driveline offset....

Bowtie · #1 (**permalink**) 07-27-2002, 04:39 AM

I bought an unfinished CR kit and am trying to finish it...heres the problem. The guy I bought it from didn't like the extended cockpit, so he had the frame and body shortened 3 inches just aft of the crossmember. (In his defense, the body work on the doors and the welding on the frame are impeccable). But now that I have the rear end in the car (Mosier 9 inch) it looks like the output shaft of the transmission and the pinion shaft are out of line by about 1 3/4 inch. It looks like the driveshaft will be about 3/8 inch from the right side of the tunnel. I've built a 575 HP 481 inch Chev motor for the car, and am going to go with a composite driveshaft due to its decreased diameter to improve clearance on the tunnel. My question is, will the extreme offset prove to be too much of an angle?? I was told that a slight offset was engineered into the car to decrease harmonic vibration (the angle of which was increased when the car was shortened in the area of the driveshaft) but I need to know how much offset is too much. Thanks for the help folks.... Bowtie

Double Venom · #2 (**permalink**) 07-27-2002, 05:01 AM

Bowtie,

I've had what I consider some serious, "Driveline" angles, when using 9" inch rear ends, but 1 3/4" seems an awfull lot for such a short distance.

A simple test would be to mock up a drive shaft. If you have at least an 1" clearance to the frame, then you wont have a problem. What I have found when using the "9" a lot of guys wont get the brackets welded right or the tubes shortened correctly.

Post some pics if you can, and please keep us posted.

DV

cobrashoch · #3 (**permalink**) 07-27-2002, 10:26 PM

This is a good subject and one that I need to look at. I am switching from motor mounts to engine plates right now and this is the time to correct any thing done wrong previous. I have been told that a driveshaft needs a small offset from tranny to rear end to keep the U-joints working all the time and to keep them oiled.
My hot rodder buddies mostly all say that if you set the shaft dead strait that U - joints will never break but it does reduce their life about 25%. For a Cobra that will never see 50K miles like mine I should be O.K. Now this is for live axles only as a independent rear is different. My rodder buddies say the rear end going up and down over bumps will "work" the U-joints enough to stay lubricated. My present offset is set at 3/8 inch.

cobrashoch

Bowtie · #4 (**permalink**) 07-28-2002, 03:49 AM

OK DV...so are you saying that as long as I have sufficient tunnel clearance I should be ok? I'll bring pics when my wife and I fly out and visit your shop...(I want one of your steering columns, and a little advice). Bowtie

Double Venom · #5 (**permalink**) 07-28-2002, 04:55 AM

Ron,
Never, never put the drive line in "straight". From what I've been told it sets up a nasty case of driveline harmonics.

You can not get a perfectly, lazer straight line, which from my understanding will cause the shaft to spin in an egg shape type circle. At the least, setting up a constant harmonic hum, or the worst, destroying the shaft.

It's early. Does this make sense?

Bowtie, ideally 3-degree's is about perfect, but I'm guessing you are far exceeding that amount. I just re-read your original post. With only 3/8's of an inch clearance to the frame and you may end up with a problem.

If you have the equipment, ie; plasma cutter and a mig welder, I think I would remove and relocate the brackets to center things up a little. I think this is going to fall into the, "fix me now - or fix me later" category.

DV -- Stop in anytime fella. I gets awfull lonely around here between Flings!

Bowtie · #6 (**permalink**) 07-29-2002, 01:42 AM

I'm starting to think that my only solution will be to send the rear end back to Mosier and have them shorten the left tube an inch and extend the right tube the same.. (ALAS!! there go my nice new 31 spline axles!!!!) Oh well...add another month to my completion date!!! Bowtie

Double Venom · #7 (**permalink**) 07-29-2002, 05:01 AM

Bowtie,

Where do the wheels sit in relationship to the body? Each wheel centered in the tub? Might have some alternatives here.

DV

Bowtie · #8 (**permalink**) 07-30-2002, 02:12 AM

Wheels sit squarely in the wells...I'm running 15X10 Halibrands in the back with 275/60 X 15's and have no room to play with....I think I may be below 7 degrees though....going to set engine and tranny in place this weekend so I can take measurements...guesstemating at the position of the output shaft and a little trigonometry puts me at about 6 degrees. I hope that the rear end will work...12 inch slicks fit perfectly right now...I'm keeping my fingers crossed!! More soon DV....thanks. Bowtie

Double Venom · #9 (**permalink**) 08-01-2002, 08:00 PM

Bowtie,
Check out this link! Bob Putnam, Campy have come up with the best description of drive line angle I have seen.

DV

Ken Greene · #10 (**permalink**) 08-02-2002, 04:07 AM

link, what link.... i don't see no stinking link!!!!!

Double Venom · #11 (**permalink**) 08-02-2002, 04:20 AM

Ooops, forgot to add the link! I think this is it

http://65.200.22.105/forums/showthre...threadid=19022

DV