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pinion yoke torque


beater72

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Any ideas on 71 12 bolt pinion yoke torque? I have a 12 bolt i picked up with the wrong yoke on it and the nut is loose. As my 72 service manual is with the car 45 min away, i cant look it up and my haynes manual doesnt say. Any help appreciated! Thanks

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Kris,

 

As near as I can tell from reading pages 4-30 ad 4-31 of the 1970 GM Chassis Service Manual, there is not a specific torque value but rather a subjective "preload" torque that was supposed to be observed prior to loosening the nut.  Since the nut was already loose on the 12 bolt you picked up, that is going to be difficult.  There is supposed to be a self-locking washer on/with the new nut to keep it in place at whatever torque you stop at.

 

Here's what the manual says about loosening the old nut and tightening the new nut:

 

Step 4: "Using Tool J-5853 with Adapter J-5810 (just a tool that holds the pinion yoke/flange) and a suitable socket on the pinion flange nut, rotate the pinion through sever complete revolutions and record the torque required to keep the pinion turning.  If flange is to be reused, mark pinion and flange for reassembly in the same relative position."

 

Step 14: "Install a new nut on the pinion shaft. Tighten nut to remove end play and continue alternately tightening in small increments and checking preload with torque wrench until it is the same as that recorded in Step 4."

 

All I can tell your from personal experience is that if you don't get this right, it can ruin your pinion and ring gears (you will know by the howling).  On my first new '70 Monte, I had the pinion seal replaced by my local Phillips 66 station (back in '72 when they actually did mechanical work).  I left KC on a mini vacation across Missouri and notice the rear end beginning to make a growling noise.  By the time I got to St. Louis, it was putting up a major howl so I wheeled into a Chevy dealership and they said the pinion nut was loose and the gears were out of alignment.  Of course, they were happy to fix it a get me back on the road with new gears.  Later the service station owner said his mechanic "forgot to tighten the pinion shaft nut".  I paid for the new parts and he reimbursed Chevy's labor charge.

 

So my best advice would be to tighten it holding the yoke/flange to take out the end play, loosen it a bit and then tighten it without holding the yoke/flange until you can still just turn the pinion freely.  Based on my personal experience (above) I might give it another eighth turn or so just to be sure it was not too loose.  BTW, I would imagine that it would take more torque to turn the pinion if the whole rear axle was assembled and on the car than just a naked 12 bolt sitting on the floor, but I can't prove that.  There are probably other members who have fool-proof methods for doing this - so maybe they'll chime in.  Good luck.
 

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You need to tighten the nut using the old bar type torque wrench until it takes I think 40-45 lbs reading to turn the rear end. Look at some websites that sell posi units, like Yukon.

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This is tricky when I change pinion seals I punch mark the pinion flange and the pinion shaft and the nut in a line and reassemble so marks line up. Unfortunately you cannot do that. On a Chevelle forum the information one person posted was on used bearings using a bar type torque wrench tighten the nut so you have 12 to 15 inch lbs to turn pinion WITH THE AXLES OUT. That came from a Chevelle forum, may or may not be correct I have no way to verify that other than what was said. One other point when I changed a pinion seal on a 12 bolt posi that I sold I removed the nut the way I described earlier and after reassembling I checked torque out of curiosity. At 180 ft lbs the nut just barely moved. So you can take it for what it is worth.

John S

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This is tricky when I change pinion seals I punch mark the pinion flange and the pinion shaft and the nut in a line and reassemble so marks line up.  S

 

I did the same thing on a 12 bolt that was in my 1967 GTO. Only thing I did differently is when retightening I tightened just slightly past the point where the punch marks were. By just slightly I mean maybe the diameter of the punch mark...maybe even less. By the time I did the seal replacement the car was a 100% daily driver and the rear remained silent for years and many miles before I sold it to a friend. I might add that the car was standing with the tires on the floor of a garage that had the old style pit as opposed to having a lift. Park break was on. Pretty easy job but I must say that I was worried about messing up the gears. Fortunately I got it right! 

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You know I got thinking about it and it takes a lot to crush the crush sleeve. It would take one heck of a impact wrench to crush that sleeve any more. I'd say tighten it down untill it stops then give it just a little more and check for smoothness while turning. Just another thought.

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