72 - 79 Differential differences
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
72 - 79 Differential differences
what are (if any) the differences between a '72 and a '79 differential?
i have a lead on a '79, will get it built up and then just do a weekend swap over into my '72. feasible?
being from downunder, parts will take a while to get here and i don't want the vette off the road for long.
it has taken a long while to even find this diff.
i have a lead on a '79, will get it built up and then just do a weekend swap over into my '72. feasible?
being from downunder, parts will take a while to get here and i don't want the vette off the road for long.
it has taken a long while to even find this diff.
Last edited by riverracer au; Feb 3, 2020 at 05:27 AM. Reason: spelling
Popular Reply
Feb 3, 2020, 09:04 AM
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
Hi guys
72 to 79 differentials are the best foundations to build a good performance diff.
There was not a perfect vette differential made from 63-82, they all have issues-some are pretty poorly made. The worst of the lot are the DANA's use in 63-4 and 80-82.
The 79 diff was the end of the line for the iron diff's and the QC at time was not the best GM offered. I recall 1979 vettes had their share of issues and the diff was one of them.
The housings are the same, the bearing caps very slightly different but not an issue at all.
The rear covers are different, the 78-79 used a 7/16 spring bolt and has a cast in pad where the spring mounts, this is for the different spring used in 78. The 63-77 used 9/16 spring bolts with a flat pad. They both have date codes on them.
The pinion yokes may be different, a 1310 & 1330 yoke were used over the years. Some were swapped out over the years with diff changes. Now if you look in the catalogs you we see the dimensions of the yokes but you don't need to measure anything to find out what you need. Look at the yoke to see how the joint is retained- if u-bolts are used then it's a 1310, if straps and bolts used it is a 1330. The only exceptions would be an aftermarket billet yoke and 63 Grand Sport yoke- I doubt you have either.
The ring and pinion are the same and were about the best. They have a date code on the side of the ring gear and GM stamped them. Also the tooth count is stamped in. The problem with a 78-79 is they went to flanged head RG bolts with no thread locker. Many and I mean many backed out. If you have them replace them with ARP's and use either #271 or 272 Loctite on them. Countersink the case holes as well to seat the ARP's.
The posi cases are the same and very good but they too can crack- so you have to check them closely. If cracked they are junk. The spiders are both 10-17 and the best. The clutches are what coined years ago as snowflakes and are junk-although some vendors still sell them today.
The axles in both are soft faced if original so they should be checked and either replaced or hardened if still in range.
Will the 79 bolt in- yes. Would I use any used diff as is- no way. If it checks out at least replace the weak parts.
72 to 79 differentials are the best foundations to build a good performance diff.
There was not a perfect vette differential made from 63-82, they all have issues-some are pretty poorly made. The worst of the lot are the DANA's use in 63-4 and 80-82.
The 79 diff was the end of the line for the iron diff's and the QC at time was not the best GM offered. I recall 1979 vettes had their share of issues and the diff was one of them.
The housings are the same, the bearing caps very slightly different but not an issue at all.
The rear covers are different, the 78-79 used a 7/16 spring bolt and has a cast in pad where the spring mounts, this is for the different spring used in 78. The 63-77 used 9/16 spring bolts with a flat pad. They both have date codes on them.
The pinion yokes may be different, a 1310 & 1330 yoke were used over the years. Some were swapped out over the years with diff changes. Now if you look in the catalogs you we see the dimensions of the yokes but you don't need to measure anything to find out what you need. Look at the yoke to see how the joint is retained- if u-bolts are used then it's a 1310, if straps and bolts used it is a 1330. The only exceptions would be an aftermarket billet yoke and 63 Grand Sport yoke- I doubt you have either.
The ring and pinion are the same and were about the best. They have a date code on the side of the ring gear and GM stamped them. Also the tooth count is stamped in. The problem with a 78-79 is they went to flanged head RG bolts with no thread locker. Many and I mean many backed out. If you have them replace them with ARP's and use either #271 or 272 Loctite on them. Countersink the case holes as well to seat the ARP's.
