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Anti-sway bar eyelet bushing misconbobulation

my kids took the truck

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My mechanic wanted to replace my sway bar bushings since the fronts are 100% shot. The fronts went easy. He took the rears and drilled out around the eyelet and pressed out the bushing and then tried to press the new OEM style rubber bushing. It did not go well. He sent my swaybar to a local Chevy guru with a shop - the sway bar came back without bushings.

For background my K5 has factory springs (original bushings) and has a mild lift from shackles in the front and 3" blocks in the rear. Without the swaybar it handles fine with the soft OEM reverse front springs. I want to keep the swaybar because it helps with keeping speed up around corners (Quadrajet, SM465, 3.08 gears, locker, and 32" tires) so I A) don't have to slow way down for a downshift or B) get into low rpm lean bucking (worse with driveline slop and locker lock/unlock jolt - can richen idle but gas mileage suffers and smell fuel at idle); there is a sweet spot that works and the swaybar helps. The K5 is a daily driver and my wife drives it half the time with the kids. But, it retains the remnants of mods for 38" tires and articulating offroad. If I want to go off road on anything more than fire roads I can remove my sway bar - it is only a few bolts.

There are threads relating to replacing the sway bar eyelet bushing (a decent baseline instructional) - to be clear this is the rear eyelet bushing where the sway bar attaches to the axle. The newer swaybars have links instead of eyelets so this relates to the older trucks.

There are a few schools of thought:

Those that give up and use two-piece poly
Those that decided two-piece poly is the better solution: I Did not find these - presumably they don't have trouble with poly and never tried the rubber bushing.

Success - those that persevere and have faith

Ditch the sway bar as useless (gets in way of crossover steering and lift springs are stiff enough)
Buy a new OEM swaybar from GM

This raised a question for me - does the poly and rubber perform any differently?

The OEM rubber bushing is a 'caged rubber torsional bushing' that provides resistance (like a shock absorber) when the axles move vertically in addition to the sway bar torsional between wheels. The poly does not provide vertical resistance, it acts like a lubed bearing and freely moves vertically, while the sway bar provides torsional resistance between tires. The answer is yes, the poly and rubber perform differently.

The next question, is there a need for the 'caged rubber torsional bushing' on the sway bar? GM engineers put it there but it could also just have been inexpensive to use rubber.

A few threads on performance -
I have no answer to the need for the 'caged rubber torsional bushing,' the biggest hint is the swaybar equation ignores the bushing - this tells me that no the 'caged rubber torsional bushing' is not needed and seems logical since the shocks dampen the vertical movement.

estimating antiroll bar stiffness (wikipedia)
220px-Antiroll_Bar.svg.png


T=Vehicle track width (inches)
K=Fractional lever arm ration (movement at roll bar / movement at wheel)
d=Bar diameter (inches)
R=Effective arm length (inches)
L=Half length of bar (inches)
S=Length of lever arm (inches)
Q=Stiffness (lb*in per degree)

B = Bushing torsional resistance???


My mechanic gives up and wants me to buy the ORD two-piece poly bushings so he can get on with his life and get my swaybar out of his shop. Of course, I don't need a mechanic to install ORD bushings - I can do that in the parking lot. The only possible complaint about poly - and nobody has ever made a thread on this but there are threads where someone heard of someone that said their poly sway bar bushings eventually squeak; this Reddit thread describes poly bushing problems on street cars and solutions.

Images I took while my mechanic went through the wtf are these the right size process...

20160319_111906.jpg

20160319_112147.jpg

20160319_121334.jpg

Any thoughts?
 
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dyeager535

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Maybe someone has done this with success and can chime in.

My only ideas are to freeze the rubber bushings, heat the bar ends, and use some dielectric grease in the channel and the bushings to give yourself as much chances at success as possible.

Doubt freezing the rubber will do much, but perhaps the inner steel sleeve (which is bonded AFAIK) and will pull the rubber in a tiny bit. Generally things like this seem to need just that tiny bit, so with all the techniques combined maybe you'll get lucky?

At some point I'll be here as well, after the body swap, every suspension bushing is slated for replacement. I'm not a fan of poly for the suspension stuff if it can be avoided, and there are a few that might be as difficult as you are finding.
 
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my kids took the truck

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The inner steel sleeve looks like it is bonded (and seems like it should be) but (per one of the threads I linked) if you press the sleeve it comes right out.

My mechanic pressed the sleeve and without it the bushing went right in by hand but he could not get the sleeve to press. By then the rubber was splitting from all the previous attempts. He said he would get a shop to press the sleeve with a new set of bushings.

