Vibrations at higher speeds. Any ideas?

builttodrive

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I get what appears to be a driveline vibration at about 100+ MPH and it get's worse and more violent the faster I go. Anything below 100 is perfectly smooth. It doesn't have anything to do with RPM and I have tried different gears including neutral and coasting and there is no change. I recently had my rear end gone through and axles inspected so I think I can rule that out. I have a Drive Shaft Shop 1 piece aluminum shaft that I have tried rotating 180 degrees and it may have made a slight difference but nothing big. I then took the driveshaft to my local driveline shop and they balanced the shaft. For wheels on the car I have American muscle 2010 GT500 style wheels with Michelin Pilot Super Sport tires and I have had the wheels checked for true and a trusted shop road force balanced them and didn't find anything of concern.

The vibration gets worse with speed and has no effect on the steering wheel. The whole car seems to be affected and can be seen by vibrations in the dash or rear view mirror. It stays the same wether I'm accelerating or coasting anywhere above 100 or so MPH.
 

me32

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What should I check? I have Griggs Racing suspension on the car that has KONI adjustable coilovers on it. It has a torque arm setup with watts link.

Check that everything is still tq to spec. A loose nut could cause vibrations at that speed. Check components for cracks or breaks, lube up any thing that is serviceable
 

me32

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Thinking about it. You having a griggs kit. Is the 1 pc driveshaft have the correct pinion angle? That will definitely give vibration. I know alot of griggs kits still use the factory 2pc.
 

builttodrive

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Thinking about it. You having a griggs kit. Is the 1 pc driveshaft have the correct pinion angle? That will definitely give vibration. I know alot of griggs kits still use the factory 2pc.

I'll check into it again. I think I researched that before and I'm thinking with the style end the driveshaft has it isn't as influenced by the pinion angle as a Ujoint. I had all the rear suspension out here recently and everything looked good from what I could see there.
 

HKusp

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I have heard that some of those Michelins will do it too. Is this the same issue that you brought up last year in March?
 

buddha93

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Almost always tires. I know you said they're balanced, but I'd check again, make sure they didn't throw a weight or have the shop recheck.
 

OX1

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Almost always tires. I know you said they're balanced, but I'd check again, make sure they didn't throw a weight or have the shop recheck.

Agree. Tires not perfectly round, can still be balanced out many times, especially on a road force.
What were the road force numbers?
 

cidsamuth

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My first instinct was to yell, "Pinion angle!"

Especially if the car has been lowered, but the one-piece driveshaft might do it too. Depending on power levels and suspension firmness (poly vs stock rubber), you will want somewhere between -1 degree and -3 degrees.
 

builttodrive

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I have heard that some of those Michelins will do it too. Is this the same issue that you brought up last year in March?
Yes same issue. I made some changes and checked some things as mentioned above but the vibration is still there. I heard of the Michelin "death Wobble" or whatever people called it but tires seem to balance decent and It's weird that I have to be going that fast before there is any issue but I'm not sure.
 

builttodrive

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My first instinct was to yell, "Pinion angle!"

Especially if the car has been lowered, but the one-piece driveshaft might do it too. Depending on power levels and suspension firmness (poly vs stock rubber), you will want somewhere between -1 degree and -3 degrees.

I know I went down the pinion angle road before and I can't remember exactly what I found out but I think the DSS driveshaft has more range than a Ujoint ended shaft. My suspension is a 3 link setup with a torque arm. The joints on the lowers are heim joints.
 

builttodrive

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I'm saying pinion angle, or tires.

Can you easily swap a 2-piece driveshaft back in? Just to try it out?

Unfortunately with the torque arm suspension it's a real pain swapping out driveshafts. Most of the rear suspension and exhaust has to be removed to get it out.
 

me32

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Front wheel bearings. Both went out in my 2007 GT500 and the car shook at speed and sounded like hell.
Thats funny. I had the same issue. Both sides were shot. I assumed it was when i was road coursing at thunderhill.
 

Catmonkey

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I'd put the rear axle on jack stands, remove the wheels and tires and bolt on the rotors and take it up to that speed. If it vibrates, you can rule out most of the possibilities. If it passes, add the rear tires to the mix (elevated off the pavement).
 

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