Poly bushings theory!
Poly bushings theory!
So I got this theory and want to see if there are any suspension experts that can shine some light on my theory, validate it or disprove it.
Theory is this.
OEM suspension and bushings are designed to take equal or equivalent load for application. Meaning that every bushing is designed to absorb certain amount of load and vibration and to pass on the rest. So if you change the parameter of one bushing (rubber to ply) would that mean that you transfer now more vibration and load to all other bushings that participate as part of the suspension geometry? Causing them to wear out quicker, respond less efficient and so on?
the thought behind it is this. I'm swapping to 5.3 diff and putting poly bushing on it and that got me thinking that now all the extra vibration and load will be transferred to sub frame bushings and cause them to wear out much quicker if they are not worn out already.
What yall think?
Theory is this.
OEM suspension and bushings are designed to take equal or equivalent load for application. Meaning that every bushing is designed to absorb certain amount of load and vibration and to pass on the rest. So if you change the parameter of one bushing (rubber to ply) would that mean that you transfer now more vibration and load to all other bushings that participate as part of the suspension geometry? Causing them to wear out quicker, respond less efficient and so on?
the thought behind it is this. I'm swapping to 5.3 diff and putting poly bushing on it and that got me thinking that now all the extra vibration and load will be transferred to sub frame bushings and cause them to wear out much quicker if they are not worn out already.
What yall think?
Never thought about that. I replaced every single bushing on the car with Whiteline and new complete suspension parts, including trans mount and motor mounts. Vibration is definitely increased. But it won't damage any stock bushings from vibrations / load. Unless your pushing some serious hp numbers or they are very very near end of life.
Never thought about that. I replaced every single bushing on the car with Whiteline and new complete suspension parts, including trans mount and motor mounts. Vibration is definitely increased. But it won't damage any stock bushings from vibrations / load. Unless your pushing some serious hp numbers or they are very very near end of life.
So I want to do poly bushing on the most important areas (compression rods, diff) and leave soft bushings in other spots. So I was wondering if that approach will in fact wear out the bushings that I leave on the suspension quicker.
It will accelerate wear in other areas that are heavily beaten, but this community has done an outstanding job of highlighting all the necessary positions whereby poly bushings should be used in a DD.
Basically, suspension mods in your standard DD should be thought of the same way as power adders and efficiency mods: find where the factory engineers screwed up, fix those problems with better designs and materials, then drive it like it would have been meant for a lawless community by a true enthusiast.
That being said, the design flaws as far as bushings were exactly what you stated; LCAs, comp rods and differential (this one's arguable). None of which should shift vibration so far thru the chassis as to ruin any other bushings, simply because almost all other bushings are very very neutral. The comp rods, LCAs and differential are not neutral, that's why they're more important.
Basically, suspension mods in your standard DD should be thought of the same way as power adders and efficiency mods: find where the factory engineers screwed up, fix those problems with better designs and materials, then drive it like it would have been meant for a lawless community by a true enthusiast.
That being said, the design flaws as far as bushings were exactly what you stated; LCAs, comp rods and differential (this one's arguable). None of which should shift vibration so far thru the chassis as to ruin any other bushings, simply because almost all other bushings are very very neutral. The comp rods, LCAs and differential are not neutral, that's why they're more important.
differential is very crucial IMO because OEM equipped it with fluid bushing which leaks out and allow diff to shift in all directions under load, making your rear hop left and right in corners and under suspension load.
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Yes, but you're asking to weigh comfort and performance. There's not really a one size fits all choice for that position. Go poly, lots of vibe. Stay stock, less feel. Other positions have better balance..this one its kind of 'one or the other'.
You're on the right track, but I don't think it's much of an issue at this point. I can see SOLID diff mounts causing additional stress on the subframe to the point of causing pre-mature bushing failure. The single rear poly bushing is so large on these cars that there's still a fair amount of play. I haven't seen any posts about replacing subframe bushings on these cars.
On the other hand, I also have a 240SX, and those cars are prone to subframe bushing failure. The reason is that there are 2 small bushings on the subframe that the diff bolts up to (4 on the older S13 models), this transfers a lot of torque directly into the subframe and to the subframe bushings. Many 240s that have been driven hard have bad subframe bushings.
