Whiteline Bushing Installation
 

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I recently did a major suspension restoration on my 350z and decided to replace the standard rubber bushings with polyurethane bushings. I accomplished this by installing the Whiteline WEK003 Bushing Kit. I purchased the Whiteline kit not because I wanted all that is included, but because the kit provides a large savings over buying individual components. They understand marketing.

After installing the Whiteline bushings, I notice a very significant difference. The car handles quite a bit better with the polyurethane bushings, but the ride is stiff and less comfortable compared to the OEM rubber bushings.

I do not know if there are any industry standards comparing different suspension/bushing materials (i.e., rubber vs. polyurethane). I think it would be useful knowing values comparing the material’s reflexive capability, wear factors and long-term serviceability, and dynamic mean and median values. Individual manufacturers have conducted studies and created tables, but I am uncertain of any legitimacy unless the values extend across the entire industry.

The stock suspension components on the 350z are equipped with rubber bushings. This provides some advantages. Rubber is excellent absorbing energy, so the car is quiet and the ride is more comfortable. Bushings made of rubber are less costly to manufacture and are often more easily placed into suspension components. The disadvantage of a rubber bushing is its faster wear resulting in a noticeable and linear reduction in quality in a shorter service period.

Aftermarket bushing components (Whiteline is an example) made of polyurethane provide very different driving/handling characteristics. The suspension is noticeably stiffer with polyurethane bushings, and you experience less difference/degeneration over time (i.e., the polyurethane bushings wear less and more slowly than rubber bushings). To avoid harsh performance, Whiteline copper bushings are lined with polyurethane.

My Whiteline bushings are newly installed, so I cannot report yet on longevity.

I have some too, that being said I might consider changing some of the other ones out for Nismo ones. I tend to favor hard rubber stock style over something that is physically different. I've had them for a few years and have no problems to report fwiw.

There are "standards" that can and are used to determine a bushing's hardness or softness. It is called a durometer rating. Durometer ratings are used to determine the hardness of almost any type of "rubber like" structure including rubber, polyurethane, and any host of elastomers. Durometer ratings are used in every industry including automotive on such things as bushings, tires, elastomer mounts (engine, trans, differential, etc.)

Problem as it applies here is that no manufacturers of bushings for cars list the durometer ratings of their parts - because they don't have to. Unlike specific high stress components used in, say, the aerospace/aeronautics industries where every detail is the difference between success/failure, life/death, the automotive industry only uses these ratings internally, say, in the design phase where, a specific "Shore durometer rating" is required to manufacture a part to make sure it can meet a specific load requirement.

And in the aftermarket, forget about this being published information because no one would really understand the difference between a "Shore durometer A" rating versus a "Shore durometer D" rating. Instead, the types of materials, say, "rubber versus polyurethane" is about the depth that non-engineering people could understand. As a matter of fact, for the sake of this discussion, that level of materials granularity is about as deep as one needs to go. IOW, "polyurethane is harder than rubber."

As far as the functional part of this discussion is concerned.... I would NEVER replace all of my bushings with poly for a street application. It's way too hard and transmits far too much NVH into the chassis from the ground AND non-compliance of bushings does nothing but put undue stress on other parts of the car through the increased vibration. There are some specific applications where it is a good fit for street use.... sway bar center and end link bushings, steering rack bushings come to mind. But any other bushing used in a compression application is going to hurt the ride of the car. ALWAYS.

Ask me how I know..... as a young sports car enthusiast, I too subscribed to the "stiffer is better" school of performance. Polyurethane, Delrin, solid aluminum... all materials used in my early sports cars. Learned very quickly that stiffer isn't always better. My chattering teeth taught me that lesson. Since then, only select components have been replaced with polyurethane.

