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  #21  
Old 08-27-2010, 08:26 AM
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Originally Posted by PabloCruise View Post
My 4" SUA is similar to Matt's, 60 series PS vs. Sag.
I flipped my rear spring pack to gain 4" of wheel base.

I do not see any need to do a shackle reversal. Jim Chenoweth is not a fan of these either, as he has seen the front driveshaft pogo-stick into the t-case and effectively destroy the t-case in a shackle-reversal rig.
I agree with Randy big time! If I built another 40 a shackle reversal would be one of my first planned mods! To be honest if I was to pick up another 40 tomorrow and plan on moderate trail use I would Buy BDS 4" springs f&R 4" shackles for the rear and shackle reversal for the front. Just that alone would improve the ride and handling of the vehicle 10 fold! Throw on some 33's and a rear Lockright and the vehicle can do 80+% of the trails out there and I could drive it anywhere all 4 seasons! And yes I would flip the rear spring pack!
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I need an FJ40....
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  #22  
Old 08-27-2010, 08:30 AM
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Originally Posted by nuclearlemon View Post
the nuclearlemon ran 4" skyjacker with extended shackles for years, no dc shaft required. did have to put 4degree shims in the front. i don't know anyone who required a dc shaft with the lift because the ujoint angles don't change. i loved the skyjacker springs, as did a few friends and they must've held up because i met a guy at cruise moab four or five years back (when we held it at that picky campground) that is still running the springs. i was number three to purchase the 4" skyjacker springs back in 91 or so. my buddy steve bought the first set made and my buddy lane bought the second set made.

i would not, however, run their shocks. i had they eye snap off one, and i know two others that had the eyes snap off. i did flip the rear springs for a bit more wheelbase (garners a couple inches) and a p.o. had already put a shackle reversal in. ran it with 35s for a while, but mainly 33s for better road (couldn't afford to do gears). i did have the front shaft extended a couple of inches a few years later. fenders were already cut in the rear from a p.o. bushwacker mod.

reference pics, stock with sagging springs, 2 1/2" kidney busters (rancho), 4" skyjackers, 4" skyjackers and nuclearlemon paint. 33" tires in all but stock
I loved the Skyjacker springs ride as well but the company will not stand behind thier product so I will not ever buy from them again! Only customer service I got was brochures with Jehovah Witness booklets from them....
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I need an FJ40....
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  #23  
Old 08-27-2010, 08:40 AM
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i don't know anyone who required a dc shaft with the lift because the ujoint angles don't change.
It's impossible to effectively raise the frame (or lower the axle if you prefer) 4" and not also increase the angles on the U joints unless you somehow lower the TC at the same time. That said, as long as you stay within the working range of the yoke/u joint from full stuff to full droop you can run it that way.

To be clear, a DC shaft is recommended ONLY when you rotate your rear diff up so the pinion points straight at the TC and the angle on the rear u joint is 0 degrees. I know, 0 on the rear and less angle on the front would seem to be a good thing. But go read any technical discussion on the topic by numerous drivetrain experts and they are unanimous in their recommendation. Apparently, when your diff is not rotated and you have angles on both top and bottom u joints, they offset each other since every time the u joints rotate they move the DS slightly off center. When there is 0 angle on the bottom joint (pinion rotated) the top of the DS moves off center while the bottom one does not, thus you lose the offset and get the same effect as an out of balance driveshaft on the top of the shaft. Over time, depending on severity, this can reduce the life of the u joint and increase the wear on the output shaft of the TC.

I drove mine like this for awhile and it worked OK but I could feel some vibration at hwy speed. If the slip splines on your shaft are worn you'll probably feel it more. Since I needed to get my DS lengthened anyways I took it up to Rocky Mtn Driveline. They looked at the setup and agreed DC was the right way to go. They lengthened my stock DS and added the DC joints on top for $200, so it wasn't much more than just getting it lengthened. I now have zero vibration.

