Does anyone have an IROC that does not have Posi, or did all IROC's come with Posi?

 

I'll bet posi was optional in non-TPI Irocs. I had an 85 Z28 with a tpi 305 and a non-posi 3.23 rear end.

 

I have a non-posi in my IROC, 88 vert with the automatic trans and LB9. I think posi was an option on all auto tranny cars, but i'm not sure

 

Posi was a $100 option until 1990 on IROCs. It was a stand alone option, but it was coupled in with packages like G92. The LB9 didn't require any other options, so you could have a peg legged LB9.

 

So if you wanted in 1986 like my car is optioned the J65 ($179.00) power disc front & rear brakes you were required to get the G80($100.00) Limited slip differential.

The tag attached to the rear differential cover sticking out by the rear sway bar states: USE LIMITED SLIP DIFF LUBE ONLY

I have the car stored at this time, but I crawled underneath and how low the IROC-Z sits in the rear it was a tight fit to get the picture.

Chet

 

To be technically correct, there is no direct correlation between IROC-Z's and limited-slip (GM's jargon). No true "posi" was offered on third gens, only limited-slip.

The correlation is between the TPI and limited-slip. And because the TPI was an option on the Z28 without the IROC-Z option (1985 - 1987), you cannot exclude Z28's.

Prior to 1987, the limited-slip was a $100 option on Z28's (with and without the IROC-Z option) and on Sport Coupes with the 305 carb (RPO LG4). I have personally seen a 1986 Sport Coupe with limited-slip and four-wheel discs (RPO J65), but that's another story.

In 1987, the limited-slip became a mandatory option with the 305 TPI and 350 TPI. It was optional on Z28's (with and without the IROC-Z option) with the base, no-cost LG4. It was not an option on the Sport Coupe or RS.

In 1988, the IROC-Z replaced the Z28. However, the conditions stated for 1987 applied.

 

Willie, tell us the story about the 86 sport coupe with 4-wheel discs and posi. Weren't those options available on any camaro from 82-86? But not often seen on anything other than a Z28.

 

Willie, tell us the story about the 86 sport coupe with 4-wheel discs and posi.

I was searching for a limited-slip, disc rear axle many years ago. I came across the 1986 Sport Coupe in a junk yard. I almost walked right by it, thinking it would not have anything I'd be interested in. But I looked anyways. It had the rear discs, so the first thing I did was look at the RPO codes. It had a 5-speed, G80, J65 and T96. Factory fog lamps on a Sport Coupe??? Yep, this was the first year it was an option ($60) on the SC!! It did not have G92 as the high-performance axle ratio was an option on the Z28 only (1986, more later). This SC was also a customer-ordered car.....duh..... The way it was equipped, it had to be. Pretty cool car, I thought.

Weren't those options available on any camaro from 82-86? But not often seen on anything other than a Z28.

Yep, from 1982 thru 1986 except maybe the Berlinetta. I'm kind of cloudy on this part. The Berlinetta had softer rate springs and you could not get the 5-speed with the 305 carb (except in 1983). The optional F41 suspension (became the SC standard in 1986) was also not an option on the Berlinetta, so I kind of doubt 4-wheel discs and/or a limited-slip was an option....

Willie

 

Thanks, Willie

I'll bet if you sweet talked your local Chevy dealer and they had some clout with GM you could probably get them on a berlinetta too.

I should add that the Camaro White book says rpo J65 required the 305 with the Sport Coupe or Berlinetta from 82-86. Is this accurate information? If so 4 wheel discs should be available on berlinettas

 

I'll bet if you sweet talked your local Chevy dealer and they had some clout with GM you could probably get them on a berlinetta too.

You never know, but from my experience with third gens, GM really did not make exceptions. I have yet to come across one.

I should add that the Camaro White book says rpo J65 required the 305 with the Sport Coupe or Berlinetta from 82-86. Is this accurate information?

Yes, it is accurate.

If so 4 wheel discs should be available on berlinettas

But I would not assume this. Yes, you had to have the 305 to get G80, which in turn opened up J65 as the next option on SC's, but this might have been as far as you could go on a Berlinetta. I mean the only 5-speed equipped Berly came with a V6 (except 1983), so I would not assume discs all the way around was an option. This would make a good survey... A Berlinetta with factory 4-wheel discs..... Does anyone have one?

Willie

 

Ok Willie, I have a question for you actually since you know a lot about the Z's.

My buddy just purchased a Z28 with the auto/LG4 and I ran the RPO codes for him. GU5 came up. Was this a seperate option? I didn't think that GU5 was an option for the LG4's? ANy idea?

