Box Rocket
SILVER Star
I've mentioned this in a separate conversation but going to factory bushings and Slee caster plates should improve your handling a bit and not put you beyond a good working pinion angle.
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To be perfectly honest caster is the one alignment measurement I do not fully understand.
I always thought the purpose of the aftermarket radius arms was to push the front axle forward to compensate for the fact that lifting a vehicle makes the axle move backwards.
From what I heard from numerous sources here and reputable shops, the pinion angle and operating drive shaft angle are the two factors behind driveline vibrations after a lift.
What I am not getting is why do the arms alter the angle/position of the axle, rather than keeping the angle of the pinion pointing at the transfer case, which eliminates the cause of vibrations.
The concern I have with the Slinky arms is whether they will keep the driveshaft angle and front pinion angle at the right position to avoid the vibrations I was having.
Pinion angle relative to the transfer case output and the type of driveshaft being used are the primary factor contributing to vibes. Caster doesn't factor into that at all. So in that sense, you are correct.
However, positive caster creates a positive, on-center steering feel and improves handling. Or another way of putting it, inadequate (less than 2* positive, zero or negative) caster will make the truck wander over the road, require more steering input (gets seriously tedious on long trips), follow the ruts in the pavement and reduce the steering wheels natural return to center. Imagine a "car scene" in a 70's sitcom... the actors are sitting in the front seat talking to eachother and a green screen is showing scenery going by in the background, and the driver is sawing away at the steering wheel while driving in a straight line.
The reason these aftermarket arms rotate the axle is to try and fix both problems at the same time. Rotate the axle to keep a good amount of caster, point the pinion level-ish with the t-case output so a DC shaft should theoretically work. The primary purpose is not to lengthen the arm.
Length of the arm in order to place the front tire in the center of the wheel well is kinda irrelevant because as the suspension compresses, the tire returns to it's natural position in the wheel well. The wheelbase is shortened at ride hight, but once the suspension is compressed, the wheel returns to its "stock" position. Not a problem unless you're running 37" plus tires that don't fit in the wheel well to begin with.
Truthfully, any sort of caster correction bolt-on, such as arms, plates, bushings, etc. Is a compromise. It will fix the caster great, or it will fix the vibes great. If you're lucky, it'll fix both. But if the bolt-on products don't get you there, the only way to truly fix both problems is to set up your pinion angle just perfect for the type of driveshaft you intend to run (DC or regular), and then cut and rotate the knuckle balls to give you the correct caster. Most consider this too drastic or too permanent, as going back to stock is pretty much no longer an option at that point. But it's common enough among the 40 and 60 crowd. Us 80 owners are a bunch of prissy whiners Plus the tie-rod location on an 80 doesn't really lend itself to this type of modification.
Hi, I also have vibrations at 2800 to 3000 rpm range. Wonder did you get your issue resolved?I took the photos before tightening everything down. Everything is tight and torqued to spec. The photos were intended to show the double-double CV joint. I was going to take a pic of it on the ground but was too excited to put it on and drive vibration free. Wish it was loose because that would be an easy solve!
@BILT4ME I tried running the single-CV DC shaft in and out of phase, with the exact same result. I have not tried it on the double-double one, but will try it this weekend. The owner of the shop that built the double-double shaft for me didn't think it would make a difference. He also suggested building this double-double shaft after he tried re-balancing the single CV shaft I already had several times, and after I tried running my buddy's Landtank DC shaft, which is running smoothly on his truck. At this point I am 99% sure the front DS itself is not the problem, which is why I am looking for other areas to inspect where I may have not looked yet.
@tacocat the way I measured final lift height is by measuring from top of the flare to the center of the wheel/hub, which nets out 24" all around. Comparing to the 20" stock height, it nets out to 4" actual lift. I am not running spacers. This measurement method is what I found on here in other threads.
The hub nuts, steering components, etc., are tightened to spec. I am not feeling any loose bearings or hubs or steering when I do the 6-12 or 9-3 tests on either wheel.
This weekend I am going to try the following:
Obviously I am grasping at straws here as all of these have been all but ruled out as culprits, but I don't have any other things to try at this point. Recording under the truck with a go pro is a long shot too because it's hard to see/capture anything unless something is obviously loose and flopping around, which I doubt it is otherwise it would be happening throughout the speed range, not just 35-45mph.
- run the truck with the rear drive shaft out, front shaft only
- turn the double-double shaft out of phase, and run it without the rear shaft
- run the truck with the tires/wheels off my Tundra to eliminate tire related issues or wheel balance issues
- drive around with a go pro mounted under the truck pointing at the TC and pinion side of the driveshaft
Any other ideas are welcome - please share.
Are you running a dc shaft now or standard type shaft? Post a profile pic of you front driveline and pinion relationship. This is not black magic.Here is the latest update on my saga:
I was having a lot of problems ever since I installed the 3" Slinky suspension and running Delta 4" arms. Factory drive shaft sounded like it's about to explode, and the DC shaft (I tried several) were vibrating/pulsating so heavily, it was borderline un-driveable. The owner of 4xo (manufacturer of slinky springs) was not helpful with troubleshooting this, which is pretty s***ty considering the exuberant cost of their suspension kit. In retrospect, I wish I stuck with my 4" slee kit which had zero vibration and worked flawlessly, so lesson learned there.
