77 EB Rear Drive Shaft Dropped - Second time in six months

[UTFLIWGYA]

OK,

So it's probably a good thing that I wasn't able to go to Uhwarrie this weekend, because I was having some "vibrations" (Not the Good ones from the Beach Boys) in my rear end that had me concerned.

Unable to discern where they were coming from (no obvious leaks, smoke, fire, etc.) I decided to "observe" the vibrations for a little while.

Background: Less than six months ago, i was having similar issues, and eventually the rear driveshaft dropped in the back, got a little dinged up on the roadway and I got it fixed. I couldn't change out the U-Joints in my garage, so I bought new one and had a local shop press the old one out and install the new ones.

So today, heading down the road at about 35 MPH, it happened again. I pulled over, put not he hazards and got to work dropping the rest of the DS. I limped home in 4X2 with the front hubs locked in.

So, now the Bronco is in garage cooling down.

Questions:

What do you suppose would cause this?

1) A warped or imbalanced DS? Should I have it professionally "tuned"?

2) What type or brand of U-Joints should I purchase to replace the ones that broke?

3) What do I need to check on the rest of the DS? Should I also replace the other U-Joints to avoid this in the future?

4) What is the maximum speed I should drive with just the front DS engaged in 4X4(2)????

Thanx guys….

Looks like I'll be riding the Harley tomorrow morning……

[chuzie]

Depends on a lot of stuff.

When the drive shaft is installed, is it a relatively straight line from the rear yoke up the driveshaft?

Extend and compress your driveshaft. Does it slide correctly on the splines?

Twist the slipshaft. Is there a lot of slop?

How much spline is showing with the shaft installed?

Can you compress the slip shaft a couple inches with the shaft installed on the rear of the transfer case?

If none of this is an issue, I would take it to be balanced. Should be cheap. I like to use cheap u-joints. I prefer them to break than an axle.

It is also possible that the new joints were installed improperly. Just takes one smashed needle to kill a joint over time.

[dougsride]

did you figure out your issue with driveshaft yet?

[Bronco Biff]

Where is it failing? I have known guys going thru ujoints quickly and found they where dogging the u-bolts on the yoke down much too tight and deforming the caps causing them to fail quickly. I broke the spiders in the rear of mine one time and removed the rear shaft, locked the front hubs and ran it 60 miles down the interstate at 60 plus MPH......no issues.

[broncomatt]

If all the shop did for you was change the Ujoints they probably didn't check the balance. To be truthful if the truck has any lift I would just bite the bullet and buy a Tom Woods Shaft. They're the best on the market and they stand behind their product. As for how much to drive in 4wd with out the shaft, you can drive it as much as you would in 2wd but watch how hard you accelerate and what the top speed you go too.