is the same car, same year. Both have the same 2.77 diff in them. With Delco-Morain iron rear disc's. The 9 bolt diffs have a metal tag with the ratio and the LSD information.

GD
I could live with 2200...I'll be in touch
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Old 04-20-2019, 06:33 AM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by Dscott View Post
My Iroc has a 3:42 5 spd. The 400 sbc has over 500ft/lbs the car buzzes down the hwy too much it's not a drag race.
Another option, T56. I love my 3.27 9 bolt highway RPM with the 6th gear. I am moving to 3.50 to get the RPM back up a bit.
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Old 04-20-2019, 06:42 AM
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Re: Any source for a 3:08 gearset for a 9 bolt?

http://www.tremec.com/calculadora.php

Stock tire 25.7 inches

Am I missing something? You should be at 2000 rpm @ 70 mph now.



Last edited by TORN; 04-20-2019 at 06:47 AM.
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Old 04-20-2019, 12:30 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?

Originally Posted by TORN View Post
http://www.tremec.com/calculadora.php

Stock tire 25.7 inches

Am I missing something? You should be at 2000 rpm @ 70 mph now.

Hmmm....I assumed it is a 3:45 because from what I read a 3:45 was the shortest gear that was available with a '89 305 tpi iroc. However that doesnt really stop anyone from swapping in something shorter before I bought the car. Maybe I'll pop the cover off or even rotate the wheel once and count the driveshaft revolutions
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Old 04-20-2019, 12:45 PM
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Re: Any source for a 3:08 gearset for a 9 bolt?





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