Toe

Ouch, what mph were you at on the dyno when the shaft came apart? A couple hemi owners have had there's gernade on them when running 122mph+. Long drive shafts like the ones on a truck at those speeds can flex too much and gernade.

Bradazz

iTrader: (2)

It broke at 119mph according to the Dyno graph. I could feel the truck starting to vibrate during the dyno run but I didnt think that my driveshaft was going to break.

Bradazz

iTrader: (2)

I saw this picture and had to post it here.

moregrip

iTrader: (8)

That looks like Naked AV's driveshaft when his let go.

I have the stock 2pc dana-spicer 3.5" steel driveshafts and they are safe to 6300/7000 rpm respectively according to dana-spicers critical speed chart and my local driveline shop. the 4" DOM reccomendation sounds like a good one to me

Mr. Sandog

You should do a little more than just replacing the driveshaft if you had vibration problems prior to it letting go.

I had a pinion angle problem that caused my driveshaft to let go at 141 mph on the dyno...but what's interesting about that is, I had noticed some vibration at 70 mph ever since I lowered the vehicle.

If your shaft let go at ~120 mph, let me ask - did you notice vibration at 60 mph, however slight? They are harmonics of each other, which means that a vibration at 60 mph reappears at 120 mph, only worse.

Make sure you don't have a pinion angle issue. The results next time with a steel shaft might not be so pretty.

Bradazz

iTrader: (2)

Yea I did not check the pinion angle after I installed the Hotchkis 2-4 drop but I will be checking it after I get the new driveshaft installed. To tell you the truth I didnt really notice any vibration except for when I got up to about 110 and then I felt a slight vibration. Thanks for the heads up, I heard that the pinion angle should be between 5-7 degs? Let me know if this is true. BTW, What kind of driveshaft did you get?

Mr. Sandog

The pinion angle should be opposite and equal to the angle of the transmission output shaft. For example, if your transmission output shaft faces downward at 5 degrees, then your pinion should face upward at 5 degrees.

When I finally had my angles looked at (well after my 2/3 drop and right after the driveshaft blew up), my transmission output shaft aimed down 4 degrees, but the pinion aimed up at 7 degrees. This fully explained the driveshaft incident.

After installing longer lower control arms (I had a 5-link in the Avalanche), the new pinion angle was then down 3 degrees. This was actually ideal, since applying Radixed torque actually moves the pinion up a degree or so, making the angles equal (4/4) under heavy torque load.

I ended up getting a stock replacement driveshaft. With the pinion angle correction, there was no problem after replacement.

Hope this helps. Definitely get it looked at by a shop that knows what they're doing.

Bradazz

iTrader: (2)

Thanks for the info, I will have somebody who knows what they are doing check it out.

gonzo 6.2

iTrader: (8)

Amazining how quick you got out of it,no over rev.

Bradazz

iTrader: (2)

Here is a picture of the new driveshaft. Dynotech 4" Steel DOM.