Car shakes above 85mph... sometimes... - TCCoA Forums
 
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post #1 of 15 (permalink) Old 01-26-2004, 01:51 PM Thread Starter
 
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Unhappy Car shakes above 85mph... sometimes...

Between 65-80 theres a small noticable vibration in the ride but doesnt overly affect the ride quality... but once I hit around 85, the whole car shakes. Not violently, but enough to know somethings not right and is quite irritating. The weird thing is, if I play with the RPMs alittle bit, it will completely smooth itself out and ride beautifully for a few seconds, and then work itself back into a nice little shake. The steering wheel goes nuts and I can feel it through my drivers seat too. I have a stock drive shaft, tranny and engine for the most part. Only upgrades I have are springs and shocks (and rims, which have been balanced). Any ideas?
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post #2 of 15 (permalink) Old 01-26-2004, 02:11 PM
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When I had that problem on my SC, i had a bad rear wheel bearing.

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post #3 of 15 (permalink) Old 01-26-2004, 02:26 PM
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Could also be worn IRS mounts.

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post #5 of 15 (permalink) Old 02-18-2004, 11:48 PM
 
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My car have exactly the same problem but it shakes about 35mph....
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post #6 of 15 (permalink) Old 02-19-2004, 01:05 AM
 
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When was the last time you had your tires rotated and balanced? That might have something to do with it. Its either that, or possibly your driveshaft balance is off.
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post #7 of 15 (permalink) Old 02-19-2004, 01:40 AM
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Does it smooth out when you let off the gas, or get on the gas, or what? That info might help narrow it down.

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post #8 of 15 (permalink) Old 02-19-2004, 03:03 AM Thread Starter
 
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Smoothes out gradually when I let off the gas, then smoothes out more when I decel under 80MPH. Plus Im not sure if its related, but when I go over bumps, something (in the suspension) sounds like its moving (clunks). But when I check all the nuts and bolts, everythings tight. I cannot tell if the shaking is coming from the front or the rear of the car though. Tires should be balanced, but I can probably get them done again.
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post #9 of 15 (permalink) Old 02-19-2004, 08:53 AM
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Gen,

Sounds like you got a bad bushing in the suspension. Do you ever feel one of the front tires dragging when you back up with the wheel turned tight to lock and coming of a "hump"? Then I'd have your strut rod bushings checked. If they need replacing, go with the urethane bushings.

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post #10 of 15 (permalink) Old 02-19-2004, 02:53 PM Thread Starter
 
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Quote:
Originally posted by PCD
Gen,

Sounds like you got a bad bushing in the suspension. Do you ever feel one of the front tires dragging when you back up with the wheel turned tight to lock and coming of a "hump"? Then I'd have your strut rod bushings checked. If they need replacing, go with the urethane bushings.
Never really had a situation like that. And all the strut stuff was replaced when I did my Tokico's... so... guess Ill have to crawl under there and see if I can see any torn bushings.
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post #11 of 15 (permalink) Old 02-19-2004, 04:53 PM
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You may or may not know this already, but a "strut rod bushing" isn't exactly associated with the shocks or struts. The "strut rod" is a brace that goes from the lower control arm to the subframe in the front of the car. The bushings on that rod are what PCD referred to.

It sounds more to me like a drivetrain or wheel imbalance than a suspension issue.

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post #12 of 15 (permalink) Old 02-19-2004, 06:23 PM
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first thing i'd do before ruleing bushings and stuff is balance teh tires and align the car....help my 3.8 wounderfully.

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post #13 of 15 (permalink) Old 02-19-2004, 09:00 PM
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Here is another possibility...

Depending on what kind of rims you have they may need hubcentric rings for the MN12 application.. Check with the manufacturer and then check to see if they are there ... if you are supposed to have them and don't have them, get them and put them in.

Hubcentricity: A wheel that is mounted on a vehicle, should be hubcentric, to assure proper fit, and hence will eliminate such issues as vibration, shimmy, and erratic tracking! A hubcentric fitment, is one where the interior of the backside of the wheel - referred to as "centerbore"-is an exact fit to the "hub"-that protrudes from the mounting surface of the wheel. The relevant issue here is that the WEIGHT BEARING of the wheel on the car is done on the HUB when it is "mated" to the wheel! This has to be an exact fit.

Just a thought...

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post #14 of 15 (permalink) Old 02-19-2004, 09:16 PM Thread Starter
 
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well, Ive had my cobra rims for over a year and this problem is maybe 2 months old... so Im confident my rims arent causing it, unless the tires are imbalanced.
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post #15 of 15 (permalink) Old 02-20-2004, 10:25 AM
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If the shake is felt in the steering wheel, then most likely the origin is in the front end.

Start with the simplest and easiest solutions, then work your way up the money tree.

1. Proper lug nut torque
2. wheel balance.
3. damaged tire (broken band)
4. Concentricity of wheel to hub (index high to low)
5. Concentricity of tire to wheel (index high to low)
6. concentricity of hub itself.

If you have a locking lug nut, try removing it and put a stock one on.

Crawl under the car and check things out. Take a pry bar and check for play in the front end.

Look at: Strut rod bushings at the lower control arm


The Shop manual has some detailed information on troubleshooting vibration isses.

If it were me, I would get the front wheels re-balanced and go from there.

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