The car is a 1994 Firebird Formula; it has a LT1, auto trans (4L60E?), and a disk rear end. I have the option to buy the rear end and I would like to know if there is any way for me to figure out what is in the diff. without pulling the cover. Also, what else on the car can I use in the lines of suspension, steering, powertrain? And if you could be so kind as to include a brief description of the modding needed to install said parts. Any help will be MUCH appreciated, they guy is wanting to move these parts quick, but I want to know what I'm buying.


Thanks again,

 

Could be 2.73 or 3.23. You will have to pull the cover to be sure, don't buy it until you do. As far as bolting it to your car its easy and goes right on. It will be about 3.5" wider though so your thirdgen wheels will stick out a bit each side. Do a search lots of good info.

 

Do the old method...Jack it up, rotate the tires & count the revolutions vs the revolutions of the pintion.

That'll give you the ratio & tell you posi or not.

 

There's no axle code like on the 3rd gens? I'd just like to do it the easy way if I can. Oh and I have C5 Vette wheels, they are already being spaced 2in on my stock axle, so the longer axle may not be a problem....


Thanks guys, keep it coming...


I'm searching too, Darkshot...

 

The wier axle will allow you to ditch the spacers.

As for a tag vs counting rotations....2 things. The tag may be gone & even if it isn't? There's no guarantee the gears haven't been changed out so.....It may read 3.42, but be a 4.10....or 2.73!

 

Thats true, I know how people love to get into things and change them, then just up and forget they ever did it. So, what I just jack it up, mark the drive shaft at the pinion, then spin the tire one revolution and count the revs. of the drive shaft? Bear with me, its late, and I'm slow , but should I have my buddy attempt to hold one tire, then I spin the other? Would that activate the LSD? That should at that point make both tires spin forward correct?


Thanks a million,

 

If it is stock, look at the shifter and see if it goes down to 1.
If it goes down to 1, that means it would have 3.23 or 3.42 (most likely 3.23)
If the shifter only goes to 2, then I am almost 100% positive it has 2.73 gears.

 

No clue was Zephyr is referring to. Shifter? Shifters don't move, uless a person moves them.

Buyt yeah, jack it up and mark & count the revoluions. As for holding the other tire, I think it might take 2 determine that. If one tire can be held still, yet the other rotates...open. If they spin in opposite directions...limited slip.

 

I should have mentioned Shift Indicator on the Console, where it has PRND321.

 

Ok, good. I'll be doing this on saturday. Only this is, I've heard that some factory 4th gen rears had some kind of "torsion" diff in them. Somthing about how the the spin the wheels on jack stands trick dosent work. Any truth to this?



Thanks,

 

Only goes to 2? Up or down? Even with OD, that would only equal a 3 speed tranny. Now, I don't know about 4th gen trannies, but a 3 speed, even including OD?

 

He's saying that on 4th gens from the factory if you have an auto and 2.73 gears they don't let you manually select first gear. Not something I knew.

But again its a useless method if somebody has changed the gears in the past, which is VERY possible and common.

 

[QUOTE=Darkshot;3747213]He's saying that on 4th gens from the factory if you have an auto and 2.73 gears they don't let you manually select first gear. Not something I knew.[QUOTE]
Interesting. Stupid of GM, IMHO, but intersting.

 

So I checked it out, its a posi (LSD). The shifter went down to first, so hopefully that puts me with the 3.42 diff. While I was in there I grabbed everything that would come off with the tools I had; complete rear end, rear susp., E-brake parts, and a borla crossflow. No way in hell am I going to ditch my duals for that , but I may put it on the 92, we'll see...


Thanks guys,

 

Since no one mentioned it, I will. NO 4th gen car with a automatic tanny came stock with 3:42 gears ony 2:73 & 3:23's. So you may have the 3:23 ratio.

 

WHAT???

I hope its the 3.23 at least. Those 2.73 airplane gears are way too high. That would leave me right where I am now. Not to mention I am running a rear wheel/tire combo that is 2in taller than stock.

Thanks man...

 

Just jack it up & do the spin test. EVERYTHING else would be assumptions on what it SHOULD.

If you were working on my old wife's old 90 RS, the change from 3.08 open to 3.73 posi would really get you to scratching your head afterwards!

 

Pop the rear cover off and you will know for sure what you got,it's the best way to do it.

 

What's so hard about removing the cover, I mean, there are only 10 bolts holding it on. Then you can also pull the axles out to check them too.

 

Is the R&P stamped with the ratio or part #?

Wuthout the ratio stamped, you'd hafta know the part #.

By simply spining the tires, that involves ZERO bolts, ZERO fluid drain (to catch & reuse or buy new fluid), and doesn't mean getting under the car. Just laying down beside the car to see the pinion.

But whatever....I've offered the simplest solution. Do what you will...

 

Ring gears are marked with a ratio that will tell you the ring and pinion ratio; it'll look like xx/xx. Just divide the second number by the first. If it's a 3.23 rear, the ratio will be 13/42 (since 42 divided by 13 equals 3.23).