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Why do you choose poly bushings over rubber for your leaf springs?
- Thread starter howdiy
- Start date
pauly383
Daddy383
Less deflection , the suspension can do most of the work , and not the bushings flexing and destroying themselves prematurely . Making for a more controlled ride and handling .
Not to mention they last longer than rubber when exposed to leaky old motors . Are easier to replace than rubber since there is no second sleeve around the perimeter to have to pound out of the spring eyes .
Not to mention they last longer than rubber when exposed to leaky old motors . Are easier to replace than rubber since there is no second sleeve around the perimeter to have to pound out of the spring eyes .
I don't. Suspension bushings are supposed to allow free movement to a point, poly doesn't. If it did, they wouldn't need greased. Leaf springs exert pressure at odd angles to the bushing, if the bushing doesn't give, something mounted to it, must. You can argue it should be the spring moving, but springs take a lot of force to twist, which is what our leaf springs must do to allow either tire to move up or down, somewhat non-relative to the opposite tire.
Longevity and replacement are better with poly, but I've never seen a GM bushing break into small pieces and fall out, nor squeak, even at 20-30 years old and worn out. Some folks very well may use their trucks hard enough to chew through new rubber bushings in short order, so I certainly won't say poly won't work.
From what I've seen, unless someone has come out with replacement stock bushings that are cheap, poly is substantially cheaper than replacing rubber with rubber.
Might as well have a religious debate.
Longevity and replacement are better with poly, but I've never seen a GM bushing break into small pieces and fall out, nor squeak, even at 20-30 years old and worn out. Some folks very well may use their trucks hard enough to chew through new rubber bushings in short order, so I certainly won't say poly won't work.
From what I've seen, unless someone has come out with replacement stock bushings that are cheap, poly is substantially cheaper than replacing rubber with rubber.
Might as well have a religious debate.
Motor/trans mounts are good uses, poly absorbs vibration, albeit less effectively than rubber, but also stands up better in that environment. Also, the force exerted on the motor mounts is different than suspension.
That's not true at all, both rubber and poly bushings need grease. The metal sleeve should be clamped between your spring mount and hence the bushing should spin around the sleeve, which is why you need to grease them.
Your point about poly being harder on the springs and mounts is a legitimate one, and probably the only potential downfall to poly mounts IMO.
I'm one of those people that has destroyed every rubber bushing on my truck at least once over. I went through a set of rubber motor mounts in a year. Poly bushings hold up MUCH better for me.
Actually, the factory rubber bushings are molded to both the inner and outer sleeve. So when it rotates, it acts as a torsional spring. This is why they don't squeak. Nothing is sliding. It's also why they say the poly bushing provides more suspension flex. The more you flex with the rubber, the more resistance it applies.
In either case, the bolt will rust to the sleeve. For rubber, it doesn't matter, except for difficulty in removal. For poly, the rust can increase the resistance to rotation as it travels onto the outside of the sleeve. Sure, you could prevent this by taking the bushing apart and re-greasing it every couple of months, but who is really going to do that?
This is a good time to add that the greasable poly bushings (i.e. drilled bolts with zerks) don't solve the aforementioned problem either because nothing forces the grease everywhere within the bushing. So the rust is only stopped along the path of least resistance from the grease hole to the outside of the bushing. The REAL problem is road salt, but my point is that rubber bushings are remarkably low-maintenance.
I have never seen a GM vehicle that has come off the line with greased bushings. Maybe I'm naive in only being limited to 90's and older GM products. Kind of counter productive since oil and grease eats rubber, which is one of the things the poly manufacturers tout as an advantage.
That is not how rubber bushings are designed to operate. The sleeve is bound to the rubber, as rubber is flexible (and poly is not), the rotation/movement of the suspension is not a large amount at the bushing, and the rubber deflects or twists. This is why you'll notice it cracks and/or tears in a relatively short period of time. If anything, I can understand greasing the bolt that passes through the sleeve for easy removal later on, and perhaps IF that squeaks.