I borrowed a set of factory arms with OME yellow poly bushings from a buddy. This reduced the caster correction so far back (likely -2*) that vibration disappeared almost entirely, but at the expense of driving feel. The truck felt very loose on the freeway and over uneven surfaces - not terrible but definitely not a long term fix. With the truck loaded up with gear and family it was downright sketchy in some parts. I also noticed small cracks starting to form in the poly bushings after only 2k miles.
I ended up scoring a set of Delta VS arms that were a "one off" production. The way Dave from DVS described them is that they have caster correction for a 2" lift, but were longer than the 2" model - so kind of like correction for a 3" lift which is in-between their 2" and 4" arms.
The arms made a huge difference - the handling improved dramatically, likely due to the combination of improved caster settings (I likely ended up at 2.5* of caster - haven't gotten it aligned yet), as well as the gain of wheelbase length - the 3" arms pushed the front wheel to the center of the wheel well. Paired with the DVS rear panhard bracket, the truck handles really well.
The downside is that the vibrations returned, although they are not nearly as bad as they were with the 4" arms - but I still feel a bit of a shake at 30-35mph, and then again at around 50mph. I noticed that the vibrations are most pronounced with engine under load, especially going up a hill. Less pronounced when cruising on side streets and easy on the throttle.
At the end of the day, the caster angles vs the vehicle height is what makes all the difference here. Unfortunately with my height (3" slinky springs) and weight (slee shortbus bumper and winch up front), I am still getting vibes - but now they are more tolerable and I am willing to live with it for now to keep the improved handling.
So, my options from here are to either deal with the minimal vibes, throw more money at the problem and try to find another suspension setup, go part time (which I really don't want to do), or see if I can add some weight in the front to lower the front end just enough to reduce/eliminate the vibes. I am going to test the last theory by strapping a couple of sand bags to the front bumper to see if lowering the front end just a bit to reduce the vibes. If that works, I see a heavier bumper (like the ARB or Ironman) in my future.
It is 100% black magic at this point. The side shot/angles of my DC shaft looks indistinguishable between the 4" arms and the 3" arms I am running now, but the amount of vibration from the driveline is very different. The angle changes are very minor but that's what makes all the difference. And yes I am running a DC shaft, have tried several of them to rule out the drive shaft. It is definitely the diff pinion angle vs the TC pinion angle relationship that causes it to vibrate more or less.Are you running a dc shaft now or standard type shaft? Post a profile pic of you front driveline and pinion relationship. This is not black magic.
Which DC did you end up using? Can you share your impressions of the DC shafts you tried?And yes I am running a DC shaft, have tried several of them to rule out the drive shaft.
You’ve probably got 4” of lift. It’s very difficult if not impossible to dial in good strong castor numbers and have a perfect pinion align meant fkr any drive shaft at 4”. There is a narrow window for lift and driveline happiness on an 80. That window goes up to about 2.5” lift. After that you get good castor and handing or a vibe free drive to the mall.It is 100% black magic at this point. The side shot/angles of my DC shaft looks indistinguishable between the 4" arms and the 3" arms I am running now, but the amount of vibration from the driveline is very different. The angle changes are very minor but that's what makes all the difference. And yes I am running a DC shaft, have tried several of them to rule out the drive shaft. It is definitely the diff pinion angle vs the TC pinion angle relationship that causes it to vibrate more or less.
How is the axle forward from the stock position with a 3" lift? If the radius arm length doesn't change, the arc that the axle travels is consistent and with any lift will actually move the axle farther back from the stock position.I consistently get caster in spec and pinion angle for a dc shaft with smooth operation at 4” of lift.
The problem as I see it is you guys insist on having something that is on the ragged edge of the designed geometry of the truck.
At 3” of lift the front axle is actually forward from the stock position and you all insist on moving it even more forward.
And then add to that the idea that you need to have 4* of caster.
these targets might theoretically have their benefits but putting them into practice seems rather challenging without divorcing caster angle from pinion angle.
Its forward because in stock form the axle is above the rear frame bolt by 2". So as you lift the truck the axle moves forward, in relation to that rear mount, and maxes out at 2" of lift. And as the truck is lifted further that distance shrinks back to where it stated at 4" of lift. If you park you truck on a flat level surface and measure the distance from the center of the hub to the ground and then the center of the rear bolt to the ground and calculate the difference you will see it's 2" less than your lift height. More or less depending on any rake your truck might have.How is the axle forward from the stock position with a 3" lift? If the radius arm length doesn't change, the arc that the axle travels is consistent and with any lift will actually move the axle farther back from the stock position.
Would that not still push axle forward? Or maybe try the 30mm spacer and the 4” caster plates with stock arms?@digitalmarker try adding a 30 mm spacer and running the 4” DVS arms with a single DC shaft. That way everything will be at a “matching 4” spec” as landtank is suggesting.