drive shaft length

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halifaxhops

halifaxhops

It's going to get stupid around here!
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I am putting a 440/727 into a 74 dart se. it currently has s6/904 in it. Everything that I have seen tells me to shorten the driveshaft approximately 4 inches. Never had to shorten a shaft before. I am sending it out to do it in the spring. Any help on length, how to measure etc. would be appreciated.
 
What you do is put the transmission yoke in the back of the transmission all the way forward as far as it will go. Then with the back of the car in the air and supported by the axle, not the frame, measure from the center of the u-joint on the yoke to the center of the u-joint for the axle.

Then subtract an inch for "installation clearance" and you have what length you need for your driveshaft.


Ps. You have to have the engine and trans installed in the car.
 
I hope your also changing out the puny 7-1/4 axle to something stronger or it'll go up in a cloud of smoke the first time you hammer it. That will also change how much you need to cut down the driveshaft. In the past I have always done the method like KrazyKuda described and it worked fine but some shops nowadays want it measured their way like Supershafts recommended so like he said check with them first.
 
fishy68 said:
I hope your also changing out the puny 7-1/4 axle to something stronger or it'll go up in a cloud of smoke the first time you hammer it. That will also change how much you need to cut down the driveshaft. In the past I have always done the method like KrazyKuda described and it worked fine but some shops nowadays want it measured their way like Supershafts recommended so like he said check with them first.
Click to expand...


The way I described, is the way the driveline shops here told me how to measure mine many years ago and made me one "from scratch".

But, yes, call the shop who is doing it to find out how they want it measured.
 
Fishy, I am using a 8.25 that is in the car with 290 something gears, going with 355's, mild cam and a torker ii and a 750 eddy and a voodoo cam, shumacher headers and install package.. Prob never going to the track, just a fun 4 door sleeper., might leave the small pipe from the six going out the rear. Just have to figure out where I want the dual to come out of.
 
halifaxhops said:
Fishy, I am using a 8.25 that is in the car with 290 something gears, going with 355's, mild cam and a torker ii and a 750 eddy and a voodoo cam, shumacher headers and install package.. Prob never going to the track, just a fun 4 door sleeper., might leave the small pipe from the six going out the rear. Just have to figure out where I want the dual to come out of.
Click to expand...

Ok. It's pretty rare to see a 8.25 behind a /6. That's why I assumed it was a 7-1/4. Sorry. The 8.25 should do you fine with your intended use.
 
krazykuda said:
The way I described, is the way the driveline shops here told me how to measure mine many years ago and made me one "from scratch".

But, yes, call the shop who is doing it to find out how they want it measured.
Click to expand...

I hear ya Karl. That's the way they always used to tell me and one shop still does but a lot nowadays have work sheets they want you to fill out. I guess their just trying to cover their butt's cause so many guys can't read a tape measure and add numbers. A buddy of mine is like that. The shop he was using told him to measure it and he didn't know how so he asked me and I told him. He gets one made and it's way too long and was mad at the shop saying they screwed up. I went down and measured and don't know how he came up with what he did but it was over 2" too long. Of course it was the shops fault and all the shop had was word of mouth so they ended up eating a driveshaft.
 
I had two driveshafts built by the same shop and they wanted it measured differently both times. Basically, on the ground yoke face to yoke face.
 
Fishy,
Yeah I was surprised it was a 8.25 also. It is an SE and I bought it from the original owner and he had some special orders added, I think he was going to use it for towing. Had a hell of a time getting a tail shaft seal for the driveshaft. Had to measure it id/od and depth and go to a seal bearing shop. I have no idea what the tail shaft is from. One tranny shop was thinking an rv! Thanks!
 
fishy68 said:
I guess their just trying to cover their butt's cause so many guys can't read a tape measure and add numbers. A buddy of mine is like that. The shop he was using told him to measure it and he didn't know how so he asked me and I told him. He gets one made and it's way too long and was mad at the shop saying they screwed up. I went down and measured and don't know how he came up with what he did but it was over 2" too long. Of course it was the shops fault and all the shop had was word of mouth so they ended up eating a driveshaft.
Click to expand...


See thats the problem the people measure there way and not what the shop wants.

Everything in the driveline world is done on CENTERS, or a overall dimension missing a component on CENTER. Every part and piece is made on a center measurement, not back of, front of, from here to there, slid in this much, and slip yokes are all different lengths and there is a reason for that also or they could all simply be 1.7" to 2" long, but they are 9" to 4" long

I usually want the tail shaft to center and seal to center, if the slip is owned i want the slip bottomed out in the trans till it can not go in any further, not against the seal or against the dust boot, i want it smashed into the trans until you hear it hit and stop.

Any deviation from what i want is 75 per chance, i explain to the customer like this, the 1st time i shorten it based on your way it is 75, the 2nd time i shorten it again your way it is 75, until the 3rd time and then its not a game any more and this isn't a hobby shop and it is 3 x 75, if you totally screw it up and it becomes to short a retube is a different labor rate and will be doubled at the 3rd try.
If you do it my way it's 75 once and only once.

Call the shop you're going to use for the work and let them tell you how they want the measurement.


.
 
halifaxhops said:
Fishy, I am using a 8.25 that is in the car with 290 something gears, going with 355's, mild cam and a torker ii and a 750 eddy and a voodoo cam, shumacher headers and install package.. Prob never going to the track, just a fun 4 door sleeper., might leave the small pipe from the six going out the rear. Just have to figure out where I want the dual to come out of.
Click to expand...

There is a point where the ratio change requires a carrier change in the 8.25. Sorry I don't recall what ratio that occurs. So a 355 gear set may or may not fit the carrier you now have. Just another point to research.
Good luck
 
Thanks, I did the research online and it appears they will work in my carrier. I was made aware of that on a different post. Yes that would stink going to the trouble and it not working.
 
Supershafts said:
See thats the problem the people measure there way and not what the shop wants.
Click to expand...


Yes, that is true.


Sometimes things are misunderstood when talking with words. It's best to draw a picture to define exactly where to measure and how.


That's why the auto industry uses blueprints as the "bible" for determining if a part is to specifications or not. It defines clearly the dimensions, taking away the "error of interpretation".

If it is called out on the blueprint, then that specification has to be met. If it is not called out on the blueprint, it can't be held to that spec.

My point is that some people may misinterprit what they are supposed to measure. It may not be their fault as it was not explained clearly to them. That is why it's best to define it as clearly as possible to eliminate "errors in translation/interpretation".
 
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