Improving '80 rear end
Thread Starter
Racer
Joined: Mar 2006
Posts: 291
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From: Guantanamo Bay, Cuba (home in Colorado Springs)
Improving '80 rear end
How best to improve the rear diff & suspension on an '80?
There seems to have been a significant design change from '79 to '80.
And on the '80 the u-joints had diffrent designs depending if the car had a manual or automatic transmission.
I'm in the process of a body-off rebuild and the engine going back will be close to 500hp. What & how can I beef up the late C3 rear end to handle this HP?
I was thinking of using diffrent differential yokes; maybe from an earlier C3 rear end, but I don't know what all is interchangable.
Thoughts & recommendations anyone?
Also, who makes alum driveshafts & half shafts for this application?
There seems to have been a significant design change from '79 to '80.
And on the '80 the u-joints had diffrent designs depending if the car had a manual or automatic transmission.
I'm in the process of a body-off rebuild and the engine going back will be close to 500hp. What & how can I beef up the late C3 rear end to handle this HP?
I was thinking of using diffrent differential yokes; maybe from an earlier C3 rear end, but I don't know what all is interchangable.
Thoughts & recommendations anyone?
Also, who makes alum driveshafts & half shafts for this application?
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
I thought about beefing up mine too,but so far with only 10" street tires,I've had no issues with the stock aluminum rear. I changed gears to 3.70's about 10 years ago,otherwise it's still stock and holding up to about 540 horses.My driveshaft is a 3" chromemoly steel,probobly overkill,but was way cheaper than aluminum,and from what I've heard will hold up better.
I gather that the half shafts are the weak link in the back end,and on the 80,I think they're 3 inches stock diameter,again I've had no issues.
Now if I had slicks...............whole different can of worms.
I gather that the half shafts are the weak link in the back end,and on the 80,I think they're 3 inches stock diameter,again I've had no issues.
Now if I had slicks...............whole different can of worms.
Melting Slicks
Joined: Nov 2002
Posts: 2,231
Likes: 7
From: Fort Pierce Florida
If you're ever going to run slicks then you want to change to an older C3 housing. Otherwise, you'll be leaving parts all over the track no matter what you do. It's heavier, but much stronger then the aluminum case. Van Steel sells a conversion kit.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
There is not anything you can do to the 80-82 except a stock rebuild. I've built iron units for guys to replace the aluminum units. They weight 100 lb and can be built much stronger. This is not a common low dollar stock type rebuild and you will need to buy the brackets, 1/2 shafts, spindle yokes, bushings etc to convert. You could get all the parts by shopping around for good used ones and locate a good iron diff. I would recommend highly rebuilding a used diff to eliminate the common weak points and modify them.
Some guys run 400 450 hp through them and they have lasted, others broke bearing caps and housings with the stock 200 hp engines.
Some guys run 400 450 hp through them and they have lasted, others broke bearing caps and housings with the stock 200 hp engines.
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
The 80-82 rear ends are very underrated IMHO. Mine is stock and I put close to 600HP or over 500ft/lbs through it on a daily basis, Dana makes good rear ends. Oh yes I have wide ZR rated sticky tires now too 
I don't rev it to 5 grand and dump the clutch but in any gear with my foot to the floor it gets max torque through it at 4750 RPM. I blew 2 stock transmissions and the rear end it still clicking or should I say still in one piece
I don't rev it to 5 grand and dump the clutch but in any gear with my foot to the floor it gets max torque through it at 4750 RPM. I blew 2 stock transmissions and the rear end it still clicking or should I say still in one piece
Last edited by MotorHead; Jan 29, 2008 at 03:24 PM.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
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From: Graceland in a Not Correctly Restored Stingray
Gary, do you know if TT has an iron or alum diff in his? Either way, it will be interesting to see how long it lasts with the potential power it'll be taking on, if he ever gets done...
Advanced
Joined: Jan 2008
Posts: 88
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From: Ferndale MI
This is a problem I have been fighting for years!!! After the 1st $200+ tow bill from the drag strip I started packing a spare half shaft and the tools to replace it on sight. I had customs set of half shafts made with spicer heavy duty truck U-Joints and this just push the problem in the diff. I finally gave up and now I am in the processes of swapping the frame for a custom jig frame that accepts C-5 suspensions. After this is all said and done it will probably not even go over 50 (lol)!