Somehow the shop misunderstood they needed to remove the sleeve. By the time he got it straight that they need to remove the sleeve then install the bushing and then press the sleeve they had moved onto other stuff; I think they were worried that someone driving a K5 was not going to pay them their shop time.

I gave my mechanic the go ahead to spend whatever it takes (I might as well have had a new sway bar gold plated when this is done) and let's just get it done without wasting time haggling over rates. This has been my mechanic for eight years and knows I understand the value of shop time and will pay a bit when it comes to my K5 but I think he had trouble conveying that info.
 
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dyeager535

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I suppose the easiest thing to do would be run a hone through the bar ends until it's just barely a press fit. Not sure why one would care if the rubber was super tight in there or not, it's not like it could slide out once assembled.
 

my kids took the truck

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Not sure why one would care if the rubber was super tight in there or not, it's not like it could slide out once assembled.

I agree. The tight fit appears the design is creating a 'caged rubber torsional bushing.' The problem is the equation to calculate the swaybar torsion does not include the bushings. Is the tight fit by engineering design or is it by manufacturing convenience?
 

dyeager535

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I agree. The tight fit appears the design is creating a 'caged rubber torsional bushing.' The problem is the equation to calculate the swaybar torsion does not include the bushings. Is the tight fit by engineering design or is it by manufacturing convenience?

On the trucks I'd be surprised if it was engineering. I know on the cars GM was thinking about the bushings and performance, but the trucks I find it hard to believe they put that much effort into it, at that time. The rubber shouldn't do much to resist twisting, otherwise they'd tear. Just don't see an advantage to making them such a tight fit.
 

my kids took the truck

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On the trucks I'd be surprised if it was engineering. I know on the cars GM was thinking about the bushings and performance, but the trucks I find it hard to believe they put that much effort into it, at that time. The rubber shouldn't do much to resist twisting, otherwise they'd tear. Just don't see an advantage to making them such a tight fit.

You got me thinking: I am looking through the GM patents and technical reports for swaybars. This approach worked for my Quadrajet questions.

First thing I found, the patent for the fulltime 4-wheel drive we all spend so much effort to disable
It was intended for a 4wheel drive rear motor buggy with 4 wheel independent suspension. The same guy's, Vic, design is behind the Blazer, Lunar rover, and the HUMVEE as well as this buggy precurser to all three http://www.offroadxtreme.com/features/vintage-monday-vic-hickey-built-1967-baja-boot/). It looks like Vic designed the blazer and he stuck that t-case design on the K5 and now I am starting to wonder what else this guy had planned for the K5; The 'real' HUMVEE is 4 wheel independent. Wow, the K5 was a redesign from the chevy truck chassis for a high speed offroad vehicle... That means the addition of the NP203 was Vic's last design implementation on the K5 for some reason they clearly moved away from his idea's and the K5 basically was unchanged from then to '91 (longest production run ever?). Maybe 4 wheel independent was his next design push for '76 and GM corp balked?

I think I found the swaybar patent (1956) https://www.google.com/patents/US2961253
They have two sources of resisting body roll (if I understand them) "The stabilizer further provides anti-roll operation due to the fact that when one wheel goes up while another is going down the stabilizer bar is subject to torsion as well as the bending in compression. "
  • The torsion force in the bar due to one bar arm pressing up and the other pressing down.
  • The bending force on each arm between the axle and the frame.
If this is correct, then the stiff rubber bushings are meant to force the arms to bend rather than 'slip' on the bushing. This provides additional sway resistance.

The question I have:
Why not just make the bar larger and get more resistance that way? On my mustang (ahem... sorry guys) I have the thickest sway bars I could get and the rears bolt solidly to my rear axle lower arms using two bolts each side with no bushing ( the lower arms have bushings so I guess there is that). Supporting this idea, here is a front swaybar design that is a rigid mount (1945) https://www.google.com/patents/US2523473. Here is the patent that adds the bushings, sounds like the bushings allow for looser manufacturing tolerances in the bar mounts "provide a stabilizer bar of one piece construction which is axially shiftable in a fashion able to compensate for structural adjustments and able to move relative to the support by a means carrying it so as to have at no portion a rigid connection therewith." (Chrysler, 1945) https://www.google.com/patents/US2626797

My best guess:
In theory with a solid axle if it only moved vertically, for the best function you should weld that sway bar to the axle with no bushing. The only bushing you need is at the frame pivot (could be ball bearings at the frame for all it matters). But, because it is a leaf spring suspension the axle cannot rotate perfectly in the arc of the sway bar and keep the sway bar perpendicular to the frame mount. The bushing allows only enough twist to allow the axle to stay perfectly perpendicular (or the axle tubes would 'want' to twist in the u-bolts) with the leaf spring. I'd guess only needs a few degrees of rotation in the bushing between high stop and low drop.

