Driveshaft Length

[Flip4ford]

Howdy to one and all,
I am planning on doing a SOA mod within the next month. I have a 4" lift (shackles and overload spring) I currently have a stock driveshaft. I will either remove the overload spring or the shackles depending on ride heighth. I know if the drive shaft is too short it will come apart, and if it is too long it will bottom out...
If I do the mod will I need a longer driveshaft?
Is there a formula for "it is so many inches from yoke to yoke so my axle tube needs to overlap this much"? I know rotating the rear axle a little will change the length too. I have a guy who works in a tranny/driveline shop who can make me one, but he needs to know the length I want for the new tube (if needed)
Has anyone else that has done the SOA mod have to change their driveshaft?

And before someone asks - I did a search but haven't found a whole lot of information on the driveshaft, allot on the SOA, just not driveshaft length. I may have missed it in the pretty good write ups on SOA, but I think I scoured the sight pretty good.

Thanks!

 

[91exploreron37]

If you have a 4in rear lift already and do a SOA then you will have a good 9" of lift in the rear and yes you will need a new driveshaft. I dont know the length you will need but hopefully someone else will be able to answer that question.

 

[seth247]

You sure you don't mean sas?

 

[Spdrcer34]

I'm pretty sure he knows what he is talking about...

SAS = Solid Axle Swap = Front Axle
SOA = Spring Over Axle = Rear Axle

Ryan

 

[Flip4ford]

I'm pretty sure he knows what he is talking about...

SAS = Solid Axle Swap = Front Axle
SOA = Spring Over Axle = Rear Axle

Ryan

Funny I think I do too...

I know I'll get 5.5" from a SOA, and I'll probably remove the shakles giving me about 6.5 -7" of rear lift. I have saggy rear springs....

Anyone have drive shaft info? Anyone who did a SOA have driveshaft issues...

 

[damarble]

When I did my SOA (no extra height from shackles or leaves) I used my stock driveshaft without modification. It is about 1/2" too short though. Basically I left it at the static position and bolted the rear on, then had the stretch it 1/2" more to get the front bolted up. It does not fall out under full droop though.

IMO you should get a double cardan from the start though.

 

[Flip4ford]

Hey thanks for the info I Da Marble!!
I have a double cardian stock shaft (not installed, yet). Thanks for the tip though.

Another quick question - Did you turn your Axle yoke upward a couple degrees to point directly at the tcase or did you leave it level?

 

[damarble]

I left it level at first but I had bad vibrations above 70. Then I put in a 3* shim and dropped the t-case 1". No vibes until after 85. BUT, the t-case drop was too much and caused issues with the front driveshaft and tranny shifter. So I reduced the drop to 1/2" and everything looks perfect but I have not taken it on the freeway since to test for vibes. If you get an angle finder you'll save some headaches and get it right the first time. I didn't have one and guestimated.

 

[Flip4ford]

I read on here that it should be 1drg above a straight line to the transfer case. that way when it is under load it is all in line. Thanks again for your input, it is helpful.

 

[damarble]

Almost. If using a double cardan, it should be pointed 1-2* below a straight line. Under load the pinion moves upward so you want it to be straight under load.

If you keep your stock driveshaft, the t-case and pinion angles should be identical under load, but also can't be more than a specified amount or you will get vibes and premature u-joint failure. I think it's something like 11* but don't quote me. So best scenario is typically to try to point the pinion upwards a few degrees more and point the t-case downward the same amount.

 

[Flip4ford]

OOOPS! Thanks I better got re-read that article again

 

[NEWDUCK]

I just did the SOA and i def need a new drive shaft. Maybe mines just a bit shorter than your guys or everyone has more balls and runs with less contact with the splines.

 

[damarble]

Is you axle still centered or was it moved back a little? Stock springs? All I know is I have enough engaged that it doesn't fall out during full flex so I call it good. Eventually I will move the axle back 1" more and then get a drive shaft 1.5" longer than I have now for good measure. Us 2dr guys can have a 4dr shaft cut down cheap/easy.

 

[NEWDUCK]

Stock springs and the axle is sitting directly below where stock was. It went from about 4in of splin contact stock to 1.5 and for off roading I want more than that. Has enyone ever had to get a front one made when doing the 5.5 superlift?

 

[damarble]

I haven't had a front made but a day prowling the junkyard may get you a cheap alternative. Jeep XJ/ZJ driveshafts are interchangeable with Explorer shafts but come in many lengths, Jeep didn't standardize like Ford did with the different tranny/t-case combos.