I have a 97 4x4 F-150.
Here is the problem...
When I apply the brakes to slow for a stop, the truck is fine until it gets down to around 40mph, and then the rear of the truck feels like it starts to "bounce" or vibrate. The bed of the truck literally goes up and down in the mirror. Now....the funny part is....it does the exact same thing when I accelerate and it reaches 40 mph. After it gets past 40 mph, both accelerating and stopping it smooths out. I have had a certified mechanic look at it and he couldn't figure it out, I took it to a Ford dealer and they said the drive train needed to be balanced, so I did that...still have same problem. Any ideas?

Please e-mail me at : jbfan1263@hotmail.com if you guys have any ideas. Thanks.
God Bless.
jbfan

 

I have the same thing at 39-40 mph. More pronouced when braking through that speed, so perhaps the front rotors are contributing? I thought it was my Bridgestone REVOS but a balance job didn't help.

Maybe its just me but it seems to be worse when the roads are wet.

edit: same as yours - 1997 F150 Ext. cab 4x4 with 5.4

 

Thanks for the reply, at least I know I'm not alone. I've had the rotors turned, but not replaced, so maybe that's my next step. It's wierd how it does it while accellerating though...maybe a caliper hanging up or dragging?
If you figure out something, please let me know. I'll let you know how the rotors work when I get them...gotta have wife's A/C worked on first!
God Bless
JBfan


Oh yeah...my brakes "grab" when it rains, when I apply them the first couple of times, but they are fine after they warm up, so it very well could be a rotor problem.

 

Do a search on this site. It's not the brakes. This seems to be a suspension design problem. Mine been doing it for years.
Ford came up with one attempt to fix by installing a hollow rear bumper then adding lead shot or sand into it to act as a vibration dampner. Helped but not a cure.
I never bothered to get mine looked at. I know it's a design error and i just live with it. Hell, after 121,000 miles I hardly know it's happening anymore.

Check this site and you'll see.


Wrong guess.
It's your brake pads absorbing moisture. Used to be a common complaint. Try switching to a better grade of pad.

 

Thanks for the reply Iggy. I am getting ready to purchase more pads anyway, so I will go with a better grade.
God Bless
jbfan

 

well just a thought
i recently had the vibration problem while accellerating and mine was a u-joint starting to go out. replacing it fixed the vibration.

on the vibration while stopping / slowing down only way i could fix the problem (until my next pad change) was to adjust the rear drums up every month or so. this would take alot of pressure off the front pads.

i would use the reverse & stop method my brake mechanic told me about.

like i said it was just a thought

 

my 97 4x2 has had the shake for a long time. mine does it at 42 mph and is cleared up by 43 ot 41mph it seems. if i stay at 42 mph it will do it all the time. its a minor disturbance so i just dont do 42 mph often. new rotors and turning the drums didnt fix the problem. i've had the drive shaft of a few times so its probably out of factory indexing. i've heard of the bumber fix but never heard of anybody doing it. they say its a bed osilation. i almost wonder if new bed mounts might fix it. but now i've got an 01 and it doesnt do it so i dont worry about the 97 much anymore just gonna drive it into the ground.

a u-joint would also be a good place to start.

 

I used to experience the same thing, but from 40 all the way down to 20 mph. I replaced my rotors with PowerSlots a week ago and changed the fluid from the rear differential. Not sure which one did it (my bet's on the rotors), but the shake is totally gone now, smooth as a baby's butt with 94K on the truck, just new brakes.