'72 Electra bolt torque question

[JohnD1956]

The drive shaft in my Electra has the double cardan rear joint.  This joint is bolted directly to a flange on the rear axle pinion. I have a re-printed  '72 service manual.  It reads on page 40-60 that these bolts are 7/16 -14 bolts.  And then it reads that the torque is 80 lbs.  That sounded way too high for such a bolt so I looked online and found a chart  here:  boltdepot torque chart  showing that a 1/2"  grade 8- coarse thread-  bolt  could go to 80 lbs.  But the 7/16th bolt grade 8 could only do 58lbs if it was a fine thread. This looks like a sure way to shear off a bolt

 

My question is what would be the proper torque for the bolts at that joint?
Does anyone have a original service manual for this year to see if it really reads the 80 lbs, or if this is a misprint in the re-printed manual? 

And if the book does read 80 lbs, am I crazy for thinking 30 lbs is the max for the 4 bolts at this joint? .  

 

 

 

 

[old-tank]

I don't know what the bolt size is but I have the same arrangement on my 76 Olds and my service manual says 95 ft pounds..  In reality when I installed it I just got it "good and tight" using a standard 1/2 inch ratchet, and when the driveline shop installed, they used an impact.

[JohnD1956]

Thanks @old-tank.  At this point I think size does make a difference.  Do you think a 7/16th inch bolt could stand up to 80 ft lbs torque?  Probably best to get some new bolts if I have to go into this. 

[jackofalltrades70]

Bolts have a torque specification.  That specification should not be surpassed intentionally unless the end result requires broken bolts. Stick with the data and check again after a little driving for peace of mind.

 

 

[Guest]

[JohnD1956]

Thanks for the charts  @Tinindian  Two interesting observations.  Cylinder head bolts for the 1942 Buick are 7/16th ?  Maybe I am underestimating the size of a 7/16 bolt?  But regardless, per the 2nd chart, the 1972 manual is still calling for 5 ft lb over the max capacity of the bolt.  I think the best course is to buy new bolts with an extra to test the torque range outside the vehicle.  

 

I also had a conversation with a driveline shop here in Albany, who opined that 80 ft lbs seemed excessive for a 7/16th bolt.  

[Ben Bruce aka First Born]

 

 For comparison only.

 

  1950 shop manual.  Engine head bolt= 7/16-14. Torque 65-70.  FWIW.

 

  Ben

[EmTee]

I had the same experience when replacing the U-joints on my '67 Riviera.  I used a 24" breaker bar and all the strength I could muster to break the flange bolts loose -- amazingly none of them snapped.  I believe the shop manual called for 85 ft lbs for them, but I got real nervous and stopped at about 75...  Worried that maybe they were that tight for a reason, I also used a little blue Locktite.