Driveshaft travel question

[RLDSL]

would anyone happen to know about how much a driveshaft compresses for each inch that the suspension compresses down on a 2wd f350 ?

When I had the driveshafts made up for my brownie installation, it looks like for the rear shaft ( aux tranny to differential ), he used the measurement I gave him as the collapsed measurement. The thing has plenty or room to extend as the axle drops , but when I went to set it in, it looked like there was only about 3/4-1" of compression left in the slip yoke.
Does that sound ok to run with or do I need to get back with him and have some taken off that shaft?

Thanks------Robert

 

[icanfixall]

That sounds good to me for travel... I'm not a math wizzard so maybe someone that is can chime in with angles and degrees of movement....Try estting it up and get a measurement of no weight on the tires and then with the tires loaded up. I really not sure its very much movement in and out as much as it is up and down...

 

[MIDNIGHT RIDER]

I doubt the splines will vary 1/8" between hanging suspended on a jack and mashed to the stops, but I can't swear to this.


I think you will be fine; at worst, it might bind and knock a little; should that happen, then, yes, cut some off.

 

[flatlander]

Maybe pick up the rear end of the truck with a bumper jack and measure the ratio of rear tire drop to slip joint expansion. Probably not perfect but it'll give you some piece of mind.

Either that or throw some jack stands under the frame, unbolt the rear u bolts and jack up the rear end until it hits the frame. Then you'll know for sure.

 

[suv7734]

The angle of the driveshaft from horizontal is what you really need to know. Basically if the driveshaft is nearly flat it won't travel much in the spline as the suspension moves. If you have a sharp angle on the driveshaft the spline will move more as the suspension travels up and down

 

[RLDSL]

The angle of the driveshaft from horizontal is what you really need to know. Basically if the driveshaft is nearly flat it won't travel much in the spline as the suspension moves. If you have a sharp angle on the driveshaft the spline will move more as the suspension travels up and down

It was pretty close to maximum allowable angle on that rear shaft( what is it, 5 deg?) , and it's a real short shaft to boot. I ended up mounting the brownie back under the bed, so I have a long front shaft and a short rear.

 

[LCAM-01XA]

man I hate shortcut buttons on my laptop keyboard, isntead of the up arrow I hit the darn "back page" and there goes my nice and long quick reply! In any case, simulate the drivshaft motion, you can do this by either jacking up the axle till it hits the bump stops (ain't got no clue as t how ya gonna do that), or you can just drop the front of the shaft the same amount of travel and measure up how much forward the slip yoke moves. From what I've seen on my truck, those 5" or so of positive axle travel ya got should make for 1/2" or less slip yoke travel, even tho the shaft is pretty short.

 

[Dsl_Dog_Treat]

What about looking at the wear pattern on the slip yoke. Gonna be a shiny area somewhere.

Or going nerd style using the Pythagorean Theorem.
See the attached.


Yes I hated math!

 

[THECACKLER]

Suspension Compression

1 Inch sounds about right to me. but as you know by reading the previous posts, it depends on the geometry of your truck's suspension. A simple phone call to a drive shaft shop can save you some work. They know these things for stock applications. When it comes to non-standard applications I use another method to compress vehicular suspensions.
Suspension Compression - Use at your own risk!
I will preface the method by stating that it is inherently dangerous to store energy in a spring or springs, so you must take the appropriate precautions and use over-rated equipment if you decide to use this method. I will not advocate this method but merely state it works for me.
I have compressed the suspension on vehicles using two serious floor jacks, like 2-1/2 to 3 ton er's, and two chains to match, no less than Grade 70 3/8 Transport chain with good forged steel hooks. It is a matter of placing the chains in a loop over the frame at the point above the axle spring perch then down to the ground leaving a loop large enough that a floor jack can be slipped in on top of the lower loop of chain on each side. Flat Oak wood blocks where chain crosses or contacts steel are suggested to prevent point loading. The chain under the floor jack must cross under the carriage of the jack square to where the lift pad is. The floor jacks must be on stable bases as the truck will be suspended by them as the rear axle is raised. The loop below the floor jack and over the frame keeps the frame to ground level constant. The lift provided by the floor jack will raise the axle and the springs will compress.
This is a method that I have used to check suspension travel. I will reiterate that it is inherently dangerous to store energy in springs, so you must take the appropriate precautions if you decide to attempt this method. Proceed slowly and with assistance. Safety is First and Foremost.

 

[OLDBULL8]

Might help.


http://www.vibratesoftware.com/html_help/html/diagnosis/Propshaft/Propshaft_Angles.htm

You can also measure the angle of the dangle by the heat of the meat.

 

[RLDSL]

What about looking at the wear pattern on the slip yoke. Gonna be a shiny area somewhere.

Or going nerd style using the Pythagorean Theorem.
See the attached.


Yes I hated math!

Well according to said theorum and my math ( which I wouldn't trust for a second It looks like there *should* only be about a half inch compression in the driveshaft from unloaded to bottomed, and about an inch of extension from static point with the axle hanging ( about an inch and a half overall travel ) meaning , I should be OK
THese figures , of course, were derived with copious use of a pair of dice, some bones and a ouija board

It should at least be OK to run long enough to take it by the driveshaft shop and have him take a peek at it first hand.

 

[OLDBULL8]

Robert; When I was changing GM Busses from stick to auto the place I had the drive shafts shortened would allow only 3/4" to 1" collapse, shaft was only 23" long and at 3*, that is with the air out of the bags, aired up shaft was at 5* . You should be fine.

 

[Dsl_Dog_Treat]

Well according to said theorum and my math ( which I wouldn't trust for a second It looks like there *should* only be about a half inch compression in the driveshaft from unloaded to bottomed, and about an inch of extension from static point with the axle hanging ( about an inch and a half overall travel ) meaning , I should be OK
THese figures , of course, were derived with copious use of a pair of dice, some bones and a ouija board

It should at least be OK to run long enough to take it by the driveshaft shop and have him take a peek at it first hand.

Robert, that sounds about right.

 

[Agnem]

Keep in mind that since your stationary spring hanger is forward of the axle, that the axle actually moves BACKWARDS as the springs compress and becomes more streight. This can actually cause your numbers to work backwards depending on your geometry.

 

[subway]

you really dont want much coming out of a slip yoke, made that mistake on a camero. i had a couple inches out the back of a turbo 350 and it vibrated like crazy.

Mel that would be right if the center of the driveshaft arc were below the front spring mount. the closer and higher the front universal is the front spring pivot the more it will push the driveshaft toward the tranny when compressing.

i would have the place check it out if you dont cycle the suspension on your own to verify. a modified system that is at your max angles can make things harder to work out.

mean while this can be some good reading
http://www.4xshaft.com/index.html