C3 differential rebuild question
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Advanced
Joined: Oct 2022
Posts: 56
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From: Orland Park Illinois
C3 differential rebuild question
I’m in the process of rebuilding my differential on my LT1 1971. No problems noted when driving. Winter project to reseal. Found both yokes bad. Found metal sludge in the oil. After cleaning everything all the gears look good. The bearings look good but notice fine lines in the rollers you can’t feel them with your nail. Checked for cracks in the carrier and housing. Not sure what I’m looking for on the posi pack the snow pack looks good no real worn spots. Probably just Change all the bearing seals and posi pack. Where can I find good quality replacement parts. Also is this a good way to go. I hate changing parts that may still be good or superior to the new ones I’m replacing. Thank you for your advice Steve
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Jan 26, 2024, 11:58 AM
Tech Contributor
Joined: Aug 1999
Posts: 15,160
Likes: 3,965
From: Connecticut, USA
Steve, all depends on how you look at it.
Here is what I would do if I owned your 71 LT1. I would drive the car, not take it to a track and beat it up but take it out for the day and drive it a full tank of gas or more. With a 4 speed and LT1 I would use a 370/373 gear, they could have been ordered with a 411 too, but 370 is idea.
So you have the diff out and apart but sounds like you're a little lost on what to do, do a cheap fix or do it right. Please note, I am not calling you cheap, it's just some people will look for the cheap way out and usually that doesn't last long. Again, if it were my car, to be used on the street with some gear pushing at times, this is what I would build.
Here is what I would do if I owned your 71 LT1. I would drive the car, not take it to a track and beat it up but take it out for the day and drive it a full tank of gas or more. With a 4 speed and LT1 I would use a 370/373 gear, they could have been ordered with a 411 too, but 370 is idea.
So you have the diff out and apart but sounds like you're a little lost on what to do, do a cheap fix or do it right. Please note, I am not calling you cheap, it's just some people will look for the cheap way out and usually that doesn't last long. Again, if it were my car, to be used on the street with some gear pushing at times, this is what I would build.
- Keep the housing, its numbers correct- if it is now? if you're not sure check the date codes and stamping. There is no VIN on them.
- Check to see which posi case is in there. Now, here I am not going to go into detail, not because I don't want to help you, but I am tired of helping those who copy my work and sell things based on my work. So, you will have to do some homework, but I will say there were two posi cases used in 1971, anybody out there know? I am not talking about 3 or 4 series cases either.
- If the posi isn't cracked then blend, radius, polish, machine and tune it. I would also cryo the parts.
- Use solid steels.
- USA Timken bearings
- Possibly a steel cap, if I wanted a little extra strength. NOTE- for anyone looking at steel caps. Only the left side needs them. Right side doen't and if you were sold one on the right, as nice as the guy may have been, he clipped you for $300. Other than looking nice,which no one can see, steel right caps are NOT needed.
- ARP Ring Gear bolts no question. The common vendor rebuilds come with the kit bolts, big difference, look for yourself. It is profit over quality. The case has to be prepped for ARP bolts and the hole depth has to be confirmed and possibly addressed. Blindly bolting ARP bolt to a stock posi case may lead to complete differential failure.
- Correct axle bearings, again kit parts are CHEAP, they come with cheap ring gear bolts and cheap caged bearings. They will work, they are not the best.
- Axles- a subject common in all my seminars and those that visit my shop. Some of those guys are on here, do those of you remember what I taught you about the new and rebuilt axles sold today? If I tell what I know about this topic here, I probably would be banned. So again, do your homework and do NOT believe some of what you read on websites. I will say, I set my endplay to 005-007" and the axles I use are the best and few are remachined and none are from China.
- Fit the caps and use SHCS. If you go to a steel cap this will be done, if you stay with the stock caps you need to check them.
Tech Contributor
Joined: Aug 1999
Posts: 15,160
Likes: 3,965
From: Connecticut, USA
Steve, all depends on how you look at it.
Here is what I would do if I owned your 71 LT1. I would drive the car, not take it to a track and beat it up but take it out for the day and drive it a full tank of gas or more. With a 4 speed and LT1 I would use a 370/373 gear, they could have been ordered with a 411 too, but 370 is idea.
