Drive Shaft Exploded!

[Keith Browning]

I just replaced a drive shaft on a 2008 F450 as per TSB 08-5-3. Road tested and finished up. Customer got in it and got onto the highway and up to speed then BANG! The harmonic balancer came apart at 70 MPH. He looked in the rear view mirror and saw cars evading the pieces, saw one half moon shaped part flying off the road.

 

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[BrunoWilimek]

There was probably a crack in the outer ring of the balancer. They crack real easy if hit or dropped. At least if they are the same as one I worked on a couple of years ago. A hairline crack would not be easily seen. Who knows what treatment the shaft got during shipping. /forums/images/%%GRAEMLIN_URL%%/cover.gif

[LARRY BRUDZYNSKI]

Keith, correct me if I'm wrong, I probably am. Aren't the Driveshafts indexed now???? I thought when we had a trainer from Ford in that he stated that the shafts had to be installed with the correct index or there would be vibration problems.

[Keith Browning]

They always have been. THe problem with this shaft was the harmonic balancer came apart, it is pressed on during production and it is intended to silence resonations.

[Jeff_E]

Quote:

Aren't the Driveshafts indexed now???? I thought when we had a trainer from Ford in that he stated that the shafts had to be installed with the correct index or there would be vibration problems.

Excellent question Larry, as it happens to be fresh in my mind!

Yes indexing is very important. When you remove a driveshaft that you are going to reinstall later, it is a good idea to make a paint mark on the pinion flange and the yoke so that you can reassemble it in the same position to avoid any balance issues, especially now that drivelines are "system balanced". Driveshaft indexing also relates to a much more important issue...the indexing of the u-joints on shafts where there is a spline between the joints. The time a technician would have to be cautious in this regard, is if he were to do something like a center support bearing replacement where you have to take apart a splined multi-section shaft to do the job. If you reassemble the shaft in any old spline-clock position you can run into big problems if the rear joint isn't "in phase" with the front joint. This is because the operating angles through which the joints operate, actually cause the shaft to speed up and slow down twice per revolution. If the joints are "clocked" in sync with each other, these speed changes cancel each other out and there is no problem. If however a multi section driveshaft is taken apart along a spline joint, and then reassembled so the joints aren't clocked identically, these speed changes don't cancel out and ultimately cause a harsh wind up condition. Since Keith's driveshaft was replaced as an assembly I doubt his problem had anything to do with to do with being out of "phase"...unless of course the guy at the factory who built the shaft was clueless about the meaning of Phase.

By the way, the operating angles of the front and rear joints have to be within a degree of each other, otherwise the cancellation effect is compromised. This is why, if you are doing a lift on a truck, it is preferable to do a Body lift rather than a suspension lift - this way you don't risk changing the driveline angles. Any Questions? Good!!! I had to sit through a 3 day NVH class to learn the concept in this post /forums/images/%%GRAEMLIN_URL%%/drinkingdude.gif

Actually here is some more info on the subject Driveline Info

[LARRY BRUDZYNSKI]

Keith any outcome on this one???

[Keith Browning]

Well, we put another shaft in it and way the truck went. I can only assume there was a defect in the metal of the heavy ring of the harmonic dampener. Kinda like the new recall on 2008 Econoline for porous metal in the slip yoke. "inspect build date and replace shaft if required."