I've got a 91' AWD extended 4.0L Aerostar. It has 91,500miles. I've got a weird rumble that starts around 40mph, gets it's worse around 45-48mph, then fades out by 65. At 70-75mph it comes back, but not seemingly as bad. I would compare the rumble to that of having a subwoofer pumping out a frequency around 25-35Hz. It's just loud enough to be annoying.

Going around corners hard enough to make the van start leaning under heavy acceleration makes the rumble very bad. (Say, around 15Mph). As some of you may have seen my previous post, my van has bad coil springs. The top 3 coils are touching. I'm wondering if it is possible this has anything to do with the rumble. It seems like as I go over bumps down the highway, the rumble will fade in and out, getting worse as the back end is going down in the bounce. I have new coil springs + Air Lift air bags on the way.

When backing the van out of the garage our out of a parking spot, I'll notice an odd rumble from time to time. This is at/around idle speed.

This rumble (going forwards and backwards) seems to come from the back of the van. I feel it in the seat and floor ever so slightly. It reminds me alot of when I had a bad U-joint in my T-bird, but this is no where near as noisey.

- Acceleration/Deceleration does not affect the rumble.
- Breaking does not affect the rumble.
- Overdrive vs. Drive does not affect the rumble.
- Putting the gear selector in "Neutral" and coasting down the highway does not affect the rumble.
- Just had wheels balanced, no affect.
- Roatating the tires does not seem to affect the rumble.
- With 4wd module unplugged under drivers seat, front wheels will not spin on gravel under heave accceleration. With the module plugged in, they will spin under heavy acceleration.
- Drove down highway with 4wd module unplugged. Made no difference.
- U-joints on entire driveline seem OK. Moving gear shifter from forward to reverse produces no "PING" sound. I've crawled under and twisted all 4 of the drive shafts by hand. I could not detect any looseness.
- I've tried wiggling the back wheels around. I can not wiggle them up or down, back and forth. Just in and out ever so slightly as expected.
- The front wheel bearings are OK. I have a bad upper ball joint on the driver side I'm changing this weekend.

HEALP!!! PLEASE!!!

 

I have an '89 and mine does the exact same thing. I would love to know why? Anyone out there that can give insight.

 

I have the same year/model and about the same time mine developed a similar rumble noise. Mine turned out to be a loose pinion nut at the rear differential. You have to drop the driveshaft at the rear and inspect the nut. It should be torqued to around 180 fl/lbs. Mine was so loose you could turn it with your fingers.

Just a thought.

 

What is involved in dropping the rear? I apologize for my lack of knowledge. I am not affraid of doing the work, I just often need to know where to start. Any help would be appreciated.

 

JMC, you just need to remove the four bolts holding the driveshaft flange to the rear differential. The pinion nut sits between the two flange mating surfaces.

Before removal, you need to mark the two flanges with paint or indelible marker so the two parts will match up correctly when replaced. The entire driveline is balanced and replacing the driveshaft improperly can throw it out of balance. Be aware, however small those bolts look, they are hard to remove due to factory applied threadlocker. Warming the bolts with a propane torch towill soften the threadlocker and make for easier removal. You don't need a lot of heat to do this.

Now, if the nut is loose, you will need at least a 24" breaker bar and room to maneuver under the van to apply the torque. (If this doesn't make sense now, it will when the time comes to do it.)

 

Aero, I just had a look-see at my Chilton's manual. It says I should only tighten it to 8-14 inch/lbs on the end yoke! Are we talking about 2 different things?

 

I think I understand now. I need to tighten the Yoke nut so that there is 8-14 in/lbs of resistance when rotating the pinion.

Will be dropping the drive line later today.

 

vanlohd,

That spec (8-14 inch lbs) is only for determining pinion bearing pre-load when rebuilding the differential on the workbench, not when mounted in the van. The addition of the axles, wheels, bearings, gear lube, etc render it meaningless. Just check to see the pinion nut is really tight at this point.

(FWIW: After I rebuilt my differential and put everything together I can remember checking the turning resistance and if memory serves, it was something on the order of 25-30 inch lbs at the pinion nut with the rear wheels elevated and a full case of gear lube. This has been several years ago, so don't hold me to these figures. I just remember it was quite higher than when doing it on the bench.)