The posi cases are the same and very good but they too can crack- so you have to check them closely. If cracked they are junk. The spiders are both 10-17 and the best. The clutches are what coined years ago as snowflakes and are junk-although some vendors still sell them today.
The axles in both are soft faced if original so they should be checked and either replaced or hardened if still in range.
Will the 79 bolt in- yes. Would I use any used diff as is- no way. If it checks out at least replace the weak parts.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
They improved the rear diff somewhere between 69 and 72. Then it stayed the same until the aluminum bat wing setup in 80 or 81. And fits all the way back to 63. Google pics of 80-up Dana 36. That is the one you don't want. Go on ebay for pics of 79-older. Have the guy send you pics of the one he is selling. AU is a small continent. But still a big place. And very little is a half hour away...
Last edited by derekderek; Feb 3, 2020 at 07:19 AM.
Race Director
Joined: Mar 2017
Posts: 11,907
Likes: 4,479
From: Virginia
what are (if any) the differences between a '72 and a '79 differential?
i have a lead on a '79, will get it built up and then just do a weekend swap over into my '72. feasible?
being from downunder, parts will take a while to get here and i don't want the vette off the road for long.
it has taken a long while to even find this diff.
i have a lead on a '79, will get it built up and then just do a weekend swap over into my '72. feasible?
being from downunder, parts will take a while to get here and i don't want the vette off the road for long.
it has taken a long while to even find this diff.
Though I am sure there are internal differences that matter to the rebuilder, what will matter most during the swap are matching the
Last edited by Bikespace; Feb 3, 2020 at 11:18 AM.
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
Hi guys
72 to 79 differentials are the best foundations to build a good performance diff.
There was not a perfect vette differential made from 63-82, they all have issues-some are pretty poorly made. The worst of the lot are the DANA's use in 63-4 and 80-82.
The 79 diff was the end of the line for the iron diff's and the QC at time was not the best GM offered. I recall 1979 vettes had their share of issues and the diff was one of them.
The housings are the same, the bearing caps very slightly different but not an issue at all.
The rear covers are different, the 78-79 used a 7/16 spring bolt and has a cast in pad where the spring mounts, this is for the different spring used in 78. The 63-77 used 9/16 spring bolts with a flat pad. They both have date codes on them.
The pinion yokes may be different, a 1310 & 1330 yoke were used over the years. Some were swapped out over the years with diff changes. Now if you look in the catalogs you we see the dimensions of the yokes but you don't need to measure anything to find out what you need. Look at the yoke to see how the joint is retained- if u-bolts are used then it's a 1310, if straps and bolts used it is a 1330. The only exceptions would be an aftermarket billet yoke and 63 Grand Sport yoke- I doubt you have either.
The ring and pinion are the same and were about the best. They have a date code on the side of the ring gear and GM stamped them. Also the tooth count is stamped in. The problem with a 78-79 is they went to flanged head RG bolts with no thread locker. Many and I mean many backed out. If you have them replace them with ARP's and use either #271 or 272 Loctite on them. Countersink the case holes as well to seat the ARP's.
The posi cases are the same and very good but they too can crack- so you have to check them closely. If cracked they are junk. The spiders are both 10-17 and the best. The clutches are what coined years ago as snowflakes and are junk-although some vendors still sell them today.
The axles in both are soft faced if original so they should be checked and either replaced or hardened if still in range.
Will the 79 bolt in- yes. Would I use any used diff as is- no way. If it checks out at least replace the weak parts.
72 to 79 differentials are the best foundations to build a good performance diff.
There was not a perfect vette differential made from 63-82, they all have issues-some are pretty poorly made. The worst of the lot are the DANA's use in 63-4 and 80-82.
The 79 diff was the end of the line for the iron diff's and the QC at time was not the best GM offered. I recall 1979 vettes had their share of issues and the diff was one of them.
The housings are the same, the bearing caps very slightly different but not an issue at all.
The rear covers are different, the 78-79 used a 7/16 spring bolt and has a cast in pad where the spring mounts, this is for the different spring used in 78. The 63-77 used 9/16 spring bolts with a flat pad. They both have date codes on them.
