Delrin vs. aluminum as a bushing material

[Def]

I need to make some 50mm wide bushings to make the Z32 rear LCA fit the S14 rear subframe I picked up.

I have some 6061-T6 aluminum rod I could turn down and make the bushings out of or could order some plain jane delrin and make them.

What's everybody's take on the two materials as a bushing?

Delrin seems more common, and might have a slightly lower coefficient of friction, but I think that all depends on the frequency of grease applications(these will have zerk fittings installed). But there are plenty of people that seem to make aluminum bushings with good result.


Car will get maybe a few thousand miles on it a year it seems like, and I would probably be greasing the RLCA at least twice a year if not a bit more realistically.

[floodo1]

pretty sure delrin isnt strong enough for this

[Def]

The bearing area would be approx 1.9x0.47 on the bushing, giving an area of about 0.89 in^2 each, or about 1.78 sq in total.

Yield strength at room temp is a little below 10 ksi for most delrin compounds, and about 4 ksi at 212 deg F.

So the ball joint would need to be loading the LCA to the tune of ~17,000 lbs at room temp, or about 7,000 lbs if everything was at the boiling point of water.

It's been a while since I looked at approximately how the loading on the spindle relates to lateral traction by the tire, but I think it's less than a factor of 2. So even at the high temp case, you're looking at one tire generating over enough lateral traction to corner the car at 1 G by itself. I think a safe loading case would probably be somewhere in the 2-3,000 lb range as a design criteria.

But yea, it is just plastic, but it's pretty strong(delrin at room temp is pretty close in strength to unalloyed 1000 series aluminum).

[Epstein]

In the domestic aftermarket, IRS Mustangs have Delrin suspension parts available. So would you keep a lip on the delrin bushing like the stock bushing? I've always wondered how aftermarket parts are kept in there seeing as how there's some axial forces at work.

[Def]

I'd keep one side bigger than the part that goes in the LCA sleeve just like stock, and might put a snap ring groove on the other side. But if it's a press fit I doubt it'll move, especially with a zerk fitting threaded into it.

The coefficient of friction seems about the same between an aluminum to cadmium or delrin to cadmium interface - so not sure what I'm going to go with... The delrin will machine easier, that's for sure.

[racepar1]

Delrin 100%! Aluminum wears faster and delrin is impreganted with carbon which makes it somewhat self-lubricating. I would still use grease though. Anyone who says that delrin is not tough enough doesn't know what they are talking about.

[Def]

There is PTFE filled delrin available too, but it's more expensive. Still not that bad in the grand scheme of things, I just wonder what the difference would be when regular greasing is involved. The price of PTFE filled delrin is a little over 4x as much as normal delrin/acetal.

[Wiisass]

Def, are you talking about using delrin/aluminum as the sleeve that goes in a rubber/poly bushing? Or using delrin/aluminum as the bushing itself?

I would definitely not use either as a bushing material for suspension arms. It would work well for stuff like sway bars that have a constant axis of rotation, but most suspension arms don't and even if it is just a small change in the axis, it will still add a lot of stress to the arm that it normally wouldn't see.

Just do the same thing you're doing with the uprights. Press sleeves with spherical bearings into the lower control arm.

[Def]

Just making a bushing out of whatever material.

Doesn't the LCA act like an A-arm, that should only rotate about its longitudinal axis through its travel?

[Caithness]

I don't see why the LCA needs to deflect or move in any way other than the simple up-and-down you're talking about. But I'm not a suspension guru so I'll leave that determination to you guys.

I happen to have personal experience installing delrin bushings on my friend's 99 Cobra IRS. They use them in the upper and lower control arms, in the inner mounts where the control arms mount to the subframe. Unlike my urethane bushings the delrin bushings have absolutely no give- they feel as solid as aluminum, just less abrasion-resistant (as we found out working on one of his arms on concrete- d'oh!) When fully installed and greased- the kit included grease fittings- they rotated almost freely in their range of motion. I was impressed- the bind was nothing compared to my urethane bushings, and for an arm that doesn't need to move on any other axis delrin seems ideal. As far as I can tell the inner mounts on these arms are of the sort that only need to move in one axis because the spindle mounts with spherical bearings top and bottom, to allow the toe arm/tie rod to do its thing.

Here's the kit we installed: http://www.svtperformance.com/forums...d.php?t=260665

As you can see they're just a press fit with a lip on one side, like you're thinking about. I believe he wanted them pressed in dry and greased only after installation to try to keep that press fit. Worst case, the mounting bucket limits how loose one of these things could get, so it could only come out so far. No catastrophic failures, at least.

[racepar1]

The rear LCA does NOT need any type of articulation, it just moves straight up and down since it has two inner attachment points on the same arm. Delrin will be fine there. The ONLY bushings in the suspension that would be fine as solid units are the RLCA bushings and the sway bar to frame bushings.

[Wiisass]

Def,

If it's has a constant rotational axis, you could use delrin/aluminum there. But I'm not 100% sure that it does or doesn't. It looks close, but that's just looking at the arm off the car. If you could fit a long bolt/solid rod through both mounting points with out any misalignment, then it should be alright. But if not, it could get bad.

Basically, I'm not a fan of delrin/aluminum used in suspension arms. Sway bar mounting is fine, but for arms, I would use bearings. And even on cars with a conventional one piece a-arm, there are a lot of places, I wouldn't use it. I mean it might work out fine, but without knowing for sure, I wouldn't risk it.

[Epstein]

I just happen to have a RLCA and a long 12mm acme rod laying around. Those bushings are definitely on the same axis.

[Wiisass]

Now put it on the car and bolt it to the spindle and put that rod through the subframe mounting points and the arm and move the suspension and make sure it doesn't load the rod at all and I'll signoff on it.

But just based on that, it should be alright, I still don't like delrin/aluminum as a suspension arm bushing, but it's not my car.

[racepar1]

Oh come on wisass! Of course it will most likely load the rod while the suspension is moving! Why does that matter? A bearing will allow exactly the same amount of flex as a delrin bushing, NONE. I really don't see why whether or not it loads the rod would be relevant. Beyond that a well designed and lubricated delrin bushing would only have a marginal amount more drag then a good, new spherical bearing. Putting bearings thare would be nice, but is 1000000000% not necessary in any way. Hell the delrin will probably last just as long as the bearing would. I say if you can make it out of delrin for a few bucks a bushing why not do it. There is no justification to spending the extra money on bearings other than it looks better on paper.