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05-20-2005, 06:31 AM | #1 |
Registered User
Join Date: May 2005
Location: michigan
Posts: 4
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why two-piece drive shaft????
bear with me im new here. 1968 short box 2 wheel
im putting in a 454, 6800 rpm cam,march serps, too much to list. truck has a slight rubber rake to it. low in front higher in back. anyhow my driveline guy keeps telling me i have to stay 2 piece because the angles wont work out with a one piece. i want a one piece. a little more here on set-up turbo 400, chetah manual reverse valve body, 4:10. motor mounts are on the way, got em off ebay from a guy in texas, said they are the best you'll ever buy, $175 whole set, yikes. truck was a strait 6, 3 on tree, then sbc, 350 turbo, now who knows where it can go. any pointers appreciated. |
05-20-2005, 07:02 AM | #2 |
blood type; Retumbo
Join Date: Jan 2004
Location: next to my reloading bench
Posts: 10,269
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the 2 piece is better in 3 ways from what I see. it distributes the load over shorter pieces & therefor able to handle more torque without twisting. its easier to get the less than 2* angle per joint. the frame flexes too much for a 1 piece.
JMO
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05-20-2005, 12:21 PM | #3 |
Just Don't Stop!
Join Date: Feb 2004
Location: Dallas
Posts: 1,239
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interesting... 6.96's @ 102 mph in the 1/8 on my 210 dollar one piece drive shaft...
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1968 C10 build in process TT LSA/6L90e/9" |
05-20-2005, 12:50 PM | #4 |
my gas saver
Join Date: Sep 2003
Location: Clarksville, TN
Posts: 2,046
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i've never had a problem with a one piece. i have a big block truck and i give it alot of hell. i'm no "driveline" guy myself but i've seen 500+ horse engines on 1 pc. shaft in these trucks, and haven't heard of one failing. i'm sure someone has though.
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85' SWB, 4.3/TH350, getting ready for paint 84`SWB, 462ci./TH400, cowl hood, 15" billet spec., flows, blazer buckets/console, flat black 71`SWB, project ebay feedback |
05-20-2005, 01:06 PM | #5 |
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Location: Tampa
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I'm also building a '68 short step and plan on having about 750rwhp and will be going with a one piece also. I don't see any reason on a short bed not to run one based on all I've ever read on this board.
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'68 Short Step LS1/T56, Hydratech, Fatman Fabrications Stage III, Baer, Hot Rods to Hell, US Body, S&W, etc |
05-20-2005, 01:13 PM | #6 |
Just Don't Stop!
Join Date: Feb 2004
Location: Dallas
Posts: 1,239
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I should be around 650 on the second stage, thats around 760 at the crank. No issues on the street. Haven't hit the second stage at the track yet...
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1968 C10 build in process TT LSA/6L90e/9" |
05-20-2005, 02:23 PM | #7 |
December 21, 2012
Join Date: Apr 2000
Location: Black Eagle, Montana
Posts: 1,634
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I had a 68 Chevy shortbox and ran a short shaft with no problems.
There is an article about driveshafts in the Classic Trucks Dec 2004 Issue addressing this issue. What determines use of a one piece shaft or a two piece shaft is critical speed. Critical speed is related to length, weight, diameter and speed of the shaft. If critical speed is reached the driveshaft comes apart. Longer, heavier driveshafts have a lower critical speed than that of shorter, lighter shafts.
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"!Ama Sua, Ama Kjella, Ama Lllulla!" Last edited by Maximum Overdrive; 05-20-2005 at 08:08 PM. |
05-20-2005, 03:41 PM | #8 |
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Join Date: Jan 2005
Location: CA
Posts: 5,648
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When I had my one-piece 4" drive shaft made for my SWB at the local drive-shaft shop, they told me that the critical rpm of the shaft was 4500 RPM. I've got 3.73 gears and 29" tires, so that means I can't exceed about 104 MPH with a 1:1 transmission. If you have a LWB truck and 4:11 gears, I'm guessing the top speed will be significantly lower than that.
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05-20-2005, 04:33 PM | #9 |
Senior Moment
Join Date: Mar 2002
Location: Pittsburg Ca
Posts: 4,156
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My 70 short bed has a 454 and a 1 piece shaft and my son has a long bed with a 350 and a 1 piece shaft. Both have NO issues at all. Just have it built by a shop that knows what there doing
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05-21-2005, 10:31 PM | #10 | |
The oddest Todd around
Join Date: May 2004
Location: Miami, Florida
Posts: 1,418
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Quote:
Doesn't the crank spin twice as fast as the cam? And isn't the flywheel / torque converter / transmission attached to the crank? The distributor is run off of the cam, which means that rpms is counted off how many rpms the cam is spinning. So therefore, wouldn't the driveshaft in 1:1 drive be spinning twice as fast as the rpms say the motor is spinning? Seems to me that "critical speed" would be reached a whole lot sooner than you thought. Todd
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05-21-2005, 11:05 PM | #11 |
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Join Date: Jan 2005
Location: CA
Posts: 5,648
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At 65 MPH my tach reads 2000 RPM. I have 29" tires, a 3.73 differential and a .7 overdrive transmission with a locking torque converter. Here's the calculation of the crankshaft RPM at 65 MPH:
(65 mi/hr) x (5280 ft/mi) x (12 in/ft) x (1 hr/60min) x (1/(29in x 3.14159265)) x 3.73 x .7 = 1967 revs/min. The tachometer displays the crankshaft RPM, not the camshaft RPM, even though the distributor is turned by the camshaft. Here's a link that has a table that shows critical RPM for driveshafts of different lengths and materials: http://64.233.161.104/search?q=cache...speed%22&hl=en |
05-22-2005, 05:51 PM | #12 |
Registered User
Join Date: May 2005
Location: michigan
Posts: 4
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thanks guys, im putting the rest of my info on and some pics,
these were from last summer when i had the 350/350 set-up. sounds like i can do the 1 piece, being my motor will spin less than 6800 rpm and a 4:10 in the rear, tire diameter @ 29IN. INPUT GREATLY APPRECIATED |
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