Differential Axle Question

**Tim T.** · December 5, 2015, 10:48 AM

Re: Differential Axle Question

Gary,
I posted over there for you
Tim

**Timothy B.** · December 5, 2015, 01:03 PM

Re: Differential Axle Question

Now I know why the rebuilder (and seller) of my 63 axle wanted to get his hands on the original 1964 rear pumpkin that was in the car. There is very little in/out movement of the stub axles especially with a new center pin.

Gary, when you spot face the ends of these axles does this remove the hardening treatment?

**Jason S.** · December 5, 2015, 05:46 PM

Re: Differential Axle Question

Gary,
I posted a thread today regarding rear diff questions I have pertaining to my '63. Perhaps you have some insight. My main question was:

My car - a '63 SWC - currently has a 4.11 rear gear but it appears that the rear diff carrier is original to the car and was a code "CF" 4.56.
It appears that Diff rebuild kits and rebuild services are widely available for '65-'79 cars - but not '63-'64s. Comments like "....cannot rebuild 1963-1964 Corvette differentials due to a lack of rebuild components for their positraction carriers...." seem common. Do you know what is NOT being reproduced for the '63-'64 Diff, and what the option for rebuilding is?

**Gary R.** · December 5, 2015, 09:20 PM

Re: Differential Axle Question

Hi Guys
Sorry for getting back late to you, we were celebrating my mom's 100th birthday today. I used to let her take my 69 4 speed or my 72 automatic out for a ride years ago!

Tim T- Thank you for posting over there, possibly it will help someone but from what I have seen posted there on diff lately I don't know.

Tim B- The 63-64 posi diff's were not all that good to be honest- but the axles were good. In reference to what I do, I grind the face if needed on a surface grinder. With a stock posi setup with the springs and with common rebuilt posi's the end play is all over the place. I had a guy call me once to ask if the .100" end play in his rebuilt diff was normal. The FL rebuilder told him that is how they came and that is what to expect. Of course that is not the case by any means, it usually means the rebuilder either didn't replace the axles or didn't take the time to set up the posi. I have found the original '63 to about '72 axles are still good. I have measured many at .200" from the face to the snap ring. This is a dimension I reference but I don't have access to the original prints to see what it was referenced at. Maybe someone here knows? Anyway I reference it and found the "good" rebuilt axle come in about .185" The bad ones are all over but usually all under .180". So with a tuned posi, a correctly done one, I find the original axles have -0- endplay in them and that is no good either. That is why I have to face them 005-009" to set the endplay to 005 -008 Removing that amount will not cut into the softer area of the axle. Same when I grind in a rebuilt axle. The cross shaft hardness is about a 60 Rc , the axles are about 55Rc. The axles I have seen that are worn or "new" are between 10-20 Rc.

Hi Jason- I will reply to your questions on your thread.

See ya guys,
PS I will be holding another seminar at corvettes at carlisle again next year and cover these type of questions there. Plan on attending if you're going next Aug.

**Joe L.** · December 5, 2015, 11:51 PM

Re: Differential Axle Question

Originally posted by Gary Ramadei (14833)

I was reading on CF today and saw a guy up in Canada had a question on why his rebuilt diff has worn axles again. I would have liked to help him but I can not respond there anymore since I am considered Satan's brother there. So if any of you know him or if he is here, here is your answer.

That might be a rebuilt diff, probably a vendor job, but look at the face of the axle. There is a center drill hole in it, it is a stock axle. Probably as John H mentioned - 72-79 axles. It is not a rebuilt axle, at least not one from the leading supplier to all the vendors. Rebuilt axles have a full face, no center drill hole & is hardened. I suspect those axles are painted originals and the owner was possibly charged for rebuilts. Original 63-72? axle faces were hardened and very few of the many I rebuilt needed new or rebuilt axles. Even on diff's with over 100k miles there was only a few thousands wear. In fact I have to face grind them when using in a tuned posi.

Now, if "new" axles were used then I have seen those come in soft faced too. They have the center drilled hole. I found 4-6 sets of them like that and stopped using them all together.

