I have a drive train problem in a 95 Areostar AWD I need to pinpoint. I'll start with the story. While driving on highway at 60 MPH a sound and vibration started . It was similiar to driving over rumble strips. This was followed by a couple of loud claterring and bang crunching noises. I limped off the road still under power and stopped. Left the engine running. put it in park. The park did not hold and the car rolled ahead. There was some strange whirring noises at that time. I shut off the engine. I had the car towed home on a flat deck truck. The next day I moved it around the yard with no apparent problem. Park now holds and it drives around the yard with no apparent problems in reverse or fwd. I have been reluctant to road test it as I may be calling the tow truck again. I took off the transmission plate. The oil was a little dirty but otherwise everything was clean . No traces of any metal fragments at all in pan or filter. I am know wondering where to look next. Any Ideas?

 

Welcome!


How many miles are on it?

As for the loud clattering and crunching and vibration, sounds like you lost a CV joint in the front. I would crawl under and check the condition of the boots. But that would not explain why when you were in park that it would roll.

I took off the transmission plate. The oil was a little dirty but otherwise everything was clean.

Are you talking about the tranny pan? If so, did you happen to check the tranny level before pulling the pan with the dipstick? When was the last time the fluid/filter was changed? And when you say the oil was a little dirty, do you mean it was brown or black? Did it smell really bad? Also did you check the magnet for large chuncks of metal?

 

There is 120,000 miles on it. I did look at the front CV joints and they appear ok but I havent tried to spin the wheels jacked up.Could we be looking at anything in transfer case like chain or whatever?

 

There is a slight chance that it is the transfer case. Now that would explain why the parking pawl did not hold the vehicle. But here is the thing, the TC rarely goes out on the Aero, especially with that low of millage and if it did, you would not be able to drive it again sense it is 100% of the time AWD.


When you test drove it in the yard, did you her a slight clunk or bang when you started to move? (that would be the TC locking)

Also are you getting any CE lights?

 

No Slight bang noticed, and no lights whatever on dash- CE meaning? Oil was brown not black, no bad smell . Sorry . too bad I didn't know about magnet and where to look for it. Interesting though about Tcase not likely to fail.
As for Transmission level I checked it warm but not running and it was way over full, same place as when I bought it a year ago. I don't know if this means much as I Iunderstand it should be checked running. I'm going to try to check oil level in transfer case if that's possible and try driving it out on the road again, and see what happens. It's very hard to tell where the noises are coming from.

 

Don't do that. Something is obviously wrong here, and you don't want to be stranded again. I would do these checks first:

1) Check oil level in both differentials and look for leaks.

2) Jack up the van and put it on 4 jack stands. Ask someone to hold one of the front wheels tightly, and try to turn the other front wheel. If one wheel can be turned without affecting the other wheel, then one of the axles broke. Do the same for the rear differential.

The part about it rolling forward in Park would worry me a great deal, since it implies either the transfer case is busted or one of the axles broke. In either case, you don't want to be stranded or loose a wheel while driving.

 

after checking diffs and and both left and right CV shafts per copper's suggestions for failures...pull drain plugs on diff's and check for metal cuttings/particles...drain plugs are magnetic and will trap ferrous particles

drain transfer case into pan and check ATF for any metal cuttings or friction material particles from TC clutch, drain plug may be magnetic, check for ferrous particles, chain is steel...TC uses Mercon ATF

rear axle will hold AWD on hill with parking brake engaged even if front diff or front axles are broken...parking pawl may not have been fully engaged after the stressful pulloff from the freeway with breakdown....parking pawl will make horrible racket when slipping and not fully engaged in teeth....steel against steel ripping sound
my wife occassionaly tries to drive in Park while going from forward gear to reverse...sounds worse than poor shifting of a non syncro manual truck tranny...rubber teeth gears?

 

OK Thanks for the advice I won't drive yet. Here is what I found out.
Both front Boots are broken.
Is it possible to check these CV Joints?
I jacked up one wheel (FPassenger) and was able to turn it somewhat. Probably like from 11 to 1 o'clock with some slight clunking noise, probably normal. Is it possible that one CV Joint could cause the whole problem? That rumble strip noise down the HWY perhaps. I remember that there was a clunk,clunk,clunk going on when you make hard slow turns in parking lots, a telltale signal of CVjoint problem

If I Jack up the other 3 wheels one at a time and try to turn them and one does turn freely does that mean that axle is broken or the CV joint is broKen?

