Hi all:

Forgive me if this has been covered. I did a quick search and didn't find anything specific to '97-'02 Expeditions.

History: I lowered my Expy 2 in. all around. I used Belltech drop spindles up front. I adjusted the rear ride height sensor to match. At the same time, I installed new ball joints, bushings, shocks, airbags, etc. Tires were rotated and balanced at the same time. The Expy has 161k miles on it.

It rides and handles great in city driving. But on the highway, I'm experiencing a high-frequency vibration from 65-80 mph. Below 65, it's smooth. Above 80, it diminishes noticeably, but doesn't disappear completely. I have confirmed that it varies only with vehicle speed, not engine RPM. Also, the vibration is transmitted through the chassis, not the steering wheel.

I think it's related to the driveshaft, because the frequency seems too high for it to be wheel-related. And, the tires were just balanced, as I said. So, I've got two theories:

1: The pinion angle is wrong. This would seem obvious, given that I lowered the Expy. But, the symptoms given for that, when I search, are more low-speed vibration. I'll check it anyway, once it quits raining here. But how close is close enough? If it is this, does anyone make adjustable-length control arms for these? That's the only way I can see to adjust pinion angle. My search turns up nothing that fits Expys.

2: From a mechanic-buddy of mine: because the u-joints in the driveshaft are now operating in a different position than they were for their first 161k miles, they're causing this vibration. Any experience with this one? If this is true, I assume I'll have to take the driveshaft in to be rebuilt.

Have I missed any other possibilities? I'll check for stuff coming loose, of course.

Thanks in advance,
John.

 

I would think pinion angle. But its usually more of the 30-45mph range
possibly the ujoints are bad. Assuming the angle isnt crazy far out, loweeed vehicles ujoibts operate with less axis rotation because the driveline is generally straighter.

You would need to actually measure your pinion angle before you do anything else.

 

Sure enough. The pinion angle is off by 3 degrees. With the radio off, on a really smooth road, I can feel a vibration from 35-40mph too. It's faint, so I didn't notice it before. But it makes sense that it would be 1/2 the speed of the of the other one. Looks like I get to order adjustable LCAs now.

 

Trucks are usually set up with a slight negative angle so as the ring climbs up the pinion it wont pull it way over positive.

you're at -3 right now? So don't bring it all the way up to zero.

 

True. But, keep in mind that the bulk of the movement on trucks is due to deflection of the leaf springs. My Expy is a four-link. The link bushings have a bit of compliance. But I doubt the pinion angle changes much at all under acceleration.

What I may do is set the rear ride height back up to stock (a two-minute job) and confirm that the vibration goes away. I'll measure the pinion angle then, and use that as my adjustment target once I put the adjustable arms on.

 

Sounds like a plan.

And yes you are correct about the leaf flexing when the pinion climbs up

 

Looking for arms. But not finding many options.

There's a guy on Ebay selling adjustable lowers:

http://www.ebay.com/itm/1997-2002-Adjustable-Ford-Expedition-Lower-Rear-Control-Arms-/201021263729?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3AExpedition&hash=item2ecdcd0f71&vxp=mtr
This outfit lists them, but says coming soon:

http://rukse.com/car-truck-parts/hd-truck-control-arms/

I contacted them for "how soon", but haven't heard back. Their fixed ones are $30 more than the adjustable ones on Ebay. So, I'm not hopeful.

That's all I've found. PMT and others just make fixed-length arms. Even these two can only be adjusted by disconnecting the arm and rotating one end relative to the other to change the length. I'd really like to find a pair that work like turnbuckles, with RH and LH threaded ends.

Any ideas for other sources? Who is a good maker of custom arms?

I took the Expy out for an errand with the trailer yesterday. At highway speeds, the vibration was awful with the load out back. Gotta get this taken care of soon.

 

Whats the price range you're looking in? Id imagine for a couple hundred you could have your factory arms fabricated into adjustable arms. Like a tie rod threaded sleeve type of setup that you can change the length in real time while installed on the truck.


any good custom jeep or fab shops around you? Might be worth calling around

 

Yeah. Expecting to spend $200-$250. I'll get the Ebay ones ($240 shipped), as a last resort. Next to churches, 4x4 shops are the most common thing around here. So I'll give that a shot. Thanks for the suggestion.

 

You might have to hold their hand and explain exactly what you want done. They may freak out if you tell them "lowered" in your vehicle description

 

 

I asked Ebay seller if he'd do turnbuckle style arms. He said he couldn't get big enough LH threaded studs. And he said they're less reliable. He also said he was leaving Ebay. Sure enough, he canceled the auction. So much for my backup plan.

UPDATE: I found him on eCRATER. So backup plan is reinstated.

 

I finally had time to do some better measuring and testing.

If nerdiness bugs you, skip this paragraph. I measured the 4-link, and made a kinematic diagram in CAD. Then I could articulate the suspension on the computer and see how the pinion angle changed. At stock ride height, the pinion angle is +5.3 degrees (from level). At a 2in drop, it changes to +3.7, or a change of only 1.6 degrees. To bring the pinion angle back to +5.3 at lowered ride height, the lower arms have to be shortened by 0.27in. All of this seems like too small a change to cause the vibration. I figure the rubber bushings deflect nearly that much. So, I tried an experiment...

I raised the rear back to stock height and went on a drive. The vibration is still there. So, unless I'm missing something, the driveshaft needs rebuilding. This is actually good news, as that will be cheaper and easier than replacing suspension links. It'll be next week before I can have the Expy down for a couple of days. But I'll report back.

 

I finally got around to having the driveshaft rebuilt. New u-joints, check balance, cleaned and painted for $80. The vibration is gone.

 

Gone for now. But glad. Still need to get the pinion angle back into spec.