Differential work today
Thread Starter
Tech Contributor
Joined: Aug 1999
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From: Connecticut, USA
Differential work today
Today I am writing this thread as a public service to those who think the high-priced shops both local or online- many times recommended here and elsewhere, are their best option for rebuild services.
I recently had a guy bring in a diff that was rebuilt by a well-known vette shop. They do high end expensive paint work and it is fantastic but the specialized mechanical work, not so much. In all honesty I don't know if they did the following work or subbed it out but either way it was shoddy work and I'm sure well over-priced.
The diff in question is a stock 1974 diff. New gears were said to be installed and the diff rebuilt 20 years and less than 5k miles ago. It started making noise and once inspected one of the axles came out of the diff over 3/8", not good. It didn't come out of the diff in the car since the 1/2 shaft was in place.
I inspected it and disassembled it. There were new imported gears installed- back then USA made gears were commonly available, so it was a cheap part used for increased profit.
Here is what I found:
1- 77-79 GM ring gear bolts were used- most likely used. Reusing RG bolts is both cheap and stupid, they are a loaded part. In addition to that, there was no Loctite used. The 77-79 GM bolts replaced the hardened shoulder bolts with hardened lock washers. Many of these bolts backed out in use and wrecked the diff, many were under warranty at the time. These bolts were not fully torqued and would have backed out in use- no question in my mind about it. Cheap or stupid- maybe both.
2-Hole drilled through the boss in the housing. I saw what looked like an impact mark on the casting and once I used a pick I found it was RTV in a drilled hole. The hole was round not rough as a cracked out or impacted hole would look like. Someone at some point drilled through the strut rod bracket hole for a diff drain. I have seen this before and it's a bad idea. Whoever rebuilt the diff had to have seen this too but just used RTV to plug it and it didn't work since the owner said there was oil leaking out the hole. Again, cheap or stupid- take your pick. I will plug the hole and have it professionally welded.
3- I found all the bearings with the exception of one, were NDH and Torrington axle bearings. Those brand names are the original bearing companies used and long gone now. Torrington is still in business but sold off that axle bearing years ago. So how do you rebuild a diff and change out one bearing? The gears were new, meaning the pressed on large pinion bearing had to be removed to install the shim and pressed back on. Cheap and stupid.
4- Axles- the axles are rebuilt axles, they look ok. The snap rings were too thin, not a common size. The loose axle had no snap ring on it, I later found it chewed up in the diff. The other axle still had the thin ring and over 050" endplay- Cheap and stupid.
So, the customer paid top dollar for a rebuilt diff, he got one new bearing and cheap imported gear set- at a time when USA made parts were both available and less than imported parts today. I call that outright stealing.
I see many times blind recommendations made, for places I know the work of and it's bad, yet people don't do their homework and let me tell you, it's no better today than it was 25 years ago when this beautiful job was sold. It's worse, the parts are not as good in some respects, those with the ability to do the work and are honest are fading away or retiring. This shouldn't be the case but it is today, be careful out there. Ask to see the work, ask how the diff or TA or Box will be rebuilt, ask who does the work, and ask for complete documentation of the work- start to finish. If you don't get those answers walk away- no matter what the website shows, of if they are racers, or experts. If they won't show their work it's huge red flag. As this doesn't even cover custom building like I do, this is your average vendor diff for $800-$1500 today.
I recently had a guy bring in a diff that was rebuilt by a well-known vette shop. They do high end expensive paint work and it is fantastic but the specialized mechanical work, not so much. In all honesty I don't know if they did the following work or subbed it out but either way it was shoddy work and I'm sure well over-priced.
The diff in question is a stock 1974 diff. New gears were said to be installed and the diff rebuilt 20 years and less than 5k miles ago. It started making noise and once inspected one of the axles came out of the diff over 3/8", not good. It didn't come out of the diff in the car since the 1/2 shaft was in place.
I inspected it and disassembled it. There were new imported gears installed- back then USA made gears were commonly available, so it was a cheap part used for increased profit.
