Any one know if the 85' auto (with 3.23 gears) IROC Z28's had a posi rear end?
And What kind of TH700R4 did thy put in them, the lock up or non lock up one?

 

1) Check for RPO G80= Limited Slip Rear.
2) Only one kind of 700R4 Transmission, Lock-up type.

 

I checked my RPO in my -88 T/A, and I have the 3,27 posi. What I´ve understood it´s a great rear, or is it? For the winter I´m going to stregthen my TH700, but is there also some great things to do with the rear? Should I stick with the 3,27 or change the gears or anything else with these?

 

If you have a 3:27 rear it is a 9-bolt and gear choices are very limited. Such as 3:45 and 3:73. I would stay with the 3:27, because it is one of the stronger rears offered in the 3rd Gen cars. I don't understand your comment about beefing up the 700R4 Tranny for the winter???

 

I´m sorry, what I meant was DURING the winter. Hey, I´m just Swedish

So, the 3,27 is strong enough? I will put on BF Goodrich Comp Drag as daily´s, but I will use slick´s when racing. Would the rear really manage the grip?

 

Yes, with the tires you mentioned. Unless you are running over
400 Horsepower. Slicks in the winter??? Not on a 3rd Gen!!

 

I´m sorry if I´ve expressed myself wrong. I´m not going to drive the car in the winter, but I´m gonna tear the tranny apart to strengthen it until next season.

The thing is, I´ll go past 400hp with the N20 (and I am gonna change more), so I wonder, what should I do with the rear? I´ve tried the search, but I´m not THAT good at english so I´m not getting the hits I whant.

 

All the RPO codes are gone.
I should have mentioned that.
I don't know what any of them are.
It has a 10-bolt also.

 

Answer for the two questioms:
1) Run the 3:27 9-bolt until you blow it up, then replace it with a 12-bolt Moser or a Ford 9" rear. Good luck.
2) No RPO codes, so the only true way to see if its a Limited Slip is to pull the cover and check it out. this would be a good time to change the fluid & gasket. again good luck.

 

my friends 85 iroc came with a 3:42 rearend and it was not a posi at all it was open, and it should be a 10-bolt in 1985 unless somebody swapped it at some point. my suggestion would be to first look at the bolts holding the rear pan on and see if one has a metal tag hanging off of it stating that its a limited slip rear, and if its not i would just freshen it up and add a posi like the one from slp for like 100 bucks and then add a nicer pan if you really plan on beating on it. the only thing you will have to do for the posi is switch to 88-92 rear axles out of any gear ratio and a v6 or v8 rear and make sure that whatever gear ratio that you have is compatible with the posi. and as far as i know all the 700r4's were lockup from the factory, i believe some people opt to not have that feature when buying a different tq converter mostly for racing purposes as far as i can tell.

hope this helps,
Nick J

 

You say slp has a posi unit for $100, how much abuse can one of those take?
I was thinking of getting a eaton and useing my 85's gear carrier.
I have a 91 3.23 open rear end, but I would prefer to leave it in my 91 RS for now.
If I were home I could add and remove all kinds of stuff on that car. I don't have my tools, sh*t I don't even have a screw driver down here with me.
There is a hobby shop on the base but I don't know if it's open to us students.
At best I could slap on a few bolt ons and change all the oils to help make the 1900 mile ride home easer.

 

My 85 IROC came without posi. Drives me nuts. The car was fully loaded, including TPI and rear disk brakes, but no posi.

Anyway... if your RPOs are gone, you can look at the rear diff cover and see if there's a metal tag on one of the cover bolts. If it's never been messed with, the posis would have a tag.

But... if you are questioning this, either yours doesn't have it, or it's totally spent, in which case you need to replace it anyway.

I've got the zexel-torsen diff from SLP in my IROC. It's only been in there for a little while, but so far I'm real happy with it. It's nice and smooth. I don't think you'll have a problem with it breaking unless you're making 350+ horsepower. Those come out of the new Z28s and Firebirds that get sent to SLP for the SS & Firehawk conversions. Those cars are putting down 300+ rear wheel horsepower and the diffs take it.

 

The so-called Limited Slip diferential stopped limiting slip long long ago in the 88' caprice i had. After a while you do a burn out and wonder why its a one-legger.

 

That's because your Caprice had the more conventional clutch-type diff. When the clutches wear, it slips. The Zexel doesn't use clutches and shouldn't ever wear out.