drive shaft length

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russhal

russhal

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I have a 71 swinger with a slant 6. I'm trying to gather my parts before I do the swap to a 408/727 with a dana 60. I know how to measure once everything is in the car but I was wandering if anyone knows the length I need from their own experience. 727 is 4"s longer. I don't know the difference in the 7 1/4 and dana 60. Thanks, Russ
 
It's really best to measure it once you have it together. The suspension needs to be loaded, as in jack stands under the rear end.

I would call a reputable driveline shop and ask them exactly how they want it measured and take it to them and have it shortened, balanced and check the run out.
 
Thanks. I've had them shortened before. I'm in the short rows of the project and a little cash poor at the moment. I thought if had a shaft I could buy something else. I'm getting excited and need to stay focused on getting it right.
 
If you're going from /6 and 904? and 7.25 to a Dana I can guarantee you the shaft will bee too long.

If you have a shaft laying around from a 727 and Dana combo you could try it.
 
Rear loaded to Minimum distance between diff and trans bushing. Measure cap centerline to bushing face...basically you want 3/4 inch play at bushing at closest suspension load. Anything off loaded suspension will pull shaft out of trans so you measure at full compression. From a custom drive shaft website.
 
I hope this doesn't offend anyone, but I robbed these 2 charts from some other threads. I keep them handy for trying to compute swaps such as you're doing.
 

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Bad Sport said:
Be careful on that second chart on rear dimensions, it isn't accurate.
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Bad Sport, I'm not being defensive here. What isn't accurate? I thought this was good info. I would hope that the axle center lines to yoke would be good - no?
 
I'm swapping my 7 1/4 to a 8 3/4. Hope the centerline part is accurate, it would be very helpful.
 
The chart definitely isn't correct on a lot of the rear end widths. It only lists one width for all B bodies from '62-70, which is completely inaccurate since there are 4 different width's in that year spread depending on the year, anywhere from 53 1/4" to 55 5/8".

The centerline measurements seem fairly accurate though. The centerline length difference from a 7 1/4 to an 8 3/4 that I've always heard is ~2.25", which is about what the chart says. I know that one because I just swapped my Duster from a 7 1/4 to an 8 3/4, and although I measured myself I ended up having the driveshaft shortened exactly 2.25".

I also thought that an 8 3/4 and a Dana 60 were about 1.25" different, which is again fairly close to what the chart says. That's from another Duster on here with a SB/833/Dana with a 48" driveshaft compared to my 49 1/4" with my SB/833/8.75.
 
So did you use your 7 1/4 drive shaft? Mine is a mild 360 build and I wonder if the 7 1/4 drive shaft is strong enough. Probably 350-375hp when done.
 
69conv said:
So did you use your 7 1/4 drive shaft? Mine is a mild 360 build and I wonder if the 7 1/4 drive shaft is strong enough. Probably 350-375hp when done.
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It should be fine, run Spicer U joints in it. I used my 7 1/4 shaft, shortened and balanced, although I'm probably not close the HP numbers you posted but I max mine out every chance I get and haven't had any problems.

If in doubt throw a driveshaft hoop in it for peace of mind.
 
69conv said:
So did you use your 7 1/4 drive shaft? Mine is a mild 360 build and I wonder if the 7 1/4 drive shaft is strong enough. Probably 350-375hp when done.
Click to expand...

I didn't use mine.

My 7 1/4 driveshaft was stepped down at both ends, so shortening it wouldn't have worked. I got a donor from a V8 Dart and had it shortened. It was also a larger outer diameter than the one that came in my Duster, and I should be pushing 400+ hp so I didn't want to take any chances.
 
Bad Sport said:
If in doubt throw a driveshaft hoop in it for peace of mind.
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So you all know the drivesahft loop is only designed to keep the front of the shaft up in the event the joint breaks. That is all that is designed for, to keep the shaft up off the floor in the event it breaks to really get the car pushed out of the way, not to prevent the myth of pole-vaulting.

If you break a shaft from rpm related issues using a factory shaft that wasn't designed for those rpms when it winds up exceeding that you'll be sitting next to a built in shredder.

Neither loop will help you there, and loops have been cleared from cars when shafts break from rpm related issues along with floors, body parts and anything else in its way.

It's why the nhra made certain classes go to scatter tubes like we have been using in boats.

After a driveshaft made incorrectly for the rpm it was seeing came apart and cut the car apart and the cage and pulverized the drivers entire right side, broken calf, leg, hip, ribs, shoulder, arm, head and helmet, she survived luckily.

.
 
Supershafts said:
So you all know the drivesahft loop is only designed to keep the front of the shaft up in the event the joint breaks. That is all that is designed for, to keep the shaft up off the floor in the event it breaks to really get the car pushed out of the way, not to prevent the myth of pole-vaulting.

.
Click to expand...

My mention of the hoop was in fact in regards to "the myth of pole vaulting". It is not a myth in my world, I had it happen to me. I was driving a 73 Coronet many moons ago, hot summer day soft pavement. As I got up to speed the front U joint let go, dropping the driveshaft onto the pavement. It immediately dug into the soft pavement and lifted the rear of the car up and rotated me to the left nearly 180*.

Regarding your other statements I would agree.
 
Thanks Bad Sport for your advice and suggestions for the U joint. I have no desire to pole vault!
 
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