Vibration on hard acceleration... 1997 Cobra - Mustang Evolution

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Old 08-13-2012, 08:42 AM   #1
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Vibration on hard acceleration... 1997 Cobra

Ill try to keep this short... But as the subject says, I have a pretty wicked vibration on HARD acceleration. If you drive very lightly, you'd never notice it. Heres a check list of things ive done/checked

- rear diff fluid with friction modifier

- check u-joints

- trans fluid (needed to be done regardless)

- checked quad shocks, removed and drove without them as well

Everything I've checked has been okay. As of now I'm leaning towards, motor mounts, trans mounts or maybe rear control arm bushings... Or it could be clutch/trans related.

I'm pretty lost right now. Any suggestions would be appreciated.
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Old 08-13-2012, 08:56 AM   #2
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Is it vibrating with acceleration at very slow speeds, like accelerating fast from a stoplight? Does the vibration happen when you rev the engine while stopped in neutral? Trying to determine if the engine is running rough or wheels out of balance, etc.
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Old 08-13-2012, 09:41 AM   #3
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Re: Vibration on hard acceleration... 1997 Cobra

Sounds like your loading your flywheel, try downshifting. Basically don't be in 3rd gear at 40 and floor it!
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Old 08-13-2012, 10:01 AM   #4
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I knew I was leaving details out.

Its ONLY from a stop, or as far as I can tell. The drivetrain has to be under a load.

There is no running rough, it does not vibrate if you rev it in neutral.

The car idle very smooth, and quiet. It runs like it was new. And it has 120k.

The drivers side motor mount does look a little dry rotted, and pushed down a little further than the right... Not sure if that has anything to do with it.
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Old 08-13-2012, 10:14 AM   #5
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I'd take a look at the motor mounts since you see they look a little weathered. That could certainly be your problem.

Does it feel like your clutch is slipping under load? Maybe when it slips, it's vibrating because it's doing a "catch-slip" deal really fast...?
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Old 08-13-2012, 10:21 AM   #6
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The clutch was one of the first things i thought of. It does release high, so i'm sure it needs replacing. I was just hoping to say "x" is the cause of my problem. Im putting a clutch in this winter regardless.
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Old 08-13-2012, 10:27 AM   #7
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Re: Vibration on hard acceleration... 1997 Cobra

Most mustang clutches release high. Mine does!
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Old 08-13-2012, 10:31 AM   #8
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Quote:
Originally Posted by drusmith
Most mustang clutches release high. Mine does!
Mine releases lower normally, then higher if I've been driving a pretty good while, like highway, etc.

Is that dependent on what clutch he has; stock or aftermarket?
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Old 08-18-2012, 07:38 AM   #9
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So I'm still totally lost. There is 100% for sure something wrong, but some of my co-workers tell my im nuts... Thats not the case. I picked my mom up last night and the first acceleration SHE even noticed it...

Only thing I'm doing now is beating the SNOT out of it till it breaks. I do need to throw my plugs and wires on though. This is really pissing me off.
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Old 08-18-2012, 10:16 AM   #10
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Re: Vibration on hard acceleration... 1997 Cobra

Put the car on jack stands or a lift and drive it slowly. If it's a wheel bearing or your tires you will be able to tell very quickly. If you have dropped your driveshaft recently and did not put it back on in the same position it will vibrate as well.
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Old 08-18-2012, 11:09 AM   #11
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I'm really starting to lean towards a posi unit issue. Clutches or gears. Its for sure in the back. And how it only happens on hard accel... I dunno.
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Old 08-18-2012, 01:33 PM   #12
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Quote:
Originally Posted by Lastoria24
I'm really starting to lean towards a posi unit issue. Clutches or gears. Its for sure in the back. And how it only happens on hard accel... I dunno.
Will the Traction-Lok engage? By that I mean, will she lay a dual patch when she burns out? If so, do you hear anything doing that?
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Old 03-14-2014, 10:19 AM   #13
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did you ever find out what the problem was I have the sme problem with my 97 gt and as you were im lost?
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Old 03-14-2014, 02:48 PM   #14
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Do you have stock drive shaft ?one vibrates under hard throttle but hoping a aluminum shaft will cure problem.
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Old 03-14-2014, 04:33 PM   #15
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yes I do but it didn't start happening until the throwout bearing exploaded and I replace everything dealing with the clutch and transmission. I used all ford racing products and got a used rebuilt trans that now it shifts like butter but it feels like its slipping under hard acceleration? any ideas on the problem?
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