I recently purchased my neighbor's '86 bone-stock IROC-Z. I also own a L98 '87 IROC-Z and was shocked at the factory performance difference between the two. I'd like to do a mild performance upgrade on the '86 while trying to keep the "factory" label. How well will the car take say a 3:23 rear end in exchange for the factory 2:73?

 

Are you replacing the complete rear end or just changing the gears in the one you have?

 

changing the gears in the one i do have

 

I would think it would be infinitely easier just to swap the rears - you can usually find GW6 3:27 disc rears just about anywhere for $3-500.

 

4th gen rear swap are incredibly easy and cheap, and show up in the junkyards pretty commonly nowadays. I got my 3:23 rear from a 95 Z/28 with positrac and discs for under $100. You have to run 4th gen offset rims or deal with the wheels sticking out, but it's still far less expensive than ordering and installing gearsets for series 2 differentials or the disc brake conversion kits, or even finding a 3rd gen disc and posi rear of the gearing you desire. The only complications to installing a 4th gen rear are the metric brake line fitting (and that's only an issue if your car is pre-metric conversion and even then an easy fix) and parking brake cables (use 91-92 disc brake cables). Everything else bolts right in.

 

Are you sure it's a 2.73? Is your car an LB9 or LG4?

 

It's quite possible to be an LB9 IROC and still only 2:73. My 1988 LB9 IROC-Z has a factory 2:73 posi rear, confirmed in the RPO codes.

 

Changing the gears is not s simple bolt in job. If you decide to take it on then I recommend reading the thread in the FAQ about 10 bolts sticky. You can get a thick 3.23 to fit your 2 series differential. You would also need a good installation kit.

 

Not in 1986. All IROC-Z LB9s came with a 3.23 that year. The best way to be sure is to check the SPID. I'm sure the original poster would be pretty pissed if he bought a 3.23 gear set, took his rear end apart, only to find that it already has a 3.23.

 

http://www.nastyz28.com/camaro/camaro86.html

http://www.f-body.org/tech/tech.htm

http://www.iroczone.com/2009/10/1986...pecifications/

The G92 axle was available, but not the standard equipment.

 

The first and third site you linked only only have a 3.23 ratio listed for an '86 LB9 IROC-Z, as I mentioned. The second one is just flat out wrong, listing a 2.73 and 3.42. That same site also has the L98 as an engine choice in '86, which we all can agree is a mistake.

I've never seen an '86 IROC-Z with an LB9, not have the GU5 code, (3.23 axle ratio), on the SPID.

 

I don't get where you're seeing this. For 1986, under LB9, all list 2:73/3:42 as the standard ratios and 3:27 ONLY for the G92. There is no "IROC only" specification anywhere, only a "Z28 only" on the first. Here's some others;

http://www.f-body.org/tech/tech.htm#ThirdGen

http://www.iroc-ss.com/history.htm

Sorry, but the LB9 IROC-Z most certainly came standard with either a 2:73 or 3:42 rear, and only if ordered with the special option G92 came with 3:32 gears. As there were some 46,000 LB9 cars produced and only 4000 or so cars had the G92, even accounting for some of the LB9s being Z28s only the numbers don't corroborate your claims.

 

And there is disagreement over the L98 1LE for late 1986.

http://www.iroc-z.com/1986pages/1986factsandfigures.htm

 

I think we'll have to agree to disagree here brother.

But a couple of things: The 3.27 listed there is for the '86 L98 which was never produced, and they don't even have a 3.23 listed for an '86 LB9 IROC and yet the several dozen '86 IROC, LB9 SPIDs I've looked at, ALL had a 3.23.

Anyway, a look at the OPs SPID will answer all of our questions.

 

I'd quit arguing about a bunch of stuff posted on the Internet. Makes you look kinda .... well, I'm not going to say that.

Whatever the OP finds when he TAKES OFF THE COVER AND LOOKS, is what he's got. It's beyond futile to argue whose Internet page is more right than the other guys when simply LOOKING AT THE PARTS will tell what he really needs to know: what's in the car NOW, regardless of what came in it 30 years ago.

OP, take off the cover and look at the parts, before buying ANYTHING. Ignore all the crap about "codes" and "my Internet page says" and all the rest of that. Be assured THE PARTS aren't paying the slightest attention to any of it, they ARE what they ARE, period.

 

Or simply jack up the rear of the car, make a chalk mark on one wheel at the 12:00 position and on the 6:00 position on the pinion, then rotate the wheel until the pinion makes 1 complete revolution while paying attention to how many times the wheel rotates, as well as if the other wheel turns in the same direction or the opposite. No need to open the rear diff at all, which means no draining, cleaning, and refilling, as well as no new gasket.

As for "a buncha stuff posted on the internet"...::looks around::...Isn't that EXACTLY all a forum is? Does that mean any information gathered here should be immediately taken as mere hearsay and disregarded? Or should the internet be used as an information source, gathered and cross checked from multiple sources, and one's own conclusions drawn?

 

The code on the front of the axle tube is 2HP. Which according to all these IROC sites out there is a 2:73. It is a LB9.

 

1983,

Here's what I see in this thread:

1. OP asks what will happen if he changes his gears from 2.72 to 3.23
2. 2 other guys come in and start beating each other over the head about what gears "their" web page says he has now
3. 1 of the 2 guys thinks that even though the OP hasn't done the simple routine maintenance ALL cars should have done to them once in awhile, arguing about web pages is still better than LOOKING AT THE PARTS to see what they are

Does this make sense?

Sure, forums are all about discussion and such as that; sure, web pages are places to accumulate information and share with all who need it; sure, I get that. OTOH, all the OP needs to know is, what gears he has; which since he has NO WAY TO KNOW that the car is "bone stock" unless he's had access to it since the day it rolled off the lot, the best way to find out what gears are in HIS CAR, RIGHT NOW TODAY, is to simply LOOK AT THE PARTS.

All of that "spin this and count that" and all that other type of stuff people post about "shortcuts" to this knowledge, is error-prone and likely to lead him astray. Sure, you or I, who KNOW WHAT WE ARE DOING BECAUSE WE'VE BEEN INSIDE DIFFERENTIALS BEFORE, can make it work; but this is one of those things where if you have to tell somebody about doing that because they don't already know it, the odds of them getting it right are slim. More specifically, the 2 rear wheels won't be turned EXACTLY the same amount.

The OP has now posted his "codes" and thinks they are sufficiently reliable to tell him what's in his rear. (car's rear that is) Personally I sure as hell wouldn't buy parts based on evidence that flimsy, but I guess we all gotta learn somehow. Which while FAR FROM 100% likely to be right, is at least ALOT better than a bunch of "my web page is better than yours".

 

sofa, I believe that you and I are in violent agreement. My simple statement to the OP is, make sure you don't already have 3.23 gears, before you buy a 3.23 gear set.

 

But with that said, if 87YELLOWZ looks at the SPID in his '86's console, it WILL say, GU5.