Differential inspection

[Gary R.]

I got in a 75 diff today that is pretty much junk. Before I part it I figured I would post some pictures you those of you who will be looking at used 63-79 iron diffs and may not be sure what to look for. This one came out of a beat up car and it's not hard to see this diff was making some noise............................................. .................................................. .................................................. .................................................. .................................................. ................................................................ .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .............................................When checking a diff and you get past the numbers, look at the axles and the seal area. There should be an 1/8" boss in front of the seal. The axles should not be touching the housing. This one has axles worn down past the snap ring groove, both sides, they hit the housing machining it. The 1/8 boss is gone, the U-bolt cut into the ears, and the shields were distorted on the axles. This is pretty bad and I don't even know if the posi case is any good. I'll probably just drop it all in the scrape iron drum for about $2.

[Paul D.]

Re: Differntial inspection

Thanx for sharing.....I've seen some wore down almost to the snap ring and was wondering if those "rebuilt" axles with the hardened ends were any good to use....Or is it best to find some good used GM axles?......P

[Gary R.]

Re: Differntial inspection

Hi Paul,,,,,,,,,,,,,,,,,I have used a lot of the rebuilt axles and while some do have QC issues, the ones I used have been fine. The ones I have had issue with were the GM licensed new yokes. I found 5 of them to be soft faced as bad as the original 73 -79 were, as pictured above. I also have a set of rebuilt axles that were very poorly built. Not sure who did these but anyone who attended the last few Carlisle seminars I held saw them. They were machine bored but the new plug end did not fill the hole and they were effectively a straw. Once the guy launched the car at the track it twisted and sheared the left axle( load side) and that was it. They came from someplace down south but again I don't know who did the work, they are unlike any others I've ever seen.Here is a picture of them.............................................. .................................................. .................................................. .................................................. .................................................. ..........

[Wayne W.]

Re: Differntial inspection

Always interested me that we had little or no trouble with these things up and until after 73-74, and by 78-79 it was at an epidemic. GM would never admit it at the time, but it was just another case of shoddy product from them during that time when they lost the market to the foreigners.

[Joe L.]

Re: Differntial inspection

Hi Paul,,,,,,,,,,,,,,,,,I have used a lot of the rebuilt axles and while some do have QC issues, the ones I used have been fine. The ones I have had issue with were the GM licensed new yokes. I found 5 of them to be soft faced as bad as the original 73 -79 were, as pictured above. I also have a set of rebuilt axles that were very poorly built. Not sure who did these but anyone who attended the last few Carlisle seminars I held saw them. They were machine bored but the new plug end did not fill the hole and they were effectively a straw. Once the guy launched the car at the track it twisted and sheared the left axle( load side) and that was it. They came from someplace down south but again I don't know who did the work, they are unlike any others I've ever seen.Here is a picture of them.............................................. .................................................. .................................................. .................................................. .................................................. ..........

Gary-------


I wish the rebuilders of these axles would make the "button" very thin (no thicker than the length of the shaft inboard of the spider gears), very hard, and retain it with a countersunk 8-18 machine screw. That way it would not significantly reduce the strength of the axle and the very hard button would render the axle "immortal" with respect to end wear.

ALL of the rebuilds I've seen use a much longer "button". This inevitably and greatly reduces the strength of the axle since the button portion of the axle is completely useless as far as imparting any strength to the axle. The remaining splined portion of the axle then has to endure ALL of the torque.

[Gary R.]

Re: Differntial inspection

Joe,,,,,,,,,,,,,,,, The rebuilt axles I use are spliced at the snap ring groove and use a Tool Steel button. Although the QC of the supplier is suspect at times, since I got in some I wouldn't use, I had not had any fail. The one pictured could be a home rebuilt unit for all I know. I can say once I had the diff here to rebuild I found other areas the previous guy screwed up. The biggest disappointment was with the new axles, as mentioned, those were soft faced and I believe were imported. For my son's 75 street/strip car I started out with 1350 30 spline axles and then moved up to 1480 30 spline which should solve axle issues.

[Gary R.]

Re: Differntial inspection

Hi Wayne--------I have rebuilt every year from 63-79 many times, the 63 to around 72 original axles hold up great. Yes, I have found some that were worn out but a good % of them I reused and in fact had to face grind them a few thousands once I tuned the posi. After 73 forget it. Many times I see where the axles were replaced with rebuilt ones and the owners still complained about the endplay. As I'm sure you know axle end play is caused by a few areas in the diff and not always with the axles. In most cases it is the posi setup and once in a while the posi case cross shaft holes are worn. All of this can be corrected, even a case hole as long as it isn't cracked.