Hello all, searched and read many threads and I think I may have this narrowed down, but thought I'd throw it out there for further thoughts.

Truck is a 99 Expy EB w/139k. Runs and shifts smooth, no issues there. Spent the day today eliminating possible causes that were items that needed to be done anyway, which included:

-Upper control arms / ball joints
-Lower control arms
-Outer tie rod ends
-Front rotors, inner/outer bearings
-Rear pads
-Rear swaybar links

New tires, Toyo Open Country H/Ts, which have been rotated a couple of times now, and road force balanced each time from a freshly calibrated machine.

The issue is at highway speed the vehicle drives and rides beautifully right up until I hit 63-65mph where a shudder/shake/vibration begins. It is not at all originating from the front suspension, even from the worn parts that were just replaced as the steering tracks straight and the wheel is vib free. The shudder can be felt in the seat and in the body of the car and can be quite significant. It remains until speeds reach ~80mph when it lessens a lot but is still there - just more manageable.

Today I had the vehicle on jacks and nosed around the engine/tranny mounts which *looked* good; exhaust, hangars and shielding were all in place; and the drive-shaft didn't show any signs of scarring as though it had been bumped or dinged. A visual inspection of the u-joints didn't show anything out of the ordinary. Lastly, the upper and lower rear control arms all visually looked good and didn't appear to be overly worn.

My research here and list of probables, at this point, include:

-double cardan joint is worn
-a u-joint is worn that I can't see
-pinion bearing, or worse, gearset
-torque converter / flex plate shudder
-rear upper, or lower control arms.

I hope like hell it's not the gearset in the diff. The pinion bearing I can handle, but I'm no gear-man. Would a bad pinion bearing cause that kind of shudder? As for control arms, my jeep TJ experience tells me to look hard at the control arms as a possible source, but they do look ok.

Other thoughts, or advice appreciated.

Thanks,
Mike

LOL...my pile o' parts after today's fun.

 

This would've been my first suggestion.

 

Thanks...

I have rebuilt a double cardan on a driveshaft from my TJ rubicon with a new centering ball kit, u-joints, etc, from Napa. It wan't too bad of a job, but it was a pain in the rear. Are there any secrets, or suggestions for pulling this D/S and rebuilding in the ford? I guess that I first need to determine that it is the problem.

thanks.

 

Ha! Just went and checked the underside of my truck and found that I didn't have a double cardan driveshaft - perhaps because it is 2wd. There is a harmonic balancer at the tranny end. Guess the u-joints could still be bad.

tranny end:


axle end:


harmonic balancer at the tranny tail cone:

 

The harmonic balancer could be dried out and not holding the drive shaft in the center.

 

Slight delamination on a tire. Wouldn't be the first time. Sometimes not so easy to see.

 

Tires are new. They were replaced as part of the process of eliminating possible causes.

 

Just to update and close this thread. The heavy driveline vibration couldn't be sourced by either a driveline shop, tranny shop, or a ford dealer. All new tires, suspension work, etc, didn't have a positive impact. Fearing a catastrophic failure with my Wife and 5 kids in the car, the ole' girl got traded in on an 07 Exp Limited last weekend.

Thanks for the tips along the way!