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.
Help me diagnose a driveline vibration - Slinky 3" lift (1 Viewer)
- Thread starter digitalmarker
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- Thread starter
- #82
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.
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.
Not push the axle forward, rather rotate it. So if you rotate too much, you have too high a caster value and your pinion angle would be off. At least that's my understanding.
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.
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- Thread starter
- #85
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
Thanks, that helps to understand how the two settings affect it. While my truck's handling at the moment is not as good as it was with aftermarket arms (Slee or Delta), it's not terrible or dangerous to drive, even at high speed.
Having said that I would love to have a set of radius arms that maximize the caster but also avoid vibes because of wrong angles.
If you go back to the beginning of my thread I have tried a LOT of different options and combinations of radius arms and driveshafts.
It sounds like a lot of people are running same or similar setups to mine, with the Delta 4" arms, and are experiencing no vibration at all.
In fact only a handful of people I've encountered are having any kind of vibration issues.
Installing the factory arms with bushings was the next on the list of things for me to try to isolate the issue, which in my case seems to be too much caster with 4" arms.
Maybe there is something else wrong with my truck that I haven't identified yet?
I am waiting to hear what pinion/driveline angles the Slinky/Blackhawk arms produce, and decide whether I want to upgrade to those.
Based on what I know today, either the Slinky or the 2" Delta arms *may* do the trick for me to maximize caster without vibes.
- Thread starter
- #86
I am also trying to make it back to the alignment shop this week or next week to get a readout of my settings... will be interesting to see how close I am to 2* or the acceptable range.
Cut and turn doesn’t offer any benefit on a 80. You are limited by the fact that the tie rod will contact the arms which happens with plates as well.
The bottom line is if you want an AWD 80 to be vibration free there are some constraints. There are lift/ caster correction combos that will vibrate no matter what you do.
The bottom line is if you want an AWD 80 to be vibration free there are some constraints. There are lift/ caster correction combos that will vibrate no matter what you do.
@digitalmarker, reviving this thread because I am currently going through the same scenario., same lift, same arms.
Did you ever make it back to the alignment shop? If so what is your caster at now?
Did you hear any more about the slinky/Blackhawk arms?
And finally are you still running the 3” lift with stock arms with offset bushings?
Thanks
Did you ever make it back to the alignment shop? If so what is your caster at now?
Did you hear any more about the slinky/Blackhawk arms?
And finally are you still running the 3” lift with stock arms with offset bushings?
Thanks
Hi, I also have vibrations at 2800 to 3000 rpm range. Wonder did you get your issue resolved?
- Thread starter
- #90
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.
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.
Road Apple
SILVER Star
Thank you for following through with great feedback on your vib problems @digitalmarker. I’m just finishing install of the 3” Slinky suspension and have started contingency planning incase my driveline gets angry. Good to hear the Delta VS 3” arms helped significantly. With a set of the new Blackhawk arms, which are .6” longer than stock, I should be ok. Your improved results give me hope. Good luck getting your truck dialed in. Keep the info coming !
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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.
- Thread starter
- #93
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.
Road Apple
SILVER Star
Which DC did you end up using? Can you share your impressions of the DC shafts you tried?
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.
I know you prefer not to go to part time but that’s about the only option other than dropping to a true 2”-2.5” lift.
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.
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.
Box Rocket
SILVER Star
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.
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.
@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.
Would that not still push axle forward? Or maybe try the 30mm spacer and the 4” caster plates with stock arms?
