I have a 2000 F150 5.4 4X4 Extended Cab w/ the 4R70W Trans. I have a vibration that occurs between 40-45 MPH. It is very noticeable when braking. The rear end of the truck bounces/vibrates. Sometimes is violent, other times you can barely feel it. It is present while cruising sometimes, though barely noticeable.


I have done the following to try to fix the problem:

1. New brakes/rotors
2. New gear lube
3. New OEM Rear Shocks
4. New U-joints in Rear Drive shaft.
5. Ruled out the torque converter (turned engine off at that speed)
6. New Trans fluid
7. Rotated tires
8 Replaced Tires

None of these things have changed it one bit. This only occurs between those speeds. Any ideas?

 

Same problem with my 97 2WD 4.6 F150. I just put new tires on it for regular maintenace.... But here is what I am beginning to think:
Did you replace front rotors?
On mine it almost feels like the front is actually the problem, but it resonates to the rear. This weekend I'm going to take a look at the front rotors and possibly resurface them. Unfortuantely mine are the hub in rotor style...

Also, my driveshaft has marks on it from someone doing a runout test on it. There are actually 2 different color marks. some are red, some are yellow. But there doesnt appear to be any runout, the lines are even.
Mine is only 2WD, so there is even less to rule out, if its not the rotors the only other thing I can think of would be the wheel speed sensors and the ABS system. If the sensors are off for some reason the TCM or PCM not sure which does the ABS, but one of those modules could be activating the abs. The wheel speed sensors are totaly within the bearing and knuckle, so any service would be minimal, and probably only able to shoot compressed air in there at best. Being that im a GM technician I'm a little stumped on what ford has done here.

Oh and I did add weight to the bed, and then take it out, it actually seemed better without the weight, ruling out the idea of ABS kicking in due to low traction... but interesting that it was better with less weight.

 

My problem actually goes away with weight in the bed or if I am towing a trailer.

 

have you aligned your driveshaft?

look to see if there are any discolored spots on the driveshaft where a weight might have been attatched. also check the tightness of you spring bolts. seems a little wierd that the vibration would go away with weight added

 

could check for runout in the drive shaft. just lift it up, let it run at like 20 mph and press chalk against the driveshaft, dont press too hard though. Then shut it off and make sure the line goes all the way around the driveshaft.
When you put new rotor on did you put them on the front or the back or both?

if wheel hubs arent cleaned off smooth when you put on a new rotor it may not lay flat and it could pulsate.

You could try removing the rear driveshaft and putting it on 4wd and you will only drive with the front, but if you are careful you can get up to 45 mph and see what happens. They test drive cars like this all the time at our shop so dont be afraid to do it.

Try setting the E brake gently as you drive, see if anything starts to pulsate.

Try pulling a fuse or diode off the ABS circuit to disable it.

 

You might check pinion angle on rear end have seen this cause problem you described. usually will see this on a 2wd when truck is lowered.