Urethane Bushing and Ride

[BuickNut]

HI,

Was wondering of those with full size 60's/70's cars who switched to urethane suspension bushings have experienced rides that were considered harsh. I realize the ride will be firmer, but is the ride too harsh beyond just adding to the tighter suspension ? Any recommendations to a shock absorber to use ?

Thanks.

Ray

[Matt Harwood]

I use polyurethane bushings on my race car, but not on my street cars. The problem isn't really ride quality, but NVH--noise, vibration and harshness. Urethane bushings squeak, no matter how much you lube them, they <span style="font-weight: bold"><span style="font-style: italic">will</span></span> squeak. You'll also feel more vibrations through the steering wheel and through the seat of your pants. You'll have to be the judge of whether it is irritating, but in my hot rod Mustang, I found it intolerable in normal driving on the street. I can imagine how dissonant it would feel in a luxury car like a Buick.

Unless you're running your car hard all the time, you won't notice any improvement in handling at all. Plus, while they may last a little longer than rubber, urethane bushings, when they fail, they fail completely and rip completely. At least rubber dries, shrinks and crumbles, but it doesn't fail all at once, but gradually.

Just my experiences having used the urethane on performance cars and on the track.

[NTX5467]

Matt's comments are pretty accurate from other things I've read on that subject.

The rubber bushings are there for a purpose, which is isolation and allowance for the parts attached to them to flex as they do their job. There are places on a vehicle where the urethane items can be beneficial (as in the sway bar link bolt attachments to the bar and the control arm) and others where they might cause some irritation. As there is less flex in them, they will transmit more of the road into the chassis and body of the car plus an increase in impact harshness that otherwise would be absorbed by the rubber chassis bushings.

The other factor not mentioned is that from my few experiences with replacement bushings, the ones that will be used to replace the old ones will be of firmer rubber than the assembly line production items. When the cars were new, there was much emphasis on smoooooothness and quietness. By the time the vehicle had enough age and time for the bushings to deteriorate, those orientations were not as prevalent as when the vehicle was new. So, the firmer rubber from heavy duty applications on the vehicles got things firmed up when the original rubber items were replaced, which brought back that "new" feel again.

I do advocate the use of the urethane bushings for the sway bar link bolts. Using them makes the bar act like it's mounted solid and is effectively 20% stiffer. This keeps things flatter during cornering and might make it a little stiffer on a rough road where the wheels aren't going up and down at the same time, but what little bit you might notice will be a good trade-off for flatter cornering.

I think that if you consider where the main loads and impacts on the suspension are, those would be the place for rubber (i.e., lower control arm attaching points on the front suspension) and the urethane might be used for the upper control arm pivot points as those points basically are just pivots. Plus the extra stiffness up there might better reinforce the suspension for a little better handling precision without much increase in impact harshness. Also, it's easier to get a grease gun on them.

In the typical GM rear suspension, about the only place for a urethane bushing might be on the ends of the track bar. Whatever flex there is at the ends of the lower control arms needs to be there, from what I've observed. If the flex isn't in the bushings, it means the control arms will have to absorb that flex, which can cause metal fatigue and other not-so-good things. Adding a rear sway bar between the lower control arms will firm things up too, if that's a possibility on the vehicle in question.

The other consideration to aid handling would be a more performance oriented tire. The added stiffness in the sidewall will firm things up a little plus make the handling a little more responsive. Whether you upgrade to 16" or larger wheels with their respective tires is your choice.

In a race car, things are very different. First thing is that the body is reinforced with a stiff roll cage. From the main cage, there will be pieces that go forward and rearward of the passenger cage area, where the suspension items will mount or be reinforced.

Then, there will be solid, greaseable pivots for the suspension items. Solid mountings to solid bearings/bushings for the maximum of feedback to the driver with respect to how hard the chassis is working for the demands the driver is putting upon it. That feedback is vital in that situation.

Most of the articles on the urethane bushings will tell you how much difference they made in the handling of the vehicle. Usually, there's some other upgrades in the mix too (springs, shocks, wheel/tire combinations) that might not be evaluated individually, but as a complete unit compared to the stock items. Sometimes, the word "extreme" is used as to the increased chassis performance orientation.

To me, the blending orientation I mentioned above makes more sense to me than just replacing everything with urethane. I feel such a blending orientation would be the best of both worlds without damaging the vehicle's structure over the long run--plus being more fun to drive and enjoy the vehicle on a daily basis. Others might have other orientations, but you could do a lot worse than just replacing the existing worn/aged rubber with fresh rubber items.

Before the urethane bushings were around, I saw an article in one of the car magazines to take small finishing nails and drive them into the rubber bushings to effectively firm them up by compressing the rubber inside the steel sleeves which held them. Another option . . .

Just some thoughts,

NTX5467