My guess was he didn't get what he expected he did and I would really check the rest of that build. Look for excessive axle endplay and also in the spiders. Cheap bearings, reused ring gear bolts, and lash/pattern issues. I have been down that "road" many times fixing others work.

Just passing along some help if I can.

Gary------

I've never seen an original axle with a drill hole in the center of the inner end. What I have seen on the inner end is a rather irregular, "as-forged" surface with, usually, what I would describe as a "dimple" in the center.

**Gary R.** · December 6, 2015, 08:57 AM

Re: Differential Axle Question

Hi Joe,
Every original diff I have opened up have over the years has a center drill hole in the face of the axle and also in yoke end for running on center for final turning. The only full face axles I have seen are the rebuilt ones with hardened tip.

Here is an original axle face.

Here is an example of a lousy axle rebuild. The splice was done well below the snap ring groove and left hollow by the rebuilder. It lasted one pass at the track.

Here is a rebuilt axle that I final ground the face to fit. No center drill hole. The new axles on the market have the center drill holes too.

Here is an original I fit to a tuned posi. Still good after 100k miles and still hardened after kiss grinding 003-005"

**Joe L.** · December 6, 2015, 12:44 PM

Re: Differential Axle Question

Originally posted by Gary Ramadei (14833)

Hi Joe,
Every original diff I have opened up have over the years has a center drill hole in the face of the axle and also in yoke end for running on center for final turning. The only full face axles I have seen are the rebuilt ones with hardened tip.

Here is an original axle face.

Here is an example of a lousy axle rebuild. The splice was done well below the snap ring groove and left hollow by the rebuilder. It lasted one pass at the track.

Here is a rebuilt axle that I final ground the face to fit. No center drill hole. The new axles on the market have the center drill holes too.

Here is an original I fit to a tuned posi. Still good after 100k miles and still hardened after kiss grinding 003-005"

Gary------

The surface shown in your first photo is worn. I've never seen a new GM axle that had that flat of a surface. I have a bunch of new GM axles but my back is telling me that I don't want to go looking through group 5 tote bins to find them right now. I would not describe the center hole as a drilled hole but that may be an apt description. The center hole in your last photo is the "dimple" that I mentioned.

The "rebuilt" axle in your second photo is the only type of rebuild that I have ever seen, although there may be other types out there. I don't like the rather long "repair section" on the end. As you mention and picture, I believe this seriously weakens the axle. I would much prefer a THIN hardened "button" on the end, perhaps 1/8", or so, in thickness. This would provide all the wear resistance one would ever need and would keep the repaired area mostly external of the spider gear splines, thus not weakening the axle. However, I've never seen a rebuilt axle done this way.

**Gary R.** · December 6, 2015, 01:58 PM

Re: Differential Axle Question

Hi Joe
The flat face axle is a rebuilt one I ground to get that surface. The typical rebuilt axle are cut at the snap ring groove and hardened button with splines pressed in. It is a solid rebuild although QC leaves a lot to be desired as sometime the splines are off a little and the fit is tight in the spider. All the original axles have the hole, save your back as I believe you would find the same.

The failed rebuilt axle is pretty bad. I am not sure who did that and I have only seen those in that one diff so it could have been a local shop rebuild attempt for all I know. It makes a good display at my seminars though.

Tom's 30 spline axles use a c-clip as the 12 bolt axles did but I grind those to size as well.

**Joe L.** · December 6, 2015, 04:16 PM

Re: Differential Axle Question

Originally posted by Gary Ramadei (14833)

Hi Joe
The flat face axle is a rebuilt one I ground to get that surface. The typical rebuilt axle are cut at the snap ring groove and hardened button with splines pressed in. It is a solid rebuild although QC leaves a lot to be desired as sometime the splines are off a little and the fit is tight in the spider. All the original axles have the hole, save your back as I believe you would find the same.

The failed rebuilt axle is pretty bad. I am not sure who did that and I have only seen those in that one diff so it could have been a local shop rebuild attempt for all I know. It makes a good display at my seminars though.

Tom's 30 spline axles use a c-clip as the 12 bolt axles did but I grind those to size as well.

