C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

'81 Iron diff swap

 
Old 08-18-2017, 02:43 AM
  #1  
Antz81
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Default '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.
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Old 08-19-2017, 10:54 AM
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Originally Posted by Antz81 View Post
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.
I did this swap on my '82 and had to modify the front differential mounting bracket, it was about 3/8 of an inch long and didn't line up with the mounting hole on the crossmember. I also had to modify my exhaust where it runs under the differential because there were clearance issues there. I'm happy with the results.
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Old 08-20-2017, 10:51 AM
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Here's the problem you'll run into.











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Old 08-20-2017, 10:56 AM
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And here's why.







The pencil line on the Dana 44 diff (above the pinion mount hole) is the top of the Eaton pinion mount hole.

Last edited by Kid Vette; 12-07-2017 at 10:22 PM.
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Old 08-20-2017, 11:20 AM
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And as you can see from the pics, you'll need a longer driveshaft.
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Old 08-20-2017, 11:56 AM
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Originally Posted by Kid Vette View Post
And as you can see from the pics, you'll need a longer driveshaft.
Good info, I had a new driveshaft made when I swapped mine and kind of forgot.
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Old 08-20-2017, 12:41 PM
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Originally Posted by Kid Vette View Post
And as you can see from the pics, you'll need a longer driveshaft.
thanks. I'd always heard shorter, but i can see that was clearly wrong.
any idea on how much longer?

Last edited by Antz81; 08-20-2017 at 12:43 PM.
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Old 12-07-2017, 01:01 AM
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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.
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Old 12-07-2017, 08:40 AM
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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.
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Old 12-07-2017, 10:45 PM
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Originally Posted by Antz81 View Post
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.
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.
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Old 12-09-2017, 02:31 PM
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Originally Posted by GTR1999 View Post
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.
Any chance this iron diff is a direct swap into a 4 speed 80?
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Old 12-09-2017, 03:43 PM
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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.
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Old 12-09-2017, 08:58 PM
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Originally Posted by GTR1999 View Post
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.
So a donor could be from 68 to 72?
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Old 12-10-2017, 04:21 PM
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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.
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Old 12-14-2017, 11:58 PM
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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.
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Old 12-24-2017, 10:56 AM
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Default IRS and diff for $300 to $400?

Originally Posted by GTR1999 View Post
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.
I may be looking at this replacement too for my '80. Concerning the cost I just want to be sure I got it right that max $400 would be for both the IRS and Diff. Thanks,
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Old 12-24-2017, 02:46 PM
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Originally Posted by vince vette 2 View Post
I may be looking at this replacement too for my '80. Concerning the cost I just want to be sure I got it right that max $400 would be for both the IRS and Diff. Thanks,
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.
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Old 12-24-2017, 04:58 PM
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So the Batwing will bolt straight up to the older diff?
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Old 12-24-2017, 05:01 PM
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Originally Posted by havesometo View Post
So the Batwing will bolt straight up to the older diff?
Yes. Bolts straight up. But remember the batwing only has 6 bolt holes not the 8 that the older covers had. So I chose to ensure that the bolts I used were as long as possible going into the diff.
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