1969 Diff
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Tech Contributor
Joined: Aug 1999
Posts: 15,154
Likes: 3,959
From: Connecticut, USA
1969 Diff
I just finished this diff and wanted to say, depending on the application, you don't have to use the most expensive parts for a car with under 400hp and no abuse. This is a driver in stock condition, the diff is built for that application. It is not your common cookie cutter, one size fits all build sold online as you can see if you know what you're looking at.
Last edited by GTR1999; Nov 20, 2024 at 08:44 AM.
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Nov 1, 2024, 11:30 AM
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,154
Likes: 3,959
From: Connecticut, USA
Thank you for your feedback, I appreciate it.
I think the parts you are referring to under the diff are just engine stand legs, I have it on a stand.
In respect to your 68 BB diff, it uses the same posi pictured. If it is a 3 series gear it uses a 3 series case, a 4 series gear used a 4 series case. Today, there are thick 4 series gears will bolt to a 3 series case. Toms Differentials started the thick 4 series gears years ago, the Chinese companies copied them today. What a surprise.
If you look close at this diff you will see there are some non-stock mods to it. I use them for a reason. The posi case is fully polished and tuned, no spring pack is needed. The ring gear bolts are ARP, and the caps use SHCS after being fit for 001" rock. Your diff, if it was pictured, I would bet would not have these mods. Look at pictures of rebuilt diff's commonly sold, some are good and some a bad, they're all cookie cutter, one level builds. For a car such as this one, the good ones would work. The bad ones fail regardless.
For years guys have overpaid for BB diff's when looking to buy a diff. The myth is they are stronger and better and command more money. The fact is the value in them is really for the guy looking for correct numbers for his restoration. Some take advantage of those guys and jack up the price. The BB diff got the so-called HD axles. They use caps and bolts instead of U-bolts to retain the u-joint. Are they stronger, maybe, but really not by much. You would probably break the joint first. The C3 axles are not as good as C2 axles because they were case hardened and by 50k miles that was worn away, exposing the softer core which rapidly worn down. If left unchecked the axle will grind into the housing, possibly wrecking it. The one advantage to the HD axle in that case is there is no bolt sticking out the back of the yoke to grind into the housing.
BB posi cases were shot peened but it didn't help much as many of them still cracked and imploded. That is why I fully radius, blend, and polish them.
If your diff is not making noise, doesn't leak, you like the performance of it, then all I would do is confirm the axle endplay the next time you check it, you want it ideally between 005-007" but up to 010" is good. However, I would not be surprised to see you have 030" or more. Axle endplay comes from 3 areas within the diff. Just check to see yours are good. Change the oil every 8-10k miles or sooner if you like. For non NCRS cars I tap drain holes, so a diff oil change is 20 minutes or less. I use Lucas 85 -140 gear oil with 2 bottles of the GM additive. You can use 90 wt if you like, you can try other brands of additive as well. What I use I have been using for decades and my customers have as well, many are here. You can use fancy brand names with the additive in it, some work, some don't. I have tried some of those years ago and they didn't work, since I started with the Lucas, I had no reason to change.
I think the parts you are referring to under the diff are just engine stand legs, I have it on a stand.
In respect to your 68 BB diff, it uses the same posi pictured. If it is a 3 series gear it uses a 3 series case, a 4 series gear used a 4 series case. Today, there are thick 4 series gears will bolt to a 3 series case. Toms Differentials started the thick 4 series gears years ago, the Chinese companies copied them today. What a surprise.
If you look close at this diff you will see there are some non-stock mods to it. I use them for a reason. The posi case is fully polished and tuned, no spring pack is needed. The ring gear bolts are ARP, and the caps use SHCS after being fit for 001" rock. Your diff, if it was pictured, I would bet would not have these mods. Look at pictures of rebuilt diff's commonly sold, some are good and some a bad, they're all cookie cutter, one level builds. For a car such as this one, the good ones would work. The bad ones fail regardless.
For years guys have overpaid for BB diff's when looking to buy a diff. The myth is they are stronger and better and command more money. The fact is the value in them is really for the guy looking for correct numbers for his restoration. Some take advantage of those guys and jack up the price. The BB diff got the so-called HD axles. They use caps and bolts instead of U-bolts to retain the u-joint. Are they stronger, maybe, but really not by much. You would probably break the joint first. The C3 axles are not as good as C2 axles because they were case hardened and by 50k miles that was worn away, exposing the softer core which rapidly worn down. If left unchecked the axle will grind into the housing, possibly wrecking it. The one advantage to the HD axle in that case is there is no bolt sticking out the back of the yoke to grind into the housing.
