Differential strength questions
Drifting
Joined: Aug 2001
Posts: 1,606
Likes: 14
From: Vacaville, CA
Last edited by BlackRocket; Sep 8, 2019 at 03:06 AM.
Melting Slicks
Joined: Sep 2016
Posts: 3,004
Likes: 104
From: NC
Isn't there an aftermarket IRS kit out there built to handle the higher power apps?
Or can't a late model Mustang IRS be fabricated to fit a Vette?
I am sure there are plenty of rolled GT-350's in wrecking yards that the parts can be sourced from??
https://www.ebay.com/i/254278064692?...gaApiLEALw_wcB
Or can't a late model Mustang IRS be fabricated to fit a Vette?
I am sure there are plenty of rolled GT-350's in wrecking yards that the parts can be sourced from??
https://www.ebay.com/i/254278064692?...gaApiLEALw_wcB
There are some kits available to bolt in(modifications are ness I'm sure) but the costs I have seen are high. A solid axle swap can be done and is probably the cheapest option if you want a stout rear axle setup.
C3. 427, 4-link, c7 z06
Joined: Sep 2019
Posts: 987
Likes: 200
From: Virginia
I would do a search on this forum, but off hand the Tom's, 12-bolt conversion of the existing setup was one of the few options for the existing, stock setup. Not sure if he is still in business. I have also seen a few custom 9" IRS setups as well as conversions to C4 rear ends. I also bought a Dragvette bracing system at one point but then sold it; never did install it. It was a lot of money for something that didn't strengthen the ring and pinion though.
You can spend a huge amount of money trying to strengthen the existing setup, but I question the bang for the buck. Heavy duty offset trailing arms, cryogenically treated axles, heavier halfshafts with heavier ujoints, halfshaft loops for safety, Dragvette bracing kit, much stiffer spring etc. In the end the ring and pinion and carrier isn't any stronger and you still have halfshafts that move up and down.
David
You can spend a huge amount of money trying to strengthen the existing setup, but I question the bang for the buck. Heavy duty offset trailing arms, cryogenically treated axles, heavier halfshafts with heavier ujoints, halfshaft loops for safety, Dragvette bracing kit, much stiffer spring etc. In the end the ring and pinion and carrier isn't any stronger and you still have halfshafts that move up and down.
David
Last edited by Corvettedave02; Sep 8, 2019 at 08:53 AM.
Tech Contributor
Joined: Aug 1999
Posts: 15,166
Likes: 3,968
From: Connecticut, USA
Tom Watt passed away almost 2 years ago, RIP. However his family is running the business and the parts are available. The good 10-17 x 30 HT spiders are the one part that is gone, there are current 10-17 x 30 spiders on the market but not like those Tom supplied for 40 years.
As mentioned anything can be done all depends on your budget. The newer diffs on the market are in the $10k range I believe, worth more then some complete cars and who knows ROI on these.
Tom's kit is the most reasonable one if you want to keep IRS. If you can do all the work you will save a lot of money but the parts will still cost you about $5k. Even the 9" kits are up there, I think the last one I heard quoted was about $5k all in. If you sub out the work be very careful, there is a recent thread here of a 12 bolt that lasted a good 2500 miles before if came apart in a very bad way.
As mentioned anything can be done all depends on your budget. The newer diffs on the market are in the $10k range I believe, worth more then some complete cars and who knows ROI on these.
Tom's kit is the most reasonable one if you want to keep IRS. If you can do all the work you will save a lot of money but the parts will still cost you about $5k. Even the 9" kits are up there, I think the last one I heard quoted was about $5k all in. If you sub out the work be very careful, there is a recent thread here of a 12 bolt that lasted a good 2500 miles before if came apart in a very bad way.
C3. 427, 4-link, c7 z06
Joined: Sep 2019
Posts: 987
Likes: 200
From: Virginia
Here is one I did on my garage floor about 10 years ago. You do have to modify your tunnel quite a bit between the two boxes behind the seats to make it work though, fyi.
https://www.corvetteforum.com/forums...erformance/237
052-autofab-4-link-9-start-weight-and-pics.html
https://www.corvetteforum.com/forums...erformance/237
052-autofab-4-link-9-start-weight-and-pics.html
Last edited by Corvettedave02; Sep 8, 2019 at 09:22 AM.
