Anyone know off-hand on a 79? 
 

For the driveshaft to diff bolts/nuts, 15-20 ft.lbs
For the halfshafts to diff yokes, 22-30 ft.lbs

Or...my fav-o-rite spec for anything..."Tighten until JUST BEFORE it breaks".....

 Well. I found hidden in the Repair Manuel, where it stated 75 ft lbs..which seemed over kill from when I had removed the drive shaft.  I remember it not being a big deal, breaking them loose.
 I was step torquing to 40 when I snapped one on the rear yoke. Just the feel told me 75 was not going to work out.
GRRREAT! All the work was going fine 'till then.  New clutch,Intake gasket refresh,Oil pan gasket replaced, cleaned and painted.... I guess I'll have to pull the rear yoke to remove the
broken bolt unless there is enough shaft  exposed to get vice grips on it. I am not looking forward to pulling that rear yoke out. Looks like not a lot of room back there to bust that big nut loose.
 Hind sight being 20/20, I should have replaced the straps and bolts to be safe and listened to that Little man saying STOP STOP .
C3VETTE2011-03-08 11:41:13

 Well the bolt broke off about half way into the yoke. I think I can get a dremel  down there in a straight line with a bit and try an easy out before I resort to a more drastic measure.
 Should I have to pull the rear yoke, is it best to raise the rear wheels and use a large wrench to hold the yoke while removing the nut, or is it fairly safe to loosen that 1 1/8 in nut with the wheels on the ground. I'd hate to tear up something inside that rear end. 
 I know I should count the exposed threads on the shaft and mark the nut and shaft before I pull things apart to get in the ball park for putting it all back together.
  

75 ftlbs for a u-joint strap bolt/nut?!?!?!? No way!
That is for the YOKE nut....but I guess you done figured that out.
Try the Dremmel/ease-out before trying to pull the yoke off.....lot less trouble that way. If you were twisting that small bolt until it snapped, it should be fairly easy to back out.

Sounds like your having a bad day..I think I would burn the manual you used..I was thinking that 75 ft lbs could be inch pounds but that's only about half of what you needed..any bolt that small should never go that high..I am assuming since you said bolt you are talking about the pinion..or input into the diff..it could be that the torque spec is for the big nut in the middle of the yoke? Not sure don't care let's get this fixed..drilling it out as it is in the car is or can be the best way to drill it out..chances are in this case a reverse drill bit will take it out since the bolt broke off and didn't bottom out..I would try that first..be very careful of easy outs..they usually cause more trouble than good..if you have to remove the pinion yoke there is more stuff in there that would need setup if you do so..that's why I would try it in the car first..whatever you do get the best bits you can and a clean tap and die set to fix any threads that may be damaged..

Rich

  Today was one of those 'stay away from the car days' when even simple things go bad.
Not only did I break the bolt, but lost a needle bearing from one of the cups when I re-pulled the drive shaft back out. No worry, I'll press out the old ujoints and put new ones in and new straps while I have the DS out. I also noticed the rear diff rubber mount was in dire straits so I am ordering a new one for that.
 I rotated the yoke for best clearance/access and pretty sure I can drill the sucker out without pulling the yoke. I've recently been to that differential gear setup thing on a Jeep and dont care to go through that again anytime soon.
  Also,using a dremel, I tested the drilling on the other half of the broken bolt and  found drilling was no problem. As long as I keep it centered,I should be ok. I do have TAP and dies and will get a proper extractor tomorrow , along with a set of New Ujoints and straps, so I am pretty confident of an on car repair.
 I am so glad I have a lift to make life easier, so things could be worse. 

UPDATE:  Surgery successful.
  With the dremel at it slowest speed, I was able to bore completely through the bolt and using a #3 Kobalt extractor and mini-crescent wrench, walked the bolt out with no thread damage.
 Now where was I...hmmmmm

Kewl beans!

Yeeeeeaaaaaaaaaaaa !!!