I wonder If an axle or the TC is broken, why will it again hold in park and I can now drive it around the yard?

 

Yes, it could potentially. The van likely has 3 open differentials. Even if the rear has an LSD, it won't really impact the situation though. By breaking a CV joint, you disconnect one front wheel from the front diff. This is the functional equivalent of lifting that wheel off the ground.

If you were driving around, then with an open diff, that wheel can now freely spin. That means that the front diff can spin up, and little torque would be sent to the other front wheel. This, in turn means that the center diff can spin up and little torque is sent to the rear axle. This is how an AWD vehicle with 3 opens can still be crippled if just one wheel looses traction.

By the same token, the park pawl will only hold the vehicle from rolling if the wheels that it is connected to have reasonable traction. In a simple 2WD example, Park holds the diff housing/carrier from turning. It does not hold prevent the differential gears from turning within the diff housing, but to do that the wheel would have to turn in opposite directions (if you were to spin one wheel by hand with the car in gear and lifted up, the other wheel always turns the other way due to the diff gearing). The fact that both wheels are connected to the ground and gravity will pull them in the same direction (either both forward or backward) prevents them from spinning in opposite directions, so Park holds the car in place.

However, if one of them is unhooked from the diff, either by lifting it up or breaking the axle shaft connection to the diff, then that wheel is free to spin. That means that there is nothing holding the one that is still hooked to the diff. Basically, gravity can pull the car, making the connected wheel roll forward, and the unhooked diff output simply spins backwards (or vice versa).

Extend that one step further - to an AWD vehicle with open diffs. Here, the park pawl keeps the center diff housing from turning. The front and rear drive shafts don't turn because they are connected to the front or rear wheels via the axles. And the axle diff housings don't turn because they're in turn held by the front and rear driveshafts instead being directly held by the pawl. This is great as long as all 4 wheels retain decent traction.

Now, one wheel gets unhooked from the system by a broken CV joint. The simple example above holds true, but because its connected to the center diff, differentiation across the center can also occur. This has the same affect on the center diff as the broken joint did to the front diff. So the rear wheels get pulled by gravity and roll, making the front driveshaft want to go backwards. Because it's connected to a differential with one unhooked output, it allows that to happen. The front diff housing then spins backwards. The "good" front wheel still wants to spin forward, and the unhooked/broken front output allows that as well. The front diff just has to differentiate at the appropriate rate, and there's nothing to prevent it from happening. So the van rolls down the hill when in Park.

So if that's all true, why could he drive it under power? Simple: the AWD clutch. It would have to have been constantly cycling, but when it was, it was locking the center diff and allowing the drive torque to go to the rear axle regardless of what the front axle was doing. And when the van was in Park, the clutch wasn't activating.

Clear as mud? It really is a lot simpler then it sounds. But you have to be able to visualize differential behavior to sort through it.

 

Now I am totally baffled . I checked all oil levels and contrary to my better advisors took it out for a drive. Everything runs smooth . Not any problems. What the heck could it have been. I best get rid of it cheap and quick. Something was definetly very wrong. It was no dream. I can't trust it for any long trips thats for sure. By the way this thing gets terrible mileage for it's size. 18 Miles per Imperial gal. Is that normal? Thanks for your suggestions everyone. I know that something is still very wrong and Any further thoughts and comments would be appreciated.

 

Yep your CV joints are toast. Once the boots are ripped all that road dirt and grime gets in there and destroys the bearings. All the noises on turns is also tale tell sign of CVs. CVs only last between 100-150kmi normally. Also being able to move the front wheel that much with the noise is a tale tell sign of CV Joints.

I would replace both sides (sense you said bothe front boots are broken.) Not to much of a terrible job, about a day for a 1st timmer. Don't waste your time with just replacing the boots, the damage is already done.

BTW CE=Check Engine Light and/or other Dummy lights.

18mpg is about average for an AWD. Even if you buy something new in realitvy size as the Aero, you are looking at the same millage with more car payments.

 

Thanks Torsen Rick, I must have been posting my last message as you posted yours. I breifly read your detailed analysis, which I will read through more slowly later on. I guess so far what it means is a CV Joint could possibly be the problem . Any way I'll check back later as I must do other things for a while . Thanks again

 

Maybe your joint popped apart, then back together again? I've seen them do that before...