Differential clutch pack shims
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Advanced
Joined: Jan 2014
Posts: 51
Likes: 3
From: Upstate NY
Differential clutch pack shims
I needed to remove my rear trailing arms to replace the bushings and while I was at it I wanted to remove the endplay from the diff's side yokes. I found all the parts I needed except the differential clutch pack shims. Does anyone know where I can buy just the shims?
1973 Corvette
1973 Corvette
Le Mans Master
Joined: Jun 2019
Posts: 7,658
Likes: 2,470
From: Indiana
my learnings here.. including shims purchased (Bairs i think )
https://www.corvetteforum.com/forums...-advice-2.html
not sure shims get you all the way there..
fyi more advice that helped me below, and man is mine working leak free and great!!!!!!
edit.. a better summary below of @GTR1999 which tells me i am going in the clutches.
So what are the 3 areas that affect endplay? I am sure many out there now know but it comes down to this:
1- axle face wear. You can clearly see the difference in yours but what is the hardness of the better looking one? They have to be hardened and the 72- 79's were not. They will always ride up against the cross shaft in the posi and that is hardened.
2- Posi setup. These are spring loaded posi's, not a bad design but the spring load also compensates for mass production tolerances building these posi's. MOST of the time the posi is not dialed in as it should be, been a problem since 1965 when the first Eatons were used in a vette. It continues to today with the aftermarket units. Those have different clutches and spiders but the design is the same as it was in 1965. I have taken apart new out of the box posi's and once the springs were removed found up to 030" endplay in the side gears. Are they all like that? who knows they are production built unit, same as always. If you tune it like I mentioned above this will dramatically change the endplay in the axles so those rebuilt axles with face dimensions all over the place may actually work. There seems to be a misunderstanding on the clutches too. Most likely because few have actually taken them apart and just pass on information and that sometimes changes as it passes from one to another. The new carbon fiber clutches will in fact wear, you can rub the material off by hand without a lot of pressure. The original steels do not wear out like that, if you want to go cheap you could measure them and I would expect you to find them in the 068 range +/- 001". They have a diamond stamp pattern on them but they were never a sharp diamond like a deep cut knurl on tool handle would be. Will you see a shiny "ring" on them - yes but that shows up when I am seating new clutches and they are not worn out. Years ago I coined the term "snowflake" clutches, it caught on here and people refer to them all the time. They were an attempt in 1972 to stop the posi chatter common with a spring loaded production built posi. they did not work. All they did was make the posi weaker and those that abused the cars ended up breaking the clutches. Look on ebay and there are still people selling these "original" clutches, they are junk. They are also what you have in a 72-79. Bottom line the best posi's are ones that use solid steels, are fully polished, and tuned. Those will go a very long time and out perform a stock spring loaded posi every day of the week.
3- Posi case cross shaft hole. Not as common as the other 2 items but something to check are the bores. They should not have a step in them and should be round. Extreme cases of wear will allow the cross shaft to move once an axle hits it which is at any turn. If the bore wear is loose but not crazy it can be rebored and a 12 bolt cross shaft fit, you would also have to install 12 bolt spider pinion gears and thrust washers. You could also bush it to original size as well but if I am going to do that work I would use the 12 bolt setup. This is something you have to weigh against just replacing the posi case. Replacing a posi case is another story- that I am not going to type out today.
In addition to having lousy axles and clutches, the 72-79's had issues with the ring gear bolts backing out. Around 1977 GM saved a penny by going from a hardened shoulder bolt and lockwasher to a flanged head bolt. Again with a production built item some were good but many were not and the bolts backed out over time. No Loctite was ever used on them. While some of the shoulder bolts also backed out in the earlier cars it was common to see in 72-79's. I rarely have seen it in pre 72's and even less in pre 68's. Same with the axles used from 63 to 71 or so. I have taken apart 100's of them and most of the time, even with over 100k miles, the original axles are still good. In fact, when used with a correctly tuned posi I have to kiss cut them on a surface grinder. This is only a few thousands so they are still hardened and the end play is dialed in to 005-007" where it should be.
Now you know more about these and can make up your mind. You have the diff out, if you have the tools and experience you can slap it together, sub it out, or build it right. Some will tell you these are harder to build then other diff's of the period and that only tells me that person either doesn't know what they're talking about or worse they are just trying to get your money. The principal is the same, you need to set the backlash correctly on what your are working on - a 77 vette or 77 C10, Camaro, etc to have it last and run as quit as possible. If you cut corners in the build it will not last.Last edited by interpon; 01-24-2022 at 03:44 PM.
interpon is online now Report Post
https://www.corvetteforum.com/forums...-advice-2.html
not sure shims get you all the way there..
fyi more advice that helped me below, and man is mine working leak free and great!!!!!!
edit.. a better summary below of @GTR1999 which tells me i am going in the clutches.
