What are the odds of both driveshafts failing at the same time?

Brian Alcorn

Brian Alcorn

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So what's the odds of both driveshafts failing at the same time ... front was recently rebuilt ... had plastic in it .. the back still has plastic in it so it's original ... all u joints are tight and have no play what so ever. Tonight I got a vibration about 30-35 that I thought the shaft was gonna come apart so I disconnected the front shaft and drove around and all was good so about an hour later I get yet another really strong vibration so 8m guessing the back is doing the same thing. I'm assuming the slip shaft part is grease free and now wallowed out... but both in the same night ... oh yeah its a 2004 rubicon with 377xxx miles
 
With 377K on the Jeep; I am surprised you still have the original driveshafts installed.
Not the answer I want to give you, but depending upon how well the driveshafts were maintained... anything is possible....
Could you provide members with a few pictures to further assist us to diagnose your problem.
 
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Not really sure what to photograph for yall.. going canoeing tomorrow but did want to get the slip apart on the front shaft if only to see it ... let me know what to photograph.. I'm guessing the slip/spline part of the shaft can wear and have excessive play and feel similar to a bad ujoint
 
I’d be surprised given the rebuild, however that’s a lot of miles on stock shafts. My front had play at 67k.

However, since both are always live (unless you have a hub kit) they should wear similarly.
 
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I think with that many miles that it is possible that you have a broken transmission mount or similar issue ...I don’t know if it’s true but these seem to be the hardest to chase vibrations and noises on considering how exposed everything seems to be relative to a standard passenger vehicle or truck.
 
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The vibes are definitely a shaft ... had a tracker years ago that would eat u joints ... the vibration is almost violent ... not like a wheel out of balance
 
To hold 2 caps in place ... had to torch the front shaft to get the caps out.... looks and smells like plastic when it melts and comes squirting out
 
CharlesHS said:
Are you referring to the smell that grease makes when it is overheated... although there is a seal between the cup and the trunion...
Click to expand...
Hes talking about the teflon injected factory u joints, takes massive heat to get that out to rebuild them.
 
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Brian Alcorn said:
The vibes are definitely a shaft ... had a tracker years ago that would eat u joints ... the vibration is almost violent ... not like a wheel out of balance
Click to expand...
If you are sure it is the shafts see if one is bent or lost a weight- the odds of both failing at once are small if both are fairly fresh

you do not want the double cardan in front to fail...it takes the transfer case with it.
 
2 pictures of the plastic in and out..second photo the empty hole is under my thumb.. also a video of the rotational play in the front shaft

20210807_130418.jpg


20210807_135116.jpg
 

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Have not removed the back shaft but when blocking the tires to keep it from rolling there is zero play in any ujoint but pushing and pulling on the splines shows play in the splines ... guessing that should not be there ... front has the same play side to side at the splines but the front is worse
 
Brian Alcorn said:
Have not removed the back shaft but when blocking the tires to keep it from rolling there is zero play in any ujoint but pushing and pulling on the splines shows play in the splines ... guessing that should not be there ... front has the same play side to side at the splines but the front is worse
Click to expand...

Many years ago I had the front driveshaft rebalanced after replacing the U joints, but found out the slider assembly was quite worn causing vibrations much the same as you are experiencing...
Verify the centering ball was replaced during the recent rebuild or this can cause also vibrations.
 
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Ok here's a little video of the rear shaft . Ujoints are tight ... twist and lateral play are in the splines ... what's the black stuff on the muffler .. looks wet but is dry to the touch and is that a harmonic balance on the output shaft on the transfer case

20210808_192523.jpg
 

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  • 20210808_192331.mp4
    32.2 MB
Ok, odds are currently 965,945 to 1, based on that many were produced and only one has done it.
 
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