Moe's 8sp build - [email protected]

[Ronan]

Sure, it's in play, but alllllll the engineering was put in for the truck in its stock form.



When is the last time you heard about a 100% stock truck snapping a driveshaft? To my knowledge, it's never happened.



That's because the pinion angle was designed to be correct at the stock ride height and the driveshaft was designed to handle the loads and rpms of the stock truck.



Start changing the angles, loads, or rpms and you've now taken the driveshaft outside the parameters it was designed for, and no one knows what sort of safety factor it had to begin with.

In my industry(steel and rigging) everything has a safety factor of at the very least ,5:1. I would imagine it would be more in a vehicle carrying people. Lowering should affect things to a degree , but then shortening and adjust pinion angle would be the fix. Seems like there is just a weakness in those driveshafts . Just my quick .02.

 

[moregrip]

Anything new with this Matt? Hope all is going well!

 

[Hemi450hp]

Anything new with this Matt? Hope all is going well!

I'm still waiting on DSS unfortunately. I've been trying not to call them daily to bother them, but they have had my stock parts for almost 2 weeks now. I thinks it's time I give them a call tomorrow.

 

[moregrip]

I'm still waiting on DSS unfortunately. I've been trying not to call them daily to bother them, but they have had my stock parts for almost 2 weeks now. I thinks it's time I give them a call tomorrow.

I know the feeling. Did you happen to catch that other link I posted?

 

[Hemi450hp]

I know the feeling. Did you happen to catch that other link I posted?

I did, but I have not called them yet. I looked through their website and I didn't see anything about two-piece driveshafts.

 

[Dubstep Shep]

In my industry(steel and rigging) everything has a safety factor of at the very least ,5:1. I would imagine it would be more in a vehicle carrying people. Lowering should affect things to a degree , but then shortening and adjust pinion angle would be the fix. Seems like there is just a weakness in those driveshafts . Just my quick .02.

Noooooo. Quite the opposite in fact.

Automotive has some of the lowest safety factors on many of their stuff of almost any industry besides aerospace. That's because a $0.02 reduction in cost on a part equals out to a HUGE cost savings when you're making millions and millions of cars.

Even in my industry, where we design BOPs and other pressure control equipment, safety factors on some components are between 1 and 1.5. Usually the material is about 10%-30% stronger than what we use in our design calculations, but still.

 

[Ronan]

Noooooo. Quite the opposite in fact.



Automotive has some of the lowest safety factors on many of their stuff of almost any industry besides aerospace. That's because a $0.02 reduction in cost on a part equals out to a HUGE cost savings when you're making millions and millions of cars.



Even in my industry, where we design BOPs and other pressure control equipment, safety factors on some components are between 1 and 1.5. Usually the material is about 10%-30% stronger than what we use in our design calculations, but still.

Well, that's just craziness!!!!

 

[moregrip]

I did, but I have not called them yet. I looked through their website and I didn't see anything about two-piece driveshafts.

yeah sorry I didn't explain where I was coming from very well; my idea was potentially giving you an option to build a stronger 1pc driveshaft that would live at the higher driveshaft rpm's vs our stocker.....keep it a little simpler and cheaper.........of course, that's if the numbers work out

 

[Hemi450hp]

OK guys, I have an update from DSS. 5" Aluminum driveshaft will be $949, and the 3.8" Carbon Fiber driveshaft will be $1599.

They are going to be using the same CV's, flange material, and shafts in these driveshafts that they use in their Hellcat application that has been proven at over 200mph and 1200hp.

They said my carbon driveshaft will be ready to ship next week, so I will be testing it as soon as it comes in. Once I can prove that it will take the abuse, we will be stocking these for those of you that are looking for an upgrade.

 

[Kotta390]

Can we get the weights for all 3 driveshafts? $1599 is very steep for a driveshaft but if it weighs next to nothing it will be worth its weight in gold because the drivetrain loss percentage will be lower.

 

[Booms]

So, does anybody have an explanation as to why these driveshafts are failing? Is it the power? Because if it was, I would assume that the minute the engine hit its tq/hp max, that would be when the driveshaft failed, not wait until it got above 100+ mph.
Somebody explain please.