Factory suspension for these trucks has so many points to flex, creak, groan, and squeak that it would be pretty hard to isolate the noise to any one specific component.
My bad, apparently I was wrong on how the rubber bushings work 
Thanks for keeping me honest fellas, you learn something new everyday
Thanks for keeping me honest fellas, you learn something new everyday
One point to make is, performance mods...
There's a reason guys go to motor plates, solids or poly mounts.. big ponies will destroy factory rubber mounts in short order.... may be it's working the material harder than it's engineered to handle.. hard compression, etc, etc..
I would think this would apply to suspension too, to a certain extent... 44's tend to put a load on things...
either way, I go poly whenever I'm in there on a project.. the future servicability and stableness are more than enough reason to ditch the rubber stuff...
I don't know about others here, but when I get done with my running gear upgrades, I'll have no issue disassembling and fresh greasing my spring bushing once a year... in addition to the periodic shot to the greasable bolts..
my .02
There's a reason guys go to motor plates, solids or poly mounts.. big ponies will destroy factory rubber mounts in short order.... may be it's working the material harder than it's engineered to handle.. hard compression, etc, etc..
I would think this would apply to suspension too, to a certain extent... 44's tend to put a load on things...
either way, I go poly whenever I'm in there on a project.. the future servicability and stableness are more than enough reason to ditch the rubber stuff...
I don't know about others here, but when I get done with my running gear upgrades, I'll have no issue disassembling and fresh greasing my spring bushing once a year... in addition to the periodic shot to the greasable bolts..
my .02
Yeah, you really need to look at the intended usage.
One thing about rubber is that it's not really "consistent". With solid or something MORE solid (like poly) you have less of a variable than something like rubber that is less solid. On trucks like ours its probably not such a big deal, especially with better shackles and flexier springs.
In a stock truck setup, the load the bushings don't absorb, is (has to be) absorbed/transmitted somewhere else. Kind of like having your u-joints as your weakest link. In a stock setup, I'd expect the shackles to bend before the poly does, in hard usage.
One thing about rubber is that it's not really "consistent". With solid or something MORE solid (like poly) you have less of a variable than something like rubber that is less solid. On trucks like ours its probably not such a big deal, especially with better shackles and flexier springs.
In a stock truck setup, the load the bushings don't absorb, is (has to be) absorbed/transmitted somewhere else. Kind of like having your u-joints as your weakest link. In a stock setup, I'd expect the shackles to bend before the poly does, in hard usage.
4by4bygod
1/2 ton status
yay for polyurethane
We did the poly bushing thing on the front / rear suspension of my wife's 79 camaro..( tied the subframes and installed a rear anti sway bar too) I wish I had 'em on everything I own. the car corners like it's on rails.
maybe what makes them good on a car disqualifies them for off road, I dunno.
here's one for ya, since we're on the subject..
one problem I've had on both my 84 & 87 K5's..they were fairly high mileage (over 100k) and they developed a habit of not straightening up after a left or right turn.. in other words, I make the turn, and it takes a bit for the truck to straighten up, even though I'm turning the wheel back to straight.. it could get kinda hairy at times..
only thing that fixed the problem was installing new front springs w/ new bushings, and shackles.. apparently the bushings ( the shackle bushings being the most likely culprit ) were shot enough that the whole front spring / axle assembly would "cock" when going around a corner, and stay that way until jarred loose by me steering the truck..
anyway, polyurethane bushings from day one new I think would have helped..
We did the poly bushing thing on the front / rear suspension of my wife's 79 camaro..( tied the subframes and installed a rear anti sway bar too) I wish I had 'em on everything I own. the car corners like it's on rails.
maybe what makes them good on a car disqualifies them for off road, I dunno.
here's one for ya, since we're on the subject..
one problem I've had on both my 84 & 87 K5's..they were fairly high mileage (over 100k) and they developed a habit of not straightening up after a left or right turn.. in other words, I make the turn, and it takes a bit for the truck to straighten up, even though I'm turning the wheel back to straight.. it could get kinda hairy at times..
only thing that fixed the problem was installing new front springs w/ new bushings, and shackles.. apparently the bushings ( the shackle bushings being the most likely culprit ) were shot enough that the whole front spring / axle assembly would "cock" when going around a corner, and stay that way until jarred loose by me steering the truck..
anyway, polyurethane bushings from day one new I think would have helped..
