70 c10 LWB driveline options - The 1947 - Present Chevrolet & GMC Truck Message Board Network

rjcamel2355 · 11-01-2023, 09:46 AM

Hey everyone, Looking for some information/thoughts on this.

I currently have a 70 C10 LWB, running a 70" U to U driveline, 4" aluminum out of a late 90's extended cab chevy.

Shaft fits fine, but I know critical speed and length are an issue here.

Engine is a 408CI ls engine with twin 6766 turbos, th400 trans and a 12 bolt with 4.11s in the rear. I intend to spin this motor up over 7000RPMS, and I have done so, but it's definitely a concern. This truck gets drove on the street far more than at the track, but will see some track time.

Most places want to move me to a carbon fiber shaft, at around $2000.00 and it may be my only option, but that's a hard number to swallow.

LS short box · 11-01-2023, 04:38 PM

I have never used a carbon fiber drive shaft but if I under stand right if they break they kind of shred into fuzzy pieces. If you blow up the aluminum shaft there's pretty good chance you are going to loose the end of your trans. At the very least either way run a good drive shaft loop.

mxerhale · 12-19-2023, 08:42 PM

Full Torque Driveshafts in Idaho did my C1500 LWB shaft in aluminum, you can see pics in my build that's on here,check my signature for the link.

So far its held up just fine to 7lbs of boost and 300 miles of some foolish driving in my truck hitting 6400RPMs on a number of occasions.

Joyridin · 12-20-2023, 10:05 AM

What tire diameter are you running? According to one of the online calculators, the critical speed of that driveshaft with a .125" wall thickness in 4" aluminum is 5950 RPM.

http://www.wallaceracing.com/driveshaftspeed.htm

mxerhale · 12-20-2023, 09:14 PM

26.6 inch tall 295/50-15 tires.

**Accelo** · 12-24-2023, 12:24 AM

The 7K engine speed only matters if it's in drive/3rd gear. All other gears the driveline speed it significantly reduced.

https://spicerparts.com/calculators/...rpm-calculator

At 7000rpm and 1:1 transmission ratio the truck speed would be 135mph.

I am no expert, however a two piece drive shaft would be supported in the middle and as such would have a reduced tendency to whip at the first critical speed.
It could be a lower cost solution? You may have enough power to run a higher differential gear ratio?

11-01-2023, 09:46 AM	#1
rjcamel2355 Registered User Join Date: Dec 2020 Location: Oklahoma Posts: 7	70 c10 LWB driveline options Hey everyone, Looking for some information/thoughts on this. I currently have a 70 C10 LWB, running a 70" U to U driveline, 4" aluminum out of a late 90's extended cab chevy. Shaft fits fine, but I know critical speed and length are an issue here. Engine is a 408CI ls engine with twin 6766 turbos, th400 trans and a 12 bolt with 4.11s in the rear. I intend to spin this motor up over 7000RPMS, and I have done so, but it's definitely a concern. This truck gets drove on the street far more than at the track, but will see some track time. Most places want to move me to a carbon fiber shaft, at around $2000.00 and it may be my only option, but that's a hard number to swallow.

11-01-2023, 04:38 PM	#2
LS short box Registered User Join Date: Jun 2015 Location: Carlos MN Posts: 2,136	Re: 70 c10 LWB driveline options I have never used a carbon fiber drive shaft but if I under stand right if they break they kind of shred into fuzzy pieces. If you blow up the aluminum shaft there's pretty good chance you are going to loose the end of your trans. At the very least either way run a good drive shaft loop.

12-19-2023, 08:42 PM	#3
mxerhale Registered User Join Date: Nov 2020 Location: northern Utah Posts: 48	Re: 70 c10 LWB driveline options Full Torque Driveshafts in Idaho did my C1500 LWB shaft in aluminum, you can see pics in my build that's on here,check my signature for the link. So far its held up just fine to 7lbs of boost and 300 miles of some foolish driving in my truck hitting 6400RPMs on a number of occasions. __________________ My 1971 GMC build

12-20-2023, 10:05 AM	#4
Joyridin Registered User Join Date: Sep 2020 Location: Cleveland, Ohio Posts: 558	Re: 70 c10 LWB driveline options What tire diameter are you running? According to one of the online calculators, the critical speed of that driveshaft with a .125" wall thickness in 4" aluminum is 5950 RPM. http://www.wallaceracing.com/driveshaftspeed.htm Last edited by Joyridin; 12-20-2023 at 10:16 AM.

12-20-2023, 09:14 PM	#5
mxerhale Registered User Join Date: Nov 2020 Location: northern Utah Posts: 48	Re: 70 c10 LWB driveline options 26.6 inch tall 295/50-15 tires. __________________ My 1971 GMC build

12-24-2023, 12:24 AM	#6
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,299	Re: 70 c10 LWB driveline options The 7K engine speed only matters if it's in drive/3rd gear. All other gears the driveline speed it significantly reduced. https://spicerparts.com/calculators/...rpm-calculator At 7000rpm and 1:1 transmission ratio the truck speed would be 135mph. I am no expert, however a two piece drive shaft would be supported in the middle and as such would have a reduced tendency to whip at the first critical speed. It could be a lower cost solution? You may have enough power to run a higher differential gear ratio?

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