It's also a little funny having both cars and being able to see that Nissan still tries to "soften" well designed suspension geometry with a giant goo filled bushing that almost always blows out. On the 240 it was the front tension rods (flip these around and now you have a compression rod), on the G it was the diff bushing. At least the compression rods weren't goo filled, but it's still a rather large piece of rubber.
As far as other bushings, this is why I replaced all the front ones with Whiteline when my compression rods went bad. I was a little worried that the stiffer compression bushing would highlight the soft control arm bushings, plus I preferred to only take the suspension apart once and be done with it.
On the other hand, I also have a 240SX, and those cars are prone to subframe bushing failure. The reason is that there are 2 small bushings on the subframe that the diff bolts up to (4 on the older S13 models), this transfers a lot of torque directly into the subframe and to the subframe bushings. Many 240s that have been driven hard have bad subframe bushings.
It's also a little funny having both cars and being able to see that Nissan still tries to "soften" well designed suspension geometry with a giant goo filled bushing that almost always blows out. On the 240 it was the front tension rods (flip these around and now you have a compression rod), on the G it was the diff bushing. At least the compression rods weren't goo filled, but it's still a rather large piece of rubber.
As far as other bushings, this is why I replaced all the front ones with Whiteline when my compression rods went bad. I was a little worried that the stiffer compression bushing would highlight the soft control arm bushings, plus I preferred to only take the suspension apart once and be done with it.
It is unfortunate that whiteline sells diff bushings as a kit, but I'm thinking only to replace one rear bushing on the diff and not bother with two front ones.
How is your front susp? vibration, road noise, squeaking sounds?
How is your front susp? vibration, road noise, squeaking sounds?
I think they sell just the front ones, at least they used to. You have to remove the diff anyway, so just replace them all. One of the front ones is goo filled also.
My front susp has some issues currently. I've got some kind of clunk when turning, hoping it's just endlinks. Could be ball joints though, the car has 193k miles on it, stuff is just wearing out. But it drives strait and handles great, so I know the bushings help. I was eating up the insides of tires constantly before the bushing install. Worn compression rod bushing = toe out under load = worn tires. Good bushing = toe remaining at alignment specs = evenly worn tires.
My front susp has some issues currently. I've got some kind of clunk when turning, hoping it's just endlinks. Could be ball joints though, the car has 193k miles on it, stuff is just wearing out. But it drives strait and handles great, so I know the bushings help. I was eating up the insides of tires constantly before the bushing install. Worn compression rod bushing = toe out under load = worn tires. Good bushing = toe remaining at alignment specs = evenly worn tires.
I think they sell just the front ones, at least they used to. You have to remove the diff anyway, so just replace them all. One of the front ones is goo filled also.
My front susp has some issues currently. I've got some kind of clunk when turning, hoping it's just endlinks. Could be ball joints though, the car has 193k miles on it, stuff is just wearing out. But it drives strait and handles great, so I know the bushings help. I was eating up the insides of tires constantly before the bushing install. Worn compression rod bushing = toe out under load = worn tires. Good bushing = toe remaining at alignment specs = evenly worn tires.
My front susp has some issues currently. I've got some kind of clunk when turning, hoping it's just endlinks. Could be ball joints though, the car has 193k miles on it, stuff is just wearing out. But it drives strait and handles great, so I know the bushings help. I was eating up the insides of tires constantly before the bushing install. Worn compression rod bushing = toe out under load = worn tires. Good bushing = toe remaining at alignment specs = evenly worn tires.
My main issue is rear now. It slides left and right with suspension load. I think it's the diff bushings, even though they don't look worn or leaking, I bet they are not 100% considering that I got 200k on the car. I was just wondering if I should just go ahead and swap sub frame bushings as well once I'm under the car, but skeptical about it as I don't want to make car undrivable as a DD.
I think the benefits of poly is that things will remain comfortable for a DD. Solid is a big nope. Will be slightly firmer than stock, but not jarring. I wouldn't mess with the subframe ones unless you can verify they're blown.
