PSA: Why these trucks have a low speed limiter.

Darth_Vader · June 7, 2017

Just a reminder for all you people out there who want the speed limiter removed on your truck. It is there because of the critical speed of the drive shaft.

Even a 4" upgraded race shaft good for over 1200 lb/ft can let go and when it does you are get lucky if it only takes out a couple of things. Took out the transmission tail housing, gas tank and of course a $700 driveshaft. And that is what I know of, there is still a chance of transmission and differential damage.

Here is what I could find of mine.

Bxnanaz · June 7, 2017

Glad you're alright.

Not sure why anyone would wanna remove the speed limiter on a truck. If 95mph (or whatever it is) isn't fast enough, you probably bought the wrong vehicle

Justin101714 · June 7, 2017

I agree, not to mention the tires aren't rated to go much faster than the limiter. They can come apart too

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dasimmon · June 7, 2017

Glad you're alright.

Not sure why anyone would wanna remove the speed limiter on a truck. If 95mph (or whatever it is) isn't fast enough, you probably bought the wrong vehicle

exactly

truckguy82 · June 7, 2017

Glad you're alright.

Not sure why anyone would wanna remove the speed limiter on a truck. If 95mph (or whatever it is) isn't fast enough, you probably bought the wrong vehicle

Because it's just an option in a tune.

I deactivated mine just because I'm not the general public, and I understand the limitations of the vehicle.

truckguy82 · June 7, 2017

Another guy on performance trucks did the same thing to his driveshaft, but I think it was at 140mph.

What speed did this happen at?

bdbake01 · June 7, 2017

For those of you who may think that a stronger/stiffer/more resilient/thicker/exotic/etc shaft is the magic solution to a "weak" shaft as the problem, I'd like to submit the Tacoma Narrows Bridge which failed due to resonance when subjected to a mere 40 mph wind:

https://en.m.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)

Darth_Vader · June 7, 2017

Another guy on performance trucks did the same thing to his driveshaft, but I think it was at 140mph.

What speed did this happen at?

103mph, but there are a lot of things to take into consideration. My critical speed was supposed to be 135mph even with 4.56 rear gears and a 29" V speed rated tire, so I have my limit set to 10 mph under that to be safe, but at the same time I was making significant power when it let go so any kind of critical vibration on this shaft compounded with being at the peak of the power band caused it to twist.

truckguy82 · June 8, 2017

103mph, but there are a lot of things to take into consideration. My critical speed was supposed to be 135mph even with 4.56 rear gears and a 29" V speed rated tire, so I have my limit set to 10 mph under that to be safe, but at the same time I was making significant power when it let go so any kind of critical vibration on this shaft compounded with being at the peak of the power band caused it to twist.

4.56 rear and 29" tires, well yeah in regards to driveshaft speed that's like doing atleast 140mph on the factory setup.

Not sure where you got that critical speed calculation, but I mean it seems obvious that's what happened.

Darth_Vader · June 8, 2017

4.56 rear and 29" tires, well yeah in regards to driveshaft speed that's like doing atleast 140mph on the factory setup.

Not sure where you got that critical speed calculation, but I mean it seems obvious that's what happened.

This wasn't the factory shaft. This was a shaft built for this setup for that critical speed.

truckguy82 · June 8, 2017

This wasn't the factory shaft. This was a shaft built for this setup for that critical speed.

oh, whoops, missed that part

Wow that really sucks then, you fixed both speed limitations, the tires and the driveshaft, and it still failed.

Darth_Vader · June 8, 2017

Should of gone CF from the start.

GRN69CHV · June 22, 2017

What vehicle was this in? 4.56 gears with a 29" tire will spin the driveshaft at about 5400 rpm at 103 mph. That's buzzing along but not as bad as could have been. By comparison, factory stock driveshaft rpm for truck set up with 3.42 gears and 32" tire at same 103 mph is 3700 rpm. I'd guess that driveshaft failure was due to impact damage that threw it out of balance.

07Softail · June 22, 2017

The PPV Tahoes have a top speed limiter of 150MPH so i'm not sure what the big deal is. My truck has seen 140+ several times with the stock (trued shaft). i have been told not to let completely shut off the throttle when doing runs like this but to reduce mph gradually as not shock the driveshaft on decel.

RT

Darth_Vader · August 15, 2017

The PPV Tahoes have a top speed limiter of 150MPH so i'm not sure what the big deal is. My truck has seen 140+ several times with the stock (trued shaft). i have been told not to let completely shut off the throttle when doing runs like this but to reduce mph gradually as not shock the driveshaft on decel.

RT

I exceeded the critical speed. Plain and simple. Now had I not been WOT in 5th gear with a Procharger pushing over 11lbs of boost while injecting 1000cc of Methanol maybe it would of held together.