So you have the diff out and apart but sounds like you're a little lost on what to do, do a cheap fix or do it right. Please note, I am not calling you cheap, it's just some people will look for the cheap way out and usually that doesn't last long. Again, if it were my car, to be used on the street with some gear pushing at times, this is what I would build.
Here is what I would do if I owned your 71 LT1. I would drive the car, not take it to a track and beat it up but take it out for the day and drive it a full tank of gas or more. With a 4 speed and LT1 I would use a 370/373 gear, they could have been ordered with a 411 too, but 370 is idea.
So you have the diff out and apart but sounds like you're a little lost on what to do, do a cheap fix or do it right. Please note, I am not calling you cheap, it's just some people will look for the cheap way out and usually that doesn't last long. Again, if it were my car, to be used on the street with some gear pushing at times, this is what I would build.
- Keep the housing, its numbers correct- if it is now? if you're not sure check the date codes and stamping. There is no VIN on them.
- Check to see which posi case is in there. Now, here I am not going to go into detail, not because I don't want to help you, but I am tired of helping those who copy my work and sell things based on my work. So, you will have to do some homework, but I will say there were two posi cases used in 1971, anybody out there know? I am not talking about 3 or 4 series cases either.
- If the posi isn't cracked then blend, radius, polish, machine and tune it. I would also cryo the parts.
- Use solid steels.
- USA Timken bearings
- Possibly a steel cap, if I wanted a little extra strength. NOTE- for anyone looking at steel caps. Only the left side needs them. Right side doen't and if you were sold one on the right, as nice as the guy may have been, he clipped you for $300. Other than looking nice,which no one can see, steel right caps are NOT needed.
- ARP Ring Gear bolts no question. The common vendor rebuilds come with the kit bolts, big difference, look for yourself. It is profit over quality. The case has to be prepped for ARP bolts and the hole depth has to be confirmed and possibly addressed. Blindly bolting ARP bolt to a stock posi case may lead to complete differential failure.
- Correct axle bearings, again kit parts are CHEAP, they come with cheap ring gear bolts and cheap caged bearings. They will work, they are not the best.
- Axles- a subject common in all my seminars and those that visit my shop. Some of those guys are on here, do those of you remember what I taught you about the new and rebuilt axles sold today? If I tell what I know about this topic here, I probably would be banned. So again, do your homework and do NOT believe some of what you read on websites. I will say, I set my endplay to 005-007" and the axles I use are the best and few are remachined and none are from China.
- Fit the caps and use SHCS. If you go to a steel cap this will be done, if you stay with the stock caps you need to check them.
Thread Starter
Advanced
Joined: Oct 2022
Posts: 56
Likes: 6
From: Orland Park Illinois
Steve, all depends on how you look at it.
Here is what I would do if I owned your 71 LT1. I would drive the car, not take it to a track and beat it up but take it out for the day and drive it a full tank of gas or more. With a 4 speed and LT1 I would use a 370/373 gear, they could have been ordered with a 411 too, but 370 is idea.
So you have the diff out and apart but sounds like you're a little lost on what to do, do a cheap fix or do it right. Please note, I am not calling you cheap, it's just some people will look for the cheap way out and usually that doesn't last long. Again, if it were my car, to be used on the street with some gear pushing at times, this is what I would build.
Here is what I would do if I owned your 71 LT1. I would drive the car, not take it to a track and beat it up but take it out for the day and drive it a full tank of gas or more. With a 4 speed and LT1 I would use a 370/373 gear, they could have been ordered with a 411 too, but 370 is idea.
So you have the diff out and apart but sounds like you're a little lost on what to do, do a cheap fix or do it right. Please note, I am not calling you cheap, it's just some people will look for the cheap way out and usually that doesn't last long. Again, if it were my car, to be used on the street with some gear pushing at times, this is what I would build.
- Keep the housing, its numbers correct- if it is now? if you're not sure check the date codes and stamping. There is no VIN on them.
- Check to see which posi case is in there. Now, here I am not going to go into detail, not because I don't want to help you, but I am tired of helping those who copy my work and sell things based on my work. So, you will have to do some homework, but I will say there were two posi cases used in 1971, anybody out there know? I am not talking about 3 or 4 series cases either.
- If the posi isn't cracked then blend, radius, polish, machine and tune it. I would also cryo the parts.
- Use solid steels.