 

[PassivAggressor]

Good to hear there will be options out there. I hope to have to never need one. I'm guessing that the are both solid and not adjustable or whatever like the stock one?

 

[Tomater03]

Thanks Mike. I'm starting to think that this truck might even see 11.9-12.0 on a stock tq converter.

I think that's very possible Matt . 1.78 60' in positive DA and 7.96/12.4x with barely any bolt ons. It's definitely got potential , I'm hoping that a 3000-3200 stall comes out for them tho. After watching a few videos, this thing doesn't come alive till about 10 feet out. But at that point it's a damn rocket. So improvement is definitely there to be had. 11.9 in about a year in these 8 speeds, I believe will be a common accurance, by then we should have stalls, trans tuning, more rpm, and a little more R@D. Should be fun

 

[Hemi450hp]

So, does anybody have an explanation as to why these driveshafts are failing? Is it the power? Because if it was, I would assume that the minute the engine hit its tq/hp max, that would be when the driveshaft failed, not wait until it got above 100+ mph.
Somebody explain please.

From the math I have done, it appears that the stock driveshaft has a critical speed of around 5350rpms. Below is a quote from the DSS website explaining how to calculate critical speed...

"To check for critical speed, calculate this equation:

Top speed ____ x 336 (a constant) x rear ratio (like 4.10), then divide it by the tire height (28” tall tire)."

Most 3.92 trucks with stock tires lose their driveshaft at 130mph, so lets do the math...

130 x 336 x 3.92 = 171225.6. Now divide that by 32, and you get 5350RPM critical speed.

My driveshaft let go at 110mph with a 27" tire, so here is the math on that setup...

110 x 336 x 3.92 = 144883.2. Now divide that by 27, and you get 5366rpm critical speed.

It is more than a coincidence that they failed at almost the exact same critical speed rpm. With stock tires, stock 3.92 gears, and the factory speed limiter of 105mph, your critical speed never goes above 4321rpm, so this is not an issue in stock form. Its when you start pushing higher speeds and spinning the driveshaft faster that they go beyond the critical speed rating of the factory shaft and fail.

 

[Booms]

^ Great explanation...

But...lol...

Doesn't the driveshaft exceed 5350 rpms in 1st gear, 2nd gear, etc.?

Why doesn't it fail in the lower gears when it exceeds it "safe" rpm limit, instead of waiting until your above 130mph?

 

[Booms]

Unless Your talking driveshaft rpms instead of engine rpms...then I get it....

 

[Hemi450hp]

Its the driveshaft rpm, not engine rpm. In 1st gear, you dont exceed 50mph, so if you put 50mph as the top speed in that critical speed equation, you are going to get a very low number.

50 x 336 x 3.92 = 65856. Divide that by 32 (tire size), and you get a critical speed of only 2058RPM. The stock driveshaft does not fail until it gets up to about 5350rpm, so it is not an issue at lower speeds regardless of the engine rpm.

 

[Booms]

Very cool explanation of the whole thing Matt....thanks!

 

[Gary's Hemi]

Thats some good info

 

[moregrip]

From the math I have done, it appears that the stock driveshaft has a critical speed of around 5350rpms. Below is a quote from the DSS website explaining how to calculate critical speed...

"To check for critical speed, calculate this equation:

Top speed ____ x 336 (a constant) x rear ratio (like 4.10), then divide it by the tire height (28” tall tire)."

Most 3.92 trucks with stock tires lose their driveshaft at 130mph, so lets do the math...

130 x 336 x 3.92 = 171225.6. Now divide that by 32, and you get 5350RPM critical speed.

My driveshaft let go at 110mph with a 27" tire, so here is the math on that setup...

110 x 336 x 3.92 = 144883.2. Now divide that by 27, and you get 5366rpm critical speed.

It is more than a coincidence that they failed at almost the exact same critical speed rpm. With stock tires, stock 3.92 gears, and the factory speed limiter of 105mph, your critical speed never goes above 4321rpm, so this is not an issue in stock form. Its when you start pushing higher speeds and spinning the driveshaft faster that they go beyond the critical speed rating of the factory shaft and fail.

Awesome man! Glad you figured it out! once you get the new DS installed you can haul the mail again and show us what that truck is really capable of!