Driveshaft U-Joint - Page 3 - Yamaha FJR Forum : Yamaha FJR Owners Forums
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post #21 of 24 (permalink) Old 08-29-2020, 11:59 PM
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I replace 20 u-joints a year and I dont know what you are saying.

They consist of a center section or cross. Caps that contain needle bearings and a grease zerk in the center of the cross on the flat plane. I have no idea how you would compress it, or drive toward it or away from it. Its position is determined by the access to service it. It cant be in the cap head because the diameter of the housing is too small. It cant be in the crotch of the cross because you would not be able to get a grease gun fitting to it.
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post #22 of 24 (permalink) Old 08-30-2020, 10:26 PM
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I know that this is hard to grasp and even harder to explain. So let me try again. Imagine the cross coming from the engine (driven) and it drives the power through the u-joint and into the cross going to the pumpkin. You want the drive side to be compressing the leg of the u-joint t Where the zerk is located, not pulling away from it. Hope that helps explain it a bit better, probably not, may have to sketch something up to explain it better.

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post #23 of 24 (permalink) Old 08-31-2020, 01:59 AM
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Quote:
Originally Posted by passx View Post
I know that this is hard to grasp and even harder to explain. So let me try again. Imagine the cross coming from the engine (driven) and it drives the power through the u-joint and into the cross going to the pumpkin. You want the drive side to be compressing the leg of the u-joint “t” Where the zerk is located, not pulling away from it. Hope that helps explain it a bit better, probably not, may have to sketch something up to explain it better.
All new concepts to me but it makes sense. If the Zerk is seated correctly you do not want to add force everytime you take off, that would, over time, weaken that bolt and cause it to fail. In other words everytime you took off you would be potentially stretching the Zerk bolt and nipple. It will fail eventually. Probably why Yamaha engineered it the way they did......it's another potential failure point that they didn't trust us to take care of. So eliminate it!!

Or I am way off base here Passx?

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Last edited by nunia720; 08-31-2020 at 02:07 AM.
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post #24 of 24 (permalink) Old 08-31-2020, 12:01 PM
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Originally Posted by passx View Post
I know that this is hard to grasp and even harder to explain. So let me try again. Imagine the cross coming from the engine (driven) and it drives the power through the u-joint and into the cross going to the pumpkin. You want the drive side to be compressing the leg of the u-joint t Where the zerk is located, not pulling away from it. Hope that helps explain it a bit better, probably not, may have to sketch something up to explain it better.
With the cross standing vertical to the path of power transfer It has four points that rotate laterally to the path of power transfer. 2 are drive and two are driven. If the joint has a grease fitting in the crotch of the cross between the arms you can position the fitting by the direction of the rotation to be between the drive and driven leg. Thus "supposedly" compressing the opening.

This supposes two separate things would have to be true at the same time. Which are not.

1) the drive load needs to be unequal between the two drive legs of the cross. The drive force would need to be greater on the drive side of the zerk fitting than the leg 180* off. This is just not true. The leg 180* off pulls just as much load as the leg with the zerk making the stress between the two equal.

2) The engineers never considered the weakening of the cross at the hole for the zerk.

Every cross joint I have ever installed with a zerk in the crotch has a boss cast into the cross for the zerk to screw into. This boss is extra support material to return strength to the crotch of the cross. The engineers have a power rating for every cross joint designed. Proper application is the key. A drilled for grease joint will be weaker than a solid joint but a solid joint rated for 10,000 lbs is no stronger than a drilled joint rated for 10,000lbs.
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