I appologize up front for the long post. My 98 F150 has a vibration at 72 mph which is pretty severe and seems to be comming from the drive train. It vibrates on deceleration, accleration or constant speed over 72 mph. If you tap the brakes to unlock the torque converter it still vibrates. It vibrates only at 72 mph or higher. If you keep it out of over drive and drive it at a different speed same rpm it does not vibrate. If you put it in nuetral when vibrating it still vibrates.

I had the tires high speed blanced, checked for out of round and matched to the rims which were also checked. The drive shaft has been checked twice for balance and is fine, rear end checked, ujoints checked, motor mounts checked, transmission mounts and transmission checked all ok, fan and water cooler are tight no play. The transmission shop did not feel it was a transmission or torque converter problem, I believe he is honest because he could have charged me for a rebuild but did not want to because he felt I would still have the problem.

I broke down and took it to the dreaded Ford dealer as a last resort hoping they could help. After explaining everything above, they kept my truck all day had four mechanics (????) drive it and said it was my tires out of balance that I should get them checked for out of round and matched to the wheels. The writer said I had modified the vehicle and Ford could not help because it was not now to Ford specifications. The service manager came out to pull me off the service writer and admitted they did not treat me correctly and asked for another chance. I put my OE rims and tires back on and still have the vibration. Any suggestions. Thanks.

WarEagle

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98 F150 Lariat extended cab, Pacific Green/Silver Frost,
Grey Leather Capt chairs, AM/FM/Cass/6-cd changer,
full tint, color matched bug deflector, vent shades,
A.R.E. hard bed cover, Ultra type 50 polished wheels,
BF Goodrich 315 55R x 16 Sport Truck Radial T/As, 4.6L,
AT, Towing Package, Airaid, Superchip, JBA headers,Flowmaster dual
exhaust, Flowmaster 50 series muffler, 4.10 gears

 

If you have put the OE wheels and tires back on it and they are balanced correctly, let Ford deal with it now. It's their baby.

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1997 XLT Reg. Cab, 4.2L V6, 5spd, Superchipped, '99 Lightning Grill, '99 White Bumper w/Fog Light Kit, K&N Air Filter, Lund Deflector, Dash Mat, Clear Corner Lenses, MagnaFlow Muffler, Hellwig Rear Sway Bar, Edelbrock Shocks, Duraliner, Extang Saber Tonneau, Painted Tailgate Handle, Bell-Tech 2" Rear Drop, Amer. Rac. Atlas Wheels Clad in 275/60/17 Eagle GTII. Likes straightaways, loves twisties.

 

Warped brake rotors???

 

U-joints!!! My 87 had a vib just as you describe, at speed and on deceleration.They were replaced before and were always greased at oil changes. Yet, still when I pulled it apart, one of the caps had no bearings in it at all, there was nothing in there but some rusty dust, only on just that one cap.You couldn't get any play at the joint, and it looked normal from the outside, until I took it apart.

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2001 F-150 XLT S-CAB 4.6 "Fully equipt, and Superchip'd!"
96 Taurus GL
93 Kenne-Bell Supercharged Mustang
"Injection is nice, but I perfer being blown!"

86 Kawasaki ZG 1000 A-1 Concours

 

Wareagle:
WOA WOA WOA WOA! What the hell do you mean you tapped the brakes and unlocked the TQ convertor. This is a whole new thing to me please explain this in some detail.

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97 F150 Longbed V8 4.6
K&N air filter
K&N FIPK tech MOD & removed elbow silencer
Tires: Yokohama 265/75/16 Geolander AT+
Hyper white xenon bulbs
Bedliner and raven shell
6 disc cd changer
Oil & filter used

Gasoline used

My Truck

 

You may want to check the shocks. I had a van with worn shocks that did that at high speeds. At higher speeds you get wheel hop that causes a vibration. Just my .02 . Hope you find the problem. I know things like that drive me nuts.