 

Well, nice try Aero! It sure sounded hopefull! After finally getting the torch out and getting the drive shaft off, the yoke nut was torqued to at least 150ft/lbs (all the higher my torque wrench goes). I pulled the drive shaft all the way off, the u-joints felt fine on both ends. There are two little ciruclar weights at the front and back of the drive shaft. I'm assuming those are for balance.

WOW, how nice it is to work with an alumnium drive shaft!! soooo lite compared to a traditional one....

When I turned the yoke, it felt good and smooth. There was a little play when rotating from clock-wise to counter-clock wise. About 1/2 a drive shaft bolt hole's worth. Is that normal? Oh yah, this is a traction-lock rear end too. Does that matter?

Could I have a drive-line out of balance? Is there something going bad in my diff? I'm I just going crazy?

I wonder with the coils being so wore out if the drive shaft is "binding". I jacked the van up under the hitch, letting the axel hang all the way down. There was just enough room to get the drive shaft up in there. So...maybe that's why it fades in and out as the van bounces up and down? The lower the back end goes, the less distance there is between the axel and transfer case which causes it to bind more which causes the rumble to get louder and louder?

I'll get to test this theory out Monday or Tuesday...hello new coils and air bags!!!

 

My coil springs came in Friday! After a mis-hap with one of the upper coil-spring bolts(snapped in half while loosening it!) and a friendly visit from the torch, drill & tap, I finished installing them today. My rear ride height is now maybe an inch to 1 1/2" higher and is still disappointing. If the air bags can bring this up about 1 to 2 more inches I'll be happy.

I have also replaced the wore out coil-over shocks for regular shocks. WOW, what a difference in ride! I don't get whiplash going over bigger bumps on the highway now

The rumble is still there, but I don't think it's as loud as it was. I need to drive it some more to get a better feel for it. I only drove it around the mile, which is 2 miles of highway + 2 miles gravel.

Dan

 

I took the van on a bit of a country-side drive yesterday. I noticed most of the time when ever I'm turning, I'll feel a bit of feedback(rumble) in my seat. Didn't matter if I was at a stop sign and just taking off around the corner or doing a rolling turn. This seems to me like I've got a rear-end differential problem. Probably something with the traction-lock.

I think the rear-end axle grease was changed about 40-50K miles ago. Could it be as simple as changing the axle grease? Does the grease just "wear out" after so long and need to be changed? My chilton's manual doesn't even have a maintenance schedule for the differential.

I'm going to go search around the forums to see what I can turn up!

 

After reading around the fourms and the internet some more, decided I'd try changing my axle grease. It's never been changed before. Thought/hopped maybe the friction modifier was just wore out. After a drive around the mile, that prooved that theory wrong. It seems like it *might* be a little bit quieter, but not like it should be.

I did notice the gears in the carrier looked like they had scratches or something on them. The ring and pinion gear looked great. Oh, except for the top of the pinion gear. It looked like there was this little flake of metal missing from the top of the pinion, going right through the ford oval. Couldn't find metal filings or anything in there, so not sure where that was from.

Air bags came in today. Look easy to install, just need to figure out where I want the schrader valves (I'm going to run two seperate lines).

 

I have a '92 AWD 4.0L with 200+k that has an almost identical problem with the annoying rumble, except the noise seems to eminate from the front. Like yours, the noise begins @ about 40mph and stays bad until 55mph, then gradually lessens until around 75mph, then gets a little louder.
One quirk is that when I corner hard to the left the noise stops. It has been doing this for the last 10k miles. I was wondering if the problem could be a hub? I'll let you know if I find the cure.

 

I had a bad hub on the passanger side...you could wiggle the wheel pretty bad in all directions. I replaced the hub, but it didn't affect the rumble.

I also had two bad upper balljoints. They didn't do much for me, other than get rid of an annoying "clunk" going over bigger bumps.

If you have that noise comming from the front, maybe there is something with one of your CV joints? It sounds reverse of a bad CV joint...OK, going straight, noisey around corners.

I'm almost convinced my rear-end rumble is because of my traction lok rear end. Any time I turned corners or go in reverse, it had an odd vibration. Felt like something rubbing. Now that I've changed the axle grease & put in new friction modifier, that seems to have diappeared or atleast quieted down.

 

I've got my airbags installed, wo-hoo! When the airbags are inflated, the vibration is silenced alot! Strange. My theory is that the coil springs amplified the vibration. Kinda like hitting a tuning fork....With the bags in there acting as dampners, the springs no longer vibrate. The noise isn't completly gone, but it's now a bareable. Strange.