- USA Timken bearings
- Possibly a steel cap, if I wanted a little extra strength. NOTE- for anyone looking at steel caps. Only the left side needs them. Right side doen't and if you were sold one on the right, as nice as the guy may have been, he clipped you for $300. Other than looking nice,which no one can see, steel right caps are NOT needed.
- ARP Ring Gear bolts no question. The common vendor rebuilds come with the kit bolts, big difference, look for yourself. It is profit over quality. The case has to be prepped for ARP bolts and the hole depth has to be confirmed and possibly addressed. Blindly bolting ARP bolt to a stock posi case may lead to complete differential failure.
- Correct axle bearings, again kit parts are CHEAP, they come with cheap ring gear bolts and cheap caged bearings. They will work, they are not the best.
- Axles- a subject common in all my seminars and those that visit my shop. Some of those guys are on here, do those of you remember what I taught you about the new and rebuilt axles sold today? If I tell what I know about this topic here, I probably would be banned. So again, do your homework and do NOT believe some of what you read on websites. I will say, I set my endplay to 005-007" and the axles I use are the best and few are remachined and none are from China.
- Fit the caps and use SHCS. If you go to a steel cap this will be done, if you stay with the stock caps you need to check them.
Tech Contributor
Joined: Aug 1999
Posts: 15,160
Likes: 3,965
From: Connecticut, USA
Steve, I don't have time to write a book so most of the custom work I know will go with me, I guess. I also stopped showing everything I do because of low life knock off artist and conmen.
Did you mark the relationship between the spiders before taking them out of the posi? I always put them back the same way. Looking at your pictures you can see the wear on the clutch retainers. Same for the bearing caps, they are line bored so side specific. Even if you did, they still need to be checked.
If that was on my bench, the ring gear bolts, clutches, retainers, axle bearings, shims, and case bearings would all be in the metal scrap bin and replaced with new.
The posi case shows typical surface and edge roughness. If you don't see any cracks you can take the time to polish it like I do and you've seen online. Makes a difference in the life of the diff.
The ring gear should be a press fit on the case, if the gear slides on and free wheels , not good.
Did you mark the relationship between the spiders before taking them out of the posi? I always put them back the same way. Looking at your pictures you can see the wear on the clutch retainers. Same for the bearing caps, they are line bored so side specific. Even if you did, they still need to be checked.
If that was on my bench, the ring gear bolts, clutches, retainers, axle bearings, shims, and case bearings would all be in the metal scrap bin and replaced with new.
The posi case shows typical surface and edge roughness. If you don't see any cracks you can take the time to polish it like I do and you've seen online. Makes a difference in the life of the diff.
The ring gear should be a press fit on the case, if the gear slides on and free wheels , not good.
Thread Starter
Advanced
Joined: Oct 2022
Posts: 56
Likes: 6
From: Orland Park Illinois
Steve, I don't have time to write a book so most of the custom work I know will go with me, I guess. I also stopped showing everything I do because of low life knock off artist and conmen.
Did you mark the relationship between the spiders before taking them out of the posi? I always put them back the same way. Looking at your pictures you can see the wear on the clutch retainers. Same for the bearing caps, they are line bored so side specific. Even if you did, they still need to be checked.
If that was on my bench, the ring gear bolts, clutches, retainers, axle bearings, shims, and case bearings would all be in the metal scrap bin and replaced with new.
The posi case shows typical surface and edge roughness. If you don't see any cracks you can take the time to polish it like I do and you've seen online. Makes a difference in the life of the diff.
The ring gear should be a press fit on the case, if the gear slides on and free wheels , not good.
Did you mark the relationship between the spiders before taking them out of the posi? I always put them back the same way. Looking at your pictures you can see the wear on the clutch retainers. Same for the bearing caps, they are line bored so side specific. Even if you did, they still need to be checked.
If that was on my bench, the ring gear bolts, clutches, retainers, axle bearings, shims, and case bearings would all be in the metal scrap bin and replaced with new.
The posi case shows typical surface and edge roughness. If you don't see any cracks you can take the time to polish it like I do and you've seen online. Makes a difference in the life of the diff.
The ring gear should be a press fit on the case, if the gear slides on and free wheels , not good.
Gary thanks for all the info will keep everyone up dated as we go along.
