Bad unit bearings after 2 months.

I polished a 30 about 2 months ago, new everything, and the drivers side unit bearing is already bad. It is a Timken from RockAuto.com and it does have a 1 year warantee on it.

The question is Did I screw up the install on this or was it faulty from the factory.

I installed new ball joints, knuckles and shafts [Yukon, because nobody had alloys at the time]. Then I put the unit bearing on, made sure there were no burrs or dirt in between the mating surfaces. Torqued the bolts to factory spec [85lbs iirc]. Installed the washer, nut, torqued it down, installed the nut holder and pin.

Someone mentioned driving it around for a day or so then retorquing the axle nut when I install the new one.

So is there anything I might have missed or overlooked since I don't want to be doing this a 3rd time.

~Alex

Torque spec is 175 ft/lbs, not 85.

I was refering to the 3 bolts that hold the bearing to the knuckle, not the axle nut. I had the FSM in front of me while doing the swap so I don't think its a fastener torque issue.

Yah, I'm thinking axle torque also.

The 3 bolts that hold the hub on to the knuckle get a pretty reasonable torque figure as I put them on with a long ratchet. The Axle to Hub nut though, that's a horse of a different color. If you under torque it, the hub will fail prematurely.

The torque on the outer stub axle is the only thing holding that hub together. People have learned that the hard way over and over again.

One more vote for the axle nut torque being the problem. Speaking from experience, unless you've got a bar longer than 3', I doubt you've overtorque it.

I'm 95% sure the initial torque was correct. I had a FSM out and a 1/2in drive snap-on torque wrench, But it was close to 3am by the time I got to that step. Since both the axle and bearing were new it could have been possible that they wore into eachother and the bearing lost some of its preload. I will be sure to double check the axle nut is torqued, then retorque it in a day or two.

Thanks for the input.

Just my experiences, but I've seen three MOOG unit bearings, that when you torque them down you can feel the bearing slip a little (I have a 3/4 drive three foot torque wrench, I can tighten slowly and get a good feel for what's happening). They then seem to get a side load that makes them hard, to impossible, to turn by hand.
I torque them down to 175 ft/lbs. back them off and re-torque to 150 ft/lbs. then I can turn them by hand.
I've done a lot of bearings (the majority in industrial machinery, a fair share in automotive). Too much pre-load generates heat, they get hot, they swell some more, which generates more heat. You may get lucky and they will wear in, you may get unlucky and they heat up enough to anneal (soften) the roller bearings
If you have the time or the inclination, hammer out the failed bearings, notch the race and disassemble the the races and rollers. Let us know what you find. What color, blue, black, or if they have spalling (the surface is flaking).
If 150 ft/lbs, makes you nervous, run them for awhile and re-torque to 175 ft/lbs. If I remember correctly 175 is the number for the newer type unit hubs anyway, 150 is for the older type.
Another reason for them to fail is a leaky seal, they are unit sealed bearings, if the grease leaks out they get dry and also overheat. Which is a warranty issue.
The older style unit hubs, have a hub seal in the rear and a seal race on the axle shaft yoke. Poor contact will allow water (or sand or mud) to run into the hub, which is likely unhealthy. The newer hubs seem to have an integrated rear seal.
I always pack the open areas in the hub with grease, two reasons; one, is if water gets in, there is some protection from the grease; two, if the bearing seal leaks, there is grease in there to heat up and possibly flow back into the bearing. The down side is it may be possible for the grease to leak out onto your brakes, though I've been packing the inside of my hubs for 20 years and have yet to have a problem.

I'm not going to be able to pop the bearing apart since its under warranty, but from what I can see it looks like the grease seal has torn or is leaking. I only have one spare hub so I will replace the worse of the two.
The XJ [and fsm] are 96 models and the axle is out of a 93, you mentioned two torque specs, which leads me to think I used the wrong spec.

alex22 said:

I'm not going to be able to pop the bearing apart since its under warranty, but from what I can see it looks like the grease seal has torn or is leaking. I only have one spare hub so I will replace the worse of the two.
The XJ [and fsm] are 96 models and the axle is out of a 93, you mentioned two torque specs, which leads me to think I used the wrong spec.

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Both of those axles require the same torque.Its not until you get into the pre 91,s that the unit bearings get different.

Wayne

175 foot pounds on the bit nut, 75 foot pounds on the 3 bolts.

Don't use an impact on the large nut either.

I just checked the bearings out. The drivers side was undertightened and the bearing had play in it. .009 thrust and .006 up and down. I put a mark on the nut and axle thread, loosened it and then torqued it down to 175lbs. The mark was about 45* further than it was before. The passengers side only moved about 5* and there was no noticable play in the bearing.
I will recheck both bearings in a week or so.

Thanks for your help.

~Alex

Are you using the cotter pin and that spring washer and the keyed cover that goes over the nut?

I have changed atleast 20 of these. Mine and friends. Tighten up with an impact and good to go. Never once have I ever seen one problem. I think you just got a bad bearing. This also includes changing and replacing many broken axles and u joints of my own. Only one that I had to replace had about 2 years of 33s and 35" tire on it.

The hammering force of the impact will hurt/damage the bearings.

If you were really lazy you could spin the nut on with the impact but do NOT let it hammer on it.

Pull out the torque wrench or estimate by hand with 1/2" drive but the worse is using an impact to tighten it down.

Yep, I am using the keyed cover and a pin. The axle must not have been seated properly the first time, or i forgot to adjust the wrench. There is alot less noise coming from the front end now.

I have used an impact in the past, but that was only because of ignorance and the fact that I didn't have a torque wrench yet. The bearing held up fine with no signs of failure after over a year. I do not recommend it though.

~Alex

bad bearing, a 45* difference in nut position can't make that much difference, stop blaming yourself and get one under warranty, good idea tho on filling the voids with grease.

45* can have a very large effect on the torque of a nut. Taking it off it only felt like 60ft/lbs. I will give it a while and if it gets loose again or makes some noise I will send it back. Its still under warranty for 9 more months.