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Discussion Starter #1
Guys,

In setting up my 8.875 pinion preload, I'm getting two different mesurments.
I'm using a Raytek solid spacer with shims (thanks BGH) and new bearings. Using a old pinion nut, and tightening to 125 foot lbs.
On the loose side, I'm getting around 16 Inch pounds, measured with a Snap-On 0-30 inch pound Torqometer. This with .038 worth of shims (.016+.012+.010.)

Shimming down .002 to .036 (.020+.016) gets me around 25 Inch pounds. I've ensured that the shims are clean and the outer races have been seated, the bearings are oiled with gearlube. I've spun the pinion many times before taking a torque mesurment. I'm amazed at how tight 25 inch pounds actually feels! It's almost like it's binding. I've learned how two thou can really make a difference in preload.

My question is, should I go with 16 or 25 inch pounds? Seems with the shims I have, I'm unable to get .037.

Cheers and thanks again, Mark.
 

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I would go with the lower value to allow for expansion from heat. It will get tighter during use.

After you assemble it and install it, shoot the case/cover with a temp gun before and after a 20-25 mile trip. If its over 180*F, its too tight. Just my thoughts and experience, but I'm not a professional axle expert, but willing to learn.
 

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Reider Racing also makes shim kits

They also make setup bearings that slip on and off while you're doing your patterns so you don't need an arbor until you're ready for final assembly
 

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Mark, You are not putting enough torque on the pinion nut. You need to torque the nut to at least 200 foot pounds. Try it with the .038 shim and tighten the nut to 200 foot pounds and see what you get. You want the preload to be between 19 and 22 inch pounds. You can add a little more torque to the nut if it is close to the right preload.
 

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Discussion Starter #6
So you think I'll actually get a little more preload by simply adding more torque to the pinion nut? I would have thought that 125 ft lbs would have just about been it, but there's actually more room for compression...hmmm.

Excellent, I'll give it a shot!

What would be the minimum safe preload that I could go with?

Cheers and thanks everyone, Mark.
 

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Discussion Starter #8 (Edited)
Just Tried 200 (with the original .036 shims). It took my preload to 30 from 16! 150 gets me about 23.

Why no less than 200 BGH?

I'll try the .038 and go to 200.
Cheers, Mark.
 

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You need the tension in the pinion shaft to hold everything in place. That is why a spacer is used, otherwise the torque on the nut would be almost nothing and there would be no tension in the shaft. It is like a connecting rod bolt, it needs a certain amount of stretch to be stronger. If the preload went up that much then something is moving. There might be some burrs on the shims or something else that is allowing it to change that much.
 

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Discussion Starter #10
No, No... don't get me wrong, I do understand why the pinion setup needs a certain amount of nut tension to keep the bearings trapping the spacer. It's just that the spacer kit recomended only 125 ft/lbs.

Yes, All the shims did have a slight die burr around the inner and outer edge on one side, but I cleaned them all up. I'll check everything very closely when I break it down for the extra shim. Your right, it must be somthing with the spacer or shims, allowing the bearings to move closer together with the extra torque.

Later,mc
 

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You need the tension in the pinion shaft to hold everything in place. That is why a spacer is used, otherwise the torque on the nut would be almost nothing and there would be no tension in the shaft. It is like a connecting rod bolt, it needs a certain amount of stretch to be stronger. If the preload went up that much then something is moving. There might be some burrs on the shims or something else that is allowing it to change that much.
Gear,

I believe the shim is only for applying correct preload and allowing the nut to be sufficiently torqued. 200 ft-lb seems like and enormous amount of stress on the pinion and nut.
Stretching something does not make it "stronger". The steel is like a spring when torqued. Stress is directly proportional to the amount of strain - higher torque = higher stress. Preload is put on connecting rods so that the cap is still tight when the piston is in the power stoke and the load on the cap bolts lowers.
Since the pinion is carrying mainly a rotational torque and a small amount of axial load from the gear helix, I don't understand the need for such a high torque on the nut.

Would you mind explaining?

Thanks,
Mike
 

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First let me say that 200 foot pounds on this nut is not a lot when you consider that it takes about 300 foot pounds or more to crush a standard crush spacer. 200 is just a standard amount that is used for most rear ends with solid spacers. If the 12 bolt solid spacer is not strong enough to handle 200 foot pounds then I would go back to a crush spacer.

The reason that the pinion shaft needs to be under tension is because the tapered roller bearings are trying to push away from each other any time they are under a load. If there is no tension in the shaft then the bearings will cause tension, which will allow them to move apart. They might not move much, but just a very little bit will allow the pinion to move off of it's center line. This will cause gear wear and possible tooth breakage. It will also cause abnormal bearing wear.

I understand what you mean about tension not making a bolt stronger. I should have said it differently. A bolt's holding ability is greatest when it has a certain amount of stretch in it. The average rod bolt is at it's peak holding ability at around .006 inch stretch. More than that will cause the bolt to be weak. I gues you can compare it to a rubber band. If you put a rubber band around a letter it will fit snug, but will easily stretch more and will not hold tight. If you put it around several letters it will hold tighter. If you try to put it around too many letters it will break, or be stretched beyond the point where it can return to it's normal size when the load is removed from it. Does that make any more sence?
 
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