Driveshaft questions on T-5 swap

Turborg · 04-10-2004, 12:15 AM

While inquiring about driveshafts at local shops I was told by two out of three that a drive shaft that is 60 inches long (approx six inches shorter than what is required on the t-5 swap) and 3" in diameter will reach its critical speed at 4000 RPM. Critical speed is defined as the rpm at which the driveshaft can fail if speed exceeded. I also checked on the internet under the heading "driveshaft critical speed" and saw the charts the driveshaft shops were using. My Volvo would be going less than 100 mph at this driveshaft speed. I would appreciate any input on this as I am ready for a driveshaft now.
I am leaning toward having the short shaft on my shortened and beefing up the carrier bearing.

boostdemon · 04-10-2004, 01:55 AM

use a 2 piece

Turborg · 04-10-2004, 10:03 AM

My car with 3.73 rear end would reach critical speed on the 3" dia, 6' long driveshaft at 77mph(4000 rpm) in fourth gear.

Greg Wong · 04-10-2004, 10:12 PM

I don't know where you are getting this 66" driveshaft figure from, but on my car, the driveshaft is about 41" tube length. Add a few inches for center-center ujoints. It's a V8 conversion with the T5 trans, and from the pictures of Doug's car, the tranny looks like it's in about the same place. So figure around 40 something inches.

My D/S is 2" diameter, and I have a 3.73 rear gear. I should be safe until somewhere around 120 mph. I have been up around 115 at least, and I haven't gotten any vibration yet. If I were starting over, I think I would do 2.5", because if you start going much larger, then you can start getting clearance probs.

And we are talking steel here. The future upgrade is to carbon fiber, which is surprisingly not too bad in price, and it has lots of bene's, including a critical rpm high enough to not be an issue.

And I am very glad not to be dealing with a 2 piece shaft. Good-bye, center bearing, it's just too bad I have 2 other Volvos with them.

Greg

Turborg · 04-11-2004, 11:49 AM

The 66 2/3" inch measurement comes from a Noah 244ti post in the T-5 article of Dougs'. He said he took his measurement from Doug.

Sean · 04-11-2004, 04:14 PM

he's talking about a 1 piece driveshaft.
Sean

04-10-2004, 12:15 AM	#1
Turborg Board Member Join Date: Jun 2003 Location: Northern Ca	Driveshaft questions on T-5 swap While inquiring about driveshafts at local shops I was told by two out of three that a drive shaft that is 60 inches long (approx six inches shorter than what is required on the t-5 swap) and 3" in diameter will reach its critical speed at 4000 RPM. Critical speed is defined as the rpm at which the driveshaft can fail if speed exceeded. I also checked on the internet under the heading "driveshaft critical speed" and saw the charts the driveshaft shops were using. My Volvo would be going less than 100 mph at this driveshaft speed. I would appreciate any input on this as I am ready for a driveshaft now. I am leaning toward having the short shaft on my shortened and beefing up the carrier bearing. __________________ My 82 242MODS http://www.pbase.com/turborg/image/34982247 My 72 142E http://www.pbase.com/turborg/my_therapy_1972_volvo_142e

04-10-2004, 01:55 AM	#2
boostdemon creative mastermind Join Date: May 2002 Location: Cary, NC	use a 2 piece __________________ "Flathood" Owners \| Motorcyclists \| Guitarists

04-10-2004, 10:03 AM	#3
Turborg Board Member Join Date: Jun 2003 Location: Northern Ca	RPM update My car with 3.73 rear end would reach critical speed on the 3" dia, 6' long driveshaft at 77mph(4000 rpm) in fourth gear. Last edited by Turborg; 04-10-2004 at 10:06 AM..

04-11-2004, 11:49 AM	#5
Turborg Board Member Join Date: Jun 2003 Location: Northern Ca	Driveshaft measurement The 66 2/3" inch measurement comes from a Noah 244ti post in the T-5 article of Dougs'. He said he took his measurement from Doug.

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04-10-2004, 10:12 PM	#4
Greg Wong Board Member Join Date: Nov 2002 Location: Boston/MA/USA	I don't know where you are getting this 66" driveshaft figure from, but on my car, the driveshaft is about 41" tube length. Add a few inches for center-center ujoints. It's a V8 conversion with the T5 trans, and from the pictures of Doug's car, the tranny looks like it's in about the same place. So figure around 40 something inches. My D/S is 2" diameter, and I have a 3.73 rear gear. I should be safe until somewhere around 120 mph. I have been up around 115 at least, and I haven't gotten any vibration yet. If I were starting over, I think I would do 2.5", because if you start going much larger, then you can start getting clearance probs. And we are talking steel here. The future upgrade is to carbon fiber, which is surprisingly not too bad in price, and it has lots of bene's, including a critical rpm high enough to not be an issue. And I am very glad not to be dealing with a 2 piece shaft. Good-bye, center bearing, it's just too bad I have 2 other Volvos with them. Greg

04-11-2004, 04:14 PM	#6
Sean Junkyard dawg Join Date: Jan 2003 Location: Bernard Malamud's Cascadia	he's talking about a 1 piece driveshaft. Sean