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I made a technical error by disassembling my differential without first recording the turning torque at the pinion shaft as stated in both of the shop manuals that I have. Now I am re-assembling and need to recover from my error. The GM manual says to tighten the pinion nut until the turning torque is the same as it was after installation of a new oil seal. The Haynes manual says tighten until it exceeds the original torque value by 1 to 5 ft-lbs. I’m not very concerned about this minor difference, but I have no idea what torque value I should seek. The gears and bearings have not been touched on my 56,000 mile ’71 LT-1. I just did new oils seals all around. Can anyone out there give me a reasonable torque value that I should achieve?
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Re: differential pinion nut torquing
Paul-----
The best way to do this is not even mentioned in the service manuals. That is to chisel mark the nut and pinion flange + count exposed threads on the pinion shaft PRIOR to removing the nut. Then, you simply return the nut to the original position and torque it just a "skoche" further.
The above is not available to you since you didn't mark as I described. The only thing that I could suggest would be to try to return the nut to the point in which the assembly is "just tight" (i.e. the point in which all looseness has been taken up). Then, tighten the nut an additional 10 degrees, or so, of rotation.
The problem with performing the procedure I suggest is that the pinion nut is a self locking nut. That makes determining the "just tight" position difficult. However, I think that you could do it by carefully tightening the nut and moving the flange in-and-out to see when all "slack" is taken up.In Appreciation of John Hinckley -
Re: differential pinion nut torquing
I did the pinion nut in a 73 just the way you described, Joe, It worked fine. Tighten until no "slack" in the fore and aft movement plus about 1/8 turn. U.S. Army aviation manuel for "field" torque value says " high torque rise plus 1/4 turn", both work. JohnComment
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Re: differential pinion nut torquing
You can feel when the nut sort of hits the wall. I guess that is what the military manual means by high torque rise. Then I tighten just until I feel a little increase in drag on the pinion.Comment
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i would also put red lock tite on the threads
with a used nut. you do not want it to come looseComment
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Re: i would also put red lock tite on the threads
Thanks for the help guys. The diff is on the bench so I have ideal access and can see/feel what is happening very well. I'm a ME in the submarine business and what you describe is often used on very large shipboard fasteners. The navy calls it the turn-of-the-nut method. The length of fastener that is being stretched is also a factor. I will apply this and check the running torque as well. I talked to a diff rebuild tech today at one of the national rebuilders and he told me the pinion bearing set should account for 10 to 15 in-lbs of turning torque. I will measure the turning torque before and after I tighten it down and look for a rise of that magnitude. He also said that it typically takes 150 to 200 ft-lbs of torque to get those results. Thanks again.Comment
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Re: i would also put red lock tite on the threads
Paul,
The diff rebuilder that you talked to today is right on the money. Rotational torque required to turn the pinion is the only accurate method of setting the load on the pinion nut. GM recommends 20 to 30 in-lb for new bearings and 5 to 15 in-lb for used bearings. (with diff case removed) Be careful, the numbers go up VERY quickly once all measureable end play is removed and it's not possible to "back up" if you've gone too far. If over crushed, the sleeve between front and rear bearings should be replaced and the process started over again.Comment
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