Ugh! I think it's the rear end!

[Buck Nasty]

Hey guys. I've been noticing a "shimmy" coming from the rear of my '98 4.6. Every time it shifts, it trembles. I only notice it at speeds over 40mph and during lighter shifts. The tranny shifts smooth and under full-throttle shifts, I don't seem to feel anything. Under acceleration, it's smooooth. It seems to be somewhat light but, noticeable. It sure feels like the rear axle to me.

Hopefully I gave enough info. Any clues? Gear issues? Low fluid?

1998 4.6L 4X4 131,000 miles.

 

[AvroAero]

You could dain the dif and take a look at the gears. If its only 40+ and depends on shifts I'd suspect more transmission.

 

[Remo]

IIRC, many 1st gen, 4x4 Expeditions are having this problem. My truck does this as well. I think it is transmission/transfer case related, even though it always does seem to come from the rear-end. I really wish we could come up with a solution for this, because I know lots of trucks have this problem and it has been discussed so many times without resolution. Sorry I can't help you...if you manage to fix it, please let me know what you did!

 

[Buck Nasty]

Thanks for the quick replies guys! I take it that no trannies/rear-ends/t-cases have grenaded as a result of this? Just an annoying vibro? No one has taken this issue to a mechanic/dealer for repair?

Weak.

 

[ROCKSBITE]

just a thought on a whim, its not awd right? then id say check the diameter of you rtires

 

[Buck Nasty]

Originally posted by ROCKSBITE
just a thought on a whim, its not awd right? then id say check the diameter of you rtires

It's a 4wd with the Auto 4X4 option on the switch. Regardless, in an AWD, as long as they're the same size, tread design/depth, it shouln't matter, right?

 

[ROCKSBITE]

on paper yes. on the truck no

the rears will wear faster then the front. if you replaced 2 and not all 4 that will throw things off.

if all tires are the same make brand type size, etc on the sidewall check air pressure. not the number on the sidewall thats maximum! open the drivers door and there is a sticker. my 2000 eb calls for 30 in the front and 35 in the rear. i get brake pulsing cause the abs sees different rotating speeds at the whell sensors. so i run 35 all around.

when i bought it the fronts were a different make but advertised same size. turns out they had a cicumfrence (sp) difference of almost 3/4 of an inch. so basically the sensors thought the front was a foot in front of the rear. (same thing that messes up the speedo) i spent alot of money on wheel bearings, ball joints etc before i found that out. ford mechanic even said the tcase was bad! f" that guy!!! hope it helps if i rambled ask.

 

[ROCKSBITE]

i went to my dads buddy who own a trans shop. i told him what it was doing he walked out side and from across the parking lot told me what the problem was! hope that is your problem. if all the tires are the same it wouldnt sound like the running board is dragging like mine but you may still have noise. jack up the side and just measure with a tape or use a string to compare lengths

also check the fluid in the rear if you have limited slip you may need to change fluid and add the friction modifier. the noise could be the clutch packs grabbing.

 

[Buck Nasty]

No noise is associated with this. Just a li'l shimmy. The running boards are chill.

I'm sure it wouldn't hurt to change the rear diff juice either! Do I get gear oil with a friction modifier or is the modifier a separate add?

Most importantly...Thanks for doing the research Rocks! I appreciate you taking the time. As well as the rest of you who replied to this post!

I may not have time right away to do this but, I will re-visit once I do!

 

[Remo]

I'm sorry...I didn't completely follow what was said here...what is the issue causing this vibration? And how can it be fixed?

I'm sorry, I'm just running on no sleep and just finished an exam so my brain is kinda shot right now. I'd appreciate if someone could summarize all of this more clearly for me. Thanks!

 

[ROCKSBITE]

if you dont have the noise i went on about sorry for confusing anyone. i searched up and down for my solution and no one had any idea. your shimmy could be control arm bushings. or if possibly your sway bar bushings.

i would start with at least checking your rear diff fluid wouldnt hurt. if teh swaybar bushings are bad the bar will have play in it.

 

[Remo]

Rear differential fluid was changed recently and it didn't do anything to help the issue...Last I checked all the suspension/steering components were in good condition--some parts were replaced. I'll keep my eyes and ears open though and let you know if I come across something.

 

[ROCKSBITE]

is the friction modifier in the rear?