If you keep your pinion in the stock location you DO NOT want a DC shaft as it will have the opposite effect and cause vibration.
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  #24  
Old 08-27-2010, 08:49 AM
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Only customer service I got was brochures with Jehovah Witness booklets from them....
Are you kidding??? Too funny...
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  #25  
Old 08-27-2010, 08:49 AM
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For those that are curious:

When one lifts a truck, with regard to drive shaft joints, there is an easy way to figure it out.

With a single cardan style, which is just your standard shaft with u joints at each end, all that matters is that the angles at each end are the same. To briefly bore you, angular velocity must be conserved throughout a spinning system. In the case of angled shafts, like a drive line with single cardan style joints, angles cancel out. Thus, if you have a 25 degree angle on your first joint, you MUST have a 25 degree angle on the second joint, in the opposite direction. This will conserve angular velocity as it is a vector function.

If you lift the rig, and the angles change the SAME amount, then you will be fine. If they are different angles, say 25 and 15, then you need axle shims or a cut/turn for the front.

The double cardan, or CV joint, is nice, because it does exactly what the name implies, constant velocity. Angular velocity is conserved through a double cardan joint, which means that you don't need a second joint to cancel the angle out somewhere else down the line.

Since driveshafts have a second joint, with a CV jointed driveshaft, you must point the pinion at the transfercase so there is an angle of 0deg in the joint. Actually, with leaf springs, you generally want to point the pinion down about a degree or two to accommodate axle wrap when under load.

Both systems work quite well. IMO, the CV style is a better way to go, simply because you get to rotate the pinion up, which gives you more ground clearance, and gets the pinion up higher, allowing for less chance of a rock contacting it and trashing it.

I know this is all probably yesterday's news to most, but I figured I'd throw it in, in case someone was reading this down the road and had no idea what the reasons were.
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  #26  
Old 08-27-2010, 09:52 AM
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This is all great information, and I very much appreciate it. I see this shackle reversal debate has the same fervor, as that of the David Lee Roth vs. Sammy Hagar debate.

Is there any other pearls of wisdom people wish to impart on the 80 PS in a 40?
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  #27  
Old 08-27-2010, 09:58 AM
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Originally Posted by Dr. Schlegs View Post
This is all great information, and I very much appreciate it. I see this shackle reversal debate has the same fervor, as that of the David Lee Roth vs. Sammy Hagar debate.

Is there any other pearls of wisdom people wish to impart on the 80 PS in a 40?
Instead of bench wheeling you could do it then you would be an expert!
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Originally Posted by AxleIke View Post
I need an FJ40....
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Originally Posted by Red_Chili View Post
Cruisers are superior
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  #28  
Old 08-27-2010, 10:03 AM
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Instead of bench wheeling you could do it then you would be an expert!
leave it to UB to set the world right
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  #29  
Old 08-27-2010, 10:16 AM
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I think it is possible to get a decent ride with 4" lift springs, depending on manufacturer, and shackle angle will also be critical for a good ride. Any time you have a spring that is thick enough and arched enough to hold the rig 4" higher in the air, it stands to reason it is going to be a much stiffer spring and will not compress as easily or droop as much, so overall suspension travel is reduced. Stills works Ok though, just not as much travel and a stiffer ride.

SOA, if done properly, allows you to use a soft spring with more up/down travel/flex while giving an overall smoother ride. It also gets your pinions up out of the way and less prone to being a rock magnet.

However, to do it properly requires a whole lot more work and expense. The improvements in ride, handling and wheeling ability are there but are only incremental. Thousands have done the std 4" lift and are happy with it. In the end you need to decide how you will drive and wheel the rig, then decide how much money and effort you want to put into it.
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  #30  
Old 08-27-2010, 10:26 AM
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Quote:
Originally Posted by Uncle Ben View Post
Instead of bench wheeling you could do it then you would be an expert!
I wheel, I just yield to authority. It takes too long to reach the point of being a sage like you and Randy. I want to build it once, the right way.
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