Here is what I found:
1- 77-79 GM ring gear bolts were used- most likely used. Reusing RG bolts is both cheap and stupid, they are a loaded part. In addition to that, there was no Loctite used. The 77-79 GM bolts replaced the hardened shoulder bolts with hardened lock washers. Many of these bolts backed out in use and wrecked the diff, many were under warranty at the time. These bolts were not fully torqued and would have backed out in use- no question in my mind about it. Cheap or stupid- maybe both.
2-Hole drilled through the boss in the housing. I saw what looked like an impact mark on the casting and once I used a pick I found it was RTV in a drilled hole. The hole was round not rough as a cracked out or impacted hole would look like. Someone at some point drilled through the strut rod bracket hole for a diff drain. I have seen this before and it's a bad idea. Whoever rebuilt the diff had to have seen this too but just used RTV to plug it and it didn't work since the owner said there was oil leaking out the hole. Again, cheap or stupid- take your pick. I will plug the hole and have it professionally welded.
3- I found all the bearings with the exception of one, were NDH and Torrington axle bearings. Those brand names are the original bearing companies used and long gone now. Torrington is still in business but sold off that axle bearing years ago. So how do you rebuild a diff and change out one bearing? The gears were new, meaning the pressed on large pinion bearing had to be removed to install the shim and pressed back on. Cheap and stupid.
4- Axles- the axles are rebuilt axles, they look ok. The snap rings were too thin, not a common size. The loose axle had no snap ring on it, I later found it chewed up in the diff. The other axle still had the thin ring and over 050" endplay- Cheap and stupid.
So, the customer paid top dollar for a rebuilt diff, he got one new bearing and cheap imported gear set- at a time when USA made parts were both available and less than imported parts today. I call that outright stealing.
I see many times blind recommendations made, for places I know the work of and it's bad, yet people don't do their homework and let me tell you, it's no better today than it was 25 years ago when this beautiful job was sold. It's worse, the parts are not as good in some respects, those with the ability to do the work and are honest are fading away or retiring. This shouldn't be the case but it is today, be careful out there. Ask to see the work, ask how the diff or TA or Box will be rebuilt, ask who does the work, and ask for complete documentation of the work- start to finish. If you don't get those answers walk away- no matter what the website shows, of if they are racers, or experts. If they won't show their work it's huge red flag. As this doesn't even cover custom building like I do, this is your average vendor diff for $800-$1500 today.
Drifting
Joined: Oct 2020
Posts: 1,565
Likes: 569
From: Wisconsin
Thank you Gary, for all you do for our hobby! I hope you don’t retire for a while yet, but if you do, I hope you will still “keep an eye” on the goings-on in the industry and keep us making informed decisions on what we do with our cars!
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,114
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From: Connecticut, USA
I will continue on as long as I can get good parts and there is interest in the way I do it. 5-7-10 more years?
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,114
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From: Connecticut, USA
I forgot to mention, the posi was never touched in this diff. It had worn retainers, thrust washers, cross shaft, and the same crappy snowflake clutches that were installed in 1974. The same clutches some still sell and use today, but they are better than the fibers in my opinion.
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
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Cruise-In VIII Veteran
I replaced my side yokes way back when. And I replaced my pinion seal about 10 years ago.
That's all that's ever been done to my diff. Now with 101 thousand miles on her. One day perhaps I should open it up.
All seems to be working as it should. I know, I should have had ring gear bolts back out, and maybe some cracks in there. But if I don't look......
One day I guess I will be looking for guidance.
Just to far to ship.
Hoping your still around.
Me, in my mid 60's and still working on Harley's. With no end in sight.
That's all that's ever been done to my diff. Now with 101 thousand miles on her. One day perhaps I should open it up.
All seems to be working as it should. I know, I should have had ring gear bolts back out, and maybe some cracks in there. But if I don't look......
One day I guess I will be looking for guidance.
Just to far to ship.
Hoping your still around.
Me, in my mid 60's and still working on Harley's. With no end in sight.
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,114
Likes: 3,905
From: Connecticut, USA
I replaced my side yokes way back when. And I replaced my pinion seal about 10 years ago.
That's all that's ever been done to my diff. Now with 101 thousand miles on her. One day perhaps I should open it up.
All seems to be working as it should. I know, I should have had ring gear bolts back out, and maybe some cracks in there. But if I don't look......
One day I guess I will be looking for guidance.
