Swift Spec R rear spring vibration?

[JPuehl]

I have been chasing a vibration from the rear of my car for some time and so has the dealer, they had my car for almost 3 weeks over 2 separate visits and didn’t find the problem. I have a vibration under load between ~48 to ~58 mph regardless of engine speed/trans gear. If I cruise in a speed in the range, the vibration is not noticeable but if I accelerate from or through speeds in the range, I get a noticeable vibration. My suspension is Swift Spec R springs and Koni externally adjustable shocks front and rear. I went back to the OEM suspension and there was no vibration. I slowly put all the components back on and when the rear springs went on, the vibration returned. I have also tried other rim/tire combos to eliminate that possibility. With the Swift springs up front, OEM springs in the rear and Konis all around, no vibration.

Has anyone else experienced this? I know that springs can have a frequency but have never experienced it. I like the Swift springs but don't like the vibration.

[Dmak]

Have you try swift spring with oem strut. I wonder if it's the koni unable to control the higher spring rate.

[ShocknAwe]

Hard accel through that speed? Happen onlky in 6th gear? Also maybe rear squat and rear arm deflection?

Just a thought!

[JPuehl]

Originally Posted by Dmak

Have you try swift spring with oem strut. I wonder if it's the koni unable to control the higher spring rate.

Yes, I did try the OEM shock with the Swift spring however I haven't tried changing the adjustment on the shock to see if maybe I'm at a spot where the shock adjustment does work with the spring rate.

[JPuehl]

Originally Posted by ShocknAwe

Hard accel through that speed? Happen onlky in 6th gear? Also maybe rear squat and rear arm deflection?

Just a thought!

Not just 6th, any gear any engine speed, so 2nd or 5th, it happens at the same speed.

[ShocknAwe]

Originally Posted by JPuehl

Not just 6th, any gear any engine speed, so 2nd or 5th, it happens at the same speed.

Would have to say related to rear wheels/tires/brakes/hub/axles then if it's only speed related and not in combination with any other dimension. My suspicion is you feel it more with the firmer suspension, but the vibration is present in the control arm via the source, whatever it is that's actually vibrating and passing it up the shock into the cabin.

Is this under any % throttle, or only at WOT?

[JPuehl]

It's under any acceleration and the intensity of the vibration increases as the amount of throttle increases, however even at its worse its not vibrating the rear view mirror for example.

[ShocknAwe]

Originally Posted by JPuehl

It's under any acceleration and the intensity of the vibration increases as the amount of throttle increases, however even at its worse its not vibrating the rear view mirror for example.

How many miles, have you changed your diff fluid? Do you have any whine? Did they check out the axle seals etc?

[JPuehl]

Originally Posted by ShocknAwe

How many miles, have you changed your diff fluid? Do you have any whine? Did they check out the axle seals etc?

The car has just under 20k miles. I had an LSD installed in September so I'm sure the fluid has been replaced and the vibration was there before and after the diff install. The dealer thought it was the driveline which they replaced under warranty because it had a slight leak in the middle joint. It's just with the Swift springs and the conditions mentioned.

[ShocknAwe]

Originally Posted by JPuehl

The car has just under 20k miles. I had an LSD installed in September so I'm sure the fluid has been replaced and the vibration was there before and after the diff install. The dealer thought it was the driveline which they replaced under warranty because it had a slight leak in the middle joint. It's just with the Swift springs and the conditions mentioned.

Figure it warrants a call to swift USA then. Sounds like you've been through it thoroughly enough.

[HP Autosport]

That is very interesting. Is something else causing the spring to oscillate at such a high frequency? I think it would need to be a vibration not capable of being damped by the rear dampers for you to hear anything.