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Old 03-15-2001, 03:28 PM   #1
93Cobra#254
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The problem seems to have appeared overnight. It's been happening for about a week or so. When I get above 50MPH on the highway... it starts vibrating...... bad. I'm not just talking about rattling, there's always been rattles in this stang. This was different, almost kinda scary. Anyway, it only vibrates above 50MPH when I am NOT accelerating. While I am accelerating (say up a hill) it doesn't vibrate at all. One other note.... when my gas tank is full, it doesn't vibrate at all, at any speed. Something to do with the weight in the back of the car? Too weird. Anyway, this stang has no mods, 151K miles, and generally drives very well. No oil burn or anything like that. Any thoughts as to what might have caused this overnight nightmare to occur. Fuel delivery problem? If it was a bent driveshaft, would I not notice vibrating at all speeds? Thanks for any input.

------------------
1988 GT-stock at
151K miles
1993 Cobra #254-
stock at 92K miles
 
Old 03-15-2001, 03:34 PM   #2
89GT
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BY vibrating I take you don't mean missing or running rough so I would rule out fuel. I would check your U joints and make sure the driveshaft is securely attached to the rearend. I would inspect your lower control arms and upper and shocks and make sure something has not broken back there or come loose. Good Luck.
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Old 03-15-2001, 04:04 PM   #3
93Cobra#254
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Not running rough. The body is just vibrating badly. The shocks are brand new, but the lower control arms are in dire need of replacement. Could these be the culprit? Should I just buy a set of tubular control arms now since I plan to mod the car big time later this year?

Thanks.

------------------
1988 GT-stock at
151K miles
1993 Cobra #254-
stock at 92K miles
 
Old 03-15-2001, 05:07 PM   #4
Mick
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This is another driveability subject that's difficult to diagnose and usually involves a lot of guesswork.

In addition to what was already suggested above, here are some things to inspect and repair/replace as necessary:
<UL TYPE=SQUARE><LI>wheel and tire balance and runout<LI>broken belts in tires<LI>engine and transmission mounts<LI>transmission input and output shafts<LI>transmission output shaft bushing<LI>driveshaft balance and runout [/list]
I'm sure there are more areas to inspect, this is just off the top of my head.

------------------

1983 Mustang GT 306/T-5(project in progress)
1994 Ranger Splash 4.0L/A4LD(daily driver)
 
Old 03-15-2001, 05:11 PM   #5
FISHTAIL
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This may sound dumb, but have you had the tires balanced lately? lol. another thing, have you removed the drive shaft anytime reciently?

------------------
-FISHTAIL
92GT "The Ghetto Sled"
CMPS major @ University of MD college park
Best run so far: 14.74 @ 100.3mph....stupid wheel spin.
VP and co-founder of CMTC www.stangbirds.com
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Old 03-15-2001, 08:44 PM   #6
Davewht85
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The first thing to check would be your tires. You need to make sure your not on the verge of a blowout.
Next, drive your car. Put it in neutral & coast at the speed it vibrates at. If the car stops shaking then this would indicate a drivetrain problem.
Its possible that you may have several problem at once with 150k miles. Along with what Mick said, worn suspension & steering parts could contribute greatly to this problem.
Check it out as soon as possible & keep us informed.

------------------
'85GT Hatchback
White w/ GT Hood Decal
MODS:
'91 H-Pipe
2 1/2 Hooker exhaust w/ Aerochambers
Energy Suspension Poly bushings in rack,shock tower & sway bar
RESTORATION:
Many new parts in Suspension,Drivetrain & EEC IV
FUTURE PLANS:
Maximum Motorsports strut tower brace & subframe connectors, 8.8 3.55 diff, 2 1/2 SS X-pipe, JBA Egual-length Shorties, Front & Rear Disc Brake Upgrade, Cam & Aluminum heads.
 