BB posi cases were shot peened but it didn't help much as many of them still cracked and imploded. That is why I fully radius, blend, and polish them.
If your diff is not making noise, doesn't leak, you like the performance of it, then all I would do is confirm the axle endplay the next time you check it, you want it ideally between 005-007" but up to 010" is good. However, I would not be surprised to see you have 030" or more. Axle endplay comes from 3 areas within the diff. Just check to see yours are good. Change the oil every 8-10k miles or sooner if you like. For non NCRS cars I tap drain holes, so a diff oil change is 20 minutes or less. I use Lucas 85 -140 gear oil with 2 bottles of the GM additive. You can use 90 wt if you like, you can try other brands of additive as well. What I use I have been using for decades and my customers have as well, many are here. You can use fancy brand names with the additive in it, some work, some don't. I have tried some of those years ago and they didn't work, since I started with the Lucas, I had no reason to change.
Safety Car
Joined: May 2001
Posts: 4,747
Likes: 1,642
From: Fairfax Virginia
Thank you for your Time and ALL the help you provide to the Forum members!
It is refreshing to see someone who is not trying to sell "everyone" a 1000Hp differential for their Corvette. A stock rebuild for a close to stock Corvette.
What are the parts under the center section in the picture you provided? It looks like something on the bottom of the case, is that normal? I know very little about Differentials other than the basics.
On my 1968 BB Corvette is there anything there I need to know to protect or extend the life of my Differential and the Posi-Traction? I have changed the fluid in the differential and replaced it with fresh gear oil and the Posi additive and everything is quiet since the Chevrolet Dealer rebuilt my Differential as the posi was talking pretty loud after sitting for years in a barn. It was rebuilt back in 1991 and has worked great ever since, Did I get lucky or do the dealers actually know how to rebuild a Differential?
I was not ready to remove the Differential by myself so I had the dealership where a buddy ran the service department. I paid them about ~ $1500 for the rebuild and the only thing they did wrong was they used shorter bolts which caused my rear to jump up sky high. I rebuilt/overhauled the rear leaf spring at the same time and they told me it would slowly drop down back to normal. It did not and I spent a lot of money with Corvette mechanics who did not recognize the spring outer bolts were shorter. A gentleman from VBP told me the answer at Corvettes@Carlisle the next year. He sold me a set of longer bolts and the rear dropped back down and the angle on my half-shafts was corrected.
Thanks again for everything you do! IF my Differential ever needs help I will ship it to you. You do beautiful work and answer the questions so effectively when people need help. I appreciate you and your fine work!
It is refreshing to see someone who is not trying to sell "everyone" a 1000Hp differential for their Corvette. A stock rebuild for a close to stock Corvette.
What are the parts under the center section in the picture you provided? It looks like something on the bottom of the case, is that normal? I know very little about Differentials other than the basics.
On my 1968 BB Corvette is there anything there I need to know to protect or extend the life of my Differential and the Posi-Traction? I have changed the fluid in the differential and replaced it with fresh gear oil and the Posi additive and everything is quiet since the Chevrolet Dealer rebuilt my Differential as the posi was talking pretty loud after sitting for years in a barn. It was rebuilt back in 1991 and has worked great ever since, Did I get lucky or do the dealers actually know how to rebuild a Differential?
I was not ready to remove the Differential by myself so I had the dealership where a buddy ran the service department. I paid them about ~ $1500 for the rebuild and the only thing they did wrong was they used shorter bolts which caused my rear to jump up sky high. I rebuilt/overhauled the rear leaf spring at the same time and they told me it would slowly drop down back to normal. It did not and I spent a lot of money with Corvette mechanics who did not recognize the spring outer bolts were shorter. A gentleman from VBP told me the answer at Corvettes@Carlisle the next year. He sold me a set of longer bolts and the rear dropped back down and the angle on my half-shafts was corrected.
Thanks again for everything you do! IF my Differential ever needs help I will ship it to you. You do beautiful work and answer the questions so effectively when people need help. I appreciate you and your fine work!
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 15,154
Likes: 3,959
From: Connecticut, USA
Thank you for your feedback, I appreciate it.
I think the parts you are referring to under the diff are just engine stand legs, I have it on a stand.
In respect to your 68 BB diff, it uses the same posi pictured. If it is a 3 series gear it uses a 3 series case, a 4 series gear used a 4 series case. Today, there are thick 4 series gears will bolt to a 3 series case. Toms Differentials started the thick 4 series gears years ago, the Chinese companies copied them today. What a surprise.
