97 Cobra With 70 Mph Vibration. Any Ideas?

Cobruh

New Member

Jun 29, 2016

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Tulsa, OK

Jun 30, 2016

#1

• Jun 30, 2016

• #1

I have a 97 Cobra with 4.10 gears, exhaust, CAI and 90k miles. I picked this little jewel up almost a month ago and it has a vibration which seems to originate somewhere along the drivetrain. I can feel it through the seat and through the shifter. It is nonexistant until I reach around 70 mph and will become less noticeable over 80 mph. Also, it is the worst when off the gas and allowing the motor to brake the car and almost totally diminishes when on the throttle. Anyone have ideas as to the cause?

Thanks!

Jon

 

Cobruh

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Jun 29, 2016

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Tulsa, OK

Jun 30, 2016

#2

• Jun 30, 2016

• #2

I forgot to mention, I have ruled out the U-joints as the source of the problem.

 

V

Vaped

New Member

Jun 25, 2016

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Jun 30, 2016

#3

• Jun 30, 2016

• #3

Iv got the same issue with a 99 GT. I am putting a new bushing / new seal in the tailshaft and a ford transmission mount as well. I have done some research and a auto parts house anchor brand transmission mount uses hard rubber instead of the soft rubber that fords uses. It has solved the issue for some people.

 

Cobruh

New Member

Jun 29, 2016

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Tulsa, OK

Jul 2, 2016

#4

• Jul 2, 2016

• #4

That's worth a shot and should be a reasonably cheap fix as well. Let me know if that works for you.

 

Darkwriter77

Resident Ranting Negative Nancy

5 Year Member

Jul 1, 2005

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Apache Junction, AZ

Jul 2, 2016

#5

• Jul 2, 2016

• #5

+1 to Vaped's suggestion. I used that very brand, Anchor, when I replaced the transmission mount on my '01 GT last week. Had the same problem, a vibration right around 65 MPH that was drivetrain-related, and replacing the mount fixed it. The old mount had almost completely separated its two halves. The new mount was only about $13 from Rock Auto - anywhere else online, places wanted between $75 and $100, which is insane.

 

Cobruh

New Member

Jun 29, 2016

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Tulsa, OK

Jul 11, 2016

#6

• Jul 11, 2016

• #6

My new transmission mount should arrive at the house today. I'll get in put on sometime in the next few days with an update and possible photos. Thanks!

 

Cobruh

New Member

Jun 29, 2016

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Tulsa, OK

Jul 11, 2016

#7

• Jul 11, 2016

• #7

So, I got to pulling everything apart this evening and ran across this bit of a problem... Is there any reason why it went from female to male? Do you think it would be okay to convert?

 

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Cobruh

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Jun 29, 2016

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Tulsa, OK

Jul 13, 2016

#8

• Jul 13, 2016

• #8

Okay so, I went ahead and converted it to this style since I already had the part and everything is holding just fine. The only problem is that it didn't fix the vibration. Any other ideas?

 

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flstang65

10 Year Member

Dec 6, 2007

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SE Georgia

Jul 15, 2016

#9

• Jul 15, 2016

• #9

Just out of curiosity, did you check the balance on the wheels/tires? Also, see if the weights from the driveshaft might have been knocked off.

 

Cobruh

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Jun 29, 2016

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Tulsa, OK

Jul 15, 2016

#10

• Jul 15, 2016

• #10

Yes, I have ruled those out as well. There is a little play in the driveshaft (more than normal) so the rearend may be a culprit and there is also a little slack in the steering column which could potentially be a sign of a problem with the rack and pinion. When I had the tires balanced, they said that one of the rims is a little bent which I'm sure plays a role in the vibration but not sure exactly how much. I'm going to put the front end back on jack stands this weekend and try to inspect the entire front end to find any other potential problems. I.e. bushings, ball joints, etc.

 

V

Vaped

New Member

Jun 25, 2016

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Jul 22, 2016

#11

• Jul 22, 2016

• #11

Still battling this as well Cobruh.

I am going to try a torque convertor next. Hell I don't know at this point.

