lzjr88

I just got an 86 IROC from my brother-in-law who let it sit in a barn for the last 10 years and when I was researching the car’s RPO list, the rear axle and came up with a ratio of 3.23 (RPO GU5) and realized that according to the 1986 Camano tech data on the thirdgen homepage that it should have a 3.42 ratio (IROC package RPO B4Z). I defiantly don’t think I have a “limited edition” or “one of one” production, I think it’s an oversight somewhere on GM’s part. Does someone have any insight to the contradiction between RPOs B4Z and GU5, or is the tech data wrong?

grassyflats

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I have not researched your exact predicament although
I know like on my 91 Z28 5.7 they did run out of disc rear ends and installed drums instead even on the G92s
perhaps this is the case for you as well
or an option if you do not solve your question
any other way

yo soy el warg

First of all what engine code do you have on your RPO list? Also, what transmission is on the RPO list? Do you have G80 or G92 on the RPO list?

JamesC

iTrader: (5)

Check the data page again, as you may have misread. BTW, My 85 IROC (B4Z) is equipped with 3.23's (GU5), manual, std. In 86, where IROC are concerned, G92 is the RPO for 3.42's (auto).

JamesC

Drew

iTrader: (58)

Your RPO codes are more important and more accurate then the Tech Data. Verify that the VIN on the SPID matches the VIN on the car. Decode the VIN number, and the RPO codes and that will tell you all you should need to know.

The Tech Data wasn't really intended to be 100% accurate. It was originally written (compiled?) to show the little differences from year to year. The idea was to give everyone a reference. Now it's been around so long and so many people have had their hands in it, it's hard to tell what's accurate. Fortunately, if you've got the correct SPID for your car, it shouldn't really matter if the Tech Data is right or wrong.

JamesC

iTrader: (5)

And if you want absolute verification, simply drop the diff cover and look (when was the last time the gear oil was changed--at least 10 years, and probably more). The following link will provide the info you need for that verification:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

lzjr88

OK, to answer some questions, my engine code is LB9 and my transmission code is MD8 (Transmission, Auto 4 Spd, THM 700R4) and I don’t have codes G80 or G92 (see attached pic). I checked the tech page again and it defiantly says that the IROC with engine LB9 and the auto transmission has a 3.42 rear end. Thanks to JamesC directing me to verify the tech page again, I think I may have stumbled onto the answer. I don’t have code G92 but I do have an IROC, so with that, because I have transmission code MD8 that probably negates the 3.42 ratio issue. What do you think?

my82roc

iTrader: (101)

My 86 Iroc originally had a 3.23 drum rear non posi.The car is an LB9 tpi with 700r4 auto trans just like yours.It has since been swapped out with a 3.27 9 bolt pbr posi disc rear from an 89 gta

scottmoyer

The 3.42 gear was available with the 5 speed cars. The autos got 3.23.