Just got back from a 600 mile round trip. On the way out I blew out the double cardan joint again. I rebuilt the shaft last fall for the same reason. The only thing I can think of is that it is over traveling some how. The leaf springs were replaced with factory new ones last spring, but this only lifted the front end back to it's original height.
Any Ideas?

 

Do you keep your hubs locked all the time?

 

Yes, always have. This didn't start until after the new leaf springs.

 

well obviously the new springs are the variable you've thrown in to the mix. Of course running the hubs engaged all the time especially on the freeway will wear out your joints faster - but 600 miles to fail is severe, you have other issues.

Although you claim they make the truck back to "stock" height, the bottom line is that you are running more space between the front output of the np205 and the front axle pinion. That said, you can/should start with the basics and do a few measurements.

Remove the front drive shaft.

Measure the angle of the np205 front output flange.

Measure the angle of the front axle yoke. - The difference is your angle of operation on flat ground of course.

CV aka double cardan drive shafts are constant velocity output from the NP205. That means that there must be little to no angle between the drive shaft and the Axle Yoke. If you are running the pinion an angle vs the shaft, you will destroy the CV joint in fast order.

(with standard U joint -non CV drive shafts, you must ensure that the output and input yokes are parallel so that the ellipses cancel each other out)

Here is some good reading:

http://www.4crawler.com/4x4/CheapTri...line-101.shtml



Ensure that your drive line is the proper length as well. Measure the distance flange face to axle yoke and compare it to your shaft - you may find that although you assume you are at stock height you are indeed have an angle between the axle pinion yoke and drive shaft (drive shaft not going straight into the pinion yoke) and/or have increased the distance beyond the maximum yield on your stock front drive line.

Pics of said truck with new springs installed?

 

Good info, thanks! I will have to take measurements and see were I'm at.
That 600 mile was the length of this trip, not how long the drive shaft was in service. It had around 6-7K miles sense rebuild. 255K ish total prior. Prior to that rebuild, it had the front u-joint replaced once in the last 100K miles. All with the hubs locked, transfer case in 2wd except when needed in 4wd.
This trip, the road conditions were severe, even bent my class 4 trailer hitch.

Notes:
The drive shaft is original to the truck.
Same shock travel length.

 

OK, this is what I came up with.
Drive shaft length is good. If you compress it all the way, you can just get it out past the yoke.
Drive shaft angle to transfer case center line is 15°.
Drive shaft angle at pinion center line is 8°.

I guess the next step will be fixing the double cardan and see how much useful travel it has verses suspension travel.

 

When I rebuilt mine a couple years ago, the parts guys actually had to match up some of the centering ball parts by hand. The spring and seal weren't listed for andodge but the all knowing guru at the local driveline shop found some Ferdinand parts that were the same. The ball and spring in the center of the double Carden need to be looked at to make sure they are holding up right.

 

I got the shaft out yesterday and the ball and spring were missing. I found parts of it on the transmission support. From the looks of it, it was not replaced at the rebuild and was badly rusted. No wonder it failed. $160 + R&R down the toilet.

 

Yeah sounds like your setup is sound. Looks like you found the problem (bad parts) and maybe have some follow up to do with the shop that o-hauled your drive shaft!

 

Follow up? With the temper I have? I wouldn't trust them anyway. I have another place I can take it to.

 

It isn't overly hard to DIY.

A ball joint press comes in handy but everything else is normal everyday tooling.

 

Precision part #606 is the centering ball kit part number.
Hope that helps.

 

Took it to a guy that builds drive shafts and he pointed out what exactly was wrong and what had to be replaced. There is a part of the cardan that has a ball on it. This piece is welded to the tube so most places will not replace it unless it is completely broken off. If the ball is worn or rusted, a new socket won't fix it. So it waits for an inopportune moment to depart the pattern.