The pinion yokes may be different, a 1310 & 1330 yoke were used over the years. Some were swapped out over the years with diff changes. Now if you look in the catalogs you we see the dimensions of the yokes but you don't need to measure anything to find out what you need. Look at the yoke to see how the joint is retained- if u-bolts are used then it's a 1310, if straps and bolts used it is a 1330. The only exceptions would be an aftermarket billet yoke and 63 Grand Sport yoke- I doubt you have either.
The ring and pinion are the same and were about the best. They have a date code on the side of the ring gear and GM stamped them. Also the tooth count is stamped in. The problem with a 78-79 is they went to flanged head RG bolts with no thread locker. Many and I mean many backed out. If you have them replace them with ARP's and use either #271 or 272 Loctite on them. Countersink the case holes as well to seat the ARP's.
The posi cases are the same and very good but they too can crack- so you have to check them closely. If cracked they are junk. The spiders are both 10-17 and the best. The clutches are what coined years ago as snowflakes and are junk-although some vendors still sell them today.
The axles in both are soft faced if original so they should be checked and either replaced or hardened if still in range.
Will the 79 bolt in- yes. Would I use any used diff as is- no way. If it checks out at least replace the weak parts.
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
not a lot of 2nd hand stuff or vette wreckers around down this way, so waiting/checking the classifieds gets very tiresome.
thanks Gary for you detailed response
that's the plan why i'm looking at another diff, have it re-built / change ratio and then do a swap and keep my original unit.
Racer
Joined: Jan 2017
Posts: 496
Likes: 153
From: San Francisco Bay Area
Hi guys
72 to 79 differentials are the best foundations to build a good performance diff.
There was not a perfect vette differential made from 63-82, they all have issues-some are pretty poorly made. The worst of the lot are the DANA's use in 63-4 and 80-82.
The 79 diff was the end of the line for the iron diff's and the QC at time was not the best GM offered. I recall 1979 vettes had their share of issues and the diff was one of them.
The housings are the same, the bearing caps very slightly different but not an issue at all.
The rear covers are different, the 78-79 used a 7/16 spring bolt and has a cast in pad where the spring mounts, this is for the different spring used in 78. The 63-77 used 9/16 spring bolts with a flat pad. They both have date codes on them.
The pinion yokes may be different, a 1310 & 1330 yoke were used over the years. Some were swapped out over the years with diff changes. Now if you look in the catalogs you we see the dimensions of the yokes but you don't need to measure anything to find out what you need. Look at the yoke to see how the joint is retained- if u-bolts are used then it's a 1310, if straps and bolts used it is a 1330. The only exceptions would be an aftermarket billet yoke and 63 Grand Sport yoke- I doubt you have either.
The ring and pinion are the same and were about the best. They have a date code on the side of the ring gear and GM stamped them. Also the tooth count is stamped in. The problem with a 78-79 is they went to flanged head RG bolts with no thread locker. Many and I mean many backed out. If you have them replace them with ARP's and use either #271 or 272 Loctite on them. Countersink the case holes as well to seat the ARP's.
The posi cases are the same and very good but they too can crack- so you have to check them closely. If cracked they are junk. The spiders are both 10-17 and the best. The clutches are what coined years ago as snowflakes and are junk-although some vendors still sell them today.
The axles in both are soft faced if original so they should be checked and either replaced or hardened if still in range.
Will the 79 bolt in- yes. Would I use any used diff as is- no way. If it checks out at least replace the weak parts.
72 to 79 differentials are the best foundations to build a good performance diff.
There was not a perfect vette differential made from 63-82, they all have issues-some are pretty poorly made. The worst of the lot are the DANA's use in 63-4 and 80-82.
The 79 diff was the end of the line for the iron diff's and the QC at time was not the best GM offered. I recall 1979 vettes had their share of issues and the diff was one of them.
The housings are the same, the bearing caps very slightly different but not an issue at all.
The rear covers are different, the 78-79 used a 7/16 spring bolt and has a cast in pad where the spring mounts, this is for the different spring used in 78. The 63-77 used 9/16 spring bolts with a flat pad. They both have date codes on them.
