03/21/2026
From time to time a driveshaft comes into the shop that presents a "learning moment". This is one of those situations. This driveshaft was an online purchase from a business that I won't name as to not make anyone look bad. This driveshaft was made with tubing that was too small in diameter for its length / speed. Critical Driveshaft Speed is a fairly complicated mathematical formula, but the major factors are 1) distance between support centers and 2) diameter of the shaft. Once you cross the speed limit....CDS not the vehicle's speed, you are asking for trouble. In most Chevy 1/2 ton trucks that use a single section driveline the shaft is between 78 and 83 inches or so...the tube is 5" in diameter. The Chevy 1/2 ton comes with an electronic speed limiter that in most cases starts cutting power to the driveline at 94 to 98 miles per hour.
If you change the tire size to smaller tires to help you "get off the line" you just got closer to CDS. If you change the gears from 3.73 to 4.11 you just got closer to CDS. If you get your "tuner" to remove the electronic speed limiter so you can go faster top speed, you just got closer to CDS If you have done 2 of the above things or all three of them, YOU ARE DRIVING A BOMB waiting for it to explode. I don't care who made it, how straight it is, how well balanced it is....it is going to come out and drivelines ejected at high speeds are destructive and deadly.
I have had many people call after chunking out their single section driveshafts and they get asked the 3 conditions above....99% of them have done at least 2 of the things that will give this result. I get the responses sometimes of "I was driving down the road at 40 MPH when it came out so you don't know what you are talking about" and I explain that this damage to the internal structural integrity of the metal is cumulative, not instantaneous and once the fatigue gets to the point where it can no longer flex, it breaks and out it comes. If you are lucky it does happen a slow speed.
Talking with people that call about this breakage I say to them "did it break about 18 to 24 inches in front of the differential?" and the response is "how did you know that?" I know that because that is where they all break after you have done 1, 2, and 3 above. I am not picking on Chevy Silverado's on purpose. The fact of the matter is 85% of these calls are from people driving them. It can and will happen to any driveline operated above CDS.
The guy that removes the speed limiter more than likely does not tell of this happening, the guy that changes your gears more than likely does not tell you this, the tire shop that puts on smaller tires more than likely does not tell you this. Put these three things together and your driveline is spinning on borrowed time. If you are doing this or thinking of doing this ask yourself "have I told the service providers doing these three things what other work I have had done or plan to have done?
The above shaft was made too long out of too small of a diameter for freeway speeds..doomed before install to fail. The attempt at patching it back together was shown as a trying very hard to fix it at home but drive lines that spin faster than 350 RPM need to be a bit straighter than this.
I watched these sections of driveshaft from my chair as Christopher was speaking to the customer....I was glad the customer did not get injured or killed in this driveline blow out. You can see from the cut out bent section this driveshaft got thrown out when it suddenly became too short to sustain its support centers.
In my 18 years of building driveshafts, I have had only one home made shaft come into the shop for balancing that was within tolerances I use to build them..only one. BE SAFE OUT THERE!!!
