Tag Archives: preload

Rubber Suspension Bushings (and Revisiting Bushing Preload)

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This isn’t the first time we bring this up to you, our customer. Actually, it is a very common problem for people setting up their suspension. Once our suspension is installed, they lower the car back to the ground and notice uneven ride height from left to right side.

We’ve found this to be an issue with a few vehicles, mainly vehicles with a multi-link or “double-wishbone” suspension. And mainly this is because these types of suspensions have more rubber bushings in their suspension arms.

Once you disassemble some suspension arms in order to access the shock absorber assembly, like in a Mazda RX-8 for example, you’ll have to reassemble the arms through their respective nuts/bolts. That’s not uncommon, and this probably sounds relatively straightforward to you.

However, what we fail to account for is the fact that we typically do this when the vehicle is in the air, on jackstands or on a lift, leaving the suspension drooping down (fully extended).

Why is this important to note? Well, once you start to loosen these nuts/bolts at suspension arm joints, you’re essentially removing any tension on the bushings associated with each arm. When that same bushing needs to be reinstalled (by way of connecting the arms with the nuts/bolts you removed), you end up tightening all these bushings while the suspension is drooping down (fully extended). Those bushings that were just recently relieved of the tension they were once under are now at zero preload. Now, when you put the suspension back on and the vehicle back on the ground, these zero preloaded bushings start to twist. The only issue is the twist isn’t necessarily going to be even from any specific corner. This leads to the uneven ride height you might be experiencing.

How can we prevent this uneven ride height? Well, this requires loading up the suspension PRIOR to tightening any nuts/bolts to these suspension arms. Obviously this isn’t easy to do since the best way to load the suspension is to put the car back on the ground. There are 4-post lifts that also serve as ramps. This gives you undercar access to these nuts/bolts that you can tighten. Those with vehicle ramps tall enough to let you creep under the car to tighten any nuts/bolts is also good. However, this is the BEST way to avoid any bushing preload issue. We must note, though, that this doesn’t cure uneven ride height completely, since all vehicles do have a weight bias from one side to the other, and of course from front to back.

Does this mean that rubber bushings are a terrible design? No, not at all. In fact pretty much all production vehicles use rubber bushings. They’re effective in terms of performance and cost, which most OEM companies are very sensitive about. Quite honestly, they’re probably more durable that some aftermarket floating bushing designs since they really don’t require maintenance (periodic greasing), with the exception of sway bar bushings. Once they’re bad, you have to either replace the bushing or replace the arm that the bushing is pressed into (the latter being the most commonly offered for ease of installation).

Again, the difference between rubber bushings compared to typical aftermarket floating bushings is that the rubber bushings have any steel components, such as the crush tube and shell, bonded together through the rubber filling. Floating bushings, typically polyurethane in the aftermarket, simply have the bushing free moving between the shell and crush tube. This is great for having free-pivoting arms, allowing the damper and spring to do their job more effectively, but also requires quite a bit of maintenance to make sure they’re greased properly (you don’t want polyurethane to dry up). Not a big deal if you really enjoy wrenching on your car, and in some cases, aftermarket bushing manufacturers have included zerk fittings to either the steel tube or crush tube to ease the greasing process! Not all bushings have easy access for a zerk fitting to be placed, however, which has led to the development of bolts being gun drilled and cross-drilled and a zerk fitting threaded to the end.

Rubber bushings, again bonded to any steel shell or tube, don’t allow this free pivoting. Instead, the bushing relies on strain, or stretching of the rubber, meaning you have a limited range of motion either up or down, or even side to side. For most cars, this isn’t a problem.

Because most rubber bushings are “maintenance-free”, over long periods of time, they will dry rot and the rubber material will break away. This creates excessive movement of the suspension arms (moving in directions not intended), and can cause poor and unsafe driveability.

Preloading It Up

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Full-length adjustable coilover spring tension is an area which many consumers aren’t too knowledgeable about. Details that  “more preload is best” or “no preload is best” have always been a talked about subject. In general, the function of the spring tension on a full length adjustable coilover is for a more fine tuning of the suspension if used competitively. Such preload adjustments for regular street driven vehicles, which seldom see a track event, aren’t really need. That’s not to say that you can not use the preload on the street. It’s just that there would not be much of an advantage unless you are looking to achieve a desired ride height or ride feel.

Preloading will change the characteristics of the spring, but not the spring rate.  As the spring is a linear in rate, the rate will not change under preload, but the spring’s reaction will be affected. With the spring compressed,  its natural instinct would be to push back to its original shape. Thus, the force already exerted when compressed will creating a more aggressive ride quality. The drawbacks to having too much preload will be spring bind or, in worst case scenarios,  a broken piston rod or damper component. Spring bind can create a loud tapping from the springs during normal use of the vehicle, not to mention terrible ride feel since spring stroke is all but eliminated. The continuous spring binding creates a kind of solid state to the coilover assembly which will transmit the road vibrations and shock over to other damper components, eventually causing it fail.The broken piston rod or component can be caused by the excess spring tension, as well.

