Got driveshafts balanced yet? Otherwise, it's like a grenade ready to go off at any time.

coachgeo

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So once they are properly Balanced your all good? Nothing to come apart


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you can help prevent problems from future wear issues potentially with a balance ring. I've not heard how effective they are on driveshafts ... but the good products like this company makes for wheels has earned their spot over time to be a true benefit... so in concept it should be good for driveshaft too.

 

Awesomeness

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So once they are properly Balanced your all good? Nothing to come apart
Generally, yes. Over time, the balance could degrade - the military testing showed this. I would be cautious, and get them checked every several years, or if you damage/replace something in the driveline. Considering how destructive it could be, this seems like good prevention.
 

Reworked LMTV

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I would say that keeping the grease zerks always greased would likely reduced the wear on the yolks and other parts. I would use synthetic since they tend to be more tacky and are not as likely to get rinsed out.
 

Ohiobenz

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From everything I've seen posted so far, it would appear that wear in the spline ends up being the destructive vibration.
Does that wear result from being out of balance? Improper phasing? Lack of/insufficient/incorrect grease? Worn U-joints? Soft spline joint materials?
I think if this was a test question the answer would be "any of the above".
It would seem that getting a new shaft built by a commercial truck shop is the best step to take.
 

Awesomeness

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While using synthetic grease can't hurt, I don't think it's going to significantly change any of this issue. The cause of the spline issues is the combination of drive angle geometry, joint style, robustness vs. weight trade-offs, and several other factors.

My interpretation is that once the Army made the upgrades in the late '90s, the number of failures dropped to more expected numbers. Think of it like this...
  1. There is a limit to how much vibration you can have before stuff breaks, the original design is very close to that limit, and so many vehicles that were at the extremes of the tolerance range were actually over that limit.
  2. The upgrades the Army made moved the design further away from the limit, and thus fewer vehicles were "in the red".
  3. Over time, some of our vehicles have pushed closer to that limit (and over it), due to a number of age and maintenance related factors (e.g. parts wearing, improper disassembly/reassembly, inadequate lubrication, etc.).
So we're seeing more issues, and that's really unfortunate for us because we don't have a logistics chain to supply free parts and engines, the way a motorpool mechanic does. Having your shafts rebalanced and repaired, installing new high-quality u-joints, keeping everything well-lubricated, and checking it regularly, should help keep your truck "in the black", and avoid most of the problems.
 

Reworked LMTV

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I was watching a 4x4 program where they were using a special u joint with twin u joints in the same unit to overcome angulation.
 

M1078MAN

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Thats what makes this site great..even as a old hat..who has been around the block on these things..the older you get the more you forget.

Helping each other and passing on the knowledge is grooming the new and relearning the old
 

coachgeo

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That's called a Double-Cardan joint. It's weaker, and one of the military engineering reports says specifically that they considered it, but couldn't get one strong enough.
yup.... the only joint that seemed to help in the study done is called an Rzeppa and it too is not manufactured large enough for commercial sized trucks. IMHO this is why they went to using the middle axle of a 6x6 as the only rear axle in the later LMTV's. It moves the driveshaft to near horizontal.
 

pkl2fly

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Just to add my 2 cents in the pile-on about drive shafts...I had all kinds of vibes that at first I attributed to tire/wheel (un)balance on the highway. Had the alternator mount come loose three times, kept losing hardware out of it.

Finally after some stupid off road tricks which scraped (but somehow miraculously didn't bend) the rear driveshaft, I noticed a spiral scratch on the shaft after driving 100 miles and checked the hinging play which was shockingly out of tolerance.

Took the driveline off to a very reputable shop and had them do me up. AMAZING! Smooth ride, alternator stopped shaking off...$1700 well spent if you ask me.

The book says something like .005" hinge play, driveline guy says it's functionally zero. If you drive these truck often, get on your back and push, if they move at all, have them rebuilt.
 

Ronmar

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Just to add my 2 cents in the pile-on about drive shafts...I had all kinds of vibes that at first I attributed to tire/wheel (un)balance on the highway. Had the alternator mount come loose three times, kept losing hardware out of it.

Finally after some stupid off road tricks which scraped (but somehow miraculously didn't bend) the rear driveshaft, I noticed a spiral scratch on the shaft after driving 100 miles and checked the hinging play which was shockingly out of tolerance.

Took the driveline off to a very reputable shop and had them do me up. AMAZING! Smooth ride, alternator stopped shaking off...$1700 well spent if you ask me.

The book says something like .005" hinge play, driveline guy says it's functionally zero. If you drive these truck often, get on your back and push, if they move at all, have them rebuilt.
In my experience, .005” of movement is about the minimum you can detect by hand…
 

coachgeo

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I do know I had presented this all before now.
Do or do not there is no try
Pretty sure; if not yourself, those pdf's and pics has been presented.

Last I checked though...... there is no one who manufactures an Rzeppa drive shaft components anywhere near Heavy Duty that would fit these rigs or any other Medium Duty or Heavy Duty truck. Hence likely a large reason that route was never pursued. The route used (raise the rear driveshaft to near horizontal via a high pinon rear axle) was the route Govt. contractors took to solve the issue and it has seemingly worked well.
 

olly hondro

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This site has evolved for the better over the years: there is much more tolerance for innovation, re-purposing, and modernizing. I once was told here that , by deviating from stock factory as-issued condition I was being disrespectful to the memory of servicmen. Ouch. I do not miss those days.
 
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