1. Ok, first off, what is the difference between G80 an G92? I tried the RPO decoder from TGO and it is very vague on the description. Any one have info on this? Are there any other codes referring to teh rear end?
2. Is there a strength difference between the 9-bolt rear and the 10-bolt rear? I always thought that when referring to GM, the more bolts the better (example: 12-bolt is generally stronger than 10-bolt).
3. What ratios are available for the 9-bolts and the 10-bolts? I know 10-bolt has the 2.73, 3.08, 3.23, 3.42, 3.73, 4.11, and 4.56. What are the 9 bolt ratios?
4. How can you figure out what gear ratio is in the rear end? I read somewhere that you can count the teeth on the ring and pinion and/or spin the tire and count driveshaft rotation. Is this correct?
5. How can I figure if a posi unit is good? Put the car in the air and spin a tire and see if the other spins with it?
6. What are the good posi units to have... eaton, torsen, auburn...? How can I tell which one is in the rear? What do the different posi units look like and and what does an open rear look like?
7. What are the good brakes to have? What year were the PBR calipers available? What size rotors were available and on what years? I thought I also read somewhere that the steel calipers where prone to malfunctions and not very good. Is that true for all them or just the calipers from a certain year range? Can PBR calipers be bolted in place of the steel calipers without any other modification? Would a different backing plate be required to do that?
8. What axle spline count was avaibale on what years. I know there is the 26 on earlier rears and 28 on later rears, but when was the cut off? Also, is there a way to check spline count without removing the axles?
9. How can I figure out the year of vehicle the rear end is out of? Is there a way to tell if the gear ratio is original to that specific rear end?

I am asking these many questions because I found a rear end in a junkyard car. It is a disk brake rear end in a GTA with the RPO code of G80. I want to verify that the posi is still good and what gears are in it before I buy it. I also what to know the year it came out of so I know if it has the stronger axles... the 28 spline count. I'm not sure but by just glancing looking at it quick it looks like the steel calipers... is this bad? Does $350 sound like to much for that kind of rear end? I don't know how many miles are on it because obviously the owner is not there for me to ask. Another thing is the car was involved in a roll over... the top of the car is shoved down at least 6 inches and pushed about 5 inches to the passenger side. Now would something like that ruin the rear end that I should keep looking, or is it strong enough to survive a crash that violent and I don't have anything to worry about?

Thanks to everyone that can even stand reading all that,
Mike

LOL, if everything I'm asking gets answered this would make for one good sticky, that is, once its organized.

 

I have the same question about the 9 bolt 10 bolt thing with strenght and which is better. I have an 88 Formula with the Borg Warner 9 bolt and 3.27 gears. Is the 10 bolt better ?

 

1: G80 means it has a posi. G92 is a performance option ratio. Some models came with a specific gear ratio. If they got the G92 option, they got a different ratio. A good example is the Z28. It may have come with the 9 bolt and 2.77 gears. If it has the G92, it will have the optional 3.27 gears.

2: The 10 bolt and 9 bolt have nothing in common. They're 2 completely different diffs. The 9 bolt is stronger because of it's design and slightly larger gear ratio however they were only available in third gens for a few years and parts are just about impossible to find unless you live in Australia. The x bolt designation refers to the number of bolts holding the cover on. GM produced 3 different types of 10 bolt diffs and all 3 are different.

3: 9 bolts have a few different options but the factory supplied ratios were 2.77, 3.27, 3.45. There was a 3.70 option available from the dealer years ago. Any other deeper ratio is from the aftermarket if you can find them listed anywhere.

4: RPO codes and axles codes can tell you what was originally in the diff. Pulling the cover, you can either get the numbers off the ring gear or count the teeth on the ring and pinion.

5: Jacking up a wheel and using a torque wrench to turn the wheel is the only real way to know if the posi is any good. It takes a specific amount of torque to overcome the frictions in the posi.

6: Everyone has their own opinion as to what's best. They all have their advantages and disadvantages. Use google to search for pictures.

7: Factory brakes are good up to a point. If you race in any type of competition such as autocross where brakes are important, a good aftermarket brake system will be much better than anything the factory has supplied. Do a search in the brake forum on converting the brakes to LS1 brakes.

8: The 10 bolt diffs used 26 spline axles to 1989. 1990 and later have 28 spline axles. If a 1989 car was built late in the production year it "may" have 28 spline axles. There's nothing stopping anyone from installing 28 spline axles into a pre 1990 differential as long as a 28 spline carrier is used. The only way to know the spline count is to pull the axles and count the splines.

9: A differential just sitting on the ground can be identified by an axle code. It's a series of stamped numbers on the front of the passenger side tube close to the center. The axle code will also give the gear ratio but to know if the diff has the original gears, the cover needs to be removed for inspection.

This doesn't need to be a sticky. All the information I gave is easy to find using the search feature.

 

Thank you Stephen.

 

He pretty much gave it to ya cut and dry, all the info is there