Is polyamide a good material for sway bar bushings?

I

inquirer

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I have upgraded my car's sway bars and the bushings of the rear one, that came along with the bar as a kit, have started to wear prematurely.

I have the chance to get custom ones from a machine shop. The shop suggested polyamide as a suitable material.

Here are my questions:
  1. Is polyamide a durable material? How would it compare to poly bushings?
  2. Is polyamide a self-lubricating material or would I need to use grease? If grease is needed what type would be suitable?
 
So.....searching around a bit it looks like the most common polyamide is 6/6 nylon.

Now I am NOT a plastics engineer, but having machined it I can tell you nylon is very "hard," at least to the touch. It would likely hold up but I would kinda expect NVH to shoot up.

Energy Suspension claims to use polyurethane which is often used in foam, footwear and elastomers.

If I were gonna try to make my own I'd use Delrin/acetal mostly because it machines pretty well (I hate machining nylon personally) and seems more forgiving. Acetal is often used in the slide blocks in 2-post lift columns....but then again abrasion resistance is not a property needed in suspension bushings. Close cousins are HDPE and UHMW.

Unless building for extreme performance I like to use stock rubber bushings 'cause they're quiet....
 
Us old racers always used polyurethane to replace the rubber bushings. I don't want to say it's the best material possible, as clearly there are other materials that are stiffer, more wear resistant or more compliant. Nylon was tried and can make for good anti sway bar ends. But the Nylon we tried was more likely to permanently deform, or just crack and disappear.

In the end, polyurethane seemed to have that magic mix of high durometer stiffness, yet still has compliance without damage, and, unlike high durometer rubber, good temperature stability. The secret has always been to use silicone grease as a lube in difficult locations. Some of us even went so far as to put grease fittings on our poly bushings and try to pump in silicone grease.

Is there something better now? I don't know, but I doubt it.

Custom-Urethane-Suspension-Bushings.jpg
 
The way I understand it when PA66 is used in this application it tends to wear quickly causing clunking. Poly is better but stay away from cheap stuff commonly found in chain stores and get high quality like Powerflex. I can vouch for Powerflex having used them in high stress applications that normally wipes out OE rubber in 2-3 years with no issues after 10 years.

www.powerflexusa.com

BMW E60, E61 5 Series (03 - 10) Front Sway Bar Bushing - 25.6 mm

This BMW E60, E61 5 Series (03 - 10) Front Sway Bar Bushing - 25.6 mm by Powerflex is a polyurethane replacement bushing that includes a lifetime warranty.
www.powerflexusa.com www.powerflexusa.com

Edit: Add link.
 
SubieRubyRoo said:
Polyamide would probably have the same ride quality as using a running jackhammer as a suppository...
Click to expand...
I was going to initially say you'd probably get similar results with aluminum bushings, but I think technically nylon would at least quiet some harmonics that Al would simply transmit through.

But I think ride quality would be similar with nylon or solid "metal" bushings :D

Also as Cujet mentions, nylon can be prone to cracking.

I just helped my buddy put an aftermarket sway bar on a 370Z and, yeah, the bushing brackets came with zerks and the bushings were thru-drilled to pass grease all the way to the ID at the bar itself
 
kschachn said:
Hmm, that’s Nylon which would be pretty hard and inflexible. Most of the time when something other than rubber is used it’s polyurethane. Are you sure they said polyamide?
Click to expand...
As far as I remember, but I can check again...
They have available other plastics too.


SubieRubyRoo said:
Polyamide would probably have the same ride quality as using a running jackhammer as a suppository...
Click to expand...

How much would sway bar bushings affect ride quality? My guess would be much less than other suspension bushings. Their point is to force the sway bar to rotate.


@Cujet & @Trav
I can't find poly bushings readily available.

@D60
How much would sway bar bushings affect ride quality?
 
Nope. Polyurethane is the best material for several reasons: it can take the abuse of flexing, it doesn't suck up water like polyamide, and you can get it in many durometers. For sway bars, 70A or 80A is good. You can machine it just fine with sharp bits and appropriate feeds and speeds.

