9 Bolt on my early build 9/89 . My question is that the code for a GM3 does not reflect on the sticker in the console , but has GU6 listed

. Would this be the case because GM3 wasn't offered as a selection on the ordering in 90 ? I've read on several forums that they used up the left over 9 Bolt rear ends on early build 90's and didnt change the code .
Any help is appreciated!
Jason

 

https://www.differentials.com/techni...dentification/

 

Its definitely 9 bolt and it's a 5-speed so that makes it a 3:45 , I'm trying to figure out why the code is not listed on the label in the console as a 9 bolt .

 

RPO list shows g-80 GU-6 (list sez 3:42)

I see G-92 also.

Funny its got those RPO IDs with a 9 bolt.

 

A 9 bolt could poss. 3:45s tho.

 

Exactly, I'm hoping there are other owners of early 90 G92 that can confirm the use of 9 bolt without the RPO code designation, or possibly a Iroc Guru that knows all !

 

It has more than likely had the rear end changed. GU6 is the 10 bolt rear, and is what the car is supposed to have in it.

My 1990, G92, 5 speed was GU6 but I guess I didn't double check which rear was in it. I just assumed it was the 10 bolt. Mine was built the 2nd week of December, so it was one of the last ones...dec 31st, 1989 was the last day IROC's were built

 

Yeah, still thinking it is original. Mine is a early build and the original owner would have removed it and put a 9 bolt in and spent all the money for no gain besides a 'better' Borg Warner. I dont see that being the case .
Still hoping theres info out there that can verify this being the case. All I have found is that several guys have 9 bolts in their 90 and talk that it was done for the early cars.

 

Considering the SPID is solely intended for Identifying the proper Service Parts, I would have to assume that GM would have used a 9-bolt code if a 9-bolt rear were being installed. Otherwise Joe Bob, Chevy service manager and Cletus, head Chevy mechanic wouldn't install the correct part when the car comes in for service. It doesn't pass the sniff test that they'd put something different on the SPID than what they put in the car. The SPID never lies.

Trying to create a plausible back story for why something doesn't add up, in this case the wrong rear end, is an exercise in futility. Who knows what motivation a previous owner may have had to change a part. The 9-bolt has often been hyped to be something "better" and that's probably all the motivation someone needed. Maybe someone thought the car should have had a 9-bolt and they didn't realize GM had switched back to the 10-bolt and thought since it had a 10-bolt it wasn't a "real" Iroc, so they did a swap. It really doesn't matter. On paper the car should have a 10-bolt. Hoping to find out it's got the correct rear in it by some obscure loop-hole is just grasping at straws.

Something to keep in mind is that the documentation was pretty sketchy before the internet, even in the early days of the internet, and even now on places like Youtube and Facebook comments. There are still fools out there that believe their 86 Iroc is "one of the 50!" with a factory 350 they read about, because some GM exec snuck it through some back door loophole, instead of the much more plausible explanation that someone changed $20 worth of stickers or emblems to look cool, or that a seller fed them some BS sales pitch.

 

I agree with Drew that the SPID never lies. Whatever is on that label is what's on the car. It has to match.

So, my theory is that in the early days, a previous owner probably trashed the 10 bolt by curbing the car during a burnout or something crazy like that. They then needed another rear end and being the 1st year of the 10 bolt, probably could only find this 9 bolt from another recently wrecked car. They probably also got lucky getting the 3.45 gears and not the highway gears.

 

Like you both said these are all theories and today's knowledge is no better than earlier.
But the data for some 90 cars having 9 bolts installed , I would like to know as well.
The axle looks to be as old as everything under the car , I would still want to know for my own curiosity.

 

I totally agree with Drew and Scott. They just do not put the wrong rear end in the car from what the SPID says. And your car was built in the 2nd month of 1990 production, so considering how many thousands and thousands of 1990 cars were built before yours, it's not exactly "early". They have the RPO code to know what rear is in the car for ordering parts, etc. Even the brakes are different between the rear ends. If the RPO says GU6, it should have the 10 bolt rear.

 

Ok I'll defer to your expertise.
On a side note, I've been in the car business 24 yrs with Ford , and we still get vehicles in that dont match the window sticker ( all from chicago plant Explorers) Its absolutely ridiculous how often its happened. Ford corrects the mistake for us , but its passing through QC with non matching seats, or extra options. Just Chicago plant has been the problem.
Thanks for the insight on my question 👍

 

I don't think there were 1000's of 90 5spd G92 cars built before sept 89. Only 295 built total right ?
That's what early build I'm referring to, not just random camaro production.

