Ok guys. Riddle me this. My IROC has an open diff with 3.42 gears and rear disks, all factory. I've seen it mentioned twice on this forum that all 4 wheel disk cars came with posi. So....is that true, or was is possible to get the disks without the posi?

------------------
The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

Jim,

I've always believed that you could not get 4-wheel discs (RPO J65) unless you ordered limited slip (RPO G80). Up through 1986, you could get G80 and J65 even on Sport Coupes. According to my 1985 Camaro sales literature, it states, "Four-wheel power disc brakes (requires V8 and limited slip differential). What do your codes say?

 

I don't remember! I'm looking all over my computer for my RPO list but I can't find it. As soon as I do, I'll post it. Maybe I've got an ultra-rare lame assed opend diff

------------------
The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

Or maybe after 15 years your posi is worn out and dead?

------------------
West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

I have to agree with kevin,if a posi unit gets worn it could act like a one wheel wonder

------------------
84 FIREBIRD-2.8 V6,5spd super economy model
no options except t-tops( not even locking),no tilt,no cruise,no delay wipers,no rear defroter,no a/c,no rear spoiler(i put one on)no pw,pdl,pm,pseat,no gauges(just a 85 mph speedo with no trip odometer and a big f***in' gas gauge)
90 FORMULA 350-
Edelbrock t.e.s,gutted cat,Borla cat-back,LT4 hot cam ,24# injectors,holley h.p. fuel pump,K&N Throttle Body mounted air filter,52mm throttle body,accel 8.8mm wires,plugs cap and rotor,ADS superchip,GTA tailights,T-tops,4th Gen 17's with 275/40ZR17 Comp T/A's,93 Z-28 seats
No E.T's yet.

Previous 3rd gen's
83 Trans-Am 305 CFI auto T-TOP
84 Firebird 305 H.O. auto HARDTOP
87 Firebird 2.8 V-6 auto HARDTOP

 

possibly, but the car only has 85k miles. I don't remember seeing a G80 or G92 RPO either. I wish like hell I could find my RPOs. I'm 300 miles from the car, plus she's all put away for the winter.

------------------
The IROC Homepage
<A HREF="http://www.rit.edu/~jli4307/camaro" TARGET=_blank>
View the restoration of an 85 IROC</A>
"I didn't know a bored out Ford could go so slow" -Shenandoah

 

Jim, My '83 has an open diff and disks. It's not wore out, and when they go, they disintigrate, and you know it.

------------------
Kenney
82 Trans Am WS7 notchback
83 Trans Am WS6 T-tops
72 Vista Cruiser 455
90 Olds Trofeo
80 K-10 w/snow plow
Painter @ Chevy dealer
GM junkie

 

J65 Brakes, power front disc and rear disc $179.00.

My information doesn't specify a particular model or rear so I believe it to be available on any car mated with any rear.

------------------
1989 Camaro Convertible
dark silver w/black top
305tbi, auto, all stock
posi
Check out Phil's Rice Boy Page

 

Maybe you have one of the fabled Eaton Locking differentials. They act like open differentials at all speeds above 25MPH, and whenever there is not a large differential in speed between the tires. Try putting a jack stand under one wheel, and placing your car in neutral. take the tire and spin it as fast as you can with your hands. If it stops with a "bang" and switches direction on you, it's an Eaton Guv-lock.

It's a piece of crap for high-performance use. When it gets worn it locks unpredictably resulting sometimes in a spin in the turns. I ripped mine out and replaced it with a Torsen!

------------------
Daniel Burk
http://www.isthq.com/~dan/fcar.html
'84 Trans Am WS6/L69
KB SFC, Moser axles, Torsen Diff. PST suspension, Braided stainless brake lines, Koni struts, 11-inch rear disks,Spohn Adj. torque arm,
Ported 305 heads w/1.94"intake valves, Comp Cams XE262H, Griffen alum. radiator,
Turbine Technologies 2500 stall converter, underdrive pulleys, Crane Hi-6 & more.
1.05g skidpad verified.
New best E/T! 14.039 at 100.82 MPH in 41 degree air at Stanton, Michigan.

 

i had an 84 trans am with limited slip and rear discs don't know if it is differnt with camaros but i have seen more than one trans am like that

 

Willie I've seen the same written for Camaros from different sources that you could get RPO-J65 but it required a V8(if not a Z28)and G80 but not G92.Again that's up thru '86.I don't know about '87 and later and don't know if Firebirds were different in requirements.Jim when you have access to your IROC check the right axle tube for the original code then you'll know if it had positraction originally.

