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Front lift affecting rear d-shaft?

A

AKswampheep

NAXJA Forum User
Location
INDIANER
I currently have about 6 inches of lift in the rear, 3in blocks :x and 3 in skyjacker leafs, the front is sittin at around 5, because of my stacked coil isolators, i have very light vibes, nothing serious at all, at highway speeds. I wanted to know if i could put 2 in. spacers on the front and maybe do some good for the d-shaft angle. I am planning on doing the SYE / front d-shaft deal with it soon, but thats after rustys longarm new 35's etc etc etc
 
Front lift does effect rear d-shaft angle. If the front is lifted less than the rear the t-case is pointed more upward, over the rear axle, creating a worse angle. If the front is lifted more than the rear the opposite. T-case is angled more downward.
 
Cherokee91Red said:
Front lift does effect rear d-shaft angle. If the front is lifted less than the rear the t-case is pointed more upward, over the rear axle, creating a worse angle. If the front is lifted more than the rear the opposite. T-case is angled more downward.
Click to expand...

Relative too what? Think about it!
 
Cherokee91Red said:
Front lift does effect rear d-shaft angle. If the front is lifted less than the rear the t-case is pointed more upward, over the rear axle, creating a worse angle. If the front is lifted more than the rear the opposite. T-case is angled more downward.
Click to expand...
that made no sence at all
 
Cherokee91Red said:
Front lift does effect rear d-shaft angle. If the front is lifted less than the rear the t-case is pointed more upward, over the rear axle, creating a worse angle. If the front is lifted more than the rear the opposite. T-case is angled more downward.
Click to expand...
:twak: :twak: :twak: Nope, if you have a TCASE drop then that affects the angles. Suspension lift in the front affects ONLY front driveshaft. The rear driveshaft is connected to the axle which is connected by the means of springs to the unibody. The tcase is connected directly to the unibody. How does the front lift make the tcase point in one direction or the other in relation to the rear axle? If you're thinking in terms of making things relative to the ground then you're correct, but things are not relative to the earth in this case, they are relative to the axles.
 
I see what he means. On a level vehicle, draw a line from front to rear through the t-case, now raise or lower the front and the rear of the t-case will point up or down more which would affect the rear DS angle. I dought it's enough to make a difference, but it does change.
 
JnJ said:
I see what he means. On a level vehicle, draw a line from front to rear through the t-case, now raise or lower the front and the rear of the t-case will point up or down more which would affect the rear DS angle. I dought it's enough to make a difference, but it does change.
Click to expand...
I don't think so. How does lifting front affect tcase rotation? Tcase is mounted to the transmission which is mounted to the engine. Those three items sit within the body on 3 mounts (two engine mounts one transmission mount). How does lifting the front suspension change the rest of the geometry? The front suspension can't change the rear in any other way then in relation to the ground. What you see when you draw a line is a visual effect. When you lift the front look at where the rear shockmounts are pointing in relation to how they pointed before you lifted the front. Did that change their orientation in relation to the body? nope. It changed their orientation in relation to the ground.
ANyways front will not change the rear, rear will not change the front.
 
I have the same problem just not as extreme. So if i lift the front will i have to do anything to the front drive shaft?
 
mavrick said:
I have the same problem just not as extreme. So if i lift the front will i have to do anything to the front drive shaft?
Click to expand...

If you have an HP D30 you should not have to do anything unless you have a lot of lift. Then you might have to start playing with slightly extending the upper CA's to rotate the pinion up just a bit, but that messes up your alignment on the other hand, so it would end up being a balancing act of the two.
 
Kejtar said:
I don't think so. How does lifting front affect tcase rotation? Tcase is mounted to the transmission which is mounted to the engine. Those three items sit within the body on 3 mounts (two engine mounts one transmission mount). How does lifting the front suspension change the rest of the geometry? The front suspension can't change the rear in any other way then in relation to the ground. What you see when you draw a line is a visual effect. When you lift the front look at where the rear shockmounts are pointing in relation to how they pointed before you lifted the front. Did that change their orientation in relation to the body? nope. It changed their orientation in relation to the ground.
ANyways front will not change the rear, rear will not change the front.
Click to expand...
Lifting the front, lifts the front of the whole drivetrain. The whole vehicle pivots on the rear tires. Remove your front tires and drop you front end down on the ground. Now your engine is lower and from front to rear it points up (the engine, tranny, t-case) but since the rear axle did not move, the rear driveshaft to t-case union is at a different angle then if the front was up on the tires. If the image works, think of the center rectangle as the drivetrain with the line going from the rear to the axle. Now, move the front of the main rectangle (whole vehicle) and see if the draftshaft to t-case relationship does not changes.
angle.bmp


