91 f150 shakes

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  #1  
Old 05-04-07, 03:57 PM
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91 f150 shakes

i have a 91 f150 that sometimes shake violenty in the front end when i hit about 45 mph. i have it raised 6 inch suspension lift and 35 inch tires that have been on for years. i have replaced driver side u/l ball joints inner and outer wheel bearings on passenger side inner and outer wheel bearings. one mechanic told me and alignment and balance the tires but the tires are newer and were done when i bought them. another mechanic told me a center drag link and a pitman arm but the pitman arm isnt that old or used. does anybody have any ideas? thank you
 
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Old 05-04-07, 05:17 PM
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Tell us anything you did or added to the vehicle just prior to this shaking.

I had a 396 hot rod once and Mickey Thompson meats on the back. I had them computer balanced after terrible out of balance feeling. The car still like shook around the road! So then I had the tires old fashion bubble balanced for the fun of it and they were WAY off from what the computer indicated. So I had them bubble balanced and that cured the out of balance shaky sensations.

You FIRST have to be absolutely certain about the wheels and tires. Then you can move on from there. Tires that size are going to have a big impact on how smooth the vehicle goes down the road. Tires that big have a lot of leverage in them off the centerline of the hub.
 
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Old 05-04-07, 07:19 PM
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thank you for your reply. but no it started around x mas i got two new tires (front) and left wheel bearings replaced mechanic told me right side was bad but could not afford ot at xmas time. truck was fine for about a month then problem started again i was thinking right side bearings and ball joints. problem is my daughter lives 45 miles away and speeds to get there are 55 to 60 mph. i would get her every week but know its every 2 to 3 weeks whenever i can borrow a vehicle. it really ticks me off cause she gets so upset when i cant get her but i dont have the cash to just replace everything
 
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Old 05-04-07, 08:16 PM
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A bent/damaged drive shaft/axle would cause shaking.
 
  #5  
Old 05-05-07, 03:06 AM
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91 f150 shakes

If you are sure all the parts are tight and none are worn, then I suggest checking the balance on them 2 front tires. You could switch them to the rear if they were the same size and see if the shake goes to rear. Usually a shake in the front end will be felt at the steering wheel and the rear will be felt in the seats and/or floor board. Anything bent, like a rim will usually start to shake early off, say around 5-10 M.P.H. and just get worse as speed increases.
Tires that are out of balance will shake between certain speeds, say between 55-65 M.P.H., it all depends on the match between the weight of the vehicle, the speed and the amount of the unbalance. Usually in heavier vehicles you wont notice vibration untill higher speeds, say 65-75 M.P.H, and compact cars might vibrate at lower speeds, say 35-45 M.P.H.
Although, a long time ago I once had a car that whenever it hit the smallest bump it would start a violent shake in the front-end that would cause me to pull over untill it stopped. Strangely enough it was caused by the tires on the back being too big (tall), this threw off the caster alignment on the front 2 wheels. Like a shopping cart, when the front wheels start to shake violently when you push real hard. That is because on those carts the front wheels have alot of negative caster. Same as on a car or truck when the caster is too much negative either because the rear was jacked up or a curb was hit real hard at the front and pushed the bottom toward the rear, resulting in too much negative caster. Not saying the caster is actually a negative reading, just that it might not be as positive as the specs call for. Usually positive caster is needed to give the driver feel at the steering wheel and since most vehicles are power steering a driver can overcome the strength they need to overcome positive caster. Look at a chopper motorcycle. That is an example of really positive caster and really hard to turn the front wheel.
So, it happened to me once. I would have the tires checked for balance first, not just balanced without checking them first, cause you wanna know if they were out of balance, then check the alignment including the caster and the (ball joint inclination), that has alot to do with caster, but means something is bent. Most shops will do that free.
 

Last edited by NewHomeowner396; 05-05-07 at 03:09 AM. Reason: mispell
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