vibration
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Senior User
Joined: May 2001
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vibration
Ok,I need some new ideas on where to look.'78 f100,302,auto.When I let off the gas and the speedo gets under 50 I start having a off-on vibration,sort of a rrrrrr...rrrrrr...rrrrrr...rrrrrr(real hard to describe on a keypad,sorry).You can feel it in the entire truck from the wheel and thru the seat but it doesn't do it when I accelerate.I've gotten under it several times and everything is tight,tires balanced,new ujoints.If I hold it on 50 it gets REAL bad.Was hoping maybe you guys had dealt with this before,any help would be great.
Moderator
Joined: Jan 2001
Posts: 56,971
Likes: 2,731
From: Virginia
vibration
Did you check for play in the driveshaft with it in neutral? This will let everything relax in the drivetrain. I would check for side to side movement of the yoke in the transmission, and side to side movement at the rearend input shaft.
Lead Driver
Joined: Mar 2000
Posts: 9,359
Likes: 1
From: Hampstead, NC
vibration
Does your truck have a two piece driveshaft? If it does, the carrier bearing might be bad. My truck does the pretty much same thing. The vibration starts at about 40mph and goes through 60mph. Above 60 or below 40 it doesn't seem to vibrate.
Mountain Pass
Joined: Nov 2001
Posts: 153
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From: Caldwell, KS
vibration
I have had the exact problem you are describing, were a vibration is present in a certain "range" of speed. Can only tell you what solved my problem. Balancing the tires. Thatsall it took, I have had the problem pop up on other vehciels with the same soloution. Often when I've gotten used tires
Elder User
Joined: May 2001
Posts: 977
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From: Houston, TX
vibration
It's my understanding that if you are feeling the vibration through your steering wheel then it's in the front of the truck. Most likely the front tires, might have one out of balance, or a rim bent, or broken belt, or tons of stuff. But most are visible with a sight inspection. And of course it could be something with the front end. I'd recommend keeping the search in the front if you feel the vibration through the steering wheel.
-j.banks-
-j.banks-
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Senior User
Joined: May 2001
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vibration
Thanks for the quick responses.I don't have the two piece shaft and I just had the tires rebalanced again.I understand what you mean about feeling it thru the wheel but haven't been able to track anything down so far.My '76 f100 had the same problem but not nearly as bad.This thing will make your brain go numb.
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Posting Guru
Joined: Jul 2001
Posts: 1,613
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From: Gainesville, FL
vibration
Motorhead,
You've got a tough one!
You have two things out of balance. As one resonates it either amplifies the second or cancels it out. If the rhythm is constant at one speed then your only dealing with two items:
1. Rear Brake drum out of round. Can get scary! Turn them.
2. Front rotors need to be turned. (Can feel it in pedal and steering wheel during braking.)
3. Axle bearings bad. (Usually gives a noise.)
4. Bent Driveshaft. (usually caused by recent event; i.e. thrown u-joint)
5. Bad harmonic balancer. Rare event, at best, should be able to see crankshaft pulley wobble; not your problem.
6. Bent rim. Guys at tire shop don't care enough to tell you. They can barely balance anything over a 31 x 10.5 anyways.
My Way is the Highway!
KingFisher
You've got a tough one!
You have two things out of balance. As one resonates it either amplifies the second or cancels it out. If the rhythm is constant at one speed then your only dealing with two items:
1. Rear Brake drum out of round. Can get scary! Turn them.
2. Front rotors need to be turned. (Can feel it in pedal and steering wheel during braking.)
3. Axle bearings bad. (Usually gives a noise.)
4. Bent Driveshaft. (usually caused by recent event; i.e. thrown u-joint)
5. Bad harmonic balancer. Rare event, at best, should be able to see crankshaft pulley wobble; not your problem.
6. Bent rim. Guys at tire shop don't care enough to tell you. They can barely balance anything over a 31 x 10.5 anyways.
My Way is the Highway!
KingFisher
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