Pinion nut torque confusion

[matrophy]

I have a weeping pinion seal on my '86 720and it is on my list to fix but the more I research the procedure for retightening the nut, the more confused I get.

 

My Haynes manual doesn't mention torqueing the nut after setting the preload with an inch-lb torque wrench but there is a torque spec of 94 to 217 ft-lb listed.

 

Is the final torque and the preload torque essentially the same number or are there 2 steps - set preload (move axle back forth in the process) and then a final torque of the nut?

 

Related question - is counting the turns on the nut a better way to go?

[Stoffregen Motorsports]

The right way is to torque the nut, but preload is super important too. So if you torque the nut all the way down and you can't spin the pinion gear, that isn't going to work.

 

I normally run the nut on with an air impact gun, then check the preload. If it's acceptable, then I remove the nut, squirt a bead of black RTV around the base of the threads (inside the flange, right where the splines and threads meet) so that the washer (or flanged nut) seal against the RTV, Then I use a good dripping of red loctite and run the nut on. Don't forget to stake the nut, but check to see that the preload is good first.

[datzenmike]

I think preload torque is the reading taken using a torque wrench on the properly tightened pinion nut. The pinion nut ranges from 94 to 217 ft lbs. Start with 97. Preload is the torque needed to just begin turning the pinion gear. If too low tighten the pinion nut to 110 ft lbs and check the preload. Keep going till within speck.

 

I changed a pinion seal by simply prying it out and pounding in another. Tightened the pinion nut on as hard as I could and it was fine.

[matrophy]

5 minutes ago, Stoffregen Motorsports said:

The right way is to torque the nut, but preload is super important too. So if you torque the nut all the way down and you can't spin the pinion gear, that isn't going to work.

 

I normally run the nut on with an air impact gun, then check the preload. If it's acceptable, then I remove the nut, squirt a bead of black RTV around the base of the threads (inside the flange, right where the splines and threads meet) so that the washer (or flanged nut) seal against the RTV, Then I use a good dripping of red loctite and run the nut on. Don't forget to stake the nut, but check to see that the preload is good first.

 

1 minute ago, datzenmike said:

I think preload torque is the reading taken using a torque wrench on the properly tightened pinion nut. The pinion nut ranges from 94 to 217 ft lbs. Start with 97. Preload is the torque needed to just begin turning the pinion gear. If too low tighten the pinion nut to 110 ft lbs and check the preload. Keep going till within speck.

If I understand correctly, it sounds like the preload inch-lb torque and the ft-lbs torque are essentially within the same range. To recap: Start with the lowest ft-lb torque, check the preload spec after moving the pinion back and forth a few times to settle the bearings and if needed, increase ft-lb torque until both are in spec.  RTV and locktite per Stoffergren's recommendation and stake the nut.

[datzenmike]

That's my understanding of it.

[Stoffregen Motorsports]

I usually cut to the chase and go all in with the impact gun. Unless you've got a NASCAR pit crew rattle gun running 300 psi, the impact will likely not overtorque the nut of a pinion flange.

 

Don't think I'm a hack though. I torque everything else, even things that most people don't. But with pinion flange nuts, I have never needed to get out the torque wrench.

 

If there is a crush sleeve (not a solid spacer with shims) it is possible to over-crush the sleeve with too much torque, but I take this into account during the assembly process and am careful with my impact gun, to not overtighten the nut.

[matrophy]

3 minutes ago, Stoffregen Motorsports said:

I usually cut to the chase and go all in with the impact gun. Unless you've got a NASCAR pit crew rattle gun running 300 psi, the impact will likely not overtorque the nut of a pinion flange.

 

Don't think I'm a hack though. I torque everything else, even things that most people don't. But with pinion flange nuts, I have never needed to get out the torque wrench.

 

If there is a crush sleeve (not a solid spacer with shims) it is possible to over-crush the sleeve with too much torque, but I take this into account during the assembly process and am careful with my impact gun, to not overtighten the nut.

That's good info. The warnings of over-torquing in the instructions had me a little nervous