Gary-------

I was able to get at a few of the NOS axles I have. I really didn't question that they have the hole, only that I would not describe it as a drilled hole----more like a tapered centering hole or "dimple". However, I suppose it's just a matter of semantics.

What I did find was that the ends were flat and smooth, at least on the axles I was able to get at. Somehow, I seem to recall that the ends on at least some of the GM axles had a rather "irregular", non-machined surface. That just "sticks in my mind".

The type of rebuilt axle that I've seen is the type that you picture in your second picture with the long repair section. Ken Carter of Carter's Corvettes (now closed) in Livermore, CA used to sell this type exclusively. These were done for him by a machinist in Tracy, CA, Steve Bradford. Steve is an EXCELLENT machinist but I never really liked this style of rebuild. In fact, Steve rebuilt a couple of axles for me like this but I worry about them. I just don't see the need for the long repair section which weakens the axle considerably.

Do the ones you show use a roll pin for retention of the repair section?

**Gary R.** · December 6, 2015, 06:23 PM

Re: Differential Axle Question

Joe,
I hope you didn't wrench your back checking your stock. I don't recall if I have seen a NOS axle to compare, all the ones I worked with were out of diff's with various amount of mileage on them. I refer to the hole as a center hole since that is how we were trained to set them up on centers in a lathe. The center hole on the yoke side is much larger. I know on the older axles the faces don't have a lot of wear on them, the next time I am going to look at the hole closer to see if it is indeed a center drilled hole.

Some of the faces are cupped but most are fairly flat.

I have never had any contact with either of those people you listed. I don't see any roll pin in the one axle I have here and don't see any in the sheared section. The sheared axle and opposite side axle were hollow and were destined to failure. The LH axle receives the load, even with posi, and let go.

**Gary R.** · December 6, 2015, 09:00 PM

Re: Differential Axle Question

Joe
I was just thinking about your NOS axles. If you still have them out and have a snap ring, can you install it and check the dimension from the face to ring? I would like to see how they compare to the 63-72's, do you know what time period they were purchased, that would help.

Thanks
Gary

**Joe L.** · December 6, 2015, 09:06 PM

Re: Differential Axle Question

Originally posted by Gary Ramadei (14833)

Joe,
I hope you didn't wrench your back checking your stock. I don't recall if I have seen a NOS axle to compare, all the ones I worked with were out of diff's with various amount of mileage on them. I refer to the hole as a center hole since that is how we were trained to set them up on centers in a lathe. The center hole on the yoke side is much larger. I know on the older axles the faces don't have a lot of wear on them, the next time I am going to look at the hole closer to see if it is indeed a center drilled hole.

Some of the faces are cupped but most are fairly flat.

I have never had any contact with either of those people you listed. I don't see any roll pin in the one axle I have here and don't see any in the sheared section. The sheared axle and opposite side axle were hollow and were destined to failure. The LH axle receives the load, even with posi, and let go.

Gary-------

The biggest problem I see with the type of rebuilt axle you pictured in your second photo is that the long repair section contributes absolutely no strength, at all, to the axle. Essentially, it's "just along for the ride". So, all of the torque applied to the axle by the spider gears is then transmitted to the axle outboard of the "splice". I would estimate that about 1/2 of the axle's strength is lost in this process. If so, no wonder the axle would fail.

**Joe L.** · December 6, 2015, 10:54 PM

Re: Differential Axle Question

Originally posted by Gary Ramadei (14833)

Joe
I was just thinking about your NOS axles. If you still have them out and have a snap ring, can you install it and check the dimension from the face to ring? I would like to see how they compare to the 63-72's, do you know what time period they were purchased, that would help.

Thanks
Gary

Gary------

Unfortunately, I put everything away. Those tote bins were so heavy I can't bear to go back right now. Maybe later.

**Gary R.** · December 6, 2015, 11:34 PM

Re: Differential Axle Question

Originally posted by Joe Lucia (12484)

Gary------

Unfortunately, I put everything away. Those tote bins were so heavy I can't bear to go back right now. Maybe later.

Not a problem, if you ever get a chance to measure them let me know. Thanks Joe.