 

My 84 Berlinetta came from the factory WITH Disk Brakes and WITHOUT POSI.

Proof:




This thread hasn't been touched for over 6 years; till today ! I love seeing these old posts that get resurrected from the dead !!!

 

Well that's excellent proof that you can't believe everything your read.But you do have a LG4 so at least it's partially true.I guess if someone sat down at the dealer and ordered it(in the days when you could as it's been stated)and the dealer put the paperwork thru well you get the point.I wish I would have went and looked at a '85 Berlinetta that the ad said V8 and 4 wheel disc brakes but hindsight is always 20/20.


And I didn't even notice the age of the original post.I need to learn to read.

 

I've owned other 84 Berlinettas that had the Disk brakes AND POSI from the factory too. Like you said - in the "Good-Ol-Days" the dealers had free rein to order what ever the customer wanted !

:driving"

 

My 83 T/A has rear disk brakes and no posi.

 

I think the answer is that there was a big shortage of posi units during some point in 1984, so cars were shipped with open units. I believe GM even sent back all WS6 orders and those car had to be re-ordered with WY6. The equivalent would have happened to Camaros as well.

Do a search on RPO WY6

 

Yes, Car distribution Bulletin 83-F-12 dated 4/27/1983 Says there was a shortage in G80 Limited slip Differential. I don’t know the end date. My car was built 6/14/83 so it was built during the shortage.

On my build sheet it still list WS6, but it references WY6 as seen in the lower line of the picture I attached. However, the upper line shows a car with full WS6 options. So instead of replacing WS6 on the build sheet the factory choose to continue using WS6 but it was understood by the factory workers that the posi rear end was not available.

 

wow, back from the dead. I never did double-check my RPOs, but a few years ago I pulled the rear end apart to install 28 spline axles and a zexel torsien diff. What I removed was an open differential, not a worn out limited slip. I do believe my car was built that way, but that doesn't surprise me because my car was very oddly optioned. My car came with the premium interior, with the power seats, power windows, locks, cruise, tilt, blah blah blah... and an AM radio.

 

That's interesting Wildjeff as my Z28 was built the 3rd week of June of '83 and has a factory posi(I've had the cover off to replace the fluid).Also the code on the axle tube denotes the code for posi and 3.23 ratio(5PZ)I wonder did it make a difference as to build plant,mine is a Van Nuys car with a Buffalo built axle.Either way I guess I'm lucky she got one.

Also Wildjeff you have a very informative website,even though I have a Z28 instead of T/Aa lot of help is in there.

LOL... Jim that certainly is an odd optioned car.Sounds like she nay have been a dealer order.

 

So could we have finally learned the real reason why the posi rearend wasn't an available option for 1983 L69 cars when the engine was released for production in the spring of '83? That was one of those things that just didn't seem to make any sense, and dealers could offer no legitimate-sounding explanation for it.

 

yea i have seen f-body's with disc and no posi. as a matter of fact there was a camaro in car craft (the junkyard crawl section) a while back the had the optional disc breaks and no posi hence why they didnt pull it according to the caption. i do think that this was only the case with the 10 bolt rears, i think all the 9-bolts had posi, not sure though

 

I ordered my 85 IROC in the winter of 84. Took till May 85 to get due to engine plant strike in Canada where certin gas and diesel engines were manufactured. When it arrived it did not have posi but did have 4-wheel disc. I had ordered posi(G80) RPO and was told they had a shortage from their manufacturer. In November of that year I was called by the dealer and they installed my posi unit and a new ring and pinion as I had already paid for it. Also, some people who ordered posi and did not recieve it on their cars simply got a refund for the option. So having a 10-bolt with 4-wheel disc and no posi is no mystery, simply another GM screwup. Badman

 

My 1985 IROC with rear disc brakes had an open 3.42 rear. Replaced it with a "low mileage" 3.27 9 bolt disc rear that only spins one wheel also.

 

I used to think that too - but was proven wrong. I've seen 3.08 and 3.70 9-bolts without POSI. I've seen 9-bolt drum brake rears too.

