Hello All:

Not sure if anyone has any ideas about this one, but I'm absolutely stumped as to where to even begin troubleshooting this one.

My truck has taken to making a noise 88 F150 4X4). It seems random, and I can't make the truck reproduce it all the time. What happens is that (on perfectly smooth pavement) the truck makes a sound like it just went over a bump in the road. I can't really describe it better than that.

Now, to eliminate a few things...

1. Truck has new front shocks. Rears appear to be in good shape still.
2. Truck has new rear springs.
3. Truck has new U-Joints in the rear driveshaft, the front drive shaft and in the axles going to the front wheels.
4. Truck has a re-built C6 transmission (AAMCO) in it with less than 5K miles. Flywheel replaced at the same time and new rear main seal installed (Ford OEM seal). I also had AAMCO change the input shaft seal on the rear diff and on the front diff. Ford OEM seals were supplied.
5. Truck has new outer tie rod ends
6. Truck has new upper and lower ball joints each side
7. Truck has new BF Goodrich All Terrain T/A tires. with less than 10K miles on them. Balanced, never had a flat tire or a tire repair.

This is going to sound a little crazy... the only way I can describe the bumping sound is that it's not a "good" sound. The suspension dosen't give, let I percive that I feel something in the body of the truck when the bump sound happens, but it's doesen't feel like suspension. It also doesen't feel at all like an exhaust rattle.

Could it be a bad engine mount or transmission mount? What does a ltd. slip differental sound like when it's going bad? I thought they howled. The rear end in my truck is definitly not new any more. The truck does have 211,000 miles on it. Also, if it's important, it's an XLT Lariat Supercab with a 351 V8. The truck has a short box.

Anyways I'd appreciate hearing from any of you guys if you've experienced the same problem or if you have any shots in the dark on this. I know I haven't really described the problem very well.

 

When the Ltd slip in my 89 went out, I would occasionally hear a "thump" noise and could feel what I can best describe as a "shift" in the body when turning.It felt like the it would shift to the side or something like that. I thought it was a steering problem so I replaced the ball joints, and tie rod ends. a week after the steering work was done the spider gears went real bad and tore up the teeth on all 4 of them. I'd suggest checking the rear end. I was unable to find a complete rebuild kit locally, so I ended up getting the gears and clutch packs separately. Good luck, and hope this helps.

 

I wonder if the splines at the transfer case end of the front and/or rear driveshaft arent binding--and then suddenly releasing-- causing the noise when the driveshaft is trying to extend or compress on the splines due to road irregularities. Are splines clean,lubricated and free of rust/dirt ??

The rear driveshaft splines are in the transfer case and are lubricated by the transfercase fluid-- arent they?? Have you checked the ATF condition and level in the transfercase??

But are long wheelbase Supercabs set up the same way?? Does the rear driveshaft going into the transfer case move in and out?? Or does that movement occur at the driveshift support in the middle of the driveshaft??

My 117 inch wheelbase truck does the same thing when it has been parked for a period of time and the splines seem to take some time to free up--and then the truck is fine.

 

Does it happen accelerating from a stop? Coming to a stop? How are the radius arm bushings?

 

trgrhappy: Unfortunately for me, what your describing sounds way too close to what my truck is doing. I think I'll have the rear end inpected.

Phoneman: Excellent questions and good info. I think I'll check this out first, even before having the rear end looked at.

Alz: It never happens from a stop. Always when "cruising", but it happens at any speed. You can hear it at 30 or 40 mph, but it does seem to happen a little more if I'm going upwards of 45. Interestingly enough, and why I'm curious about what Phoneman is saying, is that the truck suddently stopped doing it for six weeks or so. It's only started again within the last week.

 

I would bet on the radius arm bushings.... let me know what you find.

 

The drivshaft splines are lubed with grease. There should be a zerk fitting on the shaft.