Got to looking at the differential today. Figured step one is open it and see what the damage is. One of the side yokes comes right out so I know there's a snap ring in there somewhere, and maybe a half cubic inch of steel turned to powder...

And there it is...


Looks like the other yoke is about done too...


Is it safe to assume this differential's seen more left turns than right?!
Otherwise, it doesn't look bad. I'm not well versed in differentials so I took a video and I'm hoping some of the heavy weights (Mike?) can let me know their opinion on how it looks. I figure I may as well rebuild it while it's out. I have no idea how the gears sounded and I've read that it's not worth the risk? I turned the input 3 revolutions and got just a hair under 1 revolution of the side yoke. I assume this means this is 3.08 gears. Ring has 3756448 12 37 9 76 stamped into the edge. 37 I assume is teeth mating with 3885941 pinion with 12 teeth. September 1976 differential?

Any help on what I've got here? I'm assuming it's not the original as I've found all different year parts on this 72.



This says "CON"? and "F117"? What's this?





And here I see 0A 180 "7 1...



Stinger12 wrote a great how-to on rebuilding a differential. I think I'm capable of doing it, but I'm not sure I really want to. I called a local place and they said between $1,300 and $1,650 for a rebuild. Anyone know a ballpark price from Tracdogg2 based on what I've got?

Anyway, besides the yokes needing replaced, how's it look? Maybe that pinion shaft? I can't hear a single peep from anything in there while I'm turning it, all seems really smooth. Here's a video of it I took to help get opinions.



Again, I'd appreciate any info or thoughts on what I should do with this thing.

Thanks!
Mike

 

I'm interested in opinions here. I just dropped the rear end out of my car this morning. I was planning to clean it, new seals and reinstall it. But, at the same time I don't want to have to take it out again after reinstalling it.

My car did have some rear end humming noise while driving, but my buddy who has a '68 says some rear end noise is normal.

 

No it's not normal that it makes noise.

 

So it sounds like in your case Steve you're going to want to look further into that. In my case, I've never heard the thing when assembled as this project was handed to me in parts...

 

I expect I'll take it down to AZ Differential and have them go through it then. When it goes back in I don't want it coming back out.

Thanks for the input!

 

I want to say I read somewhere that Tracdogg2 is maybe around $800 for a rebuild. Sure beats the $1,300-$1,650 I got from the local place. I could be wrong on the $800 though. Hopefully I can get some more input on what I've got goin' on with mine! Nothing LOOKS wrong besides the yokes being worn, but I haven't torn into it further. I'm sure its not good to have all that worn yoke end steel floating around and run through the gears or in the posi

 

You don't use Track Dogg 2 to get a good (cheap)deal, You use him when You want it done right. If You want it done cheaply use one of the exchange services that most of the major vendors offer, they can probably beat most any local shop on price, but add in shipping.

 

Had mine done by Gary at Vtech

 

I used Steve at Perfect Pattern in Spokane Washington. It depends on how much horsepower you are running as to what you want done on the rebuild and whether you have an automatic or stick, IMHO.

 

Sorry, I wasn't implying that Tracdogg2 was cheap or didn't do the job right. I've read lots of great word about his work! I just simply didn't know what the price was.

Thanks for the input there Tim and lurch. Didn't think about power and what that might change in a rebuild. The stock base 200hp 350 is going to remain in the 72 and I'm just rebuilding it. So I guess that means basically I just want the thing rebuilt to stock specs, nothing fancy? Does the removal of the springs and doing the special shimming do anything for me at the stock 200hp level?

From what I understand/have read, GM used the springs as a "fix all" for the differentials rather than individually shimming each unit that would probably have been impractical. I assumed I'd be removing the springs and properly setting up the shims, but perhaps I don't necessarily need to?

Mike

 

If you are not going to drive it real hard stock should be fine, IMO. Also automatics are just a lot kinder to gears than sticks. I think Tom's differential pioneered posi tuning without using clutch packs, and I believe some of the videos how to do it are on Youtube. Tom's just sells diff parts now, he recommends both Tracdogg and Steve and someone else I've forgotten....good luck and have fun!

 

I forgot to mention, it's an automatic too. Sounding better...

 

Even diff work that is close to being right will work, but careful machine work lasts longer in my experience. I've set ring an pinion gears, spyder gears and side gears etc without really knowing what I was doing but I was breaking a lot of stuff with a 4 speed and a grabby clutch.
Now if you really want to stir up a hornets nest, ask which diff lube is better, synthetic or dinosaur oil....

 

It kinda sounds like You have an all stock car and intend to keep it that way. In the first post You mentioned that the Oil had metal in it. Was it really metal or just the Posi friction material ? If it was just the Posi material You might get by with just replacing the clutch pack. If you want to keep the car all stock and matching numbers, then You probably don't want to use an exchange program. However You can still send Your Rear end to any vendor, or rebuilder, and get the same one back.

 

I do think most diffs last a long time, but I'd worry about the seals leaking after all these years. It'd be a bummer to get it all back together and have it leak. How many diff's gears actually grenade from wear, not too many, mostly it's from abuse...

 

He did mine and it turned out great. Go watch his videos and you'll see why.

 

He will also ship you the box to send it in... Made shipping easy until I got the price of shipping.... Ouch

 

I didn't see any actual pieces of metal in the oil, it just didn't "look" right. So maybe it was the posi material. I think it'd be fair to say though that at some point in the past, chips have metal have been run through the gears as the yokes are worn. I guess I'm not sure HOW the ends of the yokes wear, just particulate steel that's really fine and doesn't really do anything to the gears, or is it larger chips?

In general, yes, I'm looking to keep all parts with this car as much as possible that are still original. I don't think this diff is original to the car so I don't think I'd be concerned with trade-in services. Just trying to get a good grip on what the best path is to having a stock differential that will hold up for a long time at the best value for my shoe-string budget body-off.

 

If You still have some of the Oil then a magnet will quickly determine what's in there. If the Yokes are badly worn then there is for sure Metal in there. Yoke wear is common, they almost always have that. They are to soft from the factory, and yes the newer Dana 44 had the same problem, maybe worse. Hardened Yokes are available, but the price of parts will quickly start escalating. A cheap way to fix this is to just weld up the Yokes and grind them smooth again. It all depends on how You use the car, if its a trailer queen You don't even need the Circlips , If Your going road racing You need the best of the best Yokes. You need to find where You fall between. The Numbers on the bottom of the Pumpkin will determine if it came in your car.

 

I had mine done by Gary @ V Tech Corvette. Like it has been mentioned above in this thread, watch his videos. Good guy & very helpful. I like to do my own work on my Corvette & 56 Chevy, but when it came to rebuilding the diff on the Vette, I'm glad I had Gary do this for me. Like mentioned above, shipping box will be sent to ur location. Yes shipping is expensive, but the diff is heavy. I had this done over a year ago & no issues. Hope this helps.

Rob