Hey guys, I need to know if a person could swap the 3:73 gears with a 2:73 just by swapping gears. I'm buying an '85 IROC with 3:73 and I want to put the 2:73 out of my '89 iroc into the '85. Or should I just drop the entire rear end and swap them? I just need to know the process of doing this. I'm trying to learn the most that I can here. I really appreciate your help guys!

 

swapping the entire rear end would be much easier and quicker. swapping the internal parts is very involved.

 

Swapping the entire rear would be easier.

 

Carriers are different size with 3.73 vs 2.73. So gear and carrier would have to swap. It is easier to just swap rears.

Now you can buy a 3.73 gear set for a 2 series carrier to swap from 2.73 to 3.73. I did that on my 4th gen trans am 10 bolt

 

If you swap the gears you will also have to swap the differential. The 2.73 fits a 2 series differential and the 3.73 fits a 3 series differential. When swapping gears you must set the pinion depth, backlash and bearing preload. You must know how to read the contact pattern so that you will know what adjustments need to be made to the pinion depth and backlash. This also requires some special tools that the average person doesn't have.

Just swap the complete rear end.

 

awesome, that was exactly what I needed to know, thanks!

I also am going to pull the TPI 350 out of my '89 IROC, rebuild it and drop it into the '85. My '89 was stolen and wrecked so i think it will be easier and cheaper then to repair the body. Will it be at least relatively straight forward to take the engine wiring harness from my '89 and put it into the '85? I expect to come across a few troubles but I cant imagine anything major. The '85 doesnt have an engine, butI'm told it had the 305 TPI and comes with a T5. I assume the T5 to be not original since TPI's didnt come with T5's till 1988.

 

89 irocz was likely a disc brake rear, probably a 9 bolt. It likely had 2.77's and a different style carrier than old 10 bolts so yes you have to swap rears as the parts arent interchangeable.

Watch the brake stuff. If you had disks on the 89 but drums on the 85, grab the proportioning valve too.

Check out austinthirdgen.org for wiring diagrams. 85's were alittle different as far as engine harness goes and maybe even at the firewall dash connector by brake booster

 

The '85 has rear disks as well, so it should be a pretty straight forward swap..well, hopefully haha.

As long as I use the wiring harness from the '89 and put it into the '85, how would the dash connector cause troubles?

 

I'd swap everything from the 89 into the 85 if the 89 is to far gone to repair.

 

It's repairable, but I did the math and found out it would be MUCH cheaper to put everything into the '85 then it would be to fix the body on the '89.

Thanks for the help guys, I appreciate it.

 

Well the pinouts may or may not be different at the c100. If one is an auto and one is a manual it may be different or it may not be. I am not sure. Need to check the diagrams. I am redoin a harness now and need to compare my 89 to an unknown year 85-88 harness

 

Forgive me, but what exactly does that mean?

 

C100 is the connector that plugs into firewall at the brake booster to go to the dash. There are diagrams at austinthirdgen.org that show what each wire is for, so you can see if they are direct swap or not.

Also there are some connections by the ecm that may or may not be different. Just need to see.

 

hm, Interesting. looks like I have some more research to do before I start, haha

 

As Orr mentioned, there is a pair of connections over by the ECM under the dash. Whitish plastic; about 7 pins on one side and 6 on the other? If the 85 was TPI also, they might be identical. If it was carb'd originally with an L69 or LG4, you'll need to make some changes.

 

Thats Y I was saying replace EVERYTHING in the 85 with the stuff from the 89.

Basicly gut the 85 to a shell.

The rear disc on the 85 suck compared to the one on the 89.

 

Thats what ill end up doing, replace everything, paint it and call it good. I have all summer to do it too, so I should be able to get it done. If i can cut a few corners along the way, I certainly will.