Just to far to ship.
Hoping your still around.
Me, in my mid 60's and still working on Harley's. With no end in sight.
That's all that's ever been done to my diff. Now with 101 thousand miles on her. One day perhaps I should open it up.
All seems to be working as it should. I know, I should have had ring gear bolts back out, and maybe some cracks in there. But if I don't look......
One day I guess I will be looking for guidance.
Just to far to ship.
Hoping your still around.
Me, in my mid 60's and still working on Harley's. With no end in sight.
Ring gear bolts, some last a long-time others didn't make it out of warranty, QC in the 70's was bad.
Sounds like we're about the same age, same generation.
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Joined: Sep 2005
Posts: 20,979
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From: South of giving a damn
St. Jude Donor '11, '17
@GTR1999
Gary, I have a spare 79 diff that I've disassembled. It has an odd assortment of bearings which I've spoken with you about. I suspect a stub axle issue where the bearing and axles were replaced. The axles show no wear and my hardness testing tool shows a Rockwell of over 50. Should I send these axles off to be heat treated, and if so, what language (beside harsh) should I use to make sure the facility knows exactly what I want?
Gary, I have a spare 79 diff that I've disassembled. It has an odd assortment of bearings which I've spoken with you about. I suspect a stub axle issue where the bearing and axles were replaced. The axles show no wear and my hardness testing tool shows a Rockwell of over 50. Should I send these axles off to be heat treated, and if so, what language (beside harsh) should I use to make sure the facility knows exactly what I want?
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Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,114
Likes: 3,905
From: Connecticut, USA
@GTR1999
Gary, I have a spare 79 diff that I've disassembled. It has an odd assortment of bearings which I've spoken with you about. I suspect a stub axle issue where the bearing and axles were replaced. The axles show no wear and my hardness testing tool shows a Rockwell of over 50. Should I send these axles off to be heat treated, and if so, what language (beside harsh) should I use to make sure the facility knows exactly what I want?
Gary, I have a spare 79 diff that I've disassembled. It has an odd assortment of bearings which I've spoken with you about. I suspect a stub axle issue where the bearing and axles were replaced. The axles show no wear and my hardness testing tool shows a Rockwell of over 50. Should I send these axles off to be heat treated, and if so, what language (beside harsh) should I use to make sure the facility knows exactly what I want?
Safety Car
Joined: Nov 2001
Posts: 4,424
Likes: 619
From: northern CA
I have opened up original C2 diff's with well over 100k miles and the axles were near perfect. They thru hardened them. C3 axles no way originals last that long, by 45-50k miles the cast hardening is gone and so it the axle- probably why you replaced yours.
Ring gear bolts, some last a long-time others didn't make it out of warranty, QC in the 70's was bad.
Sounds like we're about the same age, same generation.
Ring gear bolts, some last a long-time others didn't make it out of warranty, QC in the 70's was bad.
Sounds like we're about the same age, same generation.
As a side note, my ‘64 is running a ‘71, 3.08 differential. So far all seems well with the differential unit…..no noise(s) or other issues.
I don’t know how many miles are on this differential as I acquired it used. Are there better present day axles available?
Thanks
John
Thread Starter
Tech Contributor
Joined: Aug 1999
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From: Connecticut, USA
John,
That is a loaded question for me. If I tell what I know I will be in trouble from those selling axles. I have my own method when dealing with axles and I have to do it with every diff I work on. Some are a gamble on quality, some are plain poorly engineered and shouldn't be used, others are imported, and they vary from one to another.
If you have a 71 diff in the car but really an unknown history, you can left it and remove and check it, all depends on what you to do. If it's ok then maybe just drive it.
However, a stock 71 diff has some issues. There were actually 2 cases used in 71, most were the same as the 69-70. They were better than the pre 68's but still not the best. The late 71's got the revision that all 72-79 had- the 10/17 spiders, the better posi case, but weaker clutches. Some were prone to ring gear bolt failure but not as bad as the later C3's. The cases can still be broken but this was the 3rd revision on the case since 1965. All c3 axles are suspect.
That is a loaded question for me. If I tell what I know I will be in trouble from those selling axles. I have my own method when dealing with axles and I have to do it with every diff I work on. Some are a gamble on quality, some are plain poorly engineered and shouldn't be used, others are imported, and they vary from one to another.
