Drop housing/universal joint/hub oil

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rtadams89
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Drop housing/universal joint/hub oil

Post by rtadams89 » Thu Feb 25, 2021 7:49 am

I'm trying to understand the lubrication of the drop axle gears + everything outboard of the drop axle housing. The -34 TM and the dust boot replacement thread (viewtopic.php?f=148&t=133154) have been a real help. I'm a little unclear on where oil added to the drop axle should be able to migrate to, which is why I'm looking for some clarification on my understanding.

Based on the TM, there doesn't appear to be a seal between the drop axle housing and the inner shaft of the universal joint. As such, oil in the housing can migrate out towards the wheel, filling the dust boot. Is that correct? Looking at where the fill/level plug is on the housing, it appears to be near the bottom of where the universal joint shaft would enter the housing, so it doesn't seem like oil could free flow outwards past the inner u joint shaft while filling the housing with oil. Does this mean that after filling the housing and driving, oil is likely to migrate from the drop axle housing outwards to the dust boot resulting in the oil level of the housing being low?


Chuck W.
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Re: Drop housing/universal joint/hub oil

Post by Chuck W. » Thu Feb 25, 2021 2:27 pm

Yes. You need to monitor oil level in the drop housing after a boot change.

rtadams89
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Re: Drop housing/universal joint/hub oil

Post by rtadams89 » Fri Feb 26, 2021 8:15 pm

OK, I'm not crazy then. I thought I must be missing something but glad to know I was looking at it the right way. Thanks.

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Re: Drop housing/universal joint/hub oil

Post by Chuck W. » Sat Feb 27, 2021 3:46 pm

The oil will migrate into the rubber boots over time, so it's a good idea to check the oil level frequently, especially after you install new boots.

rtadams89
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Re: Drop housing/universal joint/hub oil

Post by rtadams89 » Sun Feb 28, 2021 5:34 pm

I assume the bearing in the knuckle is packed with grease. Does the oil from the drop gears that has migrated into the knuckle not end up washing that grease out?

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Re: Drop housing/universal joint/hub oil

Post by markrdje » Sun Feb 28, 2021 6:14 pm

Hmm, I thought the bearing doesn't get greased, the gear oil lubricates the bearing
change user name to mark

Chuck W.
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Re: Drop housing/universal joint/hub oil

Post by Chuck W. » Sun Feb 28, 2021 6:35 pm

Yes, the bearing is lubed by the oil from the knuckle/drop housing. I always put some grease on the bearings when I am doing a boot replacement, just to keep them from being dry until the oil reaches them, it takes some time for the oil to migrate over into the hub, so you need to keep an eye on the oil level. NEVER put grease in a drop housing.

rtadams89
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Re: Drop housing/universal joint/hub oil

Post by rtadams89 » Sun Feb 28, 2021 8:40 pm

Any reason to not fill up the knuckle with oil then (maybe through the top king pin before installing it or at the top of the boot before clamping it down) when changing boots?

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Re: Drop housing/universal joint/hub oil

Post by Chuck W. » Mon Mar 01, 2021 7:13 am

Couldn't hurt.

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Re: Drop housing/universal joint/hub oil

Post by Chuck W. » Mon Mar 01, 2021 9:50 am

Make sure you replace the O-rings on the lifting rings and axle nuts, I also like to put a little RTV on the axle splines to help seal the hub.


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