Driveline Measurement Specifics with suspension changes

[rfalker1]

Well I was wondering how to properly measure a driveline to be cut, but on top of that I was wondering when. Because not only have I changed the transmission but also the whole suspension. ANd they say the suspension has to settle first. But that wont truly happen until I start driving. SO I am confused on what to do and when to do it.

Please help. I want to get it measure today

[John Wright]

Are you asking about how to measure for a drive shaft so that it will be the correct length?

[rfalker1]

yes, because i need to get it cut

[John Wright]

Who do you plan to use? I would talk with them about how they want you to measure. You can insert the yoke in the transmission fully until it bottoms out, then pull it back out about an inch, then measure from centerline of the front u-jont cap to the centerline of the rear u-joint cap.


Let me add something to my post...had someone in my office and hurried through my answer.

Make sure "all" of the car's weight is loaded on the suspension and it is sitting level...then measure. Otherwise you will not get a good read on the length that you will need.

[rfalker1]

well basically its a driveline shop and they want the car to have the full weight before I bring the driveline out there. WHich is problem because I have all new shocks and suspension and the car will be settling even after driving it

[John Wright]

Here let me offer Denny's advice:

http://www.dennysdriveshaft.com/how_to_measure.html

[rfalker1]

thank you for the help... I shall read up on it

[The WidowMaker]

theres no need to weight it fully. our cars dont have "extreme" driveline angles like a lifted truck would. basically they want to make sure that your driveshaft is 1" short of bottoming out in the transmission. this allows for the effective length of the driveshaft to shorten through suspension travel and also allows some forward movement during acceleration. i would guess the length would change no more than 1/8th from weighted to unweighted, especially since the motor and trans put most of their weight over the front wheels which doesnt affect the measurement.

i actually did a little math. with a 50" ds and a radical 3" drop from adding weight (not going to be anywhere close), you only change the length .089". with a 1" drop its .009". now this doesnt take into effect any change in fore or aft pinon movement from the arc of the rear suspension and its links. i would still expect it to be minimal.

[John Wright]

basically they want to make sure that your driveshaft is 1" short of bottoming out in the transmission. this allows for the effective length of the driveshaft to shorten through suspension travel and also allows some forward movement during acceleration..

right......... 1" makes it long enough not to fall out when the suspension is in full droop or cause tail shaft bearing issues, and short enough not to bottom out when the suspension is fully compressed.

[rfalker1]

measured and got the driveline out of the car and to the driveline... thanks John and tim. I really appreciate it!!! help tremendously

[John Wright]

Cool...let us know how it goes. Make sure they balance it above any anticipated rpms that the drive shaft might see(especially if using an OD tranny)

[rfalker1]

while I got there amd we talked.. he asked me what kind of power I would be putting out and adviced that I upgrade my u joints to more racy ones. So I agreed and they are oft to balance it. Balance and cut it. And get it back tuesday. Hopefully i can drive it next week