If you have a 71 diff in the car but really an unknown history, you can left it and remove and check it, all depends on what you to do. If it's ok then maybe just drive it.
However, a stock 71 diff has some issues. There were actually 2 cases used in 71, most were the same as the 69-70. They were better than the pre 68's but still not the best. The late 71's got the revision that all 72-79 had- the 10/17 spiders, the better posi case, but weaker clutches. Some were prone to ring gear bolt failure but not as bad as the later C3's. The cases can still be broken but this was the 3rd revision on the case since 1965. All c3 axles are suspect.
NCM Grand Opening Veteran
Joined: Sep 2005
Posts: 20,979
Likes: 384
From: South of giving a damn
St. Jude Donor '11, '17
If they are 79 axles, they will have a large center drill hole on the face. Check to see. If there is no hole they are rebuilt. If they are original and the car has under 40k miles then you may be testing the face hardness only. Once that is gone it will be soft, now compare that to say a 65 set of axles with 100k miles on them. They show some face wear, usually a few thousands but they are thru hardened, and they do not have to hardened. Any axle past 67 is suspect.
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,114
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From: Connecticut, USA
no sorry for various reasons I no longer give out a lot of my information as I once did
Melting Slicks
Joined: Nov 2006
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From: Apple Valley, MN
Team Owner
Joined: Jan 2006
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From: Into the Mystic And yet, despite the look on my face, you're still talking TN
St. Jude Donor '09 thru '25
It's such a shame that those of us who don't have the ability or the resources to do that kind of work have to increasingly settle for shoddy work from so called experts now.
And my steering box you rebuilt is just as tight as new still
And my steering box you rebuilt is just as tight as new still
Last edited by Capt. Shark; Nov 10, 2023 at 07:48 AM.
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,114
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From: Connecticut, USA
That was about 6 years ago, time flys.
Safety Car
Joined: Nov 2001
Posts: 4,424
Likes: 619
From: northern CA
John,
That is a loaded question for me. If I tell what I know I will be in trouble from those selling axles. I have my own method when dealing with axles and I have to do it with every diff I work on. Some are a gamble on quality, some are plain poorly engineered and shouldn't be used, others are imported, and they vary from one to another.
If you have a 71 diff in the car but really an unknown history, you can left it and remove and check it, all depends on what you to do. If it's ok then maybe just drive it.
However, a stock 71 diff has some issues. There were actually 2 cases used in 71, most were the same as the 69-70. They were better than the pre 68's but still not the best. The late 71's got the revision that all 72-79 had- the 10/17 spiders, the better posi case, but weaker clutches. Some were prone to ring gear bolt failure but not as bad as the later C3's. The cases can still be broken but this was the 3rd revision on the case since 1965. All c3 axles are suspect.
That is a loaded question for me. If I tell what I know I will be in trouble from those selling axles. I have my own method when dealing with axles and I have to do it with every diff I work on. Some are a gamble on quality, some are plain poorly engineered and shouldn't be used, others are imported, and they vary from one to another.
If you have a 71 diff in the car but really an unknown history, you can left it and remove and check it, all depends on what you to do. If it's ok then maybe just drive it.
However, a stock 71 diff has some issues. There were actually 2 cases used in 71, most were the same as the 69-70. They were better than the pre 68's but still not the best. The late 71's got the revision that all 72-79 had- the 10/17 spiders, the better posi case, but weaker clutches. Some were prone to ring gear bolt failure but not as bad as the later C3's. The cases can still be broken but this was the 3rd revision on the case since 1965. All c3 axles are suspect.
I hope to drop the the differential soon to address a pinion leak and check over the general condition of the unit and stub axles.
John
Race Director
Joined: Mar 2016
Posts: 14,163
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From: Napa Valley California
Gary built my rear differential, trailing arms and steering box.
Beautiful craftsmanship.
Thats what you get from Gary, expert craftsmanship and there isn’t anyone who does it better.
Beautiful craftsmanship.
Thats what you get from Gary, expert craftsmanship and there isn’t anyone who does it better.
Burning Brakes
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From: Green Valley Ca
Bob
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