Should have made a poll.
I would have voted poly. Always have used them and always will.
I would have voted poly. Always have used them and always will.
4by4bygod
1/2 ton status
I'll bet you don't give a crap about the "squeaking" the make, do you?..I hear that complaint a lot - mostly from guys who have never used them.. I just tell folks to turn up the radio or something..
When you run a 454, or any BBC, bushing squeak is a thing of the past. You won't notice it one bit.
I didn't even get into A-arm bushings, did I? GM used stiffer *rubber* bushings (higher durometer is the term IIRC) in some of the later car RWD performance suspension setups FWIW.
Check into del-a-lums for a-arms, if they are still made. Nothing better except maybe "solids".
"Stiction" is the word I saw coined for what poly does using a through bolt without good lubrication.
The amount of "give" lost from rubber bushings may indeed make poly feel better, especially during maneuvering on independent suspension/cars where suspension travel is solely rotational (or should be) on a fixed point, unlike leafs. Not only do leaf springs move like this: | as viewed from the rear as the tire moves up and down, but when acting independently, as when flexing one tire up, and one down, the suspension must travel like this ) That side load has to be absorbed by something.
With a stiff enough bushing, a beefy shackle, shackle mount, and frame, the leaf spring will be forced to do all of the work, to include twisting. I have no doubt this is one reason why longer springs seem to work better on the trucks.
GM used stiffer *rubber* bushings (higher durometer is the term IIRC) in some of the later car RWD performance suspension setups FWIW.Check into del-a-lums for a-arms, if they are still made. Nothing better except maybe "solids".
"Stiction" is the word I saw coined for what poly does using a through bolt without good lubrication.
The amount of "give" lost from rubber bushings may indeed make poly feel better, especially during maneuvering on independent suspension/cars where suspension travel is solely rotational (or should be) on a fixed point, unlike leafs. Not only do leaf springs move like this: | as viewed from the rear as the tire moves up and down, but when acting independently, as when flexing one tire up, and one down, the suspension must travel like this ) That side load has to be absorbed by something.
With a stiff enough bushing, a beefy shackle, shackle mount, and frame, the leaf spring will be forced to do all of the work, to include twisting. I have no doubt this is one reason why longer springs seem to work better on the trucks.
On the older vettes 63-82, they have strut rods for the rear suspension, The PO owner of our car put poly bushings in them, When I took them apart they were ovaled out and cracked/failing apart. They don't move in a single plane so poly wasn't a good choice. I replaced them with fk rod ends
I have poly a-arm bushings too, Soon to be replaced by solid though. They seem to be fine though.
I don't really have much experience with poly bushings other that those two things though
All the bushings on my truck will be poly. I don't really have a choice of anything else, plus poly is so much easier to put together. I won't mind putting new bushings in every few years
I have poly a-arm bushings too, Soon to be replaced by solid though. They seem to be fine though.
I don't really have much experience with poly bushings other that those two things though
All the bushings on my truck will be poly. I don't really have a choice of anything else, plus poly is so much easier to put together. I won't mind putting new bushings in every few years
G.M.H
Registered Member
I think the trick is to grease them often,and after every run. When the suspension is cocked hard the grease is displaced leaving voids where water can get in. I also put a thin piece of sheetmetal in between the bushing and the spring to cover the crack in the spring eye. The grease definitely gets to alot more places before finding a way out.
I trashed two pairs of motor mounts before I discovered the poly replacements, no problems since.
I trashed two pairs of motor mounts before I discovered the poly replacements, no problems since.
