today I found out my 1990 5.7 has a factory 9 bolt in it and not the 10 bolt I assumed it had (did not ever look at it to count bolts). This sucks because I bought 10 bolt gears and posi now have to buy new stuff all over again.

Never occurred to me I might have a 9 bolt. I thought 9 bolts were only 305/LB9 up to model year 1989.

anyone heard of a 1990 5.7 with 9 bolt before? Is it just me or is this setup unusual?

 

Your thinking is actually backwards. The 9-bolt was for the factory performance cars... ALL GTAs came with them, even the 305/T5 GTAs. All the '890 TTAs came with them. All the IROCs got them.

Only other option was the Dana 44 that the Firehawks got.

 

No, not a 1990; the last year of it was 89.

The 9-bolt first appeared in 85 Firebirds, then spread to the Camaros in about 87; and was in most of the more performance-oriented ones (TPI) of both sticker packages until its demise.

Sounds like there was some swappage somewhere in your car's past.

 

the build date is aug/89 for the car. an early 90 I suppose, perhaps something odd on the assembly line? 2 owner car, I contacted the first owner he says rear end never touched from purchase to 2004 when I bought it. can't find any info in the RPO list on this.

 

Found this on TGO site

"...85-90 9 bolt equipped f-bodies were available with either standard open differentials or limited slip versions as well as several different ratios including: 2.77, 3.08, 3.27 (G92 w/auto), 3.45 (G92 w/stick), and a few 3.70 ratio's came in some 85 & 86 Firebird's w/L69, stick & G92=Very Rare! ..."

apparently GM also used 9 bolt as warranty replacements for troublesome 10 bolts. So who knows in my case.

btw am upgrading from a 3.27 to a 3.73

 

Yeah the 90 IROCs were all "early" production; Chevy's contract with the Int'l Race Of Champions series to supply cars to their series in exchange for the use of their name, expired on Dec 31 of 89.

Maybe your car just got one of the last of the leftovers from the previous year. Doesn't seem too remarkable, one way or the other. Sorry to hear you have that if you're wanting to upgrade. That makes it just about a PITA.

 

No 9-bolt in my IROC. As near as I've been able to discern, Camaro 10-bolts, 82-86, could be equipped with rear discs. If you wanted discs, 87-89, the rear was a 9-bolt. 90+ 10-bolt. 89-92 cars were equipped with PBR's and larger rotors (I assume the latter is what you have in car).

JamesC

 

Just feel lucky that they are finely making parts for the 9 bolt. When I blew up my original 3.70 9 bolt from my 1985 5.0l H.O t5 my only repair was to replace it. After that rear blew I rebuilt my original with parts I finally found aftermarket. Other wise I love that rear axle, and have not had any problems since.

 

They never stopped making parts for them.. The aussies (where the rear came from) are still using the rear in certain cars over there.

 

Yes, but getting the parts was not easy or cheep! For the money it would have cost it was cheeper to just replace the whole axle.

 

Well the good news is I found a new set of 3.70 gears and they are going in today. It took alot longer to get there than expected and I got 3.70s instead of 3.42s which is ok. I like the 3.7 ratio alot better and I have a . 63 OD.

BTW I have the large rotor aluminum caliper rear disk brakes I think they are 12 inch, definitely factory.

now I have to change the driven gear ratio (again).