Hello,

I have a '93 Aerostar EXT EAWD with 191,000+ miles. It is a great vehicle! Now that the snow is here I am finding that my AWD is not working. I need some help in diagnostics, please.

I have searched through this forum and have read through my Chilton's manual, and cannot find diagnostic assistance. I currently have not seen any unusually flashing the 4 wheel drive lamp, just the normal lighting before starting. My problem is that the front wheels are not being driven at all. I am assuming that this means my transfer case is not functioning anymore, but would like any help you have to offer about diagnosing what might be happening.

I have looked at www.driveline.com to get an idea of pricing, and would appreciate any specifiic details on what to do to get it repaired or replaced. I have been doing shade-tree mechanics for over 30 years and can replace or repair just about anything, but this is my first suspected transfer case failure.

A little history. I purchased this vehicle at 105,000 miles. It has performed very well over the past few years. I have replaced things as needed and have taken care of fluids regularly. Last winter the AWD was working correctly.

Thank you!

canders_00

 

How do you know the front wheels are not being driven? I always thought the default on the E-4WD is 1/3 power to the front, and that's strictly through gears and chains.

 

Because the back wheels spin and the front wheels don't spin or assist. I have tested this out by stopping in the snow, stepping on the accelerator - which makes the back wheels spin - a whole bunch of revolutions, and then getting out to look.

I have also observed the tires as another person drove. The back wheels spin and the front ones don't assist in the forward motion like they should on AWD.

 

If that's the case, I think the clutch pack in the TC either has worn down, or not being engaged.

 

Thank you!

Is there any other information that can help to diagnose this before disassembly?

I am new here and cannot attach files, or I would put the diagram here. At http://www.drivetrain.com/dana28transfercasesillust.htm there is an exploded view of the tcase. Can someone tell me where the pack is located (like inside item #12?), and if it is something that can be purchased. Drivetrain.com does not list either clutch plates or a clutch pack as one of the items that can be purchase from them.

 

It may also be the electrical circuit that engages the clutch, although you'd think that would set off some sort of trouble code. You may want to try a test light to the clutch pack wires and induce rear wheel spin before tearing it apart. The electo-mechanical clutch pack in the link you poster is part #12. I suppose if you wired a test light lead into the wires going into it at the top of the transfer case, ran it in the door and put it up on the dash you could see if it was getting power. Another way would be to tap the wires on the control module under the seat, although that wouldn't show if the wiring is bad underneath. Here's a link to the wiring diagram for the AWD -- http://autorepair.about.com/library/...s/bl419lib.htm

 

First, unplug the 4WD control box under the driver's seat. Then apply a 12V to the clutch pack to see if you can force the front tire to spin when the rear ones slip. Removing and tearing the TC apart is not that difficult. Send me a private e-mail just so I can get your e-mail address (don't post it here since Dave will erase it - that's the rule ) Once I do, I'll send you diagrams of the TC and what to do.

 

Thanks for all the help. I will try some combination of this, probably over the weekend.

After reading some of the posts I was under the impression that this was a full-time AWD vehible, but if it really is using the sensors and engaging this clutch based on wheel spin then it really isn't full-time AWD is it? Don't mean to start a major side-discussion here, just wanted to know because it is relative to my problem.

copper, I tried to get you my e-mail addy via private message. I will try again after this post.

 

Hi Canders_00

First off, let me say that I think you may not a transfer case problem. Let me explain why I think so.

Before tackling the transfer case, let's look at a similar mechanism, i.e. the rear differential. On a regular differential, if both wheels have traction, the torque is divided evenly between the two wheels and both would turn together. However, once one wheel starts spinning freely, the other wheel would stop, i.e. there is complete "slippage" between the wheels. Hence comes the "limited-slip" differential. Since I have one on my van, I'm sure you do too. If you want to find out, just jack up the rear wheels and turn one of them. If the other turns in the opposite direction, then you have a regular differential. If the other wheel turns in the same direction, then you have a limited-slip differential. On these limited-slip differentials, there is a spring loaded clutch pack that would allow the differential to put some torque on the wheel that does have traction, just so you don't get stuck when one wheel gets stuck in mud.

Your transfer case works pretty much the same way. If both front and rear axles have traction, it divides the torque 1/3-2/3 between the two axles. However, once one axle starts spinning freely, the other axle will stop. Now, that's bad since you'll get stuck. To prevent that, on the transfer case, there are two speed sensors, one for the front output shaft and one for the rear output shaft. When this condition of slippage is indicated by the sensors, the clutch pack is engaged by the computer to eliminate the slippage, albeit for only 3.3 seconds at a time and only when the brake is off and the speed is below 5 mph. Then, for a brief 3.3 seconds, the two axles are forced to rotate at the same speed, regardless of traction.

