LOOOOOOOOONG POST!
but pretty comprehensive....
read it slowly if your name is brent
i'm trying to teach you almost everything
I know (not that i know everything)
it's a lot to take in at once
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think about it this way
scenario (1) is before lift
senario (2) is after lift
you see the springs or shackles push the axle away from the jeep allowing for bigger tires but inadvertantly cause driveline problems.
you can see the angle on the drive shaft in scenario 2 is much greater (obvious exagreation but you get the point). This is very hard on the u-joints which attach the transfer case to the drive shaft and drive shaft to the rear diff (pinion).
this causes u joint failure
no biggie
they are a $14 part but if left unattended the problems can get expensive (i am proof of this).
To solve this people do a few things.
the most cheap and popular of which is lowering the center crossmember (skidplate) that the t-case is attached to by putting spacers between it and the frame rails. this helps with one side of the angle
but the angle on the rear diff is still too extreme.
that is why someone suggested 'shims'. shims are wedges that are placed between the spring and the spring perch on the axle to tilt the axle pinion to point upwards thus relieving some of the stress.
chrysler threw another monkey wrench into the works by designing the rear driveshaft very awkardly....
now,
think about it this way
your suspension moves
in essence, your axle moves up and down
so there has to be some give somewhere in the drivetrain. THE DRIVESHAFT!
you would think the driveshaft would have some sort of telescoping mechanism to absorb the ups and downs....
wrong
chrysler decided to make our lives harder and put the telescoping part (slip yoke) on the very end of the shaft.....
the driveshaft moves in and out of the t-case on the ups and downs
this means, if you go too far down the dirveshaft can pull right outta the t-case
this would explain the dropping your driveshaft comment.
have a look under there
you'll see the shiny part right at the end of the t-case
thats where it bobs in and out.
lemme just say here and now you will prolly never have to worry about your front driveshaft. The fact that it is so long means it's not as affected by the lifts...and besides....this driveshaft is telescoping!
Now
with my set up
quite similar to yours
1.25" shackles
2" aal's
1" body lift
and 33's (rarely have problems with the shackles hitting things)
The 1" body lift was actually a side effect of the 1" motor mounts i did. I did 1" motor mounts to correct the angle on my driveshaft.
I could not see lowering the t-case...this would defeat the purpose of lifting the jeep in the first place.
so think about it, lift the engine does the same as lowerign the t-case....it points the t-case down to achieve closer to stock angles but instead we are working with the other end. Going up instead of down.
this definately worked ($$$) in my case but only cured the t-case end of the driveshaft. I had not shimmed the rear axle yet and this is where i ran into problems...
i ended up exploding my t-case because of neglect
keep this in mind
don't do it half assed
use your whole ass!
do it right the first time.
Now after all that there is still another way to go about curing this problem and that is what i have done seeing as i needed to replace a buncha parts already in recent weeks.
there is somethign called a slip yoke eliminator (SYE) kit for your t-case (NP231). Including work and the new rear drivshaft you will need made this can cost over $1000 easily. Lucky for me i found a smokin deal from a super nice guy named chris siebert on this board and i got the whole deal (t-case, sye, and new rear driveshaft for $400!).
this kit changes the case's main shaft with a stronger unit and makes the t-case output 'fixed'. you are then able to swap in a telescoping driveshaft. this also cuts 4-5" off the length of the t-case making the anlges less severe.
to understand how longer driveshaft lessenes the angle take a pencil and hold it straight...
now drop one end of it down an inch
now do the same with a yard stick
the angles at either on both sticks are quite different.
the driveshaft is also a 'cv' shaft meaning it has one extra u-joint in there
makes the angles a little less steep aswell.
here's mine
have a look under yours to see how it differs
this may also come in handy
it shows the legth of the slip yoke
the shiny silver part on the bottom shaft
use it as a reference to see how much of yours is actually showing and how much you have left
more than likely your suspension will incur less than an inch of total travel on the dirveline so you should be fine
this can be easily checked
park one tire on a rock and 'max out' your suspension and see if it's close to pulling out
take some measurements
simple stuff
I'm gonna include this pic too
just for educational purposes...
this is a shot of my jeep missing the t-case
here you can see the front driveshaft not attached
it shows the u-joint pretty clearly
it's that thing that looks like a '+'
the 'slip' or telescoping part is not at the t-case on this shaft...it is further down closer to the front of the jeep. You do not have to worry about this shaft 'slipping out'.
sorry about the length but now you should know everything there is to know about the subject. It always helps to be informed.
that's about all i can think to tell you
am i missing anything?
anyone?
good luck
RJ
[edit - hey lars...feel free to add this to the YJ FAQ
Thsi was a lot of typing
if you take the time to read it please respond so i know my time wasn't wasted]
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1992 YJ with 33's
[This message has been edited by RYJAY (edited October 10, 2001).]