Old 03-16-2001, 07:41 PM   #7
Baywolf
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not to second guess but as far as putting it in nuetral if it is a loose drive shaft that will often times make it vibrate worse i had this problem after i put a rebuilt T5 in my car and i was really ticked off at the guy that did the rebuild for me and it turned out i had put the drive shaft bolts in finger tight then forgot the wrench my car acted exactly like you describe your and in nuetral was the worse because it took the load off the shaft and allowed more play
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Old 03-16-2001, 08:14 PM   #8
93Cobra#254
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I did remove the driveshaft about 4 months ago when I had the tranny pulled to replace the clutch and pilot bearing. I didn't replace the universal joints. Probably should have while I had the shaft out. Anyway, tires are balanced, 3 have about 20K miles on them and one has less than 2K miles on it. Could the lower control arms be at fault. I guess I need to find out exactly what speeds it vibrates at, and does it vibrate at the same speed when it is in 4th and 5th gear. Like I said before, only seems to vibrate at 50MPH or higher, and not while accelerating. The faster I go, the worse the vibration. I'll go test it now and let you know. I'll see if it does it in neutral going about 70MPH. Thanks for all your help. This is really frustrating.

Scott

------------------
1988 GT-stock at
151K miles
1993 Cobra #254-
stock at 92K miles
 
Old 03-16-2001, 09:01 PM   #9
93Cobra#254
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I just took her out. (Just started snowing here) Anyway. Here are my test results at 2000 RPM.

1 gear at 2000 RPM: No Vibration
2 gear at 2000 RPM: No Vibration
3 gear at 2000 RPM: No Vibration
4 gear at 2000 RPM: Very little Vibration
5 gear at 2000 RPM: Major Vibration

My point is, the vibration is occuring at varying engine speeds. (For instance, at 1600 RPM in 5th, it vibrates bad. At 1600 RPM in any other gear, it doesn't vibrate at all. Here is what the Hayne's manual says. Can I trust this?

"If vibration occurs at the same engine speed(RPM) regardless of which gear the transmission is in, the driveshaft is NOT at fault because the driveshaft speed varies"

"If the vibration DECREASES or is ELIMINATED when the transmission is in a different gear at the same engine speed, refer to the following probable causes" (Bent or dented driveshaft, dirt build-up on driveshaft, worn universal joint bearings, drivehaft and/or companion flange out of balance)

Acording to this description, it seems the driveshaft or related components ARE at fault. Anyone agree?

------------------
1988 GT-stock at
151K miles
1993 Cobra #254-
stock at 92K miles
 
Old 03-17-2001, 01:13 AM   #10
89GT
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I am not positive but I have to agree that it is your driveshaft or u-joints. Have you checked to make sure the bolts from the driveshaft to the rear pinion are tight? How does it act if you are going at high speeds and put it in neutral?
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Old 03-17-2001, 02:38 AM   #11
Davewht85
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A loose driveshaft is one thing. Worn u-joints are something else. It doesn't make sense that a worn u-joint would cause More vibration when its turning SLOWER.

 
Old 03-17-2001, 07:32 AM   #12
slider
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I had the exact same problem
it's the U-Joints

if too expensive to replace em, get the aluminum driveshaft from summit. they come with U-joints and it only cost around $150
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Old 03-17-2001, 01:05 PM   #13
93Cobra#254
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I don't have a summit catalog (at least not a new one). What is the part number? Where should I buy my rear control arms. Gonna replace those too. (I was going to just replace the bushings, but I think these are the stock arms, so I better just replace them) Anyone here have tubular control arms? How do they effect the ride of the car? Thanks again.

------------------
1988 GT-stock at
151K miles
1993 Cobra #254-
stock at 92K miles
 
Old 03-17-2001, 02:45 PM   #14
slider
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Summit:
Ford Racing aluminum driveshaft. part #
FMS-M4602G


The rear control arms cost between $200-250 for the kits. I would do a research first on what brand, size etc you need. Do you want drag arms, street etc etc?

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Old 03-17-2001, 06:01 PM   #15
93Cobra#254
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This is mainly going to be a street car, even after mods. Only sees the track...maybe once a month. Which arms would fit me best?

Thanks.

------------------
1988 GT-stock at
151K miles
1993 Cobra #254-
stock at 92K miles
 
 

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