What car is this? You can get generic bushings for all sizes of bars, so maybe you can find one the right size that will work. Or, one close enough you can adjust it a little bit. Measure your bar diameter and look around.
 
@Asterix
It's a Mitsubishi Lancer 1.5L, model of 2010.
It had a 18 mm RSB and I upgraded to one of 22 mm.
There are no poly bushings for the car.

It's not just the hole's diameter. External dimensions matter too.
 
Reuse the metal strap the holds the bushing to the car that you already have. Buy a new polyurethane bushing with the right size hole for the bar that's not too far from what you need, then work on it with a coarse file until it fits.

I see options for the 2007+ Evo 10, so maybe they're close enough.
 
inquirer said:
How much would sway bar bushings affect ride quality? My guess would be much less than other suspension bushings. Their point is to force the sway bar to rotate.
@D60
How much would sway bar bushings affect ride quality?
Click to expand...
Sway bars should only really “rotate” when both wheels move up or down in the same direction; they are not there to impede suspension motion. Sway bars are designed to use the upward motion of one side to “pull” the other side up and keep the body flat, or the same idea on downward motion. They are designed to force the opposite wheel to assume a vertical position so both wheels (and the body) are “flat”.

Sway bar links are much less of a risk to ride quality than suspension bushings, which transmit NVH directly to the frame/unibody. Even Heim joints on the end links would be less noticeable than even high-durometer control arm bushings as far as impact noise or harshness, but they will really tax your frame mounts.

This is well-known, and many of the flexi-flyers (my beloved Subies especially) have very flimsy mounts (especially the rear bar) for the sway bar bushings. There are usually strengthening kits or full-on replacement mounts to ensure you’re getting all of the force from the bar transmitted to the body, rather than using that energy to rip the mounts from their attachment points.
 
Try XJ applications....the XJ's inexplicably came with like 4 different sway bar diameters, although I'm not sure any were as small as 22mm
 
inquirer said:
@Asterix
It's a Mitsubishi Lancer 1.5L, model of 2010.
It had a 18 mm RSB and I upgraded to one of 22 mm.
There are no poly bushings for the car.

It's not just the hole's diameter. External dimensions matter too.
Click to expand...
I’ve adapted power flex bushings, or energy suspensions bushings, to cars that don’t have “replaceable” bushings. Get the right inner diameter for your bar. Fabricate new brackets, or adapt existing brackets.

Here is an example: https://www.volvoxc.com/0/resources/how-to/pdf/replacing-rear-sway-bar-bushings-01-07.pdf
 
SubieRubyRoo said:
You mean, like drilling an 1/8" hole through the shell and putting a zerk on it? (y)
Click to expand...
Yes but you also need a path through the bushing material so it may need drilled out too, and if the interior wall of it is smooth, also a small slot for the grease to travel through.

No guarantees but you can avoid this on some applications by using black poly bushings. The black color comes from carbon and acts as a lubricant.
 
Dave9 said:
Yes but you also need a path through the bushing material so it may need drilled out too, and if the interior wall of it is smooth, also a small slot for the grease to travel through.

No guarantees but you can avoid this on some applications by using black poly bushings. The black color comes from carbon and acts as a lubricant.
Click to expand...
That’s what I meant, sorry. Drilled thru so grease gets to the inner sleeve.
 
Asterix said:
Reuse the metal strap the holds the bushing to the car that you already have. Buy a new polyurethane bushing with the right size hole for the bar that's not too far from what you need, then work on it with a coarse file until it fits.

I see options for the 2007+ Evo 10, so maybe they're close enough.
Click to expand...
Evo X has 23 mm rear bushings: https://www.powerflex.co.uk/product-details/Rear+Anti+Roll+Bar+To+Chassis+Bush+23mm/1751.html so I guess it won't work. If the diameter was smaller it could get widened.

@Astro14
That's a good idea. Instead of making new bushings I could make a new bracket.
 
D60 said:
I just helped my buddy put an aftermarket sway bar on a 370Z and, yeah, the bushing brackets came with zerks and the bushings were thru-drilled to pass grease all the way to the ID at the bar itself
Click to expand...
That's something the guy at the machine shop suggested. To make holes for greasing.
 
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