I use the term "new" loosely, of course. I've been lurking in here for a while, but this is my first post. I just acquired a '93 AWD Aerostar XLT from my grandfather over the weekend, so I thought I'd drop in here and say hi.

A little bit about myself: I live near Rochester, NY. I'm an automotive engineer - I work for a company that makes limited slip differentials and AWD systems (Torsen). I'm a moderator at an offroad rangers website and an admin at the ford exp site. Obviously, I'm a Ford guy through and through.

The van was given to me by my grandfather. He's in Florida and the van was at his house in NY just sitting, so he said I could have it. Its got 180K miles on it, but it seems to run well. The clutch in the t-case does seem to be functioning properly as well. It has the usual NY cancer along the lower body. I'm hoping that it will just get me through the winter, and if it seems to be doing well after that, then I'd like to use to tow my rally car around - at least to the somewhat regional events. If not, I may replace it with a newer one.

One of the engineers at Ford that I know and work with was the head drivetrain engineer for the AWD version of the Aerostar. He suggested bypassing the t-case clutch controller with an on/off switch. He didn't tell me how to do it per se, but I'm sure the wiring can be sorted out readily enough. He said the clutch had the torque capacity to handle higher torque loads then would see above 5 mph (quite beefy he said), and that a simple on/off would probably increase its life since it wouldn't be constantly slipping in and out of engagement (makes sense to me). I see in older posts that several people have discussed doing this, but I didn't see if anyone actually had. This is probably something I'll try before long.

Among questions I've had, can anyone tell me if the front axle ring and pinion gearing is the same as the Dana 28 in the earlier Ranger and Bronco II? If so, it ought to be fairly readily swapped out for other ratios. I assume my van has 3.73:1 gears like everything I seen indicates, but I haven't yet actually read the tags. I'd like to go to at least a 4:10 for towing work. The rear 7.5" axle is easy to get gears for, but the front seems like an unknown. So, has anyone else changed gears in the front axle?

Anyway, that's a long enough post for now. I just wanted to introduce myself anyway. If anyone has axle/awd/drivetrain type questions, I'll help if I can, that's stuff I work with every day...

 

Welcome!

This is a pretty awsome place to hang out at and find out more about your 'Star.

As for installing a switch to turn off the AWD. I believe that all you need is a toggle switch and run it inline with the power wire to the box under the drivers seat (AWD module). No-one has come out and said exactly how to, but if you pull the module, you loose AWD.

As for front dif, not a clue.

Rear dif, hear are the codes, just need to read the driver door jam.:

Code Ratio
Conventional
22 4.10
23 3.45
24 3.73
25 3.27
26 3.55
Traction-Lok
B2 4.10
B4 3.73
B9 3.55

 

Why would you loose AWD? The center diff is always going to function regardless of the controller for the clutch since it's a simple mechanical device. You'd just loose the clutch function, right?

 

I am not for sure, but I believe it is an elcto-magnetic clutch (because when you loose traction it goes from 70/30 to 50/50 transfer ratio.) There have been several posts about people loosing AWD because of the module going out, or the connections corroding. Of coarse I could be completely wrong, I don't own one yet.

 

There is a clutch there, but its in parallel with an open differential.

Now, what can happen is that when the clutch function is lost and one axle looses traction, it will sit and spin that axle. The AWD is still intact, but it isn't doing anything to prevent the spin. This can happen to either the front axle or the rear axle, its just that the rear is more crippling because it gets 70% of the total torque. The behavior is just like an open diff in a rear end - you might have one side spinning, but that doesn't mean you've lost the connection to the other side. Its what people refer to as the power taking the path of least resistance. There's a little more to it then that, but that does some it up.

Even with the clutch off, you will be sending torque to the front wheels as well as the back wheels once you get unstuck and going down the road, so the AWD is still working, just not optimally. The drawback of AWD with open diffs in both axles and in the center is that if any one wheel looses traction, the vehicle is stuck. Its sounds counterintuitive, but in this case, 2X the drive wheels means 2X the ability to get stuck if the conditions are right. That's why limited slip and locking traction devices where invented, and that's Ford put the clutch in the transfer case as well an optional limited slip in the rear end.

 

Hi Torsen:

You got it. When you disconnect the module, all you actuallly miss is the clutch function. And you are also absolutely correct about getting stuck. With both axles working, you tend to get stuck later than if you only have 2WD. And when you do, it's usually harder to get out. I'm speaking from personal experience with a Dodge Caravan with AWD At that time, I thought the Forest Service would be collecting our bodies next Spring

 

Welcome aboard, always nice to have new, active members.

What advantage would you gain with a switch if the system is only active at low (e.g. less than 5-8mph) speeds? The overall savings in wear and tear would be fractional at best. The system as designed appears to have a low failure rate even in high mileage vehicles and your Ford buddy should be congratulated for his contributions on our behalf.