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Good luck to ya, they closed down a lane at my local dragstrip after a stock C5 blew his rear end and laid down a 1/4 mile of oil at my local strip. I don't go that often but I have seen it happen 3 times to a C5 and once to a stock C6 vert.
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Instructor
Joined: Dec 2005
Posts: 121
Likes: 2
From: Middletown Delaware
This question comes up often. I have seen too many blown rears at the track. I am finishing a 500 hp 383 for my 78. I would like to run sticky tires with the confidence that I won't need a roll back to bring my car home. Does anyone have any suggestions?
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Except for the batwing, Tom's or Henry's Eaton based 12-bolt IRS will take care of most C3 diff issues. BTW, come to find out my Henry's unit may have been built by Tom, as he was probably working there at the time. Don't know if GTR1999 is set up to do those. (Any plans, Gary?)
Problem is, I'm told the 12-bolt won't bolt up to the batwing, but a strengthened 10-bolt will with a little work, if that's worth the effort.
correction - actually it happens that Pepe Estrada collaborated with Henry's Machine Works to design the 12-bolt IRS prior to Pepe becoming Tom's exclusive consultant.
edit - The C3/D44 batwing can be adapted to accept a 12-bolt IRS diff with a spacer/mid-plate to make up for lack of material.
Problem is, I'm told the 12-bolt won't bolt up to the batwing, but a strengthened 10-bolt will with a little work, if that's worth the effort.
correction - actually it happens that Pepe Estrada collaborated with Henry's Machine Works to design the 12-bolt IRS prior to Pepe becoming Tom's exclusive consultant.
edit - The C3/D44 batwing can be adapted to accept a 12-bolt IRS diff with a spacer/mid-plate to make up for lack of material.
Last edited by TheSkunkWorks; Oct 1, 2011 at 09:57 PM.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
I was toying with building a 12 bolt.I have a bare case here to play with. Most street cars will work pretty good with a modified 10 bolt. The 12 bolt ratios start numerically at 373 and go up so the 12 bolts setups for the OD guys may be too steep beyond 373.
The stock iron units bolt up to the 80-82 batwings no problem. You need the iron brackets, 1/2 shaft, etc so it will add up quick to start from scratch.
For the 78 I would at least mod the diff. The clutches, RG bolts, and cap screws would go. You can add a solid sleeve, steel cap, ARP RG bolt, tune & Polish the posi and add heat treated 10-17's to really make a difference. Given enough abuse they all will break. Add solid spicer joints or step up to the the larger joints and Tom's axles. All comes down to money. Many people think a custom build should be the same price as a everyday rebuild and they're no where close to price or quality.
Good luck
The stock iron units bolt up to the 80-82 batwings no problem. You need the iron brackets, 1/2 shaft, etc so it will add up quick to start from scratch.
For the 78 I would at least mod the diff. The clutches, RG bolts, and cap screws would go. You can add a solid sleeve, steel cap, ARP RG bolt, tune & Polish the posi and add heat treated 10-17's to really make a difference. Given enough abuse they all will break. Add solid spicer joints or step up to the the larger joints and Tom's axles. All comes down to money. Many people think a custom build should be the same price as a everyday rebuild and they're no where close to price or quality.
Good luck
Advanced
Joined: Jan 2008
Posts: 88
Likes: 0
From: Ferndale MI
Thread Starter
Racer
Joined: Mar 2006
Posts: 291
Likes: 0
From: Guantanamo Bay, Cuba (home in Colorado Springs)
Diff rebuild time
Still working through the '80 rebuild and finally got around to inspecting the rear end.
The gears look good, however the spider gears shaft has significant wear. And it works like a poor-man's posi-track.
Who can I send this differential off to for a rebuild?
The gears look good, however the spider gears shaft has significant wear. And it works like a poor-man's posi-track.
Who can I send this differential off to for a rebuild?