 

T

Tyler33

Member

Jul 15, 2016

6

1

13

Jul 23, 2016

#12

• Jul 23, 2016

• #12

I have a vibration as well that seems to be worse around 35 then at 65-70. I just bought mine (01 GT Auto). I was thinking about doing an aluminum driveshaft. I think my vibration is higher frequency than what the wheels/tires are turning.

The previous owner had a shop replace the trans mount so maybe I should start there.

 

Cobruh

New Member

Jun 29, 2016

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Tulsa, OK

Jul 23, 2016

#13

• Jul 23, 2016

• #13

Clearly I'm not in this battle alone. Thanks for the responses and please keep me updated with any progress ya make. I haven't had a chance to get it back on the jack stands like I was intending to do but will update as soon as I do. (It's been a busy summer)

I did realize that if I were to speed up to 80 mph, put the stick into neutral and let it coast down in speed that the vibration is almost non-existent in the problem area of 65-75. That really throws a monkey wrench in my troubleshooting process. Does anyone have any idea what that could be a symptom of?

 

T

Tyler33

Member

Jul 15, 2016

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Jul 24, 2016

#14

• Jul 24, 2016

• #14

Looking at the invoice from when trans mount was replaced - it says part number 3164 which is the Anchor part. I guess I'll be ordering one from Rock Auto.

 

Reactions: Cobruh

Cobruh

New Member

Jun 29, 2016

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Tulsa, OK

Aug 9, 2016

#15

• Aug 9, 2016

• #15

Well, I have checked the front end and I didn't find anything of suspect so I decided to lift the rear of the car off the ground next to check the axles. That is when I may have found something of interest. The axles checked out but I can rotate the tire back and forth causing a God awful sound in the rear diff. There is quite a bit of play in the rotation of the wheel before it catches the gears and begins to spin the other wheel. You can also hear the sound reverberate up the driveshaft which leads me to believe that this may be the culprit. Not to mention, I don't think there is any fluid in the rear end. It appears that road debris may have caught the lip of the cover causing it to pull back and possible leak all the fluid out.

 

squeak93

15 Year Member

Jun 2, 2005

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Joplin, Missouri

Aug 9, 2016

#16

• Aug 9, 2016

• #16

Just read this thread based upon your bump. I was going to suggest something in the rear end due to the part where you stated it was worse upon decel when you let off of the throttle.

I'd highly recommend replacing all bearings, seals, clutch oak, and inspect the gears and axles for wear and run out. I'd honestly just scrap it all and start over. Too much risk of something got hot and is going to fail later on.

 

Cobruh

New Member

Jun 29, 2016

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Tulsa, OK

Aug 9, 2016

#17

• Aug 9, 2016

• #17

That's what I was afraid of a long time ago when I noticed the extra slack in the driveshaft. I was hoping to find the problem being caused by one of the cheaper repairs but it appears it is time to dive into a rear end rebuild. Would you happen to know of a good, cheap place to buy gears and a rebuild kit? Other than American muscle and Jegs. Thanks for your help, Squeak.

 

squeak93

15 Year Member

Jun 2, 2005

2,269

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Joplin, Missouri

Aug 10, 2016

#18

• Aug 10, 2016

• #18

Rock auto for all bearings seals etc. ford racing gears can be found at a ton of places.

 

Omega

New Member

Aug 15, 2016

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Mid-west

Aug 16, 2016

#19

• Aug 16, 2016

• #19

A vibration that you can feel in the seat/floor/shifter handle is a rear end vibration. Typically higher speed vibrations (55+) are from your wheels and tires. Get them rebalanced, and have them pay specific attention if the rims are bent at all.
Another potential problem are the U-joints. Heavy duty greaseable U-joints run about $10 a piece. Just replace them. Rent the ball-joint tool from O'reilly to press them in and out, and another potential problem area checked off the list. Also be sure to inspect the driveshaft for any damage, scrapes, whatever. Check the driveshaft to pinion flange bolts for proper torque. And if you have a shop that can balance driveshafts near you, balance it out too.

And make sure the vibration dampener is still attached to the diff. If not, this can and will cause a vibration.