Since you can see the rear wheels turn and the front wheel didn't turn, I suspect three things (provided that your control unit under the driver's seat is still plugged in):

1) Your clutch pack is shot, or it did not receive the required voltage from the control unit.

2) When you tested it on the snow, perhaps the brake was slightly depressed and the computer prevented the clutch from engagement.

3) As you described your test, maybe the rear wheel speeds up too fast and your speed (based on the rate of turning of the rear wheels) exceeds 5 mph. That would also prevent the clutch from being applied.

So, maybe you can run your test on the snow again, just stay off the brake, and go very easy on the gas.

By the way, you are near Driggs, off of the Teton River, right? One of the best fishing spots in Idaho. I really envy you

Good luck and Merry Christmas

 

Hi Canders_00

If you want a thorough check of your TC's electronics, here is what I suggest. Follow this step-by-step and if everything passes, your TC is most likely in good shape. I e-mail you a picture of the connector with the pin numbers on it. You should refer to this picture during the test.

Unplug harness from control module under the seat

Ignition on: voltage on pin 8 should be about 12V

Ignition off, battery disconnected, probe resistance between 7 and ground, and between 12 & ground. In both cases, should be less than 1 ohm. RECONNECT BATTERY.

Check that rear brake lights go on when brake is pressed. Ignition on, probe voltage on pin 6, should be about 0 when brake is off and about 12V when brake is pressed.

Ignition on, tranny in N, probe voltage between pin 5 and ground, should be less than 1V.

Leave tranny in N, turn ignition off, probe resistance between pin 5 and ground, should be close (less than 50 ohms)

Leave ignition off, put tranny in D, probe resistance between pin 5 and ground, should be open (greater than 100 ohms)

Plug the module back in, unplug both connectors to the speed sensors at the TC, turn ignition on and probe the voltage of the middle pin of the connectors. Should be at least 4V.

Remove both sensors from the TC and probe the resistances between pins. Between the two outermost pins should be about 1000 ohms. Between the center pin and the two outer pins should be 2200 and 3200 ohms. Put the sensors back in if they are OK. If not, post and I'll tell you where you can buy them cheap.

Turn ignition off, unplug connector from module, and probe resistance between pin 14 and gound. Should be open. Probe resistance between 13 and 14. This is the resistance of the coil on the TC clutch. Should be between 1.5 ohms and 4 ohms.

Finally, to verify that the clutck pack is engaged and working, unplug the connector from the module, ground pin 13 and jump a wire between 8 and 14 (to energize the coil since pin 8 would be at 12V). Then drive the car through a few tight turns. The car should drive very funny as the driveline "wind-up." The wheels might hop a little now and then. All that is because the two axles are forced to rotate at the same speed, but the tires may have slightly different diameters.

Good luck and let us know what happened.

 

Copper,

Thanks for the great description of the operation of the transfer case. I didn't know that the center diff only locked up at 5 mph or below. A couple weeks ago, I was turning onto a main street in the rain, and I was in a hurry. As I got on, I felt the rear end skid around, kind of whipped to the outside of the turn. At that time, I too started to wonder whether my center diff lock up was still working.

Also, if you want to do the test for the open vs limited slip differential, you will need to put the transmission into neutral. With the transmission in park, you will be trying to overcome the spring pressure against the clutch pack, which should give at around 40 lbs-ft torque. Then the other wheel will still turn in the opposite direction from the one you're turning, just like an open diff. This, however, is a good test of the condition of the clutch pack. If it turns too easily, it's time to replace the clutch pack.

 

A very quick test for clutch operation: 1) Firmly set the rear parking brake. 2) Jack ONE of the FRONT tires off the ground about one inch. (with a floor jack under the lower control arm.) 3) Start the engine and put the trans in drive. (Make sure to do this in an open area with nothing in front of the van.) 4) Let the engine idle and watch the wheel that has been rasied up. It should spin and stop approximatly every 4 seconds. If it spins constantly, the control and/or the clutch is not working.

FYI - The clutch can engage at any speed, but applying the brake will kick it out instantly (except below 5mph). It kicks out when the brakes are applied to avoid interfering with the antilock brake system (again, except below 5mph).

 

Well I am finally getting to this . . . So far I have found the sensor for the front drive shaft to be bad. The sensor for the rear drive shaft is good. I am going to test the clutch in a few minutes.

Thanks for all the help everyone.

Copper_90680, where can I get the sensors, please?

 

Just got done testing the clutch pack, by engizing it with 12V, and it works! So now right now I need to get that sensor replaced and then test.

 

Canders_00:

There is this outfit in Oakland, CA at www.transfercases.com. Get on their site to get the 800 number and call them up. They gave me a quote of $20 each and the shipping charge is about $10 UPS. I didn't buy from them since someone here offers me a good used one. Make sure you tell them it's the Dana 28 Transfer Case. The dealers here want $115 for a new one, which is rather ridiculous, in my opinion.

Good luck