Instructor
Joined: Apr 2006
Posts: 108
Likes: 22
From: Duvall WA
Hello ALL who are following this post involving one of the “Forums-BEST” Contributors 😊
Gary - Regarding Your post #2 above - - the last numbered subject group, You state —>
“ 10. Fit the caps and use SHCS “
What is SHCS ?
Gary - Regarding Your post #2 above - - the last numbered subject group, You state —>
“ 10. Fit the caps and use SHCS “
What is SHCS ?
Racer
Joined: Jan 2008
Posts: 295
Likes: 58
From: Arvada Colorado
Steve, I don't have time to write a book so most of the custom work I know will go with me, I guess. I also stopped showing everything I do because of low life knock off artist and conmen.
Did you mark the relationship between the spiders before taking them out of the posi? I always put them back the same way. Looking at your pictures you can see the wear on the clutch retainers. Same for the bearing caps, they are line bored so side specific. Even if you did, they still need to be checked.
If that was on my bench, the ring gear bolts, clutches, retainers, axle bearings, shims, and case bearings would all be in the metal scrap bin and replaced with new.
The posi case shows typical surface and edge roughness. If you don't see any cracks you can take the time to polish it like I do and you've seen online. Makes a difference in the life of the diff.
The ring gear should be a press fit on the case, if the gear slides on and free wheels , not good.
Did you mark the relationship between the spiders before taking them out of the posi? I always put them back the same way. Looking at your pictures you can see the wear on the clutch retainers. Same for the bearing caps, they are line bored so side specific. Even if you did, they still need to be checked.
If that was on my bench, the ring gear bolts, clutches, retainers, axle bearings, shims, and case bearings would all be in the metal scrap bin and replaced with new.
The posi case shows typical surface and edge roughness. If you don't see any cracks you can take the time to polish it like I do and you've seen online. Makes a difference in the life of the diff.
The ring gear should be a press fit on the case, if the gear slides on and free wheels , not good.
Melting Slicks
Joined: Nov 2006
Posts: 3,400
Likes: 1,813
From: Apple Valley, MN
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Melting Slicks
Joined: Feb 2018
Posts: 2,325
Likes: 720
From: Marietta GA
Like most Forum Members, I love working on my SB 73 Convertible. But if there is one thing that I have learned at my old age, is not to get in over your head when doing repairs. It seems that besides enormous amounts of time and money, the repair will turn out iffy in most cases. A perfect example, one of my car show buddies has been a office machine repairman for 35 years. He rebuilt is Quad two times and has experienced carb issues the whole 6 years he has owned his C3. I won’t go into detail with all the time and money that he had spent trying to get rid of vapor lock, among other engine issues. In my case, I just sent my Quad to Lars, and had a very knowledgeable mechanic instal it with my OEM Intake Manifold. End of story. On, my buddy installed his manifold two times before he was able to stop the leaks. Maybe C3 rear ends should be left to real pros, like Gtr1999, but some people just like to repair things over and over.
Le Mans Master
Joined: Jun 2019
Posts: 7,649
Likes: 2,466
From: Indiana
I’m in the process of rebuilding my differential on my LT1 1971. No problems noted when driving. Winter project to reseal. Found both yokes bad. Found metal sludge in the oil. After cleaning everything all the gears look good. The bearings look good but notice fine lines in the rollers you can’t feel them with your nail. Checked for cracks in the carrier and housing. Not sure what I’m looking for on the posi pack the snow pack looks good no real worn spots. Probably just Change all the bearing seals and posi pack. Where can I find good quality replacement parts. Also is this a good way to go. I hate changing parts that may still be good or superior to the new ones I’m replacing. Thank you for your advice Steve
and the great advice i got. Including
GTR.
https://www.corvetteforum.com/forums...ay-advice.html
Thread Starter
Advanced
Joined: Oct 2022
Posts: 56
Likes: 6
From: Orland Park Illinois
Just got all my parts axles, clutch plates steel, timken bearings , arp bolts and harden steel cap left side and bolts. Everything looks good except for the side yoke bearings. Will reuse the Torrington’s .
two question at this point. The yokes are remanufactured can’t see any flaws no machining hole on the end of the shafts. Any idea how they were repaired. They don’t look like the one’s on this forum where it looks like a plug.
