Flexing with the Rear Driveshaft

[01STrunner]

This is kind of a dumb question but I can't seem to find any answer.

Most driveshafts on off-road vehicles have a slip joint for obvious reasons including the custom one made for my SAS. As the diff moves up and down it get closer and farther from the t-case. Where does this extension/retraction come from in our 1 piece rear shafts? With the SOA I don't have any vibrations at highway speeds and it seems okay when I flex the truck out but am I slowly destroying my U-joints?

 

[tooltime]

If you are running spring over on your ST and killing u-joints, you have a geometry problem. Check the pinion angles at 1-at static ride height, full compression, and at full droop.
Just curious, why are many on here going spring over rather than the spring under? Is it for tires over 35"? I run high speed desert roads, and have no issues running thru sandy washes, mild rollers and small jumps on my 33's.

 

[01STrunner]

I'm not killing U-joints, I'm trying to figure out where the extra travel in the driveshaft is coming from when the truck flexes since there is no slip joint like most driveshafts I see.

I went SOA because it flexes better than an SUA setup on rocks which is the type of wheeling I'm into. I'm not jamming on the gas and the 4.0 doesn't make a ton of power so axle wrap is not as big of a deal. Also I would have needed insane lift springs if I had kept SUA to match the SAS up front.

 

[Sp0rtTr4c]

I have wondered this same thing. I figure the tires will move forward from droop and back with compression but the leafs would make that hard to do.

 

[tooltime]

Ahh thanks, that makes sence regarding the SOA articulation. As far as the solid driveshaft, here is a thought. Unless I mistaken, the spring length from the front spring eyelet to the housing is shorter than the rear of the housing to the rear shackles. With that in mind, as the rear springs cycle in its arc, the rear shackles do all the hard work in the cycle. The shackles pull inward during full droop, and outward on full compression. Thus with the factory geometry Ford has figured out how to make a stronger unit.
Regarding the 4.0l SOHC, mine runs really nice. I have a slight tune, TB spacer, I think bigger injectors, headers and gets serviced with good products often, not to mention with the tune, Im required to run 91octane. Once I finally change my gear ratio, this thing will be a nice piece.

 

[01STrunner]

Ahh thanks, that makes sence regarding the SOA articulation. As far as the solid driveshaft, here is a thought. Unless I mistaken, the spring length from the front spring eyelet to the housing is shorter than the rear of the housing to the rear shackles. With that in mind, as the rear springs cycle in its arc, the rear shackles do all the hard work in the cycle. The shackles pull inward during full droop, and outward on full compression. Thus with the factory geometry Ford has figured out how to make a stronger unit.
Regarding the 4.0l SOHC, mine runs really nice. I have a slight tune, TB spacer, I think bigger injectors, headers and gets serviced with good products often, not to mention with the tune, Im required to run 91octane. Once I finally change my gear ratio, this thing will be a nice piece.

Thanks for the insight! That definitely makes sense and I'm not quite as worried now since I still have a similar setup as stock. Sounds like you've got yourself quite a nice power plant with the tune and upgrades. Did you use an SCT tuner or something different?

 

[tooltime]

I actually do not know. I purchased it that way. A mechanic friend of mine put it on his computer and noticed some non OEM settings. Plus this thing runs horrible on 87 octane. I cant wait to re-gear this thing. Im selling my whole rear end in favore of a complete 8.8 with disc brakes and a 4.10 gear with l/s diffy. So soon I will have a stock OEM rear end that I will be trying to get rid of out here in Vegas.

 

[01STrunner]

Sounds like fun though. I'm starting to be interested in a rear axle swap for the disc brakes. MidnightRebel did the swap when he got rear ended and he likes the new setup a lot more than the old drums. Plus the one you're looking at is l/s which is always nice.

 

[MidnightRebel07]

I always had disc brakes on my 8.8, as all lat 02-05 ST's do. When I hit a patch of black ice and kissed the 10" curb it bent my axle tube, shft, shattered the spiders and destroyed everything. I used a 8.8 out of either a 99 or 01 Explorer Limited that had a V8, I already had new brakes on my axle so they swapped out the Ex brakes with mine.

 

[01STrunner]

Oh my bad I was thinking you had an 01 for some dumb reason.

 

[tooltime]

Hey Rebel, when you did the swap from the expy, did you use the rear springs also? If so, what do you think? As you kow, the expy's have a 100lb lighter spring rate than the st's. Which for me, the lighter rate is going to work in my favor. Ive been looking for any 99-01 expy like you mentioned, plus any st's that pop up. I have not found any st's with discs or for that matter, a 4.10 here in Vegas.

 

[MidnightRebel07]

I had replaced the leafsprings and Warrior Products shackles two months prior when I was rearended and had a eclipse drive under my truck. NCRanchero found me a set of springs from an '05 ST with 30k miles. The Explorer springs are too soft and the eyelet bolt holes are different sizes as well so you'd have to change out the bushings with ST bushings to work.

 

[tooltime]

Hmmm, the bushings or lack there of for the ST's is what started this snowball effect. My eyelet bushings are shot. Ford want nearly 90.00 per bushing, not including the back of the spring shackles. And as far as I can remember, I couldn't find any, anywhere. Ive had spring companies ship me what they said were replacements, but no go. So that's where the whole kill several birds with the same stone idea came to light. From a boneyard, I can get a whole rear end, springs, discs, and a gear close enough to fill my needs for about a hundred bucks more than the new ones from Ford. It doesn't matter if its an Expy, or ST. I have taken new nuts and bolts with me to the yard and screwed the nut on to a 99ish Eddie Bauer Expy with success. So far, the Eddie Bauers have everything I need in one kit. I still haven't found any ST's with the disc's, springs, or gear at any of the boneyards as of yet. Still lookin. I really don't mind the softer rate because I will be playing with the rates anyhow. My rig is like the rig build from the guy "who pulled the trigger." He has a 2wd ST, and is doing the same as me. Although, he beat me to the rear bed cage idea. Poop! lol These little ST's with the setup like my Camburg and his when tuned nicely, really are a true blast to drive the desert trails and sandy washes. Thanks

 

[600remguy]

Umm, doesn't the rear drive-shaft slip (in and out) in the rear of the transfer case to make up for suspension travel?

 

[tooltime]

My ST is a 2wd, and is a one piece unit. I cant speak for the 4x4's.