Can I determine what differential a car had by it's vin? I know it has a 5spd and a posi rear. Other than that I have no idea. There are also no RPO codes on the car anymore.

 

No info from the Vin number. Pull the cover and check the ring gear the ratio is stamped on the OD.

 

You can tell by the build sticker. My F/B has it located on the inside lid of the storage compartment in the hatch. The only problem is, you will need a code book to break down the codes on it. IIRC the rear code begins with "G". Just like the engine codes begin with "L". You probably have a 3.42.

 

Other than the option code sticker, the info is alson on the left axle tube.

 

If your car is a 90 and up, a GM dealer can pull the RPO's by vin # and see what it came with. If you want, you can PM your vin and I can run it at work on monday for you.

 

It's not from my car. But from a local guy that I might buy the posi-diff from. I haven't seen the car yet. I just don't want to waste both mine and his time.

Brutalform, do 1989 cars have the rpo's in both places, the center console and in the rear storage compartment? I thought the older cars ??-89 had them in the console, and the 90-92 had them in the rear compartment. Was '89 the x-over year for that, not 1990?

 

RPO's will be in the car in only one spot. IIRC, my friends 89 IROC had it in the center console. The 92 I removed of it's interior was in the rear compartment storage lid.

 

Not really sure, I do believe Lo-Tec is right. Depends on the car, and year.

Also if you want to check the ratio, and the rear is out of the car, spin the axle hub one complete revolution. Then count how many times the pinion yoke spins. If the yoke spins almost 3 1/2, its a 3.42. 3 1/4 turns, its a 3.23. This works if you dont want to pull the cover. (a little pass 4 turns, 4.11, but I doubt it would be that, unless they were changed)

 

This is the way I found out when I was looking for a complete rear end for my camaro at the junkyards. On the right side of the rear end there is a number stamped. Then with the hayes manual, you can crossreference it.

 

One time I had the number on the pass. side axle tube referenced, and it said my car should have had a 3.73 in it. My 92 Formula actually had 3.42 stock. Either someone at the factory, either stamped it wrong, or my eyesight is getting really bad. I even used chalk to expose it better. BTW, the car had under 10,000 miles on it at the time. No dirt.

 

Last cars to come with 3.73's were L69 HO's. No FI cars came with that ratio . What were you using as a reference to get the gear ratio?

 

Here's the vin: 1G2FS2181KL255346 It's a formula and has a 350. And again, it does have posi. Now as soon as I can, I will see how many times it takes the yolk to spin vs. the wheels.

Anyway I can tell if the rear is good or bad, with out running the car? I'm sure the motor/tranny is gone.

 

I believe it was a Haynes, or a Chilton manual. 3.42 were the steepest gears you can get stock, in a third gen.

 

A 1990-92 Formula 350 will probably have the 3.23 ratio 10-bolt rear end. A 87-89 Formula 350 will probably have a 3.27 ratio 9-bolt rear end.

 

Nada on the VIN. GM does not have RPO records for this vehicle.

 

Thanks Rick.

I looked into something about what can be causeing my rear to make such horrible noises. <------ Mexican food. J/k!!!

I have never put in GM posi-fluid, but just the off-the-shelf stuff from Vato-zone. Not that I was cheap or anything, I just didn't know. People say they get a grinding when they put the other crap in, but as soon as they throw the GM stuff in, the noise goes away. I will be trying that this weekend.