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How do you check the U Joints?

M

montanaman

NAXJA Forum User
Location
Western Montana
I know this is a dumb question, but I've never messed with u-joints before.

How can you check them for going bad? People have mentioned "chocking the wheels" so there is "no tension in the drivetrain." I'm not sure what that means. You mean putting bricks against the wheels?

It seems to me if the tranny is in neutral, there is no tension, whether the wheels are blocked or not.

When I crawl up under there, what exactly do I look for? Please put it in dummy noob terms.

Right now, in the middle of the day here in Montana, it's about 15 degrees outside, and my garage is too full to have the jeep in there with the door closed. So I'll be freezing my tail off trying to diagnose the vibrations. Please give me some info that will save me some time and save my gonads from freezing off.

Thanks!!
 
With no tension on the driveline, just grab the yoke and wiggle it. It should be tight. If there is any movement at all the joint is bad. You have to be able to spin the driveline since any tension will tighten the joint even if it's bad.
 
montanaman said:
Ok ... so does that mean the rear wheels should be jacked up and able to spin while I'm doing the check?
Click to expand...

No, pull the ebrake, scotch the wheels, put it in Neutral, crawl under there and grab the D-shaft and wiggle it in every direction. same goes for front axles also. Any play in the u-joint is bad.
 
jeepinandy said:
No, pull the ebrake, scotch the wheels, put it in Neutral, crawl under there and grab the D-shaft and wiggle it in every direction. same goes for front axles also. Any play in the u-joint is bad.
Click to expand...
Thanks for the response. And -- I know this sounds silly -- but what do you mean by "scotch the wheels?"

Thanks
 
Chocked wheels...
chocksxa7.png
 
after you chock the wheels the best way to feel for play is to jack the Jeep up, and put it in neutral. Then you can wiggle the shaft back and forth checking for any slop in the end caps of the u-joints. The caps should be tight with no play whatsoever. Look in those areas. If there is "tension" on the wheels or shaft you won't be able to move it to see. Also look to see that the caps are held firmly in place and not oscillating in the yokes which would cause the yokes to wear. That would prevent new u-joint endcaps from being held firm. If it's one of the front axle joints you are checking then just jack up that wheel. That will take the tension off allowing you to move the wheel back and forth to look for play.
 
Re: How do you CHANGE the U Joints?

Ok ... just checked it, and the front U-Joint on the rear drive shaft has lots of play between the bearings and the bearing caps. Everything else seems pretty tight. I'm going to get a set of 2 Precision brand "super-strength" U-joints tomorrow and install them.

Any tips for when I drop the drive shaft and replace the U-Joints? I'm planning on using the bench vise with large and small sockets to press out the u-joints.

I've got the drive shaft that has the welded yoke on both ends ... with the NP231 part-time xfer case.

Thanks for any advice you can provide!!
 
Tip #1 Don't pinch the tube in the vise. If it is necessary to hammer on the joint (and sometimes it is), clamp the shaft only on the hard ends...after the weld, not on the tube.

Tip #2 U-joints with Zerks fittings (where you grease them) should be install so that the zerks will be compressed when in forward motion. In other words, if you install it one way, the hole the zerk screws into becomes a good spot for a crack to start. If you install it 90 degrees from that first way, then when under acceleration it is compressing the hole.

I wish I had pictures...very hard to describe.
 
In this picture, with the Joint turning in the direction indicated, the shaft would be connected to the two blacked out caps. So when under load it compresses the zerk hole.
44srsw0.jpg
 
Yes ... I understand exactly what you are talking about. The Haynes manual didn't get into that level of detail, they just said make sure the zerk hole is facing "toward the shaft."

I'll be sure the zerk hole is being compressed under load.

Of course ... when in reverse, the opposite direction of stress will be placed on the joint. But then again, how much time do we spend in reverse?

Thanks again for your comments. I'll be sure the hole is being compressed in forward direction.

Anything else?

Oh ... and one more quick question ... Is it ok to re-use the strap/u-bolts kits that hold the u-joint onto the rear yoke? I'm asking because I'm not sure my local store has that in stock, and I need to get this fixed tomorrow, so we can leave on the 26th for Mexico.

Thanks!

JohnX said:
In this picture, with the Joint turning in the direction indicated, the shaft would be connected to the two blacked out caps. So when under load it compresses the zerk hole.
44srsw0.jpg
Click to expand...
 
Last edited:
Reusing the straps is fine as long as they are not to badly trashed. Mine have all kinds of cuts and scrapes on them...still work great.
 
You have had great advice. Please consider replacing all of your shaft U-joints at the same time. The front and the rear of a shaft are easy to replace and you will know what the age of the new joints are. I have seen a vehicle 'pole vault' when the front U joint fails, the shaft drops and then wrecks the vehicle.

Change both the front and the rear at the same time.:eeks1:
 
They recommend replacing the straps whenever you remove them. They are only a few dollars at most auto parts stores. I believe they say that because they may stretch out over time and no longer hold the caps tight allowing them to oscillate in place. If you do re-use them check to make sure the caps are held tight. I have in the past put a thin piece of brass shim stock between the cap and the strap to tighten it up. I think Haynes says this too but here goes: if after you install the new u-joint in the yokes everything feels tight then smack the side of the yoke with a hammer. This will make the yoke spring into it's proper posistion really loosening them up. I have to do this everytime I do a u-joint.
 
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