big or little u-joint?

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69B-Cuda

69B-Cuda

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ok, maybe a stupid question....
I am swapping from a 360/904 to a 440/727 in my 69 Barracuda. the 440 is nothing crazy and I don't at this point plan on building anything real crazy to put in it.
My old driveshaft has the larger u-joint in the rear and then tapers down and has a small u-joint in the front.
727 is about 4" longer than 904 so, I need to shorten the driveshaft.... 4" is right about where the taper is so, should I go with a larger u-joint up front (have to buy a new weld-in piece for the driveshaft) or stick with the smaller u-joint up front and just have the rear cut and shortened?

I guess the real question is, is there much of a difference in strength between the large and small u-joints?
 
There is a considerable increase in strength, it even matters if the are cross drilled to make them greasable. Does your rear end already have the larger yoke for the bigger u- joint? I would get a bigger yoke and u- joint for the 727 to match the larger rear joint if it were me. Why leave a weak link in the drive line, especially in the front. That's the end that if it breaks, can pole vault you into the air....
 
yes, already has the bigger one in the rear.... "There is a considerable increase in strength, it even matters if the are cross drilled to make them greasable."

thanks, that was really my question I guess. I'll go with the large then!
 
I know a guy that did the pole vault thing. Killed him after about a week in the ICU paralyzed.
 
Sorry for him... but I take it he did not have a driveshaft loop installed? If that's not a ringing (implicit) recommendation for one, I don't know what is. I've put one on every big-block 4-speed A-body. And a scattershield.
 
I'd go with the big u-joint too. Probably about the same money and stronger. Your only problem is will they be able to cut down and re-use your old driveshaft. The factory ones had a rubber insert inside to absorb harmonics. By the time their the age our cars are that rubber is usually junk and most driveshaft shops won't want to cut one down and reuse it. Once in a while you get lucky and it's re-usable. I recommend a driveshaft loop too. Cheap insurance IMO
 
Do yourself a favor and build, or have build a NEW drive shaft; buy a kit from Mancini, or your local drive shaft shop. You never know when 30 year old metal is gonna give up
 

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Thanks for the replies....

I'm heading up to drivelines NW later today to drop my driveshaft off and bringing a used slip yoke home to stick in the tranny and get them a measurement (just using the used one for a measurement, putting a NEW on on my driveshaft)... also, going with the 7290 yoke... may need a whole new shaft, we'll see......
 
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