Typical Day - Explore Failure, Give Advice...

[M.D. Holloway]

So I had this guy send in the following U-joint today and I pulled it open. Simple diagnostic. I wrote up the report and sent it to him. He calls me and tells me this is the best thing he has ever recieved from a supplier and that we had is biz for ever and ever. No big deal to me...




Conclusion

The failure was likely generated by metal-to-metal contact due to
lubrication boundary starvation. The resulting particles that were generated persisted in creating more wear. Starvation may have occurred due to a blocked grease channel or infrequent greasing. It is difficult to determine the exact cause of the starvation.

Recommendations for Greasing U-Joints

Apply grease until new grease purges from all journal cross bearing seals. Make sure the new grease is flowing from all four seals or loosen bearing cap bolts until it does (if it doesn’t purge from all four caps, replace U-Joint.

Additional General Recommendations

New Bearings
Always store new bearings in their original wrappings away from
contaminants such as dust, dirt and moisture. Never heat
bearings. Heating bearings may change the temper of the metal.

Maintain A Clean System
Always clean grease fittings and grease gun before and after each
application. Never allow the grease pump to touch the ground or any
other source of contamination.

Packing Bearings
An easy rule of thumb when packing bearings is to fill to 50%
capacity of the bearing. The following equation can also be used:
Grease Amount (grams) = 0.005 x Bearing Width (mm) x Bearing
Outer Diameter (mm). Always consult the manufacturers
recommendations.

Greasing Plain Bearings
Initial charge should be at an angle between 90° and 180° from
the grease fitting or grease entry side.

Greasing Vented Housing Bearings
Remove the vent of the bearing once it is stopped. Apply grease
until it flows from the vent opening. With the vent still removed,
slowly rotate bearing so excess grease can escape. Replace
vent and clean housing.

[Pazuzu]

So, you told him that the u-joint failed from improper greasing, and he was impressed?

Do you generally do u-joint analysis? How *else* do they fail, short of severe impact?

[gassy]

You guys said "joint"

[M.D. Holloway]

You would be surprised how many U-joints fail due to improper lubricating. With a plain bearing underlubrication is one of the more typical failure modes, then extreme loads, heat and contamination. Sometimes the load is severe but in most cases the joint is designed for it unless the tech installed the wrong unit.

When it comes to failure - can only be from 1 or a combo of 4 sources - the man, the method, the machine or the material. After that, the sources become pretty obvious with a little investigation.

I found out a few minutes ago that this guys techs do not grease the joints but once a month but when they do they do not whip off the fittings so essentially they inject in road grit right into the bearings. Sounds simple and stupid but I could show you a whole room full of stupid some day! I have a huge collection of failed parts due to stupid...

[Pazuzu]

I wish I still had my old blown u-joint...

Toyota 4x4 driveshaft joint. Full ear yokes, Toyota doesn't use straps. Damage from off-roading, knocked it just enough to create a slow grease leak over several weeks. Freeway speeds, the joint finally lets go. That cast ear, which is probably 1/2 inch or greater across, peeled back like a banana peel (oh, sorry, sore subject for you )

Put a 2 inch dent in the floorboard when it blew. I kept it around for years because it was such beautiful catastrophic damage.

[bell]

The banana peel comment get's you the post of the week award
Congratulations