OP
OP
iamdub
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Lowered any other than the PPV drop? Rubs on both sides?
Rear control arms and lowering: Thinking off the deep end
- Thread starter iamdub
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Lowered any other than the PPV drop? Rubs on both sides?
Ilikemtb999
Full Access Member
It’s an ssv with 2/3 drop and bump stop brackets completely cut off. Yes both sides and I still have the stock panhard.
Has stock size 265/70/17 ko2’s on it.
the_tool_man
Full Access Member
I'm posting partly because I want to see how this goes for the OP, as one day I'm lowering my Yukon; but also to share my experience with lowering my Expedition (don't scoff, the suspensions are similar architecture).
Right after I lowered it, I noticed a driveshaft vibration at freeway speeds. I took some measurements and did a quick CAD analysis of the suspension, only to find that pinion angle only changed about half a degree. Apparently, that's enough to matter. It seems that if the U-joints are "worn in" at a certain angle, they don't like to be run at a different one. I had the driveshaft rebuilt, and the problem went away.
I made plans to build a custom panhard bar if I had tire rub issues (was running Lightning wheels, 1-1/2" wider than stock). It turns out I had very little rubbing, usually only when crossing a depression at an angle, forcing the axle to twist relative to the frame. For me, it was rare enough that I didn't bother with the panhard bar. Again, a CAD analysis showed the axle only shifted over 3/8" on the Expy. I did notice a small amount of "tail wagging" when hitting a depression at high speeds, where the suspension would compress and rebound, while the rear end would wiggle a bit side-to-side. This was due to the panhard bar no longer being parallel to the road, I think. But again, it was rare, and hardly noticeable. So I didn't do anything about it. In my case, it would have required me to custom fabricate a relocation bracket for the panhard bar, as no one makes such a thing for Expys. If I could have bought something and bolted it on, I would have.
On a GM, YMMV, of course.
I did notice on one YouTube video I watched on lowering a Tahoe, the guy relocated the rear anti-sway bar brackets toward one side. I assume that's because with the stock panhard bar the axle is shifted over. He relocated the brackets about an inch over. That seems like a lot. If it moves that much, I'd be considering a new panhard bar, and possibly relocating one end to level it at ride height.
Right after I lowered it, I noticed a driveshaft vibration at freeway speeds. I took some measurements and did a quick CAD analysis of the suspension, only to find that pinion angle only changed about half a degree. Apparently, that's enough to matter. It seems that if the U-joints are "worn in" at a certain angle, they don't like to be run at a different one. I had the driveshaft rebuilt, and the problem went away.
I made plans to build a custom panhard bar if I had tire rub issues (was running Lightning wheels, 1-1/2" wider than stock). It turns out I had very little rubbing, usually only when crossing a depression at an angle, forcing the axle to twist relative to the frame. For me, it was rare enough that I didn't bother with the panhard bar. Again, a CAD analysis showed the axle only shifted over 3/8" on the Expy. I did notice a small amount of "tail wagging" when hitting a depression at high speeds, where the suspension would compress and rebound, while the rear end would wiggle a bit side-to-side. This was due to the panhard bar no longer being parallel to the road, I think. But again, it was rare, and hardly noticeable. So I didn't do anything about it. In my case, it would have required me to custom fabricate a relocation bracket for the panhard bar, as no one makes such a thing for Expys. If I could have bought something and bolted it on, I would have.
On a GM, YMMV, of course.
I did notice on one YouTube video I watched on lowering a Tahoe, the guy relocated the rear anti-sway bar brackets toward one side. I assume that's because with the stock panhard bar the axle is shifted over. He relocated the brackets about an inch over. That seems like a lot. If it moves that much, I'd be considering a new panhard bar, and possibly relocating one end to level it at ride height.
OP
OP
iamdub
Full Access Member
"CAD analysis"... I like this guy! lol
The pinion angle being altered is exactly my concern. The original geometry posed no problems or accelerated wear of the U-joints for almost 200,000 miles. Surely, moving the bottom of the axle back X inches while keeping the top at the same position will roll the pinion down. GM, Ford, Dodge... Brand doesn't matter in this sense. I'll be taking lots of notes and measurements of everything before I lower it: Ground to fender lip, hub center to fender, location of ride height sensors, angles and lengths of rear control arms, driveshaft and pinion angles, etc. I'm currently lifted 2/1, so it will be back to stock height a little while before lower it to be sure the springs, shocks, etc. have time to settle into their stock positions for accurate comparison measurements. I'm especially curious to know the stock pinion angle setting cuz it should be slightly low to begin with to allow it to be within spec when the driveline is loaded. A 4-link (technically 5) increases U-joint life drastically compared to a leaf-spring rear suspension due to the better control of torquing. So that preset lowered pinion angle may not exist or would be very minimal, as to account just for bushing deflection.
Rubbing is the least of my concerns as I have an adjustable panhard. I'll either center it at ride height or slightly "over-compensate" if the amount of drop puts the panhard's arc at that degree. Maybe build my own panhard relocators so it's parallel with the axle at it's lowered height- this is all easy little things to address when/if I get to that point.
As far as I know, shifting the sway bar over is really because it hits something (the shock?) on larger drops. DJM has offset endlinks that move it over. One of the frame bushings can stay in it's location because the bend in the sway bar gets pushed further away. The other frame bushing needs to be moved over because the bend near it gets pushed into it.
OP
OP
iamdub
Full Access Member
Continuing to think out loud and trying to simplify all of this:
I have two options:
(1) Use the relocators with stock lower arms just as they are designed and get the adjustable Spohn uppers to adjust the pinion angle. This would solve all questions but the Spohn uppers are $$$ when I can replicate them for under well $100 in materials and with poly bushings instead of the super stiff Delrin joints Spohn uses.