Thread Starter
Pro
Joined: Apr 2016
Posts: 512
Likes: 62
Here is one I did on my garage floor about 10 years ago. You do have to modify your tunnel quite a bit between the two boxes behind the seats to make it work though, fyi.
https://www.corvetteforum.com/forums...erformance/237
052-autofab-4-link-9-start-weight-and-pics.html
https://www.corvetteforum.com/forums...erformance/237
052-autofab-4-link-9-start-weight-and-pics.html
Thread Starter
Pro
Joined: Apr 2016
Posts: 512
Likes: 62
Tom Watt passed away almost 2 years ago, RIP. However his family is running the business and the parts are available. The good 10-17 x 30 HT spiders are the one part that is gone, there are current 10-17 x 30 spiders on the market but not like those Tom supplied for 40 years.
As mentioned anything can be done all depends on your budget. The newer diffs on the market are in the $10k range I believe, worth more then some complete cars and who knows ROI on these.
Tom's kit is the most reasonable one if you want to keep IRS. If you can do all the work you will save a lot of money but the parts will still cost you about $5k. Even the 9" kits are up there, I think the last one I heard quoted was about $5k all in. If you sub out the work be very careful, there is a recent thread here of a 12 bolt that lasted a good 2500 miles before if came apart in a very bad way.
As mentioned anything can be done all depends on your budget. The newer diffs on the market are in the $10k range I believe, worth more then some complete cars and who knows ROI on these.
Tom's kit is the most reasonable one if you want to keep IRS. If you can do all the work you will save a lot of money but the parts will still cost you about $5k. Even the 9" kits are up there, I think the last one I heard quoted was about $5k all in. If you sub out the work be very careful, there is a recent thread here of a 12 bolt that lasted a good 2500 miles before if came apart in a very bad way.
Last edited by TheGreek!; Sep 8, 2019 at 09:34 AM.
C3. 427, 4-link, c7 z06
Joined: Sep 2019
Posts: 987
Likes: 200
From: Virginia
I can't get the link to work right, sorry. Do a search for "Autofab 4-link" and you will get several. My whole kit was around $5k, but 10 years ago. I did the work.
Last edited by Corvettedave02; Sep 8, 2019 at 09:39 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
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
C3. 427, 4-link, c7 z06
Joined: Sep 2019
Posts: 987
Likes: 200
From: Virginia
You can get the Autofab bracket kit setup for $1200 and find your own solid axle. Might be the best bang for the buck way to go.
http://autofabcart.net/1968-1982corv...4-linkkit.aspx
http://autofabcart.net/1968-1982corv...4-linkkit.aspx
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,185
Likes: 9,324
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
You can get the Autofab bracket kit setup for $1200 and find your own solid axle. Might be the best bang for the buck way to go.
http://autofabcart.net/1968-1982corv...4-linkkit.aspx
http://autofabcart.net/1968-1982corv...4-linkkit.aspx
That is what I did , By far the best choice. I can transfer weight making the car 23 / 27 / 25 / 25 percent distributed to the 4 corners. Its a front loader making service simple. Its a Fab 9" housing . 4 Link w/disc brakes . Its 100% the best solution of all imop.
Race Director
Joined: Mar 2016
Posts: 14,351
Likes: 8,160
From: Napa Valley California
GTR1999, can build you a quality rear diff, Van Steel is also selling complete units and Mike Dyer is building my rear diff.
The costs to upgrade my rear diff to a HD ten bolt will run around $4,000.00 in parts alone including: all new components on the inside, Tom’s 3 1/2” HD half shafts, u-joints, outer axles, and everything to set up my trailing arms.
Labor for, machining, polishing and assembly is additional.
I’ll be running this behind a 496 / TKO-600RR (.82 od) with 3.08 gearing.
If you go with a 12 bolt you will be stuck using 3.73 or 4.11, or taller rear gears.
The costs to upgrade my rear diff to a HD ten bolt will run around $4,000.00 in parts alone including: all new components on the inside, Tom’s 3 1/2” HD half shafts, u-joints, outer axles, and everything to set up my trailing arms.
Labor for, machining, polishing and assembly is additional.
I’ll be running this behind a 496 / TKO-600RR (.82 od) with 3.08 gearing.
If you go with a 12 bolt you will be stuck using 3.73 or 4.11, or taller rear gears.
Thread Starter
Pro
Joined: Apr 2016
Posts: 512
Likes: 62
GTR1999, can build you a quality rear diff, Van Steel is also selling complete units and Mike Dyer is building my rear diff.
