'81 Iron diff swap
Thread Starter
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
'81 Iron diff swap
I'm going to be swapping and Iron diff into my 81 as my Dana diff wasn't worth rebuilding. I have a diff out of a 72 (I think) that will be going in once I sort out a few issues with it.
What issues am i likely to come across with this?
I have the correct half shafts, strut rod bracket, and adjustable strut rods for this diff, any thing else I'll need?
I get mixed info about the drive shaft. best I can say is it may need to be shortened. I have the factory 4 speed. Can anyone that has done this with this transmission tell me if it needs to be shortened or not?
Going from a 2.72 rear to a 3.36 rear should be fun.
What issues am i likely to come across with this?
I have the correct half shafts, strut rod bracket, and adjustable strut rods for this diff, any thing else I'll need?
I get mixed info about the drive shaft. best I can say is it may need to be shortened. I have the factory 4 speed. Can anyone that has done this with this transmission tell me if it needs to be shortened or not?
Going from a 2.72 rear to a 3.36 rear should be fun.
Racer
Joined: Apr 2014
Posts: 406
Likes: 22
From: Lyons Colorado
I'm going to be swapping and Iron diff into my 81 as my Dana diff wasn't worth rebuilding. I have a diff out of a 72 (I think) that will be going in once I sort out a few issues with it.
What issues am i likely to come across with this?
I have the correct half shafts, strut rod bracket, and adjustable strut rods for this diff, any thing else I'll need?
I get mixed info about the drive shaft. best I can say is it may need to be shortened. I have the factory 4 speed. Can anyone that has done this with this transmission tell me if it needs to be shortened or not?
Going from a 2.72 rear to a 3.36 rear should be fun.
What issues am i likely to come across with this?
I have the correct half shafts, strut rod bracket, and adjustable strut rods for this diff, any thing else I'll need?
I get mixed info about the drive shaft. best I can say is it may need to be shortened. I have the factory 4 speed. Can anyone that has done this with this transmission tell me if it needs to be shortened or not?
Going from a 2.72 rear to a 3.36 rear should be fun.
Thread Starter
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
Thread Starter
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
It's been a while, but I finally got the diff in today. Didn't have any issues with the front mount, it bolted straight up. Driveshaft length seems fine too, just need to swap from a 1310 u-joint to a 1330 at the diff end.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
They do vary from one car to another, some require bracket or DS mods others do not. Good job on the diff you built, it is more detailed and fit then what you would get with a common build.
Melting Slicks
Joined: Jun 2003
Posts: 2,802
Likes: 241
From: Niles, MI
Would you please post pics? I have heard other people say they have done the swap without having issues with the pinion mount location or DS length. I'm curious what the difference is.
Burning Brakes
Joined: Jan 2012
Posts: 943
Likes: 73
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
The job is pretty much a bolt in. The DS might need to be changed but other then that you get the parts from a donor pre 80, build them and install. Antony did a great job with this mod, I saw his work and it is dialed in well beyond a common rebuilt diff, no question.
Burning Brakes
Joined: Jan 2012
Posts: 943
Likes: 73
So a donor could be from 68 to 72?
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
You can use any 63-79 diff and IRS parts. The 73-79 are common and should be in the $300-$400 range out of the car, they are not worth more then that. Looking for a number matching earlier diff would cost more simply because of the numbers but the 73-79's are really not collectibles so more then $400 is pushing it. The 73-79's have the better spiders, posi cases, and housings. Look for a 308 from an automatic low HP car- which is just about all 74-79's.
Thread Starter
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
It's all in now. Got very annoyed putting in the exhaust which was on piece from the headers. Not fun on jack stands. But was able to get it started today and take it for the first drive. Love driving this car. Seems a bit quieter now too. Sorry forgot to take pics before lowering it back to the ground.
Drifting
Joined: Dec 2017
Posts: 1,302
Likes: 226
From: PA
IRS and diff for $300 to $400?
You can use any 63-79 diff and IRS parts. The 73-79 are common and should be in the $300-$400 range out of the car, they are not worth more then that. Looking for a number matching earlier diff would cost more simply because of the numbers but the 73-79's are really not collectibles so more then $400 is pushing it. The 73-79's have the better spiders, posi cases, and housings. Look for a 308 from an automatic low HP car- which is just about all 74-79's.
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
I was referring the to cost of a complete used differential out of a car. The other parts needed would cost more but there are plenty of used parts out there from 72-79 vettes. I know guys that part them out all the time, they make more money parting them out then trying to build and sell them. Typically used diff's need to be rebuilt so the $300-$400 price would be for the complete diff- cover and axles. Some out there ask a lot more so be careful of what you get and look them over good. Paying $300-$400 for a core that has a cracked posi, worn out axles, or ring gear damage is a mistake.
Thread Starter
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland