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Re: limits of stock driveshaft? [Re: dogdays] #2155853 09/16/16 05:53 PM 09/16/16 05:53 PM
Joined: Oct 2003 Posts: 7,506 Az Crizila master
Crizila master Joined: Oct 2003 Posts: 7,506 Az	Originally Posted By dogdays One thing unmentioned so far is shaft speed. If the gear numerical ratio is increased the shaft spins faster and may approach a harmonic speed that can get the shaft doing weird things. That's why it is always better to increase diameter if possible. It increases stiffness as the increase in diameter cubed, IIRC. R. 4" DOM shaft, 44" loooong, 1350 U-joints on both ends. Mid 10's and 7K through the lights. No problems. Fastest 300

Re: limits of stock driveshaft? [Re: Crizila] #2155871 09/16/16 06:23 PM 09/16/16 06:23 PM
Joined: Jan 2003 Posts: 16,376 D dogdays I Live Here
dogdays I Live Here D Joined: Jan 2003 Posts: 16,376	Large diameter, strong material, short length = a very stout shaft. R.

Re: limits of stock driveshaft? [Re: 1mean340] #2155943 09/16/16 08:27 PM 09/16/16 08:27 PM
Joined: Jan 2004 Posts: 8,360 fredericksburg,va C cudaman1969 master
cudaman1969 master C Joined: Jan 2004 Posts: 8,360 fredericksburg,va	One thing also, start with a clean non-rusted shaft, 50 year old drive shaft might be past its prime.

Re: limits of stock driveshaft? [Re: dogdays] #2156141 09/17/16 10:32 AM 09/17/16 10:32 AM
Joined: Sep 2003 Posts: 19,657 north of coder moparx "Butt Crack Bob"
moparx "Butt Crack Bob" Joined: Sep 2003 Posts: 19,657 north of coder	Originally Posted By dogdays One thing unmentioned so far is shaft speed. If the gear numerical ratio is increased the shaft spins faster and may approach a harmonic speed that can get the shaft doing weird things. That's why it is always better to increase diameter if possible. It increases stiffness as the increase in diameter cubed, IIRC. R. my one buddy is constantly complaining about vibration problem on his brand "c" street car. he has had a couple of new shafts made by the local truck shaft shop, but no improvement. he is more sensitive to stuff than i am due to one of my medical conditions, but i mentioned this very thing about increasing shaft diameter. that, plus having the shaft balanced at a higher rpm than the typical truck shaft shop of around 1000-1500rpm which is high speed for them. as i understand it, most only go 500-1000rpm. with 3.73 gears and overdrive, shaft speed can get up there even at just cruising speed.

Re: limits of stock driveshaft? [Re: moparx] #2156289 09/17/16 03:44 PM 09/17/16 03:44 PM
Joined: Jun 2008 Posts: 10,847 Oakdale CT gdonovan I Live Here
gdonovan I Live Here Joined: Jun 2008 Posts: 10,847 Oakdale CT	Originally Posted By moparx my one buddy is constantly complaining about vibration problem on his brand "c" street car. he has had a couple of new shafts made by the local truck shaft shop, but no improvement. Been there, done that. Max speed they balance at is 2000 rpm. I laughed at the guy when he told me he "high speed balanced it" and said are you aware how fast the shaft is spinning while jamming through the traps at the track? Try 6k+ Truck shops. pfft. That being said I pounds the crap out of my GTX with a stick, slicks and healthy 440 for hundreds of passes without failure, shaft is still in the car to this day. For a fairly mild car I'd not have a concern as long as the factory shaft is in good shape. "I think its got a hemi"

Re: limits of stock driveshaft? [Re: gdonovan] #2156317 09/17/16 04:50 PM 09/17/16 04:50 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	The shaft needs to be good for added torque, traction and rpm... those are the 3 major factors... the factory shaft isnt held to all the greatests tolerances but not bad.. if you have .010 run out you might feel it.. if its more you will.. diameter is strength along with the material.. I have had stock shafts be bad from the factory(just a small vibration).. I took it into work and took it to the lab that balances them.. it was bad and he balanced it and added weight to get it right... that big weight that hangs off the trans is there to change the frequency that the vibration was at to a point that is out of the normal shaft speed... I buy a new shaft for all my builds.. Dynotech is who I use for all of them.. never had any issues with there parts

Re: limits of stock driveshaft? [Re: MR_P_BODY] #2156355 09/17/16 06:05 PM 09/17/16 06:05 PM
Joined: Oct 2003 Posts: 7,506 Az Crizila master
Crizila master Joined: Oct 2003 Posts: 7,506 Az	Originally Posted By MR_P_BODY The shaft needs to be good for added torque, traction and rpm... those are the 3 major factors... the factory shaft isnt held to all the greatests tolerances but not bad.. if you have .010 run out you might feel it.. if its more you will.. diameter is strength along with the material.. I have had stock shafts be bad from the factory(just a small vibration).. I took it into work and took it to the lab that balances them.. it was bad and he balanced it and added weight to get it right... that big weight that hangs off the trans is there to change the frequency that the vibration was at to a point that is out of the normal shaft speed... I buy a new shaft for all my builds.. Dynotech is who I use for all of them.. never had any issues with there parts >010" is a good rule of thumb on run out. More than that and you will feel it. Fastest 300

Re: limits of stock driveshaft? [Re: 1mean340] #2156446 09/17/16 09:13 PM 09/17/16 09:13 PM
Joined: Mar 2006 Posts: 9,883 MI, usa dvw master
dvw master Joined: Mar 2006 Posts: 9,883 MI, usa	I've measured lots of shafts. Know what the spec is. Never seen any below .030 " Doug

Re: limits of stock driveshaft? [Re: dvw] #2156452 09/17/16 09:23 PM 09/17/16 09:23 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Originally Posted By dvw I've measured lots of shafts. Know what the spec is. Never seen any below .030 " Doug My Dynotech has .006 EDIT also if it has a minor vibration turn the shaft 180* on the diff yoke to see if it goes away or gets worse.. there is a test you can do with a aircraft clamp.. tighten a clamp on the shaft in the center... mark where the screw part is.. put 3 other marks on the shaft equally spaced(you have 4 marks now) try it at all 4 spots to see if it gets better or worse.. then if it changes(either better or worse) you will need to balance it Last edited by MR_P_BODY; 09/17/16 09:44 PM.

Re: limits of stock driveshaft? [Re: 1mean340] #2156632 09/18/16 03:34 AM 09/18/16 03:34 AM
Joined: Nov 2004 Posts: 6,890 North Alabama M Monte_Smith master
Monte_Smith master M Joined: Nov 2004 Posts: 6,890 North Alabama	I love all the "we did this stories" people recite when topics like this come up. Like any of that means a damn thing.........People have also lived when their parachute didn't open. Doesn't mean I will be rushing out to sky dive without a chute though. People do less than intelligent things everyday and get away with it. Still doesn't make it a good idea

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