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Relieving preload from the spring or creating “negative preload” would change the ride height of the vehicle along with the dampers’ piston stroke. The drawbacks to excessive negative preload would be a loss of piston stroke, noise from the spring, poor ride quality, and eventually damper failure. The piston stroke loss would allow for the damper to bottom out, which in turn would create a poor ride quality as the dampers’ upper springs seat or mount would be riding against the bump rubber. With the constant bombardments, the bump rubber will eventually break down causing some of the rubber material to fall in between the seal which can then cause the seal to fail. This can also create noise caused by the spring’s loose condition, which will shift back and forth on the damper assembly when the damper is extended and compressed. This occurrence is most common over uneven road surfaces such as driveways, dips, or at times freeway expansion joints. This could cause damage to the damper body threads, spring seat, and upper mount.

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If you are uncertain as to the preload of your full-length adjustable coilovers, the best recommendation is to set the spring seats to the installation manual’s suggested position. This position will offer the optimal damper stroke and adjustability.

Mazda RX-8 and Miata MX-5 Lowering Spring Installation Precautions

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Hey everyone. This had been brought to our attention a few months back from two consumers having ride height issues with the S.Tech lowering springs on their 2004 Mazda RX-8 (SE3P chassis) 2006 Mazda Miata MX-5 (NCEC chassis). This ride height claim had become puzzling to us as we had encountered this type of issue which was a quick an easy fix by preloading the suspension but for some reason this did not seem to work.

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Baffled, we requested the customer send the lowering springs to us for further inspection to determine if the springs had any manufacturing defects and to our surprise they were within spec. Looking to further find a solution to this issue we decided to bring a car in for testing to determine the cause. This is where it became a little more interesting, as we were able to physically do the installation rather than reference the consumers photos and measurements. We proceeded with the spring install following the bump rubber cut and all to find that we too were having the same issue even when preloading the suspension.

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Concerned, we had to confirm all of the suspension bushings and components conditions which all were found in excellent condition. At that moment a light bulb lit up and someone had an idea. The bushings on the control arms. (when the control arm is pivoted) had an extremely short amount of give/ movement. With this in mind we tried preloading those bushings, as well as those which the dampers bolt on during the second install. Once the vehicle had been placed back on the ground the ride height corrects were immediate. The vehicle ride height was within the kits values without any further complications with ride height and with excellent ride quality feel.

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 Both images shown above and below would illustrate a Red circle drawn on the bushings detailed in the post.

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Now this was an issue found on these two particular models but has not occurred with any other manufacturer. Please keep in mind that these vehicles did use the OEM shock absorbers. The use of any aftermarket type shock absorbers may also effect the ride height values as we had only done testing on the stock shocks absorbers. Please be cautious with the selection should the new dampers be required.

I do hope this post helps any consumers out their who may have encountered this situation with the aforementioned vehicles. Always remember that should you have any further concerns with these applications utilizing our lowering springs or any of our other product lines, please don’t hesitate to drop us a line. Also for further details on the process of suspension preloading, please revisit the  TEIN Blog post “Applying Suspension Preload” for a breakdown of how to do.
http://teinusa-blog.com/applying-suspension-preload/

Applying Suspension Preload

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What’s up, people? Here I go again with some helpful tips when installing lowering springs and coilover kits.

I have to honestly say that we hear the following questions countless times during the work week.

“Why is one corner of my car higher than the other?” Or, “Why is my ride height uneven?”……………..(AHHH..here we go again)..lol.

The solution is actually quite simple. The first things to check are for worn-out suspension components. We advise to check all components carefully and thoroughly. Anything can contribute to the issue previously mentioned. Worn out bushing, incorrect spring, blown damper, spring perches are not even, missing or mis-installed components, etc. If everything checks out fine, then the only candidate that would contribute to uneven ride height would be suspension pre-load. This issue is commonly encountered when installing lowering springs and/or dampers on vehicles with double wishbone or multi-link suspensions.

In some cases the lowering spring or coilover kit is installed while the suspension is in a full droop.  This means that the bolts on the lower control arm were tightened while the arm was hanging down. In other words, there is no load on the suspension when tightening all components.  When the vehicle is brought back down the bushings twist causing the suspension to not settle correctly thus resulting in a uneven ride height.

The first thing you want to do is lift the car back up. Them loosen the bolts on the control arm and shock absorber. Once in the air use a second jack to apply load on the control arm. This simulates as if the car was on the ground and the control arm is back to its original position. Then re- tighten all the bolts loosen in the previous step. Follow this process with all four corners, then bring the vehicle back down. If you follow these instructions, this should help get the vehicle to the correct ride height. Plus,
you will have learned another method on how to correct uneven ride heights, if you ever run into a similar situation in the future!