U-Joints keep breaking

Hello folks. I need some help. I keep breaking u-joints on my 78 CJ5 with no lift. I was towing the jeep this time a few days ago and again it broke. I have tried to figure this one out. It looks like maybe my sideways angle is off.. any suggestions on diagnoising this? Please ask for more information as I am not sure what to even say here. I can tell you that once i broke the front u-joint on the rear shaft, then I broke the rear u-joint on the rear shaft and this last brake while towing just pretty much broke things completly about. Even put a whole threw my floor board under the seat.

 

Flat towing means that you 1) put trans in Neutral, 2) put transfer case in Neutral, 3) unlocked hubs. Yes?

It's possible that one of the above was not exactly as it should be, causing something to bind/lock up and thereby throwing your drive shaft off.

Preferably, disconnect and remove the drive shafts and stow them somewhere safely while flat towing.

 

Its hard to diagnose without a pic but here is a great resource..
http://4xshaft.com/index.html

go to their tech info section and look through their "geometry 101" page. alto of good info.


From your post, it sound like you are flat towing the jeep behind another vehicle. One good way to reduce wear is to make sure the front hubs are unlocked, and then disconnect the rear drive shaft from the rear axle while towing. Its only takes 10 minutes, and will cut out alot of wear.

 

Yes everything was in neutral. I had already gone 400 miles in a week with no issues. but like I said, I had broke the u-joint twice before and not towing it. If i look from under it looks like my angle from the rear yoke on the transfer case to the rear dif is about 2 inches off.. i would have to twist my engine and tranny about two inches to get a perfectly straight line... is it normal for this to be off so much? I have looked online for angles on this but could not find anything.

 

as a general rule, that's bad, but some jeeps came from the factory with a slight offset. One solution would be to get a custom shaft with CV style double cardan joints at both ends.

 

DO NOT PUT THE TRANSMISSION IN NEUTRAL!!!!!! Do a search under "flat towing". I've gone over this many, many times why you don't. It's a recipe to be replacing the transmission.

As far as checking the angles, check out Tom Wood's web site for angle info.
http://www.4xshaft.com/index.html

If you can post a pic that shows the angles that might be helpful. If the angles are off you most likely are setting up vibrations that are wiping out your u-joints. This is bad not only for obvious reasons but the vibes can also cause damage to the transfer case and diff bearings.
Next question would be what brand of joints are you using? Parts house cheapies or quality ones like Spicer's?

 

Are you replacing the grease the u joints are packed with from the store with high quaility grease? The grease most ujoints come with are only for preventing corrosion it has almost no lubricaton properties.
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yes I pump them fully with grease. I still think the issue is because of the 2 inch out of centerline from yoke to dif.

 

Are you actually breaking the U joints or are you just wearing them out? As far as your concern about angles, when you drive the Jeep do you get any vibration?

 

Which U-joint is breaking? The one at the diff or at the T-case or both?

Couple quickie solutions:

1) disconnect your rear shaft and hang it up safely while you're flat-towing. You're probably spinning it a lot faster than you normally would using the Jeep's engine power. Furthermore, when you're putting power to the rear axle via the Jeep's engine the rear pinion climbs a bit, reducing the angle. When you're flat-towing there's no pinion climb and sometimes there can even be a bit of pinion dive from the friction/drag from the tranny/t-case/tires.

2) Check the U-bolts on your rear springs. If your U-bolts are loose, you'll rotate the pinion up and can bind the U-joint, snapping it.

 

Yes.. actually breaking them.. I get a very slight vibration but nothing out of the norm for a 30 year old thing. This last time however it was the yoke nut that came off which caused the issue. I have found all the parts here ( cant believe) and i will have this thing together today. I do have ONE more question now. I have read all over the place about gear lube in the TC. read SAE 50 motor oil, and 80/90 GL4 gear lube.. which is the right one. I sure hope its the SAE 50 cause i spent all day yesterday looking for GL4 gear lube here. NADA!!! not even at an Auto Zone .

 

For a '78 CJ-5 you should have the Dana 20 T-case. Use gear oil. I think 50W engine oil is too thin unless you're wheeling at the north pole. 80W-90, 85W-140, etc.

My flattie had a severe offset on the rear driveshaft (offset Spicer 18 T-case and centered rear axle) and it spit the yoke at the T-case on its maiden voyage 'cause I forgot to put red Loctite on the yoke nut. Do that for good measure. Red Loctite and then gun down the yokes just to be safe.

Before you do the rear, somebody here should chime in because I can't remember if the AMC Model 20 rear used a crush sleeve to set the pinion bearing preload. If it does, you've got to torque the nut to about 150lb-ft or you'll overcrush the sleeve. If it's got shims like a Dana 30, 44, etc then just gun it down as tight as you like.

 

Ok.. On the gear lube.. I can find GL3 and GL5 BUT NOT GL4... which should I use? as far as the yoke nut.. I actually went out and bought a breaker bar to tighten the sucker up.. NO actual Torque wrench though. so best I think I can do is locktight and crank her down.

 

I'm sure others will chime in, here, but you can't just crank down on the pinion nut, of an AMC 20. This can put too much preload on the bearing. There's only supposed to be around 17 inch pounds of rotational force.

Rich

 

Ok.. i am going to go out again today and try to find GL4 gear lube. Also, If anyone knows the actual torque spec for the rear yoke nut on my 1978 Dana 20 TC please let me know.

 

http://www.novak-adapt.com/knowledge/dana_20_rebuild_guide.htm

 

OK folks.. after forever and a day, looks like I have things together. I read somewhere that after tighting the rear yoke nut I should be able to just barely able to turn the yoke by hand.. I hope this is right cause that's what I have now. I remember before this I found the yoke nut loose and i was unable to really torque things down without it "binding". Now its smooth, just a giggle of gear play which I can't control really. I'd say .001 to .002 of play. I found GL4 at a tractor supply store here and only paid 130 pesos (11 bucks) for a bucket that I used for both the tranny and the TC. Almost perfect ampunt. Only had about a cup left over. Jeep dealer wanted 320 pesos (28.00) a quart. heck they wanted 300 pesos just for a yoke nut... I found one for free!!!. Anyway. Thanks for all your help people. I will not know if its really in good working order for a while as I am flat towing this and I leave Sunday for Huatulco which is 500 miles away so I am NOT putting on the rear drive shaft till I actually need the Jeep (baby buddha). So for the 10,000 pesos the mechanic wanted here to fix me up I did it for less than 1000. I am ON THE ROAD. Thanks so much for all your help. Adios Amigos, or as I like to say to gringos.. Asta la way we go, Ryan, Jo-Ann, Buddhaventura and the Babybuddha.

 

Just a heads up GL5 would be ok in your Tcase. Matters what transmission you have if its ok in your Tranny. I usually end up putting GL4 in the manual trannys and GL5 in everything else