If you look close at this diff you will see there are some non-stock mods to it. I use them for a reason. The posi case is fully polished and tuned, no spring pack is needed. The ring gear bolts are ARP, and the caps use SHCS after being fit for 001" rock. Your diff, if it was pictured, I would bet would not have these mods. Look at pictures of rebuilt diff's commonly sold, some are good and some a bad, they're all cookie cutter, one level builds. For a car such as this one, the good ones would work. The bad ones fail regardless.
For years guys have overpaid for BB diff's when looking to buy a diff. The myth is they are stronger and better and command more money. The fact is the value in them is really for the guy looking for correct numbers for his restoration. Some take advantage of those guys and jack up the price. The BB diff got the so-called HD axles. They use caps and bolts instead of U-bolts to retain the u-joint. Are they stronger, maybe, but really not by much. You would probably break the joint first. The C3 axles are not as good as C2 axles because they were case hardened and by 50k miles that was worn away, exposing the softer core which rapidly worn down. If left unchecked the axle will grind into the housing, possibly wrecking it. The one advantage to the HD axle in that case is there is no bolt sticking out the back of the yoke to grind into the housing.
BB posi cases were shot peened but it didn't help much as many of them still cracked and imploded. That is why I fully radius, blend, and polish them.
If your diff is not making noise, doesn't leak, you like the performance of it, then all I would do is confirm the axle endplay the next time you check it, you want it ideally between 005-007" but up to 010" is good. However, I would not be surprised to see you have 030" or more. Axle endplay comes from 3 areas within the diff. Just check to see yours are good. Change the oil every 8-10k miles or sooner if you like. For non NCRS cars I tap drain holes, so a diff oil change is 20 minutes or less. I use Lucas 85 -140 gear oil with 2 bottles of the GM additive. You can use 90 wt if you like, you can try other brands of additive as well. What I use I have been using for decades and my customers have as well, many are here. You can use fancy brand names with the additive in it, some work, some don't. I have tried some of those years ago and they didn't work, since I started with the Lucas, I had no reason to change.
I think the parts you are referring to under the diff are just engine stand legs, I have it on a stand.
In respect to your 68 BB diff, it uses the same posi pictured. If it is a 3 series gear it uses a 3 series case, a 4 series gear used a 4 series case. Today, there are thick 4 series gears will bolt to a 3 series case. Toms Differentials started the thick 4 series gears years ago, the Chinese companies copied them today. What a surprise.
If you look close at this diff you will see there are some non-stock mods to it. I use them for a reason. The posi case is fully polished and tuned, no spring pack is needed. The ring gear bolts are ARP, and the caps use SHCS after being fit for 001" rock. Your diff, if it was pictured, I would bet would not have these mods. Look at pictures of rebuilt diff's commonly sold, some are good and some a bad, they're all cookie cutter, one level builds. For a car such as this one, the good ones would work. The bad ones fail regardless.
For years guys have overpaid for BB diff's when looking to buy a diff. The myth is they are stronger and better and command more money. The fact is the value in them is really for the guy looking for correct numbers for his restoration. Some take advantage of those guys and jack up the price. The BB diff got the so-called HD axles. They use caps and bolts instead of U-bolts to retain the u-joint. Are they stronger, maybe, but really not by much. You would probably break the joint first. The C3 axles are not as good as C2 axles because they were case hardened and by 50k miles that was worn away, exposing the softer core which rapidly worn down. If left unchecked the axle will grind into the housing, possibly wrecking it. The one advantage to the HD axle in that case is there is no bolt sticking out the back of the yoke to grind into the housing.
BB posi cases were shot peened but it didn't help much as many of them still cracked and imploded. That is why I fully radius, blend, and polish them.
If your diff is not making noise, doesn't leak, you like the performance of it, then all I would do is confirm the axle endplay the next time you check it, you want it ideally between 005-007" but up to 010" is good. However, I would not be surprised to see you have 030" or more. Axle endplay comes from 3 areas within the diff. Just check to see yours are good. Change the oil every 8-10k miles or sooner if you like. For non NCRS cars I tap drain holes, so a diff oil change is 20 minutes or less. I use Lucas 85 -140 gear oil with 2 bottles of the GM additive. You can use 90 wt if you like, you can try other brands of additive as well. What I use I have been using for decades and my customers have as well, many are here. You can use fancy brand names with the additive in it, some work, some don't. I have tried some of those years ago and they didn't work, since I started with the Lucas, I had no reason to change.