Hmmm, got ahead of myself. If the leafsprings were attached, I suppose the axle (Pinion angle) would rotate with the body/drivetrain. I guess I needed a picture. :)
 
JnJ said:
Lifting the front, lifts the front of the whole drivetrain. The whole vehicle pivots on the rear tires. Remove your front tires and drop you front end down on the ground. Now your engine is lower and from front to rear it points up (the engine, tranny, t-case) but since the rear axle did not move, the rear driveshaft to t-case union is at a different angle then if the front was up on the tires. If the image works, think of the center rectangle as the drivetrain with the line going from the rear to the axle. Now, move the front of the main rectangle (whole vehicle) and see if the draftshaft to t-case relationship does not changes.
angle.bmp
Click to expand...
OK, nope, nope and nope. What you are describing is a VISUAL effect. When you lower your front suspension the engine doesn't go lower, it's the whole body that dips. The engine and transmission and transfer case are part of your body. So is the rear axle. The direction of the pinion of the rear axle in relation to the body is controlled by how it hangs on the rear leaf springs. While it is true that when you drop the front suspension lower the direction the rear pinion changes, but it changes in relation to the earth as the rear of the vehicle ROTATED around the tires. The rear axle stays constant in relation to the body. Everything you described is in relation to the horizon and you cannot look at that as your "world" at that point should be limited to the vehicle itself.
 
Kejtar said:
OK, nope, nope and nope. What you are describing is a VISUAL effect. When you lower your front suspension the engine doesn't go lower, it's the whole body that dips. The engine and transmission and transfer case are part of your body. So is the rear axle. The direction of the pinion of the rear axle in relation to the body is controlled by how it hangs on the rear leaf springs. While it is true that when you drop the front suspension lower the direction the rear pinion changes, but it changes in relation to the earth as the rear of the vehicle ROTATED around the tires. The rear axle stays constant in relation to the body. Everything you described is in relation to the horizon and you cannot look at that as your "world" at that point should be limited to the vehicle itself.
Click to expand...
Ya, I realized that, hince the sentence below the picture.....
 
LOL I missed that sentence :D

I got a nice and nifty pic though to prove my point and since I spent so much time on it.. here it is
Tangent of the angle between the driveshaft to the output of the tcase would be r2/r1 for the rear and f2/f1 for the front. So changing the front has no effect on the rear as the rear.
Look at the picture:
shaftangles.jpg
 
Don't forget that if you lift the front you effectively shift more weight onto the rear springs, causing the rear to have "less lift" in effect.

This changes both the rear pinion and rear DS angles....


This is why if the difference between front and rear is 1" in height (higher in rear)....you don't just add one inch of coil spacer beacuse that would be too much. See what I mean?
 
Nine Mile said:
Don't forget that if you lift the front you effectively shift more weight onto the rear springs, causing the rear to have "less lift" in effect.

This changes both the rear pinion and rear DS angles....


This is why if the difference between front and rear is 1" in height (higher in rear)....you don't just add one inch of coil spacer beacuse that would be too much. See what I mean?
Click to expand...

Ummm not really. Take the vehicle and measure weight on each axle, then drop an inch or two on the front and weight on each axle (on a truck scale) and tell me how much weight has changed.
 
Kejtar said:
LOL I missed that sentence :D

I got a nice and nifty pic though to prove my point and since I spent so much time on it.. here it is
Tangent of the angle between the driveshaft to the output of the tcase would be r2/r1 for the rear and f2/f1 for the front. So changing the front has no effect on the rear as the rear.
Look at the picture:
shaftangles.jpg
Click to expand...
You spent more time on your picture then I did on mine. :D
 
Kejtar said:
Ummm not really. Take the vehicle and measure weight on each axle, then drop an inch or two on the front and weight on each axle (on a truck scale) and tell me how much weight has changed.
Click to expand...

Don't have the ability to do that on the current jeep....but I can tell you from 10 years of trying to get various Jeeps to sit level that to correct a 1" difference in height, you only need to add lift to one end about 65% of that.

So what you are telling me is that if I park on a hill with nose down, my front suspension does not compress any more than normal? And vice versa?
 
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