 

My buddy just purchased a Z28 with the auto/LG4....

What year? Every year there were minor variations as to what ratio was standard.

....and I ran the RPO codes for him. GU5 came up. Was this a seperate option?

GU5 = 3.23 to 1
No, it was not a separate option. Although the actual ratio varied by year, there were only two choices: The standard ratio and G92.

....I didn't think that GU5 was an option for the LG4's? ANy idea?

For example, my database shows the 1984 LG4 Z28 with auto came with 3.23's. No optional ratio (G92) was available. Could your buddy's car be a 1984 Z28 by chance?

Willie

 

... but how many TPI cars came with 4 wheel disks and an open diff?

(No need to answer, I know compounded stats aren't available).

My IROC has just that... an open 3.42 diff with rear disk brakes. If I remember tonight I'm going to double-check my RPOs, but I don't recall having the G80 rpo, plus there's no tag on the diff.

 

It's actually a 87. It also has the round shifter **** which I thought was phased out by 86 and all automatics were sqaure shifters in 87.

 

The 82 Pace Car came with GU5 where all other LG4 Z28's came with the 2.73 gears. Just some not so well documented trivia.

 

The 87 also does not have G80.

 

Yes it does.

 

scottmoyer,

I just noticed on your window sticker that the dual horns became standard in 1987.

I had to pay $12.00 for the UO5 dual horns.

I noticed other things that were changed for 1987 comparing my window sticker to yours.

Interesting, Chet

 

Sorry I was directing that comment to Willie....no biggie it was my fault.

 

I have owned 12 of Berlinettas,.......... 8 of them were V8 with Disk brakes. Here are the option tags from 2 previously owned cars; an 84 & an 86 berlinetta.

I have never owned a V8 Berlinetta WITHOUT 4-Wheel disk brakes. I'm not saying that they do not exist....... but the Berlinetta was usually pumped full of options and it ssme like if the saleman was able to convince the buyer to buy the optional V8 than he was also able to convince the buyer to go with the better drivetrain to compliment the engine.

 

According to Hi Performance Pontiac, Dec 84, the Borg-Warner 3.27 axel was a "true posi (as opposed to an Eaton Locker)"

I would like some clarification on this please.

 

I did a little research the other day and found GM code G80 has two meanings.

1. 1986 Camaro Z28 Limited slip differential (posi)

2. 1998 HD 8600 LB GVW rating Locking Differential-rear axle

On the 98 HD truck the way I understand it is the rear wheel must slip one and half turns before it locks the clutch pack together and then unlocks as your speed goes over 20 mph. So its an open axle till slip occurs at low speed.

Chet

 

Looks like 4 wheel disc berly's might be fairly common

 

Notice the G80 Codes;

The same thing holds true (in my experience) regarding the POSI - or Limited Slip - in the Berlinetta. If it has J65, then the G80 code was also listed on the Sticker......... (in my experience)

Hey Guys,...... Isn't the 9 bolt the closest thing to a "true" POSI in the ThirdGen ??

Now - I haven't used a 10 Bolt in a while (except in my 95 Z) But won't the "limited Slip" 10 bolts turn the tires in opposite directions sometimes when the car is lifted off the ground. But the 9 bolt ALWAYS spins the wheels the same way (unless the carrier is Crap !)

 

I will add more here from the same article, here are some of the things they say about the B-W rear .

It was built by in Austrailia.

Externaly they are the same as previous axles but inside is 7-3/4 ring gear and 28 spline axels.

The extra duribility comes from a four pin differential, the weak link in rears are the ones with only 2 pinions.

Elimination of the C clips and the use of tappered roller bearings at the wheels are additional strong points.

Is stronger than the chevy 26 spline, 7-5/8 ring gear.

Is stronger than a 8-1/2" Dana 44 !!

Only axel to stand up to the Woodward test (more on that if you are interested)


Don

 

1986 Camaro Z28 Limited slip differential that my car has which is the 2HY, 3.23:1 spins the tires when off the ground in the same direction.

Chet

 

I like your 85 Trans am, 85 T/A WS6,

I would like to hear more on the 9 bolt rear that withstood this test.

 

Thanks Darth

The more I learn about my 85, the more I like it too

The Woodward Schedule was a test where Pontiac launched the car by side stepping the clutch at 4000+ RPM and power shifting thru every gear at redline.

They ran about 30 axles through 200 Woodward tests without a single failure.

The Danas broke in this test.

 

So Willie, was the GU5 a normal option for a 87 Z28?

 

well my 88 iroc has a 305 tpi and a 2.73 posi. I belive it was an option.