Note: even my race cars did not use full poly or Delrin because there are some areas that compliance (or "give") was a good thing. Transmission mount as an example. At that time, Datsun Competition (later Nissan Motorsports) offered a solid steel transmission mount for my D-Production SRL. Problem we found at the track was that the solid mount was causing motor mounts to break, u-joints to lose their needle bearings, and so forth. Reason: NO movement at the tail shaft of the transmission didn't allow the engine/trans to naturally torque under load; putting the torsional stress on all of the other components that weren't designed for such lateral loading. It was our feedback that led to the high durometer rubber transmission mounts for all competition Datsuns. Harder and harsher than street/passenger cars but allowing enough deflection to absorb the torque load.

Oh, make no mistake... There is no doubt the quest for ultimate performance is better served with higher durometer bushings and mounts; just not at the expense of the driver's comfort, and that is important to keep the driver (most important part of the equation) focused on being able to drive 10/10ths without the distraction of a sore ass or headache.

Mic, thanks for additional information. The lack of quantitative values from some of the manufacturers make it difficult to compare bushings.

Powerflex does provide durometer values. They have three different levels of rigidity in their bushings. This graph, showing different durometer readings of their products, is from Powerflex's product information.
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EDIT: To avoid confusion I should point out that this chart has two different scales, Shore A and Shore D. The Shore D scale is used for “harder rubbers” while the Shore A scale is used for “softer rubbers” (such as suspension bushings).

SECOND EDIT: I should also mention that some bushing manufacturers publish the durometer value in Shore D while others use Shore A. These are very different values, so you also need to know the Shore scale as well as the durometer value. Yikes!
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Great chart. Like it's said, a pic is worth a thousand words.... and that one explains my thousand word essay in a single shot. Hahahahaha.

I agree with your comments. If you are satisfied with performance and handling from the stock bushings, there is no reason to replace these with aftermarket polyurethane bushings unless you decide you need this for the track. And, your point about maintaining a good compromise between performance and comfort is wise. The OEM rubber bushing provide good handling and comfort. And... Thanks for the longevity/reliability comment.

Is installing the subframe bushings difficult?

Yep. It will take you a day or two.

I recently bought the private marketplace posting of the full whiteline bushings. I should have front and rear installed within the next week or so. I'll let you know you guys know my thoughts coming from a 100k mile car.

I wonder about subframe bushing vs Z1's subframe collars.........the install in under an hour per video. That is about all I know........seems like they just make the subframe solid, as in no flex, so just negates the bushings???

Hope not too OT

I just ordered urethane dif bushings and am going to get They save soo much time and effort on installation. Having spent countless hours under my car I definitely think they're worth it.

I put those poly diff bushings in combined with the Bell diff brace Z1 sells and the difference was incredible. I'll be doing the collars ASAP.

Then I'll turn my attention to the front suspension. Z1 recommended spherical bushings for control arm and compression rods........ I wanted firmness comparable to the new rear end.

I put poly's in my front lower control arms last year. They're nice and sturdy now. Just be careful with the ball joints. (Specifically if the castle nut is rusted on) If something happens, It'll turn into a nightmare.

I have not been able to absolutely verify the Durometer value of the Whiteline WEK003 Bushing Kit components. My best guess it is around 85 to 90 on the Shore A Durometer scale. That means it is good for the street, and acceptable for the track. So, as is the case with every dual-purpose component, there are compromises that provide an increase in functionality.

Whiteline does a nice job here. You get the best of both worlds (Street and Track).

Ok the whitelines are installed. Complete suspension bushings front and rear.
All I have to say is wow. The difference is night and day. The car feels solid and tight now.

My two main concerns before the install were the possibilities of increased noise and ride harshness.
So far there has been zero creeks or squeeks. 100% silent operation.
Ride quality hasn't suffered much. You feel the bumps more, definitely, but it isn't a harsh shock. You just feel the extra stiffness.
You'll want some coils with relatively high spring rates to complement these bushings.

I have a set of subframe bushings I never installed, and a subframe in which I installed them in lol. I ended up going with the collars because I didn't want to deal with all the extra work =D