 

If we deduce that a previous owner swapped rear ends, that ends the mystery. An added piece of information, just for the sake of curiosity, would be to verify the axle ratio in the 9 bolt.

 

Wouldn’t there be a date code on the axle? That might help to figure things out.

 

Good idea , any idea where that date code might be stamped ?

 

Would a date code really help since the 9bolt was built in aussie land? I'd think they were probably built in batches and shipped over??

 

The SPID shows GU6. Even if this was some factory deal, as it appears it's wanted to be believed as, how can it be proved? When we had the Norwood meeting years ago, the topic of cars getting "upgrades" was discussed and how it didn't exactly happen due to checks in the process. If it was some mistake or "upgrade" from the factory, how can it be proved? Proving it came that way from the factory and not changed within the first few years by previous owners would would be difficult. The car is nearly 32 years old.

 

Another thing that no body mentioned was to check the calipers.Should have the Aluminum pbr calipers if it’s a later model 9 bolt.The earlier 9 bolts have the cast iron calipers

 

The reason I say this is, although I agree that the SPID never lies, if the axle ratio is not a 3.45 and is, say a 3.27, there is absolutely, positively, no way that unit was factory installed.

And these would be left over MY 1989 units, anyway.

 

Aren't the date codes and whatnot printed on the label stuck to the cover on 9 bolts anyway? Looks covered in undercoating in OP's pics. Mineral spirits or degreaser might make it legible, but it might also damage what's left of the label. Moot point since there's no guarantee the cover is original to the rear. The one time I located and decoded the stampings on a thirdgen rear, the codes didn't match the printed materials anyway. I'm not sure they're all that accurate.

Maybe it's just me, but it's a lot more plausible that the car was damaged in shipping and the dealership slipped a 9-bolt under it to fix the problem, or it was stolen, stripped, and a 9-bolt is what the rebuilder found locally, or any number of other simpler explanations than GM shipped the car with the wrong data on the SPID.

The data available on these cars has NEVER been better than it is right now. The people replying to this thread are more interested in the minute details and smallest oddities of these cars than the people that designed and built them. If it ever happened the way you suspect it did, it'd be documented here if it was documented anywhere. All you can really do now is wait for other people with 90's that have 9 bolts to pop up and add credibility to the idea. It's however much more likely than any documentation and proof that someone will create another thread saying how they heard about how 9-bolts were used in 90, and how that explains that his 92 RS had a 4cyl engine from the factory, or some similarly unrelated stretch of the imagination. Subscribe to the thread and see...

 

I thought about insurance claims and used a contact I have and there's no record of and claims to stolen or recovered.
What is possible is it may have been replaced by dealership for a warranty concern early . If I could find any evidence of damage or replaced parts I wouldn't be as curious.
I'm a bit OCD and like to know back stories . Too many yrs in investigation for me probably.
I appreciate all the feedback from the members here that have been with these cars much longer than I.

 

Or someone simply did a big clutch dump and grenaded the 10 bolt and wanted a better rear end

Original to the car or not, the 9 bolt is a better rear end

 

Do you have a picture of the caliper and caliper backing plates?

 

I have a 1990 Iroc 305/5Speed/.G92 ALSO built in Sep 1989 and it has a 9 bolt. The RPO says it should be a 3.42 diff.

I wondered if someone swapped it .. but also if they used up old stock.

 

I tried to compare the codes on the 9 bolt with my 1989 1LE car and other tags. Wasn't able to decode the numbers (or I gave up too soon). The diff looks like it has been in there since 1990 ... so either a replacement back in the earliest day, or a GM swap.

 

That's interesting!

 

I will see if the date code is still on the Diff. Curious what the build date is ...

The Tag on the the diff is 10142077.

My 1989 car has 10085391. So one is earlier and one is later. I don't have details when they changed the tag number.

Mark.

