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  #1  
Old September 24th, 2013, 11:43 AM
RickM
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Rick Mabus
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Dumb U Joint Question

Ok. I have done a bit of searching here, and now I am confused about a u-joint question. I am getting and odd vibration from my rear drive shaft, that started the minute a guy at Firestone tried to replace the bearings in my rear drive shaft. I stopped him immediately, and told him that I thought the drive shafts were not rebuildable. Now I am seeing the Precission 344 U-joints as a replacement. My concern here is bearing play, and installing the bearings properly. Based on the picture online I saw, I cannot tell if the bearings are in place on the U joint online.

Sooooo. Is there something I need to be worried about in regards to rebuilding my rear drive shaft??


EDIT Please dissregard my ignorance. I found me a nice youtube video that explained it all. Please Move along!! Nothing to see here!!
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  #2  
Old September 24th, 2013, 12:00 PM
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Richard
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U-joints are generally not rebuildable, and are relatively cheap anyway. You can generally check for a bad u-joint yourself by jacking a wheel (rear, in your case) and making sure the tranny is in neutral. Grab the shaft close to each joint and shake it. ANY hint of play means a bad joint, and it should be replaced. I generally prefer to go with genuine on these, but aftermarket really is not a bad choice either.

While you are under and checking, look to see if there is dif oil coming from the input flange of the dif. Not a bad idea to check the level of gear oil if you see any seepage, or if you haven't thought to check the dif before.

------ Follow up post added September 24th, 2013 11:05 AM ------

One more tidbit on the u-joint. If you are a do-it-yourselfer, do NOT take out the joint before you center-punch a small allignment mark in the flange and the driveshaft, as it does matter that these parts are kept in allignment. Replacing the joints is not a bad job, but it might be smart to have someone guide you through the process the first time. RP
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Old September 25th, 2013, 10:46 AM
RickM
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Rick Mabus
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Ok. So let me understand this some. Alignment and the center punch idea is great info.

So the ujoint is not somewhat self centering I take it, or are you talking about making sure the the non drive flange goes back on the same side of the drive shaft that it came off of?

I did some more searching on youtube and my thinking is simply to mark the crap out of everything.
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  #4  
Old September 25th, 2013, 11:12 AM
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Richard
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While the u-joint is self-centered, the reason for keeping the flange and driveshaft alligned is that they are balanced as a unit by the factory, and they may not be as perfectly balanced if you don't get the parts back together in original allignment. While the vibration is not as noticable as that of a worn u-joint, you can get a bit of that "unbalanced" feel at speed if you happen to get the parts 180 out. Plus, it works the new joints and bearings in the dif and/or transfer case a bit harder.

------ Follow up post added September 25th, 2013 10:21 AM ------

And yes, mark the flange of the driveshaft to the flange of the dif/transfer case, just for the heck of it. Just makes you feel better, somehow. But don't get too anal here; I can't imagine that the factory bothers to balance the entire driveline as a unit. Imagine having to replace your driveshaft - no way to keep the driveline in exact same relationship.
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Old September 25th, 2013, 11:22 AM
RickM
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Rick Mabus
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That is interesting, and makes me wonder if the wanker at firestone screwed this up for me, way back when. I notice a vibration that is not constant, but is noticable at one speed and is basically rythmic. in other words about every second and a half vibrates for a half a sec.
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Old September 25th, 2013, 11:29 AM
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Richard
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The only way to know for sure is to mark the driveshaft and flange, take the u-joint back out, and rotate the parts 180 degrees, then see if the vibration goes away. You might also see if you feel any up/down play in the bearing of the closest connecting unit (unkikely, but it happens). Remember to jack and take all torque off of the driveshaft before you check. And by all means, replace both of the u-joints in the offending shaft.
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  #7  
Old September 25th, 2013, 11:39 AM
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Richard
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I seem to keep having afterthoughts; Look for the mechanic's allignment marks when you inspect. If you don't see any, therer is a 50/50 chance he got it wrong. Thinking about your "at certain speed" vibration, this is likely a harmonic balance induced by any rotating part that is out of balance, including your wheels and tires as well as your driveshaft. Definitely something is out of balance somewhere, but it is out of balance all of the time. When the vibration reaches a certain speed, it "harmonizes" with body, frame, etc, and you then feel it more. Try the simple stuff first. Rotate your tires, or beter yet, have them checked for balance.
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  #8  
Old September 25th, 2013, 12:42 PM
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Tom Rowe
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I assume you mean he tried to replace the u-joints, not the needle bearings in the u-joints.
The propshafts are rebuildable using new u-joints.
As mentioned, if he had it half done (or completed it) and didn't mark the two yokes then there's a 50/50 chance he got it wrong. Or it could be coincidental.
be careful what you watch on youtube. There's at least one video there of some guy hammering the bearing caps back in, which should never be done. At least never unless it's an emergency field repair and there are no alternatives. The caps are hardened and should never be banged on.
This post on another forum should give you some good pointers, even if you're not doing it yourself.
http://landroverforums.com/forum/gen...02/#post164811

If he didn't actually replace them, which it sounds like, then a seized u-joint (which you can't detect without removing the propshaft) will also cause vibrations.
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