Bad U Joints

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Jun 22, 2003
Ok. So after I posted my problem a few months ago, I finally had my U Joints checked out. My issue was a big "CLUNK!" when I was sitting still and let off my brake. I also heard it (felt it) at times when I was coming to a quick stop and the auto trans was down shifting. Some on the board said it was probably a U Joint problem.

I recently had a full mechanical inspection and on thing that was noted was 4 bad U Joints. My question is, what issues am I looking at (aside from the clunk) if I don't replace them?

92' FJ80, 134k miles
Issues - Vibration, or sitting on the side of the road with the driftshaft hanging down. A u-joint without grease will get very hot and fail. One with a lot of play will snap. I have broken several. FWIW, on one that the cups were held in with a U-bolt, I was able to find a socket that fit the joint and the U-bolt, and was able to limp in shaking like dog just out of water. On one other one the U-joint sheared at a 45 degree angle where it came out of the cup. I put it back in, went to pull out and it just wound out again. Then it dawned on me that with that angle it only did it one way, so I put it back together and BACKED up for about three miles to where I could leave it. Had a crink in the neck for a couple of days. :D You may get away with it for awhile but it will probably let go at the worst time/place.
is it possible that if you blow a uni that a 2 piece shaft will fall appart, leaving you with half a shaft, the other one down the road?

Thunder_horse get them done, it shouldn't be to much
Not normally if the U-joint snaps but if the driveshaft itself snaps, then yes. Had one once let go on a GTO at over 100 MPH. The front piece came out of the transmission, oil went all over the exhaust resulting in a fire. The danger is too, if the U-joint/driveshaft busts say in the back, the driveshaft gets to whipping around and starts taking other things with it - like the exhaust, gas tank, etc.; before you can get stopped. Had a dump truck once that let go in the rear on a hill and took the exhaust. The funny part was the emergency brake worked on the driveshaft so I could not put it on to get out to direct traffic around. I had to sit there roaring with my foot on the brake with the traffic behind me playing tunes on their horns till they finally got tired and went around and I could back down to a flat spot.
do them your self, get 4 new OEM(preferred, cost around $200 for 4) U-joints, drop the shafts and replace them, it;s not hard, but takes some time, can be done with nothing more than a hammer and socket, I prefer to use a vise........last time I missed the socket with the hammer and wasted my thumb......OUCH. Make sure you mark the 2 shaft halfs so you get them back in phase(rear) and out of phase(front) make sure the zirts face the rigth way(so they are compressed when spining).

If you don;t want to do them yourself, take the drivelines out and take em to a driveline shop and have then replace em(might have them balance the shafts at same time) they dont charge much, they will prolly not use OEM joints but they will still use a quaility joint(prolly TRW) If you don't have a spare car to drive, just take one shaft at a time in to be fixed, then drive in front or rear wheel drive.

I have seen a bad joint get so hot it glows red! highly recomened replacing ASAP, they will fail at the worst time...

John H
why do the fronts go in out of phase?
[quote author=bad_religion_au link=board=2;threadid=5010;start=msg38486#msg38486 date=1062860403]
why do the fronts go in out of phase?

because thats the way its designed, why I don't know, its the only Cruiser that is like this, I didn't believe it either but its true.
the uni's in my 40 are now in phase, and when i ran it at 100 there didn't seem to be a problem with them in phase
I believe that is very important to stress something that Bill mentioned in his usual under stated fashion:

Crawl under the vehicle and look at the fuel tank and it's relation to the rear driveshaft. How far do you think it would need to get "out-of-bounds" to slam and probably rip open the fuel tank? Next, look at the "HOT" exhaust just to the otherside of the driveshaft and the fuel tank.

Now, slide to the front and notice how the front drivshaft runs along next to the transmission and just below the engine oil pan.

Would you really like either one of them flopping around under there? ::)
Here's a couple of other worst case scenarios: 1) u joint on front of driveshaft fails and driveshaft drops straight down and digs into road and then back joint breaks and driveshaft punches up through floor - not pretty. 2) or u joint on front of driveshaft fails and driveshaft drops straight down and digs into road; back joint doesn't break but instead the driveshaft "pole vaults" the truck up in the air - this isn't pretty either.

Neither scenario is common, but both have happened in the past.
Well that clears some things up! :eek: Thanks to all for the posts and words of warning. I guess I didn't realize just how nasty this could get. By the end of this week, I will have new U Joints...

I'm betting the clunk is NOT your U joints, but with all these scenarios running through your head you'll probably call to increase your life insurance before driving it to the nearest shop :)

If this vehicle has had the joints greased a couple times in its life, your U joints are probably fine. You can lay under there on a level surface and shake/twist the joints to see if there's slack yourself. I suspect you'll find the actual slack is not in the shaft joints.

The reason I say this is the ridiculously low miles on your 80. Unless it's both been neglected mechanically, AND abused offroad I suspect the joints are fine. That engine really can't stress those joints much.

If I were a betting man, I'd say your slack is in the front drive plates.

I have a sudden urge to shoot grease into my U-joints :p
i know i just regreased mine after reading this
Interesting. I have posted before of the same clunk. My driveline lines rotate .25" -.5" about axis under no load. But the joints seem to be tight, its the whole driveline assembly before the go back into the diff. This goes for front and back shaft. My guess to date is the diff bearings(pinions,front,back,etc.). I would think it has more to do with the transfer case or does it.
Any suggestions?

Yep, keep those shafts greased - reduces all manner of vibes and clunks. Even helps the truck ride better since the shaft must elongate/shorten with suspension movement. Let 'em get dry, apply some engine torque and they'll move only with a herky jerky movement. Grease 'em and they glide and slide like Mr. T intended.

Just don't overgrease the spline grease fitting. Once you see movement, STOP.

Chris - You're seeing what I think Thunder will see if he takes the time to look instead of accepting someone else's assesment of his truck. The U joints are way stout and not likely to be an issue here. With a full time system including all three diffs and 6 shafts (4 axle shafts, 2 drive shafts), some movement is normal. But if you have dry/sticky U joints and shafts the slack will come out with a clunk. Now that I think of it, I was assuming his joints were properly greased, but I should say directly that is the first thing I'd do when tracking down a drivetrain vibration or clunk - lube 'em.

O lubed the shafts and the yokes last year. A friend of mine has a 96LC his rotational play is about .125(1/8)" rotation vs. my .5(1/2)" big difference for normal play in the system. Trying to pinpoint if this is dif bearing problems or transfer case problems. The yokes, u-joints and shafts seem strong till they enter the diff(front and back) and transfer case housing.
Rotational play should have nothing to do with bearings. It would more likely be caused be gear backlash. Some backlash is normal for expansion and lubrication. I don't know if there is a spec. for what is abnormal the way you are twisting the driveshaft. One adjustment would be to have the ring and pinion resetup. If you are so inclined you could drop the driveshaft and see which end has play in it. Other things can contribute to this type of play such as worn yoke or axle splines etc. Hope this helps.
Opened up a whole new can of worms now...
Doug, you are correct. The U Joints looked ok. What I did find however is a front drive shaft that rotates with about 180 degrees of play. That seems a bit excessive. Not being very technical myself, I had it looked at by a shop and they didn't want anything to do with it. All they do is replace them and ballparked about $3k. Any ideas? Is there another fix for something like this?
180 degrees :eek:

I think I would remove the shaft and check the transfer and front diff and the driveshaft, while it's out, to see where it's coming from. That is a HUGE ammount of movement.

Users who are viewing this thread

Top Bottom