The steel end cap has to be filed to .001. Not sure what to do here.
thanks
two question at this point. The yokes are remanufactured can’t see any flaws no machining hole on the end of the shafts. Any idea how they were repaired. They don’t look like the one’s on this forum where it looks like a plug.
The steel end cap has to be filed to .001. Not sure what to do here.
thanks
Tech Contributor
Joined: Aug 1999
Posts: 15,160
Likes: 3,965
From: Connecticut, USA
I just answered a post above about differentials and have to say I am getting tired but will make some quick notes. I say this because I am cutting back on my free coaching time.
- You have gone this far, replace the axle bearings and use the correct full complement bearings. I have a box of the caged bearings on my shelf, the next trip to recycling I will have to take them. Torrington hasn't made them in over 20 years. They sold the line to Timken, who later sold the line to KOYO. They are online or from any bearing house.
- ARP Ring Gear bolts are great, I use them all the time. The posi case has to be countersunk and the bolt depth checked and machined if needed. I just installed ARPs in a brand-new Yukon 373 RG. The holes varied, some of the bolts were bottoming out. IF you don't check this or countersink the case they will back out and the diff will break.
- Steel cap- either Tom's or Mark Williams. Unless you machine it yourself. I can machine them but I buy them from Tom's. I still have to machine them. Every housing is different. The pads are not on center, the cap are line bored. Fitting a steel cap requires squaring and then either reboring or grinding the pads. I know how to do it, I have a Bridgeport, Surface grinder and lathe. Attempting to do it with a file is not impossible it is impractical. They take me anywhere from 3-5 hours to correctly fit, The face of the cap needs to be matched and the hole center to center can be off. If you know all this disregard what I said and good luck to you.
- Rebuilt axles, good luck with them. Some are great, some are not. Some are tipped, some are cored not knowing the difference can be an issue and I don't think I am allowed to really state what I mean so that's all I will say.
Thread Starter
Advanced
Joined: Oct 2022
Posts: 56
Likes: 6
From: Orland Park Illinois
Just getting back to the diff this week. So I watched the videos read the articles went to the library. Can’t believe I have so much time vested in putting this rearend together. Must be over thinking it. So I put .040 on each side no way the pinion pin will go through the carrier so I drop to .030 that didn’t work. I have .010 on the ring gear side left and .040 on the right. Turns nice like Tom’s video and pinion pin slides in and out nicely. The original shim stack when I took the posi apart was .010 on the left and .045 on the right. The overall dimensions of the clutch pack and shims on the left is .631 and .665 right. Does this seem right. End play on the shaft is .005 to .008 pushing the shaft outward . Also using thin snap rings. Really want to use the originals they are about .010 thicker. I guess I have to mill the shafts hate do do that. Think the thin snap rings are okay.
thanks for your advise.
thanks for your advise.
Last edited by Catsteven; Mar 2, 2024 at 08:11 PM.
Tech Contributor
Joined: Aug 1999
Posts: 15,160
Likes: 3,965
From: Connecticut, USA
While every differential is different, I can say I must have tuned literally 100's of Eaton vette posi's and never had one with a 010" shim on one side and a 040" on the other. I don't think I ever had any under .025" and that isn't common. Usually they're in the 035-060 range. I just tuned two new Eatons and they were 031 & 030 with one case and .035.037 with the other. They are both balanced, no lash, no endplay, no binding. Run in 800 times in forward and reverse, left and right. The machining on the original cases was not a close as the new cases CNC machined but even so that is a huge difference. Without inspecting it, I would have to say it's not setup correctly, but anything is possible. If it is not dialed in it will either break the spiders or possibly the case, or it will function like an open diff.
Thread Starter
Advanced
Joined: Oct 2022
Posts: 56
Likes: 6
From: Orland Park Illinois
While every differential is different, I can say I must have tuned literally 100's of Eaton vette posi's and never had one with a 010" shim on one side and a 040" on the other. I don't think I ever had any under .025" and that isn't common. Usually they're in the 035-060 range. I just tuned two new Eatons and they were 031 & 030 with one case and .035.037 with the other. They are both balanced, no lash, no endplay, no binding. Run in 800 times in forward and reverse, left and right. The machining on the original cases was not a close as the new cases CNC machined but even so that is a huge difference. Without inspecting it, I would have to say it's not setup correctly, but anything is possible. If it is not dialed in it will either break the spiders or possibly the case, or it will function like an open diff.