 

I'm still digging for the answer just for my own curiosity weather GM used 9bolt replacement for warranty claims or these were built with them .
Members that know much more about these things have stated it wasn't possible to be placed on the car without the code being used during production.
To this day , we still get Ford executive demo's from the Ford Auction that have 'extra' options on the vehicle that don't show up on ordering guides . Ford reps can order what they want on their cars they use when they get to a certain level. Their last name is in the bottom of the window sticker , I've seen several with wheels not available or various trim combos we cant duplicate.
I'm happy to see another Sept build 90 has the 9 bolt ! Hopefully more will come to light.

 

I just reached out to the guy I sold my 44k mile, 1990, G92, 5 speed to and asked him to verify which rear end was in the car FOR SURE. (I never paid any attention). RPO says 10 bolt, and it has a 10 bolt in it.

 

Do you remember what the cars assembly date was ?

 

3rd week of December, 1989

 

Ok , thanks. Still could be any number of possibilities obviously. Yours produced in final month , I believe August/September was switch over to 90 production?

 

I think there are a few differences with that example you've been raising. A car having "Platinum" trim wheels on a "Limited" trim car is fairly different than a car having a different rear axle than what the build sheet or SPID shows. One is a marketing deal. The other is more technical. When you get into stuff like the powertrain, that's more involved and you can't just do anything. A different rear axle ratio changes fuel economy numbers, speedometer readings and replacement parts. Also, a car having options that the order guide may not show is very different than a car having options that the SPID or buildsheet don't show. I'd be more interested in the build sheet, than a window sticker that is less technical, to see what the car was built as.

 

That's a very good point. I dont think any drivetrain differences have ever turned up on those exec vehicles as far as my dept would know. I would have to ask service if they have ever seen anything like that, my thought would be no. Thanks for pointing that out, but its worth asking a few seasoned upper mgr service reps I know on the Ford side just for curiosity.

 

https://www.thirdgen.org/forums/faq-...w-about-2.html

 

I also have an early built 90 g92 5-speed and my rpo says it should be a 10 bolt 3.42 But it’s a 9 bolt 3.45 . GU6 is my code but it’s the gm3 rear. I’ve been told every year the earlier built cars get the remaining stock from the previous. It looks all original and never been touched .

 

They did use whatever was handy when the car comes down the line.

Any codes on the axle tube?
Have you taken the cover off to look at numbers on the gears ?
Got pics?

 

Over 30 years lots of 10 bolts were torn up and replaced with 9 bolts because they were said to be a better rear end. Done it myself, this is what happened here. 100%

 

I agree. If they were using left over parts, the RPO will still say what rear end was in it when it left the factory

 

When I started with GM SPO as a Field-Engineer (as 4th-Gens were receiving LS1s) I ask my original Supervisor a stupid amount of questions regarding his time with GM during the Third-Gen Era...

As I am certain many of you already know, Problematic 10-Bolt Diffs, did receive 9-Bolt Diffs through WPC (The Warranty Parts Center) including any other parts needed for the swap.
There were quite a few "Internal Engineering Documents" and publically available "Service Information Documents" regarding this.

We were supposed to attach a Decal, similar to the GM "Recall Complete" Decals...
to the vehicle regarding the WPC Differential Change.

More often than not, these Decals were never installed, or removed by the owner.

Dealers also had the ability to offer the swap as a "Dealer Installed Option".

 

Good info , that could definitely be the case on mine . I’m the third owner and I assumed it was a 10 bolt until I looked into getting a bigger gear and realized I had a 9 bolt car . But my rpo is gu6. I’ve owned a few of these cars and my others had 10 bolts . My build date is 9/89 .

 

Out of curiosity...

Did anyone here receive the Dana-44 Differential under warranty for having issues with the 9-Bolt?
I know that people did... I just have not come across anyone who did, in a very long time.

 

We are having a conversation on my FB page, Thirdgen Expo https://www.facebook.com/groups/thirdgenexpo about the 500 mile '90 IROC which broke a record a couple days ago. SPID says GU5 but has a 9 bolt.

 

https://www.facebook.com/groups/thirdgenexpo/permalink/6309412735741658?comment_id=6334466069902991&reply_comment_id=6334939239855674&notif_id=1662388126364956&notif_t=group_comment&ref=notif

 

I don't think I can share.

 

Probably easier just to link this thread to the ThirdGen Expo FB page, which I'll do.

 

Not sure why we can't share fb stuff but it's interesting to see another car come forward with the 9bolt and the GU 10bolt code

 

And one with super low miles ... with no reason for the Diff to be swapped.