OK Sorry for being so dense.  But in the photo I see the mushrooming and the worn right side yoke, but...are they supposed to be flush against the vertical shaft in the middle?  Is that the pinion?  I'll open 'er up and take a pic this weekend.

The yokes are suppose to ride against the center pin.If the yokes were not worn so badly the "C" clip would be much closer to the metal plate just to the outside of it that the blue springs are against. As Joel stated the one on the right is much worst. The camera was a little off center so it's hard to see the space behind the "C" clip.

The yoke ends should butt right up against the center pin, yes. These yokes are worn bad enough to have too mech clearance between the snap-ring, and the side gear of the diff.

The amount of metal you see in between the two red vertical lines here is how much metal is worn off of the OTHER side of the snap-ring. With good yokes, the snap-rings would actually be snugly up against the side gears, instead of close to the center pin. This wear will allow the yokes to move in/out of the diff, and when they do, the tops of the tires/wheels will also move in-out, which effects handling and alignment.


On the heli-coil repair...yeah...that's kinda messed up right there! I see now why you want to replace the cover.
Checking for wheel bearing play on the t-arms is normally easier with the suspension still in the car, but, the general rule is if you can FEEL any play in the bearings, they are too loose.

Thanks guys, heres a pic of mine.  It is off center as well but now I know what I'm looking for.  There is end play but what is the tolerance supposed to be?  And how do you measure it?  Hate to have to buy new yokes (couple hundred here, couple hundred there pretty soon we're talkin' real money!) but then again, don't want to drop the diff again anytime soon!  Also in second picture why would my carrier have those gear marks on it?  Is that common?  It's not rubbing against the pinion nor does anything seem out of whack when I turn it, maybe from a prior incident?  I can tell Bubba has had this open before (found three different length bolts holding the cover on!)

The gouges on the carrier are obviously from previous damage. It is where the pinion bearing took a doo-doo, and the pinion ran back into the carrier. You would know if there was a problem with it now, so it has to be from a previous encounter of the closest kind.

Hard to see in the pics, but it doesn't appear that the yokes have much wear. As far as how much is too much? Dat's a gud kweschun.....You should have some play, around .040" or so. I've never really seen any specs on it, but .040" is pretty good for new, unworn yokes and posi clutch packs. The play is adjustable to an extent by using different thickness snap-rings, and shims on the clutch packs.

Mario,
Your yokes look a whole lot better than mine. When I was doing research on how to do this differential stuff I found out that later C3's, including '78 had bad yokes. Soft metal wore quickly. My oil was like a metallic paste.
Joel, That's pretty cool the way you can put notes on a picture. Someday i learn how to do that stuff. Use the pic anytime you like.  

Just a quick note to say thanks for all the great information here... One day I too will be tackling rebuilding the back mechanicals and love to read all I can. 

Yes this forum is a wealth of info, thanks to all ...I find myself accessing regularly....now an update.  Trailing arms off to be rebuilt, need new cores since the old ones were pretty beat up by previous owners, but  "while I'm at it", anyone have experience with rebuilding calipeers?  Mine look pretty good but thinking of switching to O rings, any thoughts?  Sorry if this off topic.  Also should I flush the differential before refilling?  What would one use?

I just did all 4 on the white vette last fall. O-ring kits from bairs and new rebuild kit for master cylinder. Easy job just time consumming. I have lots of pictures need to turn them into a tech article.....ebo

|UPDATED|4/29/2013 9:13:13 AM (AZT)|/UPDATED|

...And put it in the next installment of "Shark Bytes", right?