Conclusion:
Assuming all that is correct then the replacement eyelet bushings should be bonded with the center sleeve. The sleeve is what 'locks' the swaybar to the axle through the bolts. Those bolts have a lot of torsion on them and need to be torqued down to transfer all the torsion from the steel insert to the bolt. That is probably why those bolts are so large. Are the OEM bonded to the sleeve?

Real world:
How big a difference would it make if the bending of the sway bar arms was eliminated and only the torsional forces on the bar was available?

Test:
I bet the answer is in the resisting force of that rubber bushing since it cannot transfer any more bending force on the swaybar arms than that. And then compare the rubber resisting force to the sway bar torsional resistance as a ratio and see if the bending of the arms is 5%, 10%, 20%, 30% of total resistance.

Thoughts:
They don't seem to have a specific patent for the front swaybar on a solid axle 4x4 so they might have never ran the numbers to see, they just knew it 'worked better' with the rubber bushings. This patent specific to the sway bar mounting point at the axle makes no mention of the need to form a rigid mount to form a bending in the bar arm - they are just trying to get the mount back so to allow the longest arm length to increase the torsion in the bar (Porsche, 1963) https://www.google.com/patents/US3275313

EDIT: Can tell when I am procrastinating a report I don't feel like working on... three hours of detailed research into my truck's sway bar axle connection; then I discover this guy Vic grandfathered the K5.
 
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919jackass

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been here and done that. i have tried everything you mentioned. Freezing, heating, pressing with a 60 ton press then went to the dealer everything. Then found these.
http://offroaddesign.com/catalog/swaybarbush.htm
These are a 20 min install and work out great. I gave up after I messed up the second set. NOTHING WORKS !!!! I beat my head against the wall for several weeks on it. i put these in from ord and never looked back.
 

my kids took the truck

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Then found these. http://offroaddesign.com/catalog/swaybarbush.htm These are a 20 min install and work out great. I gave up after I messed up the second set. NOTHING WORKS !!!! I beat my head against the wall for several weeks on it. i put these in from ord and never looked back.

That is basically what this thread is trying to resolve - what is the difference in performance between the OEM style rubber bushing and the ORD style polyurethane bushing , and does the performance difference matter. So far, it is clear that A) the OEM style bushing performs better and B) for the effort it takes to install the bushings you might as well buy a new OEM swaybar if you can find one in stock at GM.
 

Blue85

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Swaybars are getting junked left and right around here. Just pick up one with decent used bushings.
 

JoshHefnerX

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Don't have a ton to add here except that silicone grease seems to help squeaks. Put some aftermarkets in my G8, one squeaks one doesn't, but the silicone last a bunch longer to keep them at bay. The squeaks come from the front on mine - lots more 'movement' in that bushing then the end rods would have.
 

diesel4me

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The parts man in me would be trying to find some stock type upper control arm bushings from some other application,with metal shells & sleeves that would press fit into the sway bar..(I assume you were dealing with the bushings at the U-bolt end of the sway bar ? )..

--.that was one advantage to working at a parts store--you got to open boxes and measure things,and find something that'll work for those "NA" listings !..
 

my kids took the truck

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The parts man in me would be trying to find some stock type upper control arm bushings from some other application,with metal shells & sleeves that would press fit into the sway bar..(I assume you were dealing with the bushings at the U-bolt end of the sway bar ? ).
The upper control bushings are fine - it was the eyelet bushings they could not get pressed in. My mechanic had to close up the shop and move to a new location to make way for a roundabout of all things. That was the end of that. The ORD are a split bushing so not need to press them. Problem solved. I saw your suggestion to find a replacement swaybar with good bushings in the eyelet and I seriously considered that idea. I sent a few emails out to GM parts looking for a new OEM swaybar in stock but did not get a response. Whe I get more time I will look for a new bar or try getting the bushings pressed; unless the poly seem fine then I will just leave it.
 

diesel4me

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No,what I meant was I'd have been trying to find ANY steel shelled bushing with a steel sleeve,like what a car or 2wd conrol arm uses,that could be pressed into the sway bar eyelet,and had the right inner and outer dimensions..

Most every 4x4 GM sway bar on my trucks had those bushings at the spring pad end of the sway bar very cracked and dried out looking,but I imagine it'd be hell trying to get new ones to go in without destroying them..

I'd like to know how GM did it to begin with...
Maybe they used liquid nitrogen or something ?.:thinking:..
 
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