The pinion yokes may be different, a 1310 & 1330 yoke were used over the years. Some were swapped out over the years with diff changes. Now if you look in the catalogs you we see the dimensions of the yokes but you don't need to measure anything to find out what you need. Look at the yoke to see how the joint is retained- if u-bolts are used then it's a 1310, if straps and bolts used it is a 1330. The only exceptions would be an aftermarket billet yoke and 63 Grand Sport yoke- I doubt you have either.
The ring and pinion are the same and were about the best. They have a date code on the side of the ring gear and GM stamped them. Also the tooth count is stamped in. The problem with a 78-79 is they went to flanged head RG bolts with no thread locker. Many and I mean many backed out. If you have them replace them with ARP's and use either #271 or 272 Loctite on them. Countersink the case holes as well to seat the ARP's.
The posi cases are the same and very good but they too can crack- so you have to check them closely. If cracked they are junk. The spiders are both 10-17 and the best. The clutches are what coined years ago as snowflakes and are junk-although some vendors still sell them today.
The axles in both are soft faced if original so they should be checked and either replaced or hardened if still in range.
Will the 79 bolt in- yes. Would I use any used diff as is- no way. If it checks out at least replace the weak parts.
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Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
Thanks guys.
I prefer to pass along information as no one ever helped me 42 years ago when I started with these cars. I hold free seminars for corvette owners, ( Rebuilders and vendors are not welcome thank you), to teach them how to build nothing but the best units. I don't mind helping someone if I can, I just don't like the lowlifes that take my info for their own profit then cut the procedures to add to their gain while letting their customer think they are getting the best build for a discount. Many of you out there have been taken and don't even know it. I hear there is some ocean beach front property in AZ for dirt cheap for those guys.
Back to your questions
The 72 & 79 covers will bolt on to any 63-79 iron diff, it is the spring mount that changed in 78.
The best clutch plates to use?
That depends on who you talk to. If it's someone who sells fiber coated clutches or still wants to sell you weak junk snowflakes you will get them as a reference. Me, I only use the solid steels, still available from any Eaton distributor.
Being in Oz I guess you are limited although I have some buddies there running my work, they might be a resource for you but I don't know if you are near them. Considering the size of Oz that might be asking if I am close to someone in LA from CT. I strongly suggest you do your homework when it comes to building a vette diff or having it built. I can write a book on what I have seen and repaired over the years. I have taught guys worldwide on how to do it though so if you have access to good tools, measuring tools, and a toolroom you might be able to do it yourself. You won't have anyone to blame for it but yourself and if you follow the procedures, have a lot of patience, will build a diff better then what you will get. However, you have to be the judge if that is what you want to do. The threads on rebuilding diff's I wrote here are over 10 years old now and I don't even know if they are still here. I don't go into great detail like I once did or post as much as I once did. If you think you want to do this send me an email and I will get you the link to my more current info with a lot of pictures to help you.
Good luck brother!
I prefer to pass along information as no one ever helped me 42 years ago when I started with these cars. I hold free seminars for corvette owners, ( Rebuilders and vendors are not welcome thank you), to teach them how to build nothing but the best units. I don't mind helping someone if I can, I just don't like the lowlifes that take my info for their own profit then cut the procedures to add to their gain while letting their customer think they are getting the best build for a discount. Many of you out there have been taken and don't even know it. I hear there is some ocean beach front property in AZ for dirt cheap for those guys.
Back to your questions
The 72 & 79 covers will bolt on to any 63-79 iron diff, it is the spring mount that changed in 78.
The best clutch plates to use?
That depends on who you talk to. If it's someone who sells fiber coated clutches or still wants to sell you weak junk snowflakes you will get them as a reference. Me, I only use the solid steels, still available from any Eaton distributor.
Being in Oz I guess you are limited although I have some buddies there running my work, they might be a resource for you but I don't know if you are near them. Considering the size of Oz that might be asking if I am close to someone in LA from CT. I strongly suggest you do your homework when it comes to building a vette diff or having it built. I can write a book on what I have seen and repaired over the years. I have taught guys worldwide on how to do it though so if you have access to good tools, measuring tools, and a toolroom you might be able to do it yourself. You won't have anyone to blame for it but yourself and if you follow the procedures, have a lot of patience, will build a diff better then what you will get. However, you have to be the judge if that is what you want to do. The threads on rebuilding diff's I wrote here are over 10 years old now and I don't even know if they are still here. I don't go into great detail like I once did or post as much as I once did. If you think you want to do this send me an email and I will get you the link to my more current info with a lot of pictures to help you.
