Why not use bushing grease on a-arm bushings? Options

[914bub]

They are torsilastic bushings.














































Thank you De Anza Auto Tech.!..... All that schooling finally paid off!

[Tdskip]

As a sidenote to this discussion on the British cars that I’ve worked on, specifically MGB and Triumphs and Healeys The reproduction rubber bushings or atrociously bad, they will crack and degrade even if the car sits in a temperature controlled garage. As a result I only use poly bushings when I do maintenance on the suspensions and as Dylan has said there are a range of different compliance available. On those cars at least I would never use anything other than poly.

[IronHillRestorations]

The factory front bushings are relatively cheap, $25-30 each. I used KY and a small hydraulic press and some custom guides I had made, it was pretty easy.

[Mikey914]

If you get a Powerflex bushing to bind you have done something seriously wrong (IMG:style_emoticons/default/laugh.gif)

@mikey914 that's just it, they are never at 0 preload. If every car was exactly the same weight and at the same height for the life of the car this could be true. But variation in weight (empty vs full fuel tank) and height adjustment means they are always preloaded in some direction.

The torsion bar doesn't need a return force by nature they create it when twisted.

The rubber bushings are a classic "cost vs performance vs comfort" production car compromise.

Race cars use pillow ball, spherical or delrin (or similar materials) for bushings not poly unless some special need arises.

Bushing technology has come a long way since the rock hard Weltmeister poly bushings of the 80's and a whole lot further than the rubber compounds used in the 60's and 70's.

If you're doing a "correct" restoration sure use rubber
If you drive your car and want the best handling with little to no change in nvh there are better options available.

We actually spend quite some time looking at whether to make in a poly or use the rubber. Often material improve and make the old material a better selection.

What we discovered actually did surprise us a little as we made the assumption the newer material was better. The factory designed the front suspension to have a preload.

So when it's on the ground it has some tension on the bushings. Zero reference point is with the suspension fully lowered. Yes it has a pre load that works with the struts, springs and if you have one sway bar.

That was the problem with the ones Elephant was showing. The smaller bushings would slip, and not uniformly. This created uneven loading. So if you made a bunch of hard right turns, and got the feel for the suspension, you go to make a hard left and it will not behave like the turn to the right, it will be harder. It MAY work itself out, but do you really want random variable loading on your front suspension?

The factory ones lasted at LEAST 25 years. Many are still driving around on the factory ones. I think they got it right at the factory here.

The ones we sell are a little over $15 each, meet factory spec. and if you buy our bushings we will sell you a tool for a little less than $25 that you can use to install them.

Also, Poly bushings do require lubrication.

By the way we can run several different poly compounds in our tool. Just would need to have enough folks that want them. We just didn't see the need.

Price point is similar, if we set up to do about 50 cars worth.

[Chi-town]

If you set up the bushings according to the angles elephant and other specify as "correct" the arm isn't at full droop, its almost horizontal. (angled downward just a hair)

I'm not saying they don't last, I'm saying there is better options for the time, effort, and money.

It's $60 for a set of rubber units and about 1-2 hours or killing yourself getting them back on "correctly"

It's $75 for a set of Powerflex units and about 10 minutes to put them on.

As for lubrication, yes about every 30k miles you'll have to apply some new PTFE based grease (IMG:style_emoticons/default/laugh.gif)

Yes, I talk up the Powerflex units, why you ask? (No I don't work for them )
They last almost forever / I've never had a failure
They out perform any rubber bushings and don't squeak
They don't smash from road impacts like Delrin or Bronze liners
They Fit well on every car I've ever used them on (Porsche, Mini, Subaru, Toyota, Honda)
There is almost no perceptible difference in NVH in the car after install, in fact sometimes it lessens it. (binding / twisted rubber units transmit more NVH by nature)

If you're interested you can find them Here
And you can do your own homework to see if they are up to your standards.

I keep badgering them to make a 914 rear trailing arm bushings but right now the Daystar Polygraphite (sold by AA and others) units are the best I can find.

[Mikey914]

We are making the rears now and will be ready in a few weeks. For those that want them we can do the poly at the same time as an option. So 2 birds ones stone.

I'll start up a GB. See where it goes.

I have to ask, how do you lubricate the bushings once installed?

[Chi-town]

We are making the rears now and will be ready in a few weeks. For those that want them we can do the poly at the same time as an option. So 2 birds ones stone.

I'll start up a GB. See where it goes.

I have to ask, how do you lubricate the bushings once installed?

It takes 3 bolts and the adjuster to pull the arm down. With basic hand tools about a 20 minute job for both sides.

At 30k miles per service that'll be once a lifetime for most 914 (IMG:style_emoticons/default/laugh.gif)

[Superhawk996]

There is a obviously a heated debate of poly vs. rubber. Each has it's place depending on whether you intend to use the car primarily on the street or whether you want to trade comfort and maintenace for decreased compliance.

But ask yourself this. Why is it that all major OEM's use rubber busings?

It is not simply money. Check under any new Porsche, Ferrari, Lamborghini, Audi, BMW, etc., you will find rubber bushings. Each OEM referenced could use polyurethane if it were simply the "smarter" choice. The fact is that rubber is simply superior when it comes to balancing all the conflicting trade-offs (ride, steering, NVH, durability, freedom from maintenance to name a few).

There is far more to a modern rubber bushing than meets the eye.

