2000 Expy XLT Vibration issue

[RunningonExpy]

First time poster here...already scanned through the forum looking for my exact issue and I couldn't find an exact solution so here's the problem...

Have a 2000 Expedition 5.4L Triton with the 4r100 tranny code verified. I've had a constant vibration issue that also initially had a hesitation/bucking issue when accelerating quickly (felt like the COP/plugs change problem that has been well documented in this and other forums). Changed the COP's and a bad plug even though several readers showed no codes and never got a check engine light, vibration/hesitation on acceleration problem stayed the same (slight improvement but nothing worth celebrating after the changeout).

Kept on looking through this forum and found the 104 fuse trick and pulled it, all of a sudden the acceleration hesitation/bucking problem went away BUT the vibration has continued. Had my tires rebalanced today and all of them were way out of balance but after balancing them the ride is a bit smoother but the vibration continues.

The vibration is as follows: After accelerating to about 20 miles an hour vibration starts without the steering wheel shaking (feels like something below the floorboard but not at the wheels), vibration gets worse at 40mph and continues higher in RPM's until 55 where once again it gets worse. At no point over 20 does the vibration go away, just diminishes at certain speeds and above 55 gets even more intolerable. Since I seemed to resolve the hesitation/bucking issue (probably something to do with the front AWD drivetrain?) what could the vibration be? During the rebalancing I looked under the front end and everything seemed in place; mechanic said the rear u-joint was a little worn but nothing major.

Ideas? Since it's an older expy I would like to try to attack the exact issue instead of throwing money down the drain with "exploratory" diagnostics that may not get anywhere. Love the power, not the expense lol!

I can try the brown wire mod to shut off AWD permanently if necessary, but I don't think that will get rid of the vibration.

Thanks for any hints!

 

[RunningonExpy]

Edit: Jumped the gun to test a theory...clipped the brown wire (not modded, just clipped so the AWD would go to 2WD) and put the 104 fuse back in...vibration still there, however switching manually to 4H did not produce the hesitation/bucking like before, and none in 2WD with the fuse in. No improvement on the vibration problem though (although backing up in 4H sounded like a lot of creaking/crackling somewhere in the front end). Any closer to a solid idea?

 

[Machete]

My bet is drive train. Perhaps drive shaft or u joints.

 

[RunningonExpy]

Which part of the drive train? Should I focus on the front drive shaft or the rear one? Any idea of which u joint tends to go out first?

 

[Trainmaster]

I'm with Machete. Check your universal joints. I had a 2000, and I replaced them several times over the 250,000 miles it was on the road. Sometimes you can check them in the car. Raise the front wheels and twist and shake the driveshaft, paying attention to play in the u-joints. Then do the same with the rear wheels and driveshaft.

It's probably best to just remove the driveshaft and see if the joints move smoothy. Sometimes just shaking it won't tell you anything. If I recall, you need a 12-point socket. You don't say where you are, so I can't tell you how difficult it will be. Rust plays a part in all of this. The shaft comes right out -- the rear one has an annoying guard that has to come off and one of the bolts is rather hidden and fights with you.

When you take the shaft(s) out, mark the position with chalk, as it should go back in indexed the same as it came out.

Pressing in new u-joints can be a bear. Don't buy Chinese ones, or you'll be doing it again in three months. You can try using a c-clamp but again depending on rust, but if you monkey-hammer it you can bend the ears on the driveshaft. If it fights, take the driveshaft to a driveline place and let them replace them.

Here's a tool, but you can use a regular socket too:
https://www.amazon.com/CTA-Tools-4340-Drive-Socket/dp/B008FJXA9G
or Sunex 212ZUMDL, which appears to be better quality.

 

[Plati]

Could there be a bad tire … problem with a belt in a tire?

I'm not sure about this but sometimes the frequency of a vibration can indicate its source. If you could associate the frequency with the period of rotation of the tires that might be a clue. Also, could put the spare on one wheel at a time to eliminate a tire/wheel issue … but that's a lot of effort.

 

[Killer Ride]

It could be your tires. I had a problem with mine once and it wound up being a seriously blemished tire. But if the guy working on the truck said Ujoint was suspect I would start there

Sent from my SM-G950U using Tapatalk

 

[RunningonExpy]

Great ideas everyone...I'm going to focus in on the u-joints with a buddy who's a mechanic and see if there's too much play on the front one first, where the vibrating is coming from. Could a bad u-joint(s) also cause the AWD bucking/hesitation or would that be a separate issue? Since I cut the brown wire to only enter 4HI manually I didn't get any bucking either from 2WD or 4HI. I'll post what I find later this week when I get them changed out.

Thanks for the quick replies and ideas!

 

[Machete]

Great ideas everyone...I'm going to focus in on the u-joints with a buddy who's a mechanic and see if there's too much play on the front one first, where the vibrating is coming from. Could a bad u-joint(s) also cause the AWD bucking/hesitation or would that be a separate issue? Since I cut the brown wire to only enter 4HI manually I didn't get any bucking either from 2WD or 4HI. I'll post what I find later this week when I get them changed out.

Thanks for the quick replies and ideas!

Bucking and hesitation doesn’t make me think of u joints. That sounds like an engage/disengage issue w differential excluding electrical issues. But hard to diagnose this way.

Have mechanic check it out. Sounds like a system problem not just a worn part.

 

[RunningonExpy]

Bucking and hesitation doesn’t make me think of u joints. That sounds like an engage/disengage issue w differential excluding electrical issues. But hard to diagnose this way.

Have mechanic check it out. Sounds like a system problem not just a worn part.

Would it matter in the long run as long as I use it in 2WD? I live in an area where I would most likely never use 4WD for anything, and using the brown wire mod to force 2WD (or manually engaging 4WD) seems to prevent the issue from occurring. From what I've read on the forums changing to 2WD from the default A4WD has no long term effects. I really don't have the resources to fix the issue other than the u joints and driveshaft at the moment, and I really don't need A4WD in my location. Can anyone confirm that disabling A4WD long term will eventually break down the system irreparably or just maintain the status quo indefinitely? I will definitely get the u joints checked/changed and/or check/repair the drive train, but trying to diagnose the A4WD system might be more than I can afford...

BTW, you guys are awesome!!