Transmissions and DrivetrainNeed help with your trans? Problems with your axle?
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dose a 1986 Iroc z28 have a rear posi?? because when i rearly do burnouts i only see one line in the street. is there somthing i need to do or fix to make it 2 lines in the street?
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I think you're question is this, in 1986 did Iroc's come with a posi unit standard? I'm honestly not sure if they did or didn't. The easiest way to tell would be to pull the diff cover and look; if you see clutch packs on either side of the case than yes you have a posi, if not you don't. You could also check your rpo sheet, but its a very real possibility the origional rear was rebuilt or replaced along the line sometime. I suggest popping the cover off simply to change the gear lube if nothing else, it's probably been a long time since it was done. While you're in there you can figure out if you have a posi carrier and what gear ratio you are running as well. If you are only spinning one wheel chances are you have an open rear, if your only spinning 1 wheel but find a posi unit installed chances are the clutches are shot and it needs to be replaced or rebuilt. If you're not sure what you're looking at take some pictures once you pull the cover and post em up here and we can tell you what you have. So to answer your question you either need to rebuild your current posi unit if you in fact have one, or replace it with a new unit. While you're at it you could also swap to a better gear set since your auto car most likely came with 2.73's installed(if that's the case you would probably want to upgrade to a series 3 carrier, although you can get some thick 3 series gears that are made to work with a series 2 carrier). Also you posted this under the wrong subforum, mods may want to move to transmission and driveline.
Last edited by 89RsPower!; 05-12-2009 at 11:28 PM.
i believe some came with a ratio of 3.42 posi, and some came with 3.23
No '86 IROC's with the auto option came with 3.23's. In '86 IROC auto's had either 2.73 or (if equiped with the "G92" RPO) 3.42. Out of the 49 something thousand produced there were 50 350 equiped IROCS and all coming with either TPI or CARB. If it is carb'd you are doomed with the 2.73 if it is TPI it could be 2.73 or 3.42. As stated you should pull the cover and verify if you have a posi that needs repair or if you are doomed to one wheel peels. Of course this is all assuming that you have the factory rear-end in there still.
Last edited by allboutspeed; 05-19-2009 at 08:01 PM.
Reason: oops
If it was a IROC-Z28 then it would have have the G80 limited slip rear option. Your problem is the car has had too many burnouts over its lifetime the the rear limited slip is history.
The '86 could have had the Auburn or the Governor Lock. If it's the Auburn then it's worn out and needs to be replaced. If it's a Governor Lock then the gear on the governor may be broke, which will not allow it to lock up. Either way I recommend replacing it with a new Eaton Posi.
The '86 could have had the Auburn or the Governor Lock. If it's the Auburn then it's worn out and needs to be replaced. If it's a Governor Lock then the gear on the governor may be broke, which will not allow it to lock up. Either way I recommend replacing it with a new Eaton Posi.
Don't recall an f-body ever having a gov lock from the factory..
Yes they did. You have a GM 9 bolt Borg Warner BTR 78 7.75 inch ring gear with a cone type LSD. You can rebuild it or replace it with another diff like a Ford 9 inch. There is a German LSD clutch type that is very very expensive and totally not worth it that will fit. No one anywhere makes a Helical gear LSD for it. The GTO's will not work. If your IROC started out as a 305 you might have a 10 bolt. In which case you can get a Truetrac for it but the 10 inch is worthless and weak so I would swap it for a 9 inch best deal I have seen is Currie about $1300 bucks but you will have Ford rear discos.
Yes they did. You have a GM 9 bolt Borg Warner BTR 78 7.75 inch ring gear with a cone type LSD. You can rebuild it or replace it with another diff like a Ford 9 inch. There is a German LSD clutch type that is very very expensive and totally not worth it that will fit. No one anywhere makes a Helical gear LSD for it. The GTO's will not work. If your IROC started out as a 305 you might have a 10 bolt. In which case you can get a Truetrac for it but the 10 inch is worthless and weak so I would swap it for a 9 inch best deal I have seen is Currie about $1300 bucks but you will have Ford rear discos.
The 7.75 9 bolt didn't come in these cars until 1987. The 86 had the 7.625 10 bolt. Also, in 86 all IROC's had the 305 (some with the HO option) except for the "rumored" 50 that were equipped with the 350.
The 7.75 9 bolt didn't come in these cars until 1987. The 86 had the 7.625 10 bolt. Also, in 86 all IROC's had the 305 (some with the HO option) except for the "rumored" 50 that were equipped with the 350.
I stand corrected in anycase toss the center and put a truetrac in there. The 10 bolt still won't be all that strong but you will have traction and cost is less the $ 500 for the part otherwise go to a 9 inch but that will cost you.
The 7.5 rear end is the only one that I have ever seen in a car that had the Gov Lock installed from the factory. I've never seen the 8.5 in a car with the Gov Lock from the factory. I think the 7.5 might have got the Gov Lock because of a shortage of the Auburn or a lack of something better to put in it.