 

This is a supposition but perhaps my '83 Z28 was a situtation like your '85 IROC Badman.The original owner had it installed at no charge.Or she was the exception to the rule and came with it from the factory.It would seem odd being a June '83 build she would have it but I've seen it and the axle code clearly.Did it matter what axle plant it came from or was it supplier wide shortage - anyone know?

 

coolram62 – Thanks, my site is a work in progress. As I collect more data I’ll add it. I choose to concentrate on 82-83 firebirds but your right about a lot of the data is shared between the two models.

Maybe when your car was built the posi rear ends where starting to trickle in, or Van Nuys had more left over.

 

Well here's some more proof of plant mistakes: My '86 LG4 'Bird has a 2:73 10 bolt w/ posi, drum brakes and NO G80 RPO code. It still had its alum "limited slip fluid only" tag. Look at my garage page...RPOs at the bottom. I bought it from a woman 6 1/2 years ago with only 74,000 mi & was untouched performance wise. This car was kinda weirdly optioned. I dunno if all WS3 cars got a posi or not, but mine does. It has a "WS" steering box w/ the steering cooler line, 34mm front & 23mm rear sway bars. It also has power windows, premium cloth interior, and manual locks...go figure. I havn't found my build sheet yet, but I'm hoping its under the carpet or in the doors.

 

It's always funny to see a really old thread come back to life. My '85 was really peculiar (IMO). The guy ordered the 4-wheel disks and posi, but with an LG4. Who does that?

Mike

 

One of my ( now wrecked ) 84 Berlinettas had the same deal.... Engine was a LG4 with an IRON intake manifold & the gears were 3.08's. The 84 Berlinetta didn't even get a rear sway bar from the factory !!!!!!


Like you said - who does that ??

 

my 84 T/A has January 1984 on the door sticker. It came with an L69 and the WY6 option (rear disk brakes, open differential). It really sucks that they had that shortage... it robbed alot of early firebirds of the WS6 designation.

 

A friend of my brother in law ordered a car specifically without the posi. But it had disc brakes. He said he wanted to spin the tires...

John

 

I guess I don't need to feel bad. My 1985 L69 IROC had Aluminum rear drums, 3.73 gears and NO POSI. I was certainly disappointed when I opened it up. Its a wierdo option car, from Miami, rear window defog, wiper and washer option, but no wiper. It is all original.

 

Actually we never had a "Posi" unit as such, the term went away before the 3rd gen was introduced. They call our axel a "Limited Slip" The difference is probably superficial but in some cases one wheel will spin independantly under some conditions, like turning to the right and hitting the gas where load is much higher on one tire than the other the right rear tire can spin.

THe Limited Slip does just that it allows only a limited amount of slippage. If there was no slip your tires would skip or chirp as you turned corners even at slow speeds, in reality thats why they changed the design from "Posi" to limited slip. One interesting factoid is some of the literature such as the parts & illustration catalogs stoll refer to the axel as Posi.

John

 

Huh, I just checked the codes on the silver '85 IROC that I bought last week... it too has a 3.42 disc rear with an open diff. Has about every other option, but no posi.

 

I will throw something in for you guys to think about. I ordered my 91 Formula with limited slip, 3:42 gear rear and 4 wheel disk. When the car came in there were drums on the back, but I did get the limited slip and the 3:42 gears. Dealer showed me a letter from GM about there being a shortage on disk brake rear ends and they would knock $200 off the list price.

 

Actually All Formulas and GTA';s from 1987 thru 1992 were suposed to get the 3.42 (or 3.45 depending on year) ltd slip, and disc brakes when ordered with the LB9/M5 combo. In 1991 like you stated there was a shortage of disc brakes for one reason or another and they used the aluminum drums instead.

What I always found interesting is from 1982 thru 1988 the proportioning valve was different for the 4 wheel disc brake cars than those with rear drums. When they went to the larger (1LE type) rear disc brakes with the aluminum caliper They used the same proportioning valve...

In short it means that Drum brakes area actually stronger for ONE use than disc brakes. The Aluminum drums offset the fading problems caused by iron drum brakes because they cool better. Interesting factoid, my 1967 Riviera has Aluminum Front drum brakes. They are about 14" in Diameter. Talk about Stopping I can lock up the brakes at 70+ Mph.

John

 

I have a 1985 Iroc tpi car with 3.42 gears and an open differential. I bought the car with 55,000 original miles and in perfect shape.

 

^ Resurrection #2. This thread will never die.