Good luck brother!
Last edited by GTR1999; Feb 4, 2020 at 06:52 AM.
Drifting
Joined: Aug 2015
Posts: 1,939
Likes: 477
From: NSW, Australia
C3 of Year Finalist (track prepared) 2019
Riverracer - I'm in Australia, I ordered all my diff bits from Summit when I rebuilt/upgraded my diff. I did it myself and it's worked great so far. There's some really good threads about how to do it on here, and check out Tom's videos on youtube for the "clutch tuning" if you want to eliminate the springs too. Makes for a a much more progressive diff that as a side benefit also drives nicer/smoother on the street and in parking lots etc, but still locks up very effectively when driven hard.
Solid steel clutches: https://www.summitracing.com/parts/ETN-29403-00S?
Ring gear bolts: https://www.summitracing.com/parts/arp-230-3001/
Bearings/gasket/seals etc: https://www.summitracing.com/parts/rat-3016k/
Solid pinion spacer: https://www.summitracing.com/parts/rat-4110/
Pinion tool: https://www.summitracing.com/parts/rat-18002/
Yokes are available from a number of suppliers, on Garys recommendations I bought "reconditioned" (old yokes with hardened caps fitted) rather than new. Hope it helps.
Solid steel clutches: https://www.summitracing.com/parts/ETN-29403-00S?
Ring gear bolts: https://www.summitracing.com/parts/arp-230-3001/
Bearings/gasket/seals etc: https://www.summitracing.com/parts/rat-3016k/
Solid pinion spacer: https://www.summitracing.com/parts/rat-4110/
Pinion tool: https://www.summitracing.com/parts/rat-18002/
Yokes are available from a number of suppliers, on Garys recommendations I bought "reconditioned" (old yokes with hardened caps fitted) rather than new. Hope it helps.
Last edited by Metalhead140; Feb 4, 2020 at 08:59 PM.
Race Director
Joined: Nov 2018
Posts: 13,170
Likes: 78
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
The steel clutches were used in 63-79 Dana & Eaton posi's. The Dana's used a different type then the Eaton's. The tabs on the Dana clutches would break off. The Eaton clutches are much better.
The Eatons were used in 65 to 79, one of the issues they were and are known for is clutch chatter. This varies from mild to very hard but was always a complaint. Various oil additives were used to "treat" the problem, the GM additive working about the best. So to deal with it the clutch design was changed in 1972 to slotted clutches. I started calling them "snowflakes" and the name caught on here years ago. The snowflakes were designed to allow more oil/additive in between them to stop the chattering. Did it work? no. It only made them weaker and with enough abuse they broke into pieces. The solid steels don't break and if they are correctly setup last long and chattering is not an issue. If not setup correctly they will chatter. The most recent attempt to stop chattering was the use of fiber coated clutches with huge springs. This is what comes in the new loaded posi's, I just got one and rebuilt it. Yes I rebuilt a brand new posi. What is not said about them is there is one less clutch & plate per side in order to get them in the. The fiber material does look better then the junk I first saw years ago when I opened one up, the spiders are smaller in size then the 10-17's that were used. Smaller in diameter and small tooth contact area but I was able to tune them with new solid steels. I steel won't use the fibers.
Did I answer your question? There is no cost savings using fiber clutches, no sense in still using snowflakes, leave the best at a reasonable price. The 80-82 Dana does not use any of these.
