My formula was stock when i got it so rear should be 2.77 open according to tech (87LG4 w 700R4) The tranny is being rebuilt now with transgo stage 2 kit and 2600 stall TC. I have a bit of $ left and wanted to know what i would need to swap to a 3:42 with a posi. Did a search but got a bit lost.confused: a posi would be good but wreckers don't have a lot here, mostly v6 cars.
Thanks...
ps can get gm parts at cost new:

 

2.77 is a 9-bolt ratio.

3.42 is a 10-bolt ratio.

First thing to do is identify which rear you actually have. Then we can tell you what you need to do.

 

i will check on car ASAP i assume 9bolts on the rear confirm my 2.77 stock rearend then. anything else i should check? rpo#s are not in car that i could find

 

count the cover bolts and it'd help out a lot to know what ratio you actually have, and that would require pulling the cover.

 

Not exactly....

There are other 9-bolt ratios besides 2.77. If you have a 9-bolt, that only means that you can't put 3.42s in it, since 3.42 isn't available for a 9-bolt. 3.45 however is available.

Also, there are very very few open 9-bolts in the world. Virtually all of them are posi. So, the likleihood of your car actually having a 2.77 open, is quite low.

More likely, you have a 2.73 open 10-bolt, that being very common in the low-perf cars like the LG4 and L03 ones.

But, step the first, is to identify what you actually have. Pay no attention to codes or tags or "count the revolutions" stuff, it's not accurate enough to use as a basis go buying parts. Take off the cover and count the teeth, or find the ratio stamping on the edge of the ring gear. Once you know what you really have, then you can start researching what you need in order to change it.

 

Ok i got some help at the dealership and looked on the car. it is a ten bolt and i found the code GU5. Their computer identified this as a 3.23. it was suggested that i get a posi 3.42 set out of a 4x4 s10 to save $. Got someone willing to help with work as i am obviously new to this end of the car any advice on how to proceed would be great.

 

Step 1: Forget the codes. They only tell what the factory put there, not what's there now.

Step 2: Take off the cover and look, see what you've really got.

Step 3: Come back and tell us what's really in there, and we can give you alot more reliable help.

 

Thanks everybody. i guess this will have to wait for spring cuz its waaay too cold to work under a car even if i had it at home so i think i will pull the cover in the spring before i park the winter beater and then go get what i need when i can do it. i understand what you say about factory versus now and don't want to learn stuff the hard way but i can trace ownership back to the dealer and the lady who owned it since 1992, whom i bought it from just thought it would be cool to drive a firebird, she called it "freddy" and never changed the sparkplugs, let alone the rearend. we'll see what i see in the spring and i'll repost.
Tim

 

Well, look at it this way.... if she never changed the spark plugs, then she probably never changed the rear end fluid either; so it's long overdue for its 30,000 mile replacement. So, since on the first pretty day you get, when it gets up over 20° F or so, you'll be catching up on stuff like that and you'll have the cover off anyway doing the overdue maintenance, just make a point of looking at the gears while you're there.

Problem is, the LG4 cars in that year almost all came with either 2.73 gears if they're auto or 3.08s if they're stick. 3.23s would have been a special order item and as such highly unlikely. If it has the 87 rear end in it, you have 26-spline axles, which means the SLP 4th gen take-out posi won't work with your current axles; and you don't want any of the stock 26-spline posi units that you can find in the junkyard, above all NOT the Eaton "Gov-Lock" that comes in the S trucks and some early 3rd gen F cars. Plus, if you have 3.23 gears you have a 3-series carrier which will accept 3.42 gears, but if you have 2.73 or 3.08 gears, you have a 2-series carrier which won't accept 3.42s unless you either buy the "special" thick gears (not a great idea IMHO) or use a ring gear spacer with standard thickness gears. So as you can see there's lots of room for uncertainty, and lots of ways to buy stuff that won't fit, and lots of ways to end up with stuff you don't really want, and lots of ways to spend massive amounts of money (especially since it sounds like you'll be paying somebody to do all this gear swapping for you) and still end up with less than you thought you would. That's why the very first thing to do is to find out with certainty, by inspection, what's in there now, so you know where you're starting from.

 

i hear you and plan to post again with gear oil under my fingernails. i don't know what the car should have without the rpo codes, altho i hear all kinds of things every time i ask or look on the net so i will be curious to see with my own eyes what is there. i ordered the canadian pontiac historic kit today so that should be fun but i am learning to verify on the car what i read on paper. thanks again

From everything i read from you tho i guess i should consider getting a new rearend

 

http://cgi.ebay.com/ebaymotors/ws/eB...category=33731

 

Thanks
Good to see prices are in my league, but i will need to open mine up to see what i need and then decide what i want. From what i read that posi for a nine bolt is hard to find but im no expert...
Latest mod: function starter for winter beater, was great owning 3 cars with 1 working!

 

Hehe, funny how that works. A 3.27 posi just went here for $51!

http://cgi.ebay.com/ebaymotors/ws/eB...category=33728

 

who ever won that is lucky. That a good price if i had my rear at that time i would have bid. damn