 

For day to day driving, it would be a marginal advantage at best. I think, though, that for crappy weather days (like Rochester this time of year), the clutch could see a lot of engage/disengage cycling when driving from stop light to stop light on snow covered roads. You accelerate from a stop, the rear starts slipping, the clutch locks, the slip stops, and then off you go to the next light. And so on and so forth. If the center was just locked and stayed locked, that cycling would be reduced. But, as you say, if they seem to still hold up well 15 years later, then it might be a moot point.

For my usage, though, I think it would be quite handy. I also intend to use this vehicle for scouting road rally routes (I usually organize 1 or 2 a year), as an occasional stand-in for my TSD road rally car (I use a 4x4 Ranger for these functions now), and then as double duty for performance rallies - both as a tow vehicle to get the rally car there and as a recce vehicle to make pace notes of the route, since we can't use the actual rally car for the recon runs (by NASA rules). So all in all, it stands to see a lot of dirt and snow road use. Being able to lock the center on demand and as needed can be a great help to me in that.

I've spent a lot of time driving on loose surfaces in all sorts of vehicles with all sorts of 4WD systems, so I have a fair idea of what I getting into with this...

 

You can readily see the engineer's mind at work here. Good points all, regarding the intended uses, so why not go ahead and wire one up. Until such time, you may want to continue driving it around as I think you will be impressed with versatility of the E-4WD system. We've towed snowmobiles through deep snow, campers across loose, dry, sand beaches and hauled skiers up plenty of snow packed mountains with ease and aplomb.

 

I know one thing, It has enough torque to crack or break the front axle support. I have read where many have had this happen, Me included. I got lucky and seen the stress crack and welded some 1/4" steel to it and it's rock hard now.

I would install it, better to have it and not need it, Then to need it and not have it!

 

Rick

If you want to put a switch on the T/C clutch, I would suggest you use a momentary push button switch. The front axle is pretty light duty and is not made to withstand wheel-slip wind-up torque on a regular basis. Having said that, you can control the clutch by grounding the negative lead of the clutch. This is what the controller does. The clutch coil always has 12 volts running to it. The controller simply grounds the negative lead wire to activate it. The conventional thinking would be to apply 12 volts to the positive lead, but it is actually just the opposite.

Another suggestion would be to wire a small 12 volt beeper or buzzer to the clutch wiring so you can know when it is activating. This would give you an idea of the road conditions and when the "button" might be needed.

FYI: There is a myth that the clutch ONLY engages below 5 MPH. This is incorrect. It will engage at ANY speed that it is needed, but NOT when the brakes are applied. The brake light signal will disengage it for proper anti-lock brake function. The exception to this is below 5 MPH. Since this is a safe speed the brake signal is disreguarded and the clutch IS allowed the operate. Please pass the word.

Your understanding of the transfercase differential is absolutely correct. You still have mechanical AWD without the clutch. It is a 33% front, 67% rear torque split.

I have engineering knowledge from the supplier side of the development of the AWD system for Ford. If you would like more info, check out SAE paper #892538.

PS. If you really want that Aero to go, put an Auburn diff in it (just kidding).

 

Well, a momentary override wouldn't really be practical given the driving conditions when I would need it. I understand your concern about the front axle sizing, however, I think I have a pretty good idea of when not to use the lock and how to preserve the axle. Part of my job is breaking axles and diffs, so I know what causes them to fail...

Anyway, why would I put an Auburn in there? I have a Torsen for a 7.5" axle sitting on my desk!

 

This is fabulous having two drivetrain engineers onboard. Perhaps either of you can address a common complaint with the Aerostar E-4WD system - the occurrence of low speed transfer case lock up and associated front axle judder/bang when on dry surfaces. This is commonly reported when turning into a parking spot or when backing out of a parking spot on dry pavement - the front wheels scrubbing under torque load or a sudden quick "bang" sound when the torque releases. From references in the Ford factory manuals and other sites, I gather the problem was one of speed sensor activation which, according to the sources, can be due to mismatched tires or low tire pressure on one side. I had several instances of this happening right after we acquired the van as a two year old lease return. The dealership replaced the half-shafts (for lack of something better to do) but it still occurred several times afterwards but has never happened again in the last 10 years. I thought the tire difference explanation made sense until I had a flat one day and put on the space saver spare. It is considerably smaller in diameter than the standard tire but never elicited any problem with the front axle binding - which kind of shoots that theory down. Do either of you have a more plausible explanation?

 

My apology, I think that myth was started by me. I read the service manual a little too quickly. You are correct that the clutch is disengaged above 5 mph only when the brake is applied.

Thanks

 

I second Aerocolorado's request. That bang cracked my front differential support bracket However, I had a bad speed sensor on the front output shaft, so maybe that's the cause.

Nowadays, I just unplug the connector under the seat. No point in having that in Southern California. When I really need it, I'll plug it in