So what are the 3 areas that affect endplay? I am sure many out there now know but it comes down to this:
1- axle face wear. You can clearly see the difference in yours but what is the hardness of the better looking one? They have to be hardened and the 72- 79's were not. They will always ride up against the cross shaft in the posi and that is hardened.
2- Posi setup. These are spring loaded posi's, not a bad design but the spring load also compensates for mass production tolerances building these posi's. MOST of the time the posi is not dialed in as it should be, been a problem since 1965 when the first Eatons were used in a vette. It continues to today with the aftermarket units. Those have different clutches and spiders but the design is the same as it was in 1965. I have taken apart new out of the box posi's and once the springs were removed found up to 030" endplay in the side gears. Are they all like that? who knows they are production built unit, same as always. If you tune it like I mentioned above this will dramatically change the endplay in the axles so those rebuilt axles with face dimensions all over the place may actually work. There seems to be a misunderstanding on the clutches too. Most likely because few have actually taken them apart and just pass on information and that sometimes changes as it passes from one to another. The new carbon fiber clutches will in fact wear, you can rub the material off by hand without a lot of pressure. The original steels do not wear out like that, if you want to go cheap you could measure them and I would expect you to find them in the 068 range +/- 001". They have a diamond stamp pattern on them but they were never a sharp diamond like a deep cut knurl on tool handle would be. Will you see a shiny "ring" on them - yes but that shows up when I am seating new clutches and they are not worn out. Years ago I coined the term "snowflake" clutches, it caught on here and people refer to them all the time. They were an attempt in 1972 to stop the posi chatter common with a spring loaded production built posi. they did not work. All they did was make the posi weaker and those that abused the cars ended up breaking the clutches. Look on ebay and there are still people selling these "original" clutches, they are junk. They are also what you have in a 72-79. Bottom line the best posi's are ones that use solid steels, are fully polished, and tuned. Those will go a very long time and out perform a stock spring loaded posi every day of the week.
3- Posi case cross shaft hole. Not as common as the other 2 items but something to check are the bores. They should not have a step in them and should be round. Extreme cases of wear will allow the cross shaft to move once an axle hits it which is at any turn. If the bore wear is loose but not crazy it can be rebored and a 12 bolt cross shaft fit, you would also have to install 12 bolt spider pinion gears and thrust washers. You could also bush it to original size as well but if I am going to do that work I would use the 12 bolt setup. This is something you have to weigh against just replacing the posi case. Replacing a posi case is another story- that I am not going to type out today.
In addition to having lousy axles and clutches, the 72-79's had issues with the ring gear bolts backing out. Around 1977 GM saved a penny by going from a hardened shoulder bolt and lockwasher to a flanged head bolt. Again with a production built item some were good but many were not and the bolts backed out over time. No Loctite was ever used on them. While some of the shoulder bolts also backed out in the earlier cars it was common to see in 72-79's. I rarely have seen it in pre 72's and even less in pre 68's. Same with the axles used from 63 to 71 or so. I have taken apart 100's of them and most of the time, even with over 100k miles, the original axles are still good. In fact, when used with a correctly tuned posi I have to kiss cut them on a surface grinder. This is only a few thousands so they are still hardened and the end play is dialed in to 005-007" where it should be.
Now you know more about these and can make up your mind. You have the diff out, if you have the tools and experience you can slap it together, sub it out, or build it right. Some will tell you these are harder to build then other diff's of the period and that only tells me that person either doesn't know what they're talking about or worse they are just trying to get your money. The principal is the same, you need to set the backlash correctly on what your are working on - a 77 vette or 77 C10, Camaro, etc to have it last and run as quit as possible. If you cut corners in the build it will not last.Last edited by interpon; 01-24-2022 at 03:44 PM.
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Thread Starter
Advanced
Joined: Jan 2014
Posts: 51
Likes: 3
From: Upstate NY
I did not see it on Bairs' site but I did reach out to them to ask.
I found a few inks on CF about this issue with some good info but I must have missed your thread. More good info, thanks.
I found a few inks on CF about this issue with some good info but I must have missed your thread. More good info, thanks.
Le Mans Master
Joined: Jun 2019
Posts: 7,658
Likes: 2,470
From: Indiana
Le Mans Master
Joined: Jun 2019
Posts: 7,658
Likes: 2,470
From: Indiana
anout 1200 miles and zero issues.
weird i swear that when giving a little more gas in a turn the tires chirp a little more than with spring pack.
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