The costs to upgrade my rear diff to a HD ten bolt will run around $4,000.00 in parts alone including: all new components on the inside, Tom’s 3 1/2” HD half shafts, u-joints, outer axles, and everything to set up my trailing arms.
Labor for, machining, polishing and assembly is additional.
I’ll be running this behind a 496 / TKO-600RR (.82 od) with 3.08 gearing.
If you go with a 12 bolt you will be stuck using 3.73 or 4.11, or taller rear gears.
The costs to upgrade my rear diff to a HD ten bolt will run around $4,000.00 in parts alone including: all new components on the inside, Tom’s 3 1/2” HD half shafts, u-joints, outer axles, and everything to set up my trailing arms.
Labor for, machining, polishing and assembly is additional.
I’ll be running this behind a 496 / TKO-600RR (.82 od) with 3.08 gearing.
If you go with a 12 bolt you will be stuck using 3.73 or 4.11, or taller rear gears.
Last edited by TheGreek!; Sep 15, 2019 at 12:51 PM.
Team Owner
Joined: Sep 2002
Posts: 38,322
Likes: 2,071
From: California
If you go with the 12 bolt you won't necessarily be stuck with 3.73 or taller gears, I mean, after all, doesn't a 3.73 gear need a 3 series carrier? If I'm not mistaken you need to go with a 4 series carrier when the gear ratio is 3.90 or higher so the 3.73's should need a 3 series carrier. I don't want tall gears in my car, it has 3.08 gears right now and I want to keep that ratio. I don't want tall gears with a supercharged big block because for one it doesn't need them (the car is frighteningly fast already) and for two the gas mileage is bad enough as it is right now, no need to make it even worse. Also, the speed limit on the highways out here is 75mph and I don't have overdrive. Trying to maintain that speed with a 3.73 or larger gear and no overdrive would suck, it would run hot and eat gas like it's going out of style.
Instructor
Joined: Jan 2004
Posts: 109
Likes: 13
From: Johnson City TN
Has anyone tried Dragvette's rear end? They're offered with either a posi or spool, and they claim the posi build will handle up to 650hp. They're also making their own 30-spline inner axles they claim are stronger than Tom's.
Tech Contributor
Joined: Aug 1999
Posts: 15,166
Likes: 3,968
From: Connecticut, USA
Anyone interested in going to a custom diff has to do their due diligence. Get pictures of all the diff's showing the internals and setup. compare them to each other to see the differences, educate yourself on what parts should be used and ask to see them. Do not go by a build name since some use a common name and cut corners in the build. No pictures, buyer beware, This is not a one size fits all application and those who bought titled builds for a great price most likely don't even know what they got.
Team Owner
Joined: Sep 2002
Posts: 38,322
Likes: 2,071
From: California
Has anyone tried Dragvette's rear end? They're offered with either a posi or spool, and they claim the posi build will handle up to 650hp. They're also making their own 30-spline inner axles they claim are stronger than Tom's.
Thread Starter
Pro
Joined: Apr 2016
Posts: 512
Likes: 62
A 3.73 gear won't work on a 4 series carrier without a ring gear spacer. I don't see any reason why a 3 series carrier can't be put in place of a 4 series carrier, the only difference between them is the thickness of the flange that the ring gear bolts to. They are physically the same size, have the same dimensions, use the same carrier bearings, same spider gears, etc. The only difference is the in the flange for the ring gear. A 2 series carrier has the thickest flange, a 3 series. carrier has a thinner flange, and a 4 series carrier has the thinnest flange because the thickness of the ring gear gets thicker as you go up in gear ratio.
Tech Contributor
Joined: Aug 1999
Posts: 15,166
Likes: 3,968
From: Connecticut, USA
The 12 bolt vette conversion uses a machined 4 series case so it's neither a 4 or 3 series. The 12 bolt R&P is a special grind set, unless you go real old school and machine a stock set of gears as they were originally done 45 years ago. Whlle I have the prints to do that I wouldn't bother. 373 411 or 456 are the only ratios. Some old 355 were made by Tom many years ago but that was pushing it and I don't recall him offering that ratio.
Last edited by GTR1999; Sep 16, 2019 at 07:51 PM.
C3. 427, 4-link, c7 z06
Joined: Sep 2019
Posts: 987
Likes: 200
From: Virginia
Didn't someone post a 12-bolt option for you? Did the deal not work out? Not trying to be nosy, but it seemed like that might work out for you. I would have snatched that up if I hadn't already converted to the 4-link setup.