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PSA: Why these trucks have a low speed limiter.

Darth_Vader

By Darth_Vader
in Engines & Drivetrain

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Darth_Vader Enthusiast

Darth_Vader

Posted
Posted

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.

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Bxnanaz Enthusiast

Bxnanaz

Posted
Posted

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 Enthusiast

Justin101714

Posted
Posted

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

 

 

Sent from my iPhone using Tapatalk

dasimmon Enthusiast

dasimmon

Posted
Posted

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 Senior Enthusiast

truckguy82

Posted
Posted

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 Senior Enthusiast

truckguy82

Posted
Posted

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?

Darth_Vader Enthusiast

Darth_Vader

Posted
  • Author
Posted

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 Senior Enthusiast

truckguy82

Posted
Posted

 

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 Enthusiast

Darth_Vader

Posted
  • Author
Posted

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 Senior Enthusiast

truckguy82

Posted
Posted

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.

  • 2 weeks later...
GRN69CHV Enthusiast

GRN69CHV

Posted
Posted

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 Senior Enthusiast

07Softail

Posted
Posted

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

  • 1 month later...
Darth_Vader Enthusiast

Darth_Vader

Posted
  • Author
Posted

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.

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