The Eatons were used in 65 to 79, one of the issues they were and are known for is clutch chatter. This varies from mild to very hard but was always a complaint. Various oil additives were used to "treat" the problem, the GM additive working about the best. So to deal with it the clutch design was changed in 1972 to slotted clutches. I started calling them "snowflakes" and the name caught on here years ago. The snowflakes were designed to allow more oil/additive in between them to stop the chattering. Did it work? no. It only made them weaker and with enough abuse they broke into pieces. The solid steels don't break and if they are correctly setup last long and chattering is not an issue. If not setup correctly they will chatter. The most recent attempt to stop chattering was the use of fiber coated clutches with huge springs. This is what comes in the new loaded posi's, I just got one and rebuilt it. Yes I rebuilt a brand new posi. What is not said about them is there is one less clutch & plate per side in order to get them in the. The fiber material does look better then the junk I first saw years ago when I opened one up, the spiders are smaller in size then the 10-17's that were used. Smaller in diameter and small tooth contact area but I was able to tune them with new solid steels. I steel won't use the fibers.
Did I answer your question? There is no cost savings using fiber clutches, no sense in still using snowflakes, leave the best at a reasonable price. The 80-82 Dana does not use any of these.
Last edited by GTR1999; Feb 14, 2020 at 08:13 PM.
Race Director
Joined: Nov 2018
Posts: 13,170
Likes: 78
The steel clutches were used in 63-79 Dana & Eaton posi's. The Dana's used a different type then the Eaton's. The tabs on the Dana clutches would break off. The Eaton clutches are much better.
The Eatons were used in 65 to 79, one of the issues they were and are known for is clutch chatter. This varies from mild to very hard but was always a complaint. Various oil additives were used to "treat" the problem, the GM additive working about the best. So to deal with it the clutch design was changed in 1972 to slotted clutches. I started calling them "snowflakes" and the name caught on here years ago. The snowflakes were designed to allow more oil/additive in between them to stop the chattering. Did it work? no. It only made them weaker and with enough abuse they broke into pieces. The solid steels don't break and if they are correctly setup last long and chattering is not an issue. If not setup correctly they will chatter. The most recent attempt to stop chattering was the use of fiber coated clutches with huge springs. This is what comes in the new loaded posi's, I just got one and rebuilt it. Yes I rebuilt a brand new posi. What is not said about them is there is one less clutch & plate per side in order to get them in the. The fiber material does look better then the junk I first saw years ago when I opened one up, the spiders are smaller in size then the 10-17's that were used. Smaller in diameter and small tooth contact area but I was able to tune them with new solid steels. I steel won't use the fibers.
Did I answer your question? There is no cost savings using fiber clutches, no sense in still using snowflakes, leave the best at a reasonable price. The 80-82 Dana does not use any of these.
The Eatons were used in 65 to 79, one of the issues they were and are known for is clutch chatter. This varies from mild to very hard but was always a complaint. Various oil additives were used to "treat" the problem, the GM additive working about the best. So to deal with it the clutch design was changed in 1972 to slotted clutches. I started calling them "snowflakes" and the name caught on here years ago. The snowflakes were designed to allow more oil/additive in between them to stop the chattering. Did it work? no. It only made them weaker and with enough abuse they broke into pieces. The solid steels don't break and if they are correctly setup last long and chattering is not an issue. If not setup correctly they will chatter. The most recent attempt to stop chattering was the use of fiber coated clutches with huge springs. This is what comes in the new loaded posi's, I just got one and rebuilt it. Yes I rebuilt a brand new posi. What is not said about them is there is one less clutch & plate per side in order to get them in the. The fiber material does look better then the junk I first saw years ago when I opened one up, the spiders are smaller in size then the 10-17's that were used. Smaller in diameter and small tooth contact area but I was able to tune them with new solid steels. I steel won't use the fibers.
Did I answer your question? There is no cost savings using fiber clutches, no sense in still using snowflakes, leave the best at a reasonable price. The 80-82 Dana does not use any of these.
Tech Contributor
Joined: Aug 1999
Posts: 15,136
Likes: 3,939
From: Connecticut, USA
The clutches are steel not organic like a brake pad or trans clutch. They do not wear as much as you might expect, maybe 001-003" on high mileage units. Now the soft faces axles used from 72-79 do wear and the metal is floating around inside, if the diff has been PM'd on a regular basis a lot of it will be removed. However, there is a greater risk of damage from a soft axle crashing into the housing then wrecking the gears from dirty oil. Now the fiber coated clutches are a different story.