i have a borg warner 9 bolt rear end. i belive to be a posi. it is off the car on jack stands and if i spin one side the othe side spins the same way. also when i spin it one full turn at the wheel the center turns 3.25 so i belive it is a 3.27 gear. is this correct? i belive it came out of a 1990 iroc but the origanial owner said the rear came out of a firebird so not sure what it came out of. is there anyway i could tell what it came out of? i have a 92 rs with one wheel spinning all the time no trackshion what so ever. so i would like to have a posi with better gears but i am not to sure about this stuff. also the 9 bolt is disk brakes . is this a good rearend ?any help would be much apprecited. thanks in adavance.

 

Sounds like you've identified the ratio & verified the posi action.

9-bolts are stronger than 3rd gen 10-bolts, but the 93-97 4th gen 10 bolts got a better differential & the same 28-spline axles, so they are a bit stronger in the middle, but still have the c-clips holding the axles in. 98-02s are a bit better & have larger discs.

You could consider just putting a 98-02 4th gen rear axle.

 

i just pulled the cover off and it is a 3.27 . i thought about the 4th gen rear scence i have 93-94 firehawl rims but i have this rear end and dont really want to buy another . is the 3.27 a good gear or not ? also is there a way to tell what year it came off so i could get new brakes . i want to know it needs new pads rotors are rusty and cabliers . i have read that i need porporition valve but not sure what kind and where to get it. also will there be anything else i need ? i have found casting numbers on it but not sure where to look to find out what they mean. thanks for the help.

 

The 9 bolt is a good rear end. The 3.27 gears are also good. The 3.27 uses the 3 series differetnial, which means that you can put 3.70 gears in it later if you want. The '90 disc brakes should be the PBR? If so then they are the better brakes.

 

82-88 disc brake rears would have Delco-Moraine iron calipers with 10.5" rotors. 89-92 would have alum calipers (PBR's) and 11.7" rotors.

JamesC

 

just measured the rotors there 10.5 so prob not the 90 iroc rear right? the cabilers are froze guess because i have had this sittiln for couple yaers in garage and sitting on car couple years befor i took it out. so how do i know what parts to get for brakes not sure what car it came from. also you say the newer style are better could i get those or get the kind thats on there . i dont want to spend an arm and leg to get this in .if so i would get some aftermarket brakes just want to go to parts store and get parts . i know if i get the brakes that are on it or the pbr (not sure what they are) it still have to be better than whats on the car now with drum brakes. thanks for the help everybody.

 

Just the rusty calipers tell me you have the smaller rotors, without measuring. In 89, the 9-bolts went to the aluminum PBR calipers & bigger rotors.

You could put the PBR calipers & rotors on it, but if your already having to buy all new stuff, I suggest getting the LS1 brakes. I don't have the specifics of doing that, otherwise I'll tell ya, but I know its been done.

 

Parts stores will have what you need for the Delco-Moraines, probably on the shelf. The newer and older styles are not interchangeable without modification. Should you wish to upgrade to PBR's or at least see what they are, check the following link for pics and info:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

JamesC

 

You can use the better brakes if you change the brackets and everything. You would have to find the complete assembly to change them.