A rubber bushing can be designed to have a wide variety of characteristics via rubber durometer, section thickness, voids, bonding methods, physical construction methods affect it like axial pre-load by squeezing it into a "can", etc. Want dual durometer rubber in the same part? Dual durometer can, and, has been done. Rubber bushings can be tuned to a combination of static rates (simple deflection in any single axis), Dynamic rates (how does the rate respond to varying road frequency inputs). They can be designed to have incredibly high damping characteristics at a single freqency via tuned chambers that contain glycol (called hydro bushings).

Yes, I acknowledge that the 1970's era 914 bushing is indeed very simple, but, they were engineered for a purpose which was to optimize the balance between ride, handling, maintenace, and outright durability. You may shift any of the conflicting characteristics (like ride vs. handling) to gain an advantage, but, you will not find a better material than rubber to provide an optimal solution for general street use.

[Mikey914]

We are making the rears now and will be ready in a few weeks. For those that want them we can do the poly at the same time as an option. So 2 birds ones stone.

I'll start up a GB. See where it goes.

I have to ask, how do you lubricate the bushings once installed?

It takes 3 bolts and the adjuster to pull the arm down. With basic hand tools about a 20 minute job for both sides.

At 30k miles per service that'll be once a lifetime for most 914 (IMG:style_emoticons/default/laugh.gif)

So it is disassembled? That's the only way I see how it can be done. Short of having a grease fitting.
Just curious. If we make the Poly, I'd like to have a recommendation as to how it should be done. Disassembly seems a bit much. They are in an area that will get a lot of dirt and grime.

[Chi-town]

Modern rubber bushing design is completely different than anything in the 60's- 80's.

If we were comparing current design bushings this would be a different conversation.

Look under most sports cars today and you'll find a pillow ball bushing anywhere there's a real bind from the STI rear toe link to the Boxster caster arm. I'm seeing this more and more in modern cars as it eliminates binding or loaded rubber bushings therefore reducing NVH and helping handling consistency.

How many 914 owners see 30k miles of use?

If you do than disassembling, cleaning, and greasing things is just par for the course. And poly control arm bushings are a lot easier and cleaner than greasing CV joints (IMG:style_emoticons/default/laugh.gif)

[Mikey914]

EPDM that was used on the OEM parts has stood up for much more than the 30,000 miles. I'm just thinking that it will be good for another 20 yrs minimum.

Is the Poly going to outlast the natural rubber, yes, but will require more maintenance. Is there any data to show the material will offer a superior ride?

We are also using a compounded rubber that is at the minimum equivalent to the OEM in performance.

The ultimate design would be to go to a roller bearing assembly.

[Superhawk996]

The ultimate design would be to go to a roller bearing assembly.

Nope. Not for street use. It would be awful. I've been in a race cars converted to spherical bearings to decrease complicance for improved handling at all cost. The ride degradation is brutal. The road noise inside the car increases dramatically. OK for a a race car, but, I'll just say that I have no desire to subject myself to that on the street.

The other thing that hasn't been talked about with a move from rubber to an actual bearing is the increase in impact loads transmitted to the body attachments. Rubber does a great job at damping damaging peak impact loads. Hard materials like Delrin and spherical bearings have no ability to damp impact load and they result in "spike" loading. This results in either quick wear and deformation of the Delrin or brinelling of the bearing. Once you have some relative movement between the two parts as the Delrin deforms, the "spike" loading gets even worse. Worst case can lead to ovaling of the body mounting points over time. The brinelling of a roller bearing would be very fast due to the limited range of motion and high point loading. Pretty soon you would have the rollers sitting in small pockets in the raceway and a very rough motion as it rotated. Likely would break down the rollers pretty quickly.

Agree completely that the EPDM rubber bushings will hold up over time. Just look at how long OEM rubber has held up not only over time but also miles.

The key is to use quality rubber designed for use as a bushing which isn't as simple as it seems as I'm sure you're aware. As others have mentioned, low quality (improperly spec'd rubber compound) rubber bushings can have a very low glass transition temperature that leads to craking of the rubber in when temperatures dip below as little as 30F. There are a variety of "summer" and AX tires that will crack if rolled under load in 30F weather. In this case, the cracking isn't "poor" quality rubber, but rather rubber that was never intended to operate under that temperature vs. load condition. All rubber is not the same.

Again I'm not oppposed to Poly bushings for certain applications, but, let's not kid ourselves. Poly does not come without its own trade-offs. Let each person decide with eyes wide open. The Poly bushing aftermarket spends a lot of money advertising in the magazines and they only give their side of the story.

[Chi-town]

I completely agree with @Superhawk996 on this one.
I never recommend spherical, delrin, or bronze lined bushings for street use. Way to many possibilities for damage or loss of control.

There's no argument that EPMD production bushings do the job just fine for production cars.

I'm always looking for the best component I can get when it comes to fixing or upgrading my cars.

Will I give up a tiny bit of ride quality for better handling? Yes, all day every day.

Am I willing to maintain my car every 30K miles? I have to do it with my other 3 vehicles I own why not my 914?

I don't have to make the compromise that the OEM did. (IMG:style_emoticons/default/laugh.gif)

@Mikey914 I would grab a set of the Powerflex units to take a look at before you put yours into production. There is a few features in them you might like.

[Mikey914]

We are trying to restore our 75 bumpers and noticed that most of the plastic clips that attach the rear rubber bumper skin to the metal structure are missing. Does anyone have these for sale?

The part number is: 99959155440 but are NLA from Porsche.

Any help would be appreciated!

Darren

I will definitely review that design to see if there are any improvements that can be made. I Am always looking to see if we can apply different aspects of a design in the manufacture of a part we make.
As you mentioned it's always a mater of trade offs. We just want the best product we all can use.
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