(2) Using the adjustable uppers and relocators on stock lowers will push the axle back in addition to what the relocators do, depending on how much extension is needed to correct the pinion angle. This may be totally negligible, but I need to know before I dive in. If it goes back too far, I'd have to shorten the lowers to compensate. In this case, I'd just as well not use the relocators in the first place and just lengthen the lowers while accounting for the lengthened uppers and attaching them to their original axle mounts. I wanna plate the bottoms of the lower arms, anyway, so cutting and welding on them will happen regardless.
I know it all sounds complicated, and probably OVER-complicated, but it's not. What it'll boil down to is dropping it with what I have since plenty others have done the same drop. I'll measure what needs to be changed and modify new lower arms accordingly and buy or build adjustable uppers accordingly so I'll have some adjustability for fine-tuning. Then just swap all the new arms in, fine-tune the pinion, and it'll be a done deal with no reason for anything to wear prematurely as it'll all be as close as feasibly possible to the factory design that has operated flawlessly for almost 200K miles.
I have two options:
(1) Use the relocators with stock lower arms just as they are designed and get the adjustable Spohn uppers to adjust the pinion angle. This would solve all questions but the Spohn uppers are $$$ when I can replicate them for under well $100 in materials and with poly bushings instead of the super stiff Delrin joints Spohn uses.
(2) Using the adjustable uppers and relocators on stock lowers will push the axle back in addition to what the relocators do, depending on how much extension is needed to correct the pinion angle. This may be totally negligible, but I need to know before I dive in. If it goes back too far, I'd have to shorten the lowers to compensate. In this case, I'd just as well not use the relocators in the first place and just lengthen the lowers while accounting for the lengthened uppers and attaching them to their original axle mounts. I wanna plate the bottoms of the lower arms, anyway, so cutting and welding on them will happen regardless.
I know it all sounds complicated, and probably OVER-complicated, but it's not. What it'll boil down to is dropping it with what I have since plenty others have done the same drop. I'll measure what needs to be changed and modify new lower arms accordingly and buy or build adjustable uppers accordingly so I'll have some adjustability for fine-tuning. Then just swap all the new arms in, fine-tune the pinion, and it'll be a done deal with no reason for anything to wear prematurely as it'll all be as close as feasibly possible to the factory design that has operated flawlessly for almost 200K miles.
randeez
Full Access Member
hey dub
i did all that crap.... full spohn arms/panhard with del-sphere, belltech 4" lowering spring, belltech spring relocators, eibach sway bars, djm links, free travel mod, also have the 14bolt and qa-1 shocks in the rear. it gets crowded pretty quick
pinion angle was a few degrees positive the rear yoke with the stock arms and forward in the wheel well a noticeable amount.
i didnt have any problems/vibrations with rear drive shaft angle before the spohn arms (although angle not correct) , my problems started after i had the gears swapped and the front diff messed up (pretty much locked up) causing the rear end to push thru it and that would turn the rear pinion way up.
you need to move the swaybar over to the passenger side so it doesnt hit the panhard mount on the frame, then the swaybar gets close to the shock on that side - i was able to turn the shocks i have over to allow for a little more room.
i had the spohn panhard bar with poly ends before (now del-sphere) neither gives much clearance to the rear diff cover. It would be easier to offset it around the cover or even just weld the bar off center of on the ends would provide a good bit more clearance
i did all that crap.... full spohn arms/panhard with del-sphere, belltech 4" lowering spring, belltech spring relocators, eibach sway bars, djm links, free travel mod, also have the 14bolt and qa-1 shocks in the rear. it gets crowded pretty quick
pinion angle was a few degrees positive the rear yoke with the stock arms and forward in the wheel well a noticeable amount.
i didnt have any problems/vibrations with rear drive shaft angle before the spohn arms (although angle not correct) , my problems started after i had the gears swapped and the front diff messed up (pretty much locked up) causing the rear end to push thru it and that would turn the rear pinion way up.
you need to move the swaybar over to the passenger side so it doesnt hit the panhard mount on the frame, then the swaybar gets close to the shock on that side - i was able to turn the shocks i have over to allow for a little more room.
i had the spohn panhard bar with poly ends before (now del-sphere) neither gives much clearance to the rear diff cover. It would be easier to offset it around the cover or even just weld the bar off center of on the ends would provide a good bit more clearance
OP
OP
iamdub
Full Access Member
Excellent input.
I have a feeling I'll be using the arm relocators to fix the angle AND extending the lowers to center the axle. Of course, I'll be looking to see if I can lower the upper link's axle side mounting point to coincide with the lower arm's drop.
Really, it all sounds like I should just measure the mounting locations of upper and lower link arms and how far back the axle needs to go and make some plates that weld to the axle tube and/or existing mounts to do everything I'm trying to accomplish.
I have the DJM end links, so the rear swaybar will be slid over. I'll modify accordingly it there's a clearance issue. Did you use shock extenders? I have some and planned to use them, even bought new Belltech shocks sized for the drop and use of the extenders.
I was unaware of the possible clearance issue with the Spohn arm. I guess it's just another step I"ll have to investigate.
Thank you for your input.
CrashTestDummy
Full Access Member
What spacers are you using? Do you have P/Ns, or at least brand name and application? I'm looking to add some short spacers to the back of our PPV to get a bit more distance between the bump stop and axle after our 2/3 drop kit install. Pretty much all I'm seeing on the resellers web sites are Ford applications, and zero specifications of the parts. What are you using, and how well do they fit? Thank you.
