Which rear end did the 89 Firebird Formula w/5.0 come with? Did it come with a Posi, or standard? Also, what gears do you think came with it? I'm not sure, so I figured I'd ask Thanks again.


Nate -

Edit - It's an auto, forgot to mention that...

 

My 1990 Formula originally was a 305TBI and had a 2:73 peg leg.
I have since swapped in a 350TPI and a 3:73 posi rear.

 

Did they come with Posi's from the factory at all?

 

Some did. Some didn't.

It could have started out life as anything from a 2.73 one-wheel-peel 10-bolt if it's a TBI auto car, to a 3.45 9-bolt if it's a TPI 5-speed G92 car. There are ALOT of possible variations.

I think it doesn't matter what gears it came with, because they might or might not still be there. I think it mostly matters what's in there now. I think the only way to know that for sure is to take off the cover and look. I think the same thing about whether it's a posi or not.

 

How can I tell what gears they are and if it's a posi or not? Bah...I am such a newb


Nate -

 

Count the teeth on the pinion and divide that by the # of teeth on the ring.

Inside the carrier, which is the big round thing with the gears bolted to it. If it has a pin about ¾" in diameter and some plates and springs and 4 small gears, it's a posi. If all that's in there is a pin and 4 small gears, it's not.

 

Ok thanks! That clears it up nicely. I don't know if this is any help, but last time I drove it I was on a gravel road and when I floored it both wheels started to spin and she swung out a bit (good times ) as we took off. But I'll take the cover off and have a look anyway, see how it looks inside and what not..



Nate -

 

I think if you have rear disc brakes its likely that you have a 9-bolt posi. Not positive on that though.

- Count the bolts. (9 or 10 bolt)
- If it is 9-bolt chances are that its also posi.

If its a 9 bolt:
- Gear ratio tag is at 9-o'clock on the cover (use wire brush)
- Posi tag is at 4:30 (if you have it)

Open it if you want to change the fluid anyways. Its probably due.

 

Yea, thats why I was thinking of taking it apart anyway. If this helps it has drums in the rear.



Nate -

 

Like RB said, the only real way to know is to pull off the cover and look. That will tell you for certain what gears are in there and wether or not you have a posi.

Might as well change the oil in there anyway, right?

 

Yup, probably about due anyhow

 

Look for the passenger side axle tube stamp, it will be facing the front. That code will tell you what the ratio is and if it is a posi or not.

This will help you cross check your gear inspection.

If its a posi dont forget the additive.

 

Well I just got off the phone a bit ago with her, (my friend who I am buying the car from) and she said she welded the rear end, it did not originally have a posi. She also said it might need to be rewelded a bit.
Is this something I should really be concerned about?


Nate -

 

id be scared if its welded,

id look for another axle for it,

inside tire on turns will be skipping spinning on the pavement, will eventualyl bust spider or shaft anyways

i wouldnt want to be driving it when that happens!


welding a unit for street daily driver use is not safe and is not smart

but its fine ofr dirt track and demo derby and straight track offroad use though,

if the welds even hold up that is,.,.



but anyways good luck

 

I tore apart a 87 GTA burned and it had a posi. 2.41 rear gear it was a 350 TPI car

 

I tore apart a 87 GTA burned and it had a posi. 2.41 rear gear it was a 350 TPI car