85 Z28 or posibly Iroc rear diff
 

I'm buying a rolling chassis IROC-Z28 or so that's what the guy is telling me. All I find is z28 badging and none Iroc. Well my question is from my experience the only posi that can in those years was a 9 bolt if I'm not mistaken? But this car has a 10 bolt. Could this 10 bolt be a posi?

they came with 9 and 10 bolt posi rears

Ok so how can I tell if its a posi with out taking it apart? Any codes stamped on the diff?

I would just pop the rear cover off...it's a 10 minute job

A guy at work told me that if I take it apart I have to go though a process to make sure it works right afterwards

if you take off the rear diff cover all you have to do is reinstall the cover and refill the diff. as long as you dont take anything inside the diff it'll be fine. there should be a ring/pinion number stamped in the ring gear, divide the pinion count into the ring gear count and it'll give you the gear ratio. it may have the ratio stamped right on it too. Also on the drivers side axle tube there is a 3 digit code stamped on the front side. Find that code and post it up, i have a list that beaks down what the diff is like posi or open, and gear ratio.

check ur RPO codes in the console... should be sumthin to do with the rear on it, if its the original rear to the car

Try doing a burnout, should be real clear then.

Well I was hoping I would be sure before installing it in the camaro

Ah, just noticed the rolling chassis part.

go to camarosource.ca, you can put your vin in and see what it kicks back as options. also just check your RPO sheet and see if you have RPO code BZ4. Should be under the center console lid

I'm worried if its not the original diff. He usto use it to race.

Well then hike it up off the ground, put it in neutral, and spin the back wheels, see if they spin in different directions, or in the same direction. I wouldn't worry too much about 3rd gen diffs, it's seen 26 years of abuse if anything. Just get an Eaton setup and move on if it's shot LSD

i got the RPO sheet and the ones that it says is B4K, B9K, B94, B97.

i took the rear diff out and cleaned it and on it said "GM N 22522676 K 8 5"

is there a stamping on the front side of the axle tube on either side? should be a 3 digit code. use a wire brush to clean the tubes off

9ja co63 1

If your RPO code sheet does not have the designation B4Z, then you do not have an IROC. In case a door was replaced, you could always look at the 8th digit and see if it' the letter. If it does, then there is hope. Almost all IROC's had an 8th digit of G.

Well I'm most positive that its a Z28 . I'm not keeping it . All I wanted was the diff and a couple other goodies .

3rd gen RPO sheets are located under the center console lid, not on the door, and the VIN engine code G is for the 305HO (L69). All '85 Camaros that had the L69 should be IROCs (they will also be 5spd manuals and have 3.73 gears. IROCS were also available with the LB9 (305 TPI, vin code F). These would all be automatics with either 3.23 or 3.42 gears. Final IROC engine option was the base LG4 (305 4bbl, vin code H).

- Justin

9ja doesnt come up but 8ja is from a 85 rear and should be a 3.08 open diff. are you sure the 9 isnt a 8? sometimes the housings get rusty as hell and are difficult to read.

I said center console in an earlier post, got used to telling people to look at their door for GVW when selling brakes, so I typed that without thought :lol:

Well I decided to to open it. When I opened it I found that it is a posi with springs. I also found out that it looks like the input shaft got pushed in and engraved its teeth into the posi housing. It did some damage but the components are all still in tact. I'm not looking to make big numbers with it . I just wanted to get a posi rear to play with and also the rear that bibbly has now got hit and bent the axle so it felt like the right time to change it. And it was great when a coworker told me about this z28, so I got a rear and a couple other goodies to makes the daily driver more lively

What? I need pics of that

I would post one but I can't do that from my phone. Ill see about posting one tonight.