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

2.73 Posi to 3.42 Open?

Old 04-10-2019, 04:49 PM
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2.73 Posi to 3.42 Open?

I finally have the time to put into my 89 IRoC this spring/summer which I haven't driven since 2012, thank you very much Mr. Military.

Currently my car has a 305, 700R4, long tube 3" headers, with a 26 spline 2.73 Posi diff and drum breaks. I have the option of purchasing a 4th gen rear with disc breaks & 3.42 diff, 28 splines but it is Open and not Posi.

I was wondering if that would be a worthy upgrade even though it is not Posi? I'm not looking to invest a ton of money into a after market rear, I would just like to slowly upgrade parts as I go. Eventually I'd like to have a 383 but my rear is the first item I'd like to upgrade/change.

Is gaining the gear ratio, 28 splines and disc breaks suitable for a future 383 or should I just hold onto my 26 spline Posi until I can afford a decent after market?


Thanks.
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Old 04-10-2019, 05:34 PM
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Re: 2.73 Posi to 3.42 Open?

Go for it.

You'll hate the open. But it's easy enough to swap a posi in later.
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Old 04-10-2019, 05:39 PM
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Re: 2.73 Posi to 3.42 Open?

yea ill say do it if its a great deal your gaining gearing and disc brakes

if your just driving and not aggressive driver you wont notice a difference
you can score posi Zexel from junk yard at times and classifieds ls1tech or on here
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Old 05-12-2019, 11:09 PM
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Re: 2.73 Posi to 3.42 Open?

Riwe, I have a 26 spline posi with 3.42 gears if you are interested.
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Old 05-13-2019, 12:00 PM
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Re: 2.73 Posi to 3.42 Open?

#1 learn to spell brakes properly

#2 I'd keep the posi. Have any of you driven an 85 or 86 IROC or Z28 with a LB9 and 3.23 or 3.42 open diff? They are a one wheeled smoke show much of the time, especially the 85s with 215hp. As much as the 2.73 sucks, I'd keep it just for the limited slip. You can get a used 3.42 gear set really cheap and you're going to have to buy a limited slip differential anyway, I'd keep the 2.73 posi.
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Old 05-14-2019, 07:51 AM
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Re: 2.73 Posi to 3.42 Open?

fourth gen with 3.42 is probably a posi - if its a torsen unit when doing the posi test of turning axle it acts like single track 3.42 IIRC only came with 6 speed cars- I'd bet it has a torsen unit in it - no loss of posi and it will wake up your car very well
99 and later rears are torsens 98 and older were Auburn's which when worn out they're junk
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Old 05-14-2019, 11:33 AM
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Re: 2.73 Posi to 3.42 Open?

Originally Posted by zman1969 View Post
fourth gen with 3.42 is probably a posi - if its a torsen unit when doing the posi test of turning axle it acts like single track 3.42 IIRC only came with 6 speed cars- I'd bet it has a torsen unit in it - no loss of posi and it will wake up your car very well
99 and later rears are torsens 98 and older were Auburn's which when worn out they're junk
V6 cars had posi and 3.42 as optional so there are some rears that came with 3.42 open
all v8 cars had posi if I'm not mistaken 3.42 was option in autos and standard on manuals
I could be wrong
if you get a open for a steal can find a Zexel aka torsen aka gear type posi to drop in for cheap
or clutch type posi for cheap as well now dollar for dollar get the posi rear over open but if you
don't care about one wheel burn outs autocross or drag then it doesn't matter really get what
fits your budget and needs

like he said above avoid the auburns there is one company in Australia I believe
that rebuilds them and sell parts for them

Last edited by Zach/90\irocZ; 05-14-2019 at 11:36 AM.
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Old 05-14-2019, 09:34 PM
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Re: 2.73 Posi to 3.42 Open?

Sorry Zach, you are mistaken. MANY V8 cars came without posi.

But as someone pointed out earlier, it's a piece o cake to install a posi. Go ahead and get it, and look ahead toward acquiring a posi for it.
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Old 05-15-2019, 01:33 AM
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Re: 2.73 Posi to 3.42 Open?

For 4th gen Camaro’s ? We are talking about right or referring to 3rd gen

I’m speaking about 98-2002 rear ends in 4th gen
for the LT1 I believe z28 and ss all had posi
Base z28 possibly had open don’t quote me

V6: all manuals 3.23 open or posi, auto is 3.08 open diff, 3.42 posi.

V8: all manuals 3.42, autos 2.73 or 3.23 all of them posi

98 had Auburn’s and 99+ had Zexel but I believe slp had Auburn’s

and thus far from junk yard only opens I seen have been v6

i could be wrong tho but that’s my understanding of it from notes I saved
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Old 05-15-2019, 02:37 PM
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Re: 2.73 Posi to 3.42 Open?

also if your know if car is a v8 sometimes it can act as a open diff aka worn auburn and with Zexel it can act as a open at time when trying to turn wheel
best way is to open diff cover and visual check people assume that both wheels turn and that's not always the case

3.42 open should of came out of a v6 manual car to OP
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Old 05-15-2019, 04:53 PM
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Re: 2.73 Posi to 3.42 Open?

All 4th gen V8 cars had a 5.7 and a posi. Thirdgens should have went that route. 5.0s should have never been in these cars imo.
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Old 05-15-2019, 05:14 PM
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Re: 2.73 Posi to 3.42 Open?

Originally Posted by dmccain View Post
All 4th gen V8 cars had a 5.7 and a posi. Thirdgens should have went that route. 5.0s should have never been in these cars imo.
well for thirdgens it was just a G80 option or special order option that can be order regardless of gear and engine I believe and it was th g lock or something like
seen very few
then there was the 9 bolt as option and all had auburn type posi

but with 4th gens the performance improvement and wanting better handling car was the addition of posi as a standard option on v8 and option on auto v6 depending on options equipped
and sense then have been standard option on 5th 6th gen v8 and manual v6 and I believe option on auto v6
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Old 05-15-2019, 06:47 PM
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Re: 2.73 Posi to 3.42 Open?

Nine bolts are far superior to the Auburn but a cone style instead of clutch style. When u wear em out its hard to find parts for the Aussie 9bolt. They did hold up pretty good in third gens though. I think 89-90 was last year they run 9 bolts.
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