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(Gots)
98 SC 4x4 ORP
4.6L
3.55 LS
Raider Vagabond Cap
Bedliner
Westin Chrome Steps
Chrome Brush Gaurd

Dime size door ding in P side door courtesy of some uncaring B#$t@&d (soon to be fixed)

(Ordered)
Airaid FIPK

(Wants)
Ravin 55 SI/SO

 

Find out if the dealer has an EVA [electronic vibration analyzer] and if they know how to use it. It is a ford tool but most dealers are too cheap to buy one. With that u can isolate the problem using rpm, speed and frequency of the vibration. Then u can isolate the vib to driveline, tires etc... also 1st order and second order vibrations. U need a dealer or more precicely, technicians who are willing to go the extra mile to isolate the CAUSE of your vibration. We have fixed some vibrations just like u describe by changing the driveline angle and the rear diff....even though it was in spec. You also need to check axle run out, tire runout..etc, which I am sure you have, it sounds liek you are fairly educated on the subject..or getting educated with your truck!!!!
WE also have had some flexplates at the engine or torque converters caus vibrations but htey are genuinly rppm related as opposed to speed related. IF you can figure out the Hz [hertz] that the vibration is and the exact speed range it occurs at, I can help u pinpoint the most likely area causing the vibration. also..is it rpm related or no???
ON the torque convertor lockup to the other member..[moose man] when u get a signal on the BOO [brake on off] switch, the torque converter unlocks or goes to 0% duty cycle so the engine wont stall and for driveability reasons...try it...cruise along at a steady speed and tap the brake pedal and watch your rpms......
Good Luck
Dave

 

Thanks to Crash and SuperDave666! I believe Ford isolated the problem. Seems they have been having trouble with 4.6 L supercab drive shafts causing high speed vibrations. They replace the drive shaft with a new one that is .5 inches greater in diameter, replace the u-joint flange assembly and replace the tail extension assembly. The parts are in and I get the work done Monday. The best part since I am out of waranty is that they are doing it all for a $100 deductible. Who said Ford wouldn't support out of warrenty problems! Anyone having a similiar problem with a 4.6 L check service bulletin # 6242. If you have the problem with a 5.4L you are out of luck because they say they don't have a solution. I'll let you know if it works! Thanks to all who responded to my cry for help.

WarEagle

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98 F150 Lariat extended cab, Pacific Green/Silver Frost,
Grey Leather Capt chairs, AM/FM/Cass/6-cd changer,
full tint, color matched bug deflector, vent shades,
A.R.E. hard bed cover, Ultra type 50 polished wheels,
BF Goodrich 315 55R x 16 Sport Truck Radial T/As, 4.6L,
AT, Towing Package, Airaid, Superchip, JBA headers,Flowmaster dual
exhaust, Flowmaster 50 series muffler, 4.10 gears

 

Check your tail shaft bushing on the transmission. The 98 and 99 crown vics had a vibration problem at high speeds (police cars had to have the top speed turned down). I believe they were using AODE transmisions which are identical to the 4R70W trans used in many of the F-150's.

 

Thanks to all who tried to help with their input. The culprit has ben found and repaired! The drive shafts on the extended cabs are sometimes to small in diameter for their length causing a harmonic vibration at high speed. Ford changed the drive shaft (the new one looks huge!), the extension housing and the u joint assembly. No more vibration! Only three months to figure out. Only cost me $100 bucks even though I am out of warrenty. Anyone with a vibration at high speed needs to get this checked out.

WarEagle

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98 F150 Lariat extended cab, Pacific Green/Silver Frost,
Grey Leather Capt chairs, AM/FM/Cass/6-cd changer,
full tint, color matched bug deflector, vent shades,
A.R.E. hard bed cover, Ultra type 50 polished wheels,
BF Goodrich 315 55R x 16 Sport Truck Radial T/As, 4.6L,
AT, Towing Package, Airaid, Superchip, JBA headers,Flowmaster dual
exhaust, Flowmaster 50 series muffler, 4.10 gears