How 4405 t-case actually works?

[Eki]

As gijoecam (-Joe) wrote at 09-15-2005:
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Wheels and Hubs, Explorer
The Dana 35 IFS axle used on the Explorer utilizes a disconnect mounted on the axle housing. The disconnect consists of a shift motor which operates a shift fork and locking collar, an indicator switch which operates the 4WD light on the instrument panel, a vacuum switch and a vacuum harness.

When the 4WD mode is selected, a signal is sent to the generic electronic module (GEM) which energizes an electronic valve located in the right front cowl that draws a vacuum on the disconnect shift motor.

The 4WD locking collar on the transfer case engages the front driveshaft. During this time there will be a 3- to 4-second delay while the inner shaft comes up to speed. The vacuum that is drawn on the disconnect motor moves the shift fork located inside the disconnect housing against a locking collar and slides it between the inner shaft and the constant shaft which locks them together and puts the vehicle into 4WD.

To disengage the transfer case, select the 2WD switch position. This will unlock the transfer case and reverse the direction that the shift motor moves the fork which slides the locking collar from between the inner and constant shafts and disengages them.

The four-wheel drive has two modes: low and auto. Low mode is used to increase torque for extra pulling power. The auto mode senses a slip condition and automatically engages 4WD similar to the Aerostar by distributing torque between the axles.
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Still I'm stupid enough not to understand how 4wd low should work. And yes I have a problem.
I have '96 4.0 XLT, 5R55E, t-case is 4405 (I guess)

When I take battery cable off to reset the system. Always after reset when I first time switch to 4WD Auto while moving (on the fly) it will not engage, both lights start flashing after a while. If I switch to 4WD Auto when I'm not moving (once is enough) then she will engage always on the fly.

- while ignition is on (engine is not running) when I switch on 4WD Auto I can hear vacuum hiss and 4WD light on the instrument panel goes on.
- When the gear is in Neutral and I switch 4WD Low, I can hear it actually shift. 4WD Low light goes on.

All seems to work OK, but according to road test it's not working. Proper testing (other than low range=low speed) is difficult since we don't have snow in Finland (yet). Sooner or later it will snow, it allways does, believe me Yes I could go an try on mud field, but I hate the idea leaving my Ex there

So far what I thought about 4WD Low:
- Transfer case should share 50/50 torque to rear and front, no diff?
- driving on 4WD low she would rather go straight than doing 360 circles?

Could it be:
Low mode is used to increase torque for extra pulling power. Low mode also senses a slip condition and automatically engages 4WD?

Is there any easy way to test 4WD?

20 years ago I had '72 Range Rover. Comparing my EX to Range I think everything isn't right.

best regards
-Eki

 

[Mbrooks420]

Welcome to the site. There is an Electromagnetic ramp clutch in the t case. In 4auto it works like an AWD setup. There is always a small amount of power going to the front axle(not in 2wd)and uses speed sensors to detect slippage between the front and the rear. When there is slip it sends pulses of power to the clutch in the t case, and sends more power to the front axle. In low it locks up the clutch and you get a 50/50 power distribution to both axles. There are no lockers in low. In low there is a 2.5:1 ratio I believe. Low should only be used when the wheels can get a little slippage so there insn't driveline bindup. Sharp turns in low will bind it up.

 

[Mbrooks420]

Oh, and in 1995 the trannies were 4r55e's, and switching to low range should be audible. I don't know why the 4wd lights would flash, after resetting the computer.

 

[Eki]

Hi and thanks for your answer. Yes I know that '95 and '96 trannies are 4r55e's. My Ex is late '96 from germany and it has 5 speed auto which is 5R55E and tranny is 4405!
I have done some sharp turns in low it turns smoothly, cannot feel anything pulling back the steering wheel. Although I haven't done it on asphalt, only on "solid sand surface"

-eki

 

[gijoecam]

Eegads!! Never thought my own quotes would be resurrected like that LOL!

mbrooks is right about the ball-ramp clutch.... basically it works like the air conditioner clutch, although it's a very different design. Essentially, when the GEM calls to engage the transfer case, the power is fed to the transfer case clutch coil and it locks the front and rear driveshafts together for a 50/50 split.

Now, that being said, the computer does not 'vary' the power to the clutch in auto mode, it varies the <i>duty cycle</i> of the clutch. That's not the same thing as varying the power. The reason people that do the brown wire mod see the light is that yes, there is a small amount of power flowing through the coil all the time, but that's the nature of a solid-state relay. The Torque On Demand relay sends power to the clutch all the time, HOWEVER, it's not enough current to engage the clutch coil. The nature of a solid state relay is that it cannot ever completely shut off the power flow through itself, hence the reason for the glow for those that have done the brown wire mod on the '97-ups. The clutch coil is either engaged or disengaged, not partially engaged.

(Essentially it's the same thing as a lighted doorbell switch on a house.... although the current flows through the switch all the time, it doesn't hold the doorbell plunger against the chime)

Now, the hiss you hear on your '96 is probably just the vacuum on the engage side of the front hubs. There are a pair of solenoids (controlled by the GEM of course) that engage the locking hubs. The solenoids, vacuum lines, and hubs themselves are prone to failure. I think (and this is only my opinion) that's part of the reason they did away with that system and went to a full-time front axle in '97. (but I digress)

Now when your lights start flashing, it's indicating a problem with the system. Unfortunately, without being able to connect it to a tester, there's no way to pull that code from the GEM to pin-point the problem. If it was mine, it'd be worth it to pay the $100 to have them connect it and pull the codes for me. Without them, it's a guessing game.

If you can find a loose gravel road or parking lot, you can test it there. Leave it in 2wd and the 2 rear wheels will leave skid marks under acceleration. Lock it into 4 auto or 4 low and all four should dig. If they don't, there's problems with the front axle engaging. That could be due to a bad component in the front axle (hubs, diff, etc), a bad engagement system (lines and solenoids), or a bad transfer case (clutch coil). Again, without the code, it's tough to tell.

Does that help shed any light on the matter?

As for the other noises you mentioned.... 4wd auto is just that: automatic engagement of the 4wd. It is ABSOLUTELY NOT the same thing as an AWD system. Automatic is 2WD until the rear wheels slip, then it engages the 4wd for a moment, then releases it, then checks to make sure the rear wheels are turning the same speed as the fronts, and if they start to slip again, it engages the front again. As it stands, you have no full-time 4wd where the transfer case stays locked, UNLESS you put it in low range. Low range locks the transfer case, providing power to the front and rear wheels until you click the switch back out.

That being said, there is a way around it should you want full-time 4 high. I like to call it the <b>anti-brown-wire mod</b>. If you want more info, I can certainly provide it, but the short version is that it forces the transfer case to stay locked instead of relying on the GEM to trigger and release the TOD relay. Essentially you'd flip the switch into 4 auto to lock the front hubs, then flip the *other* switch to lock the transfer case.

Hope that helps! (Sorry 'bout the length... I sometimes get diarrhea of the fingers )

-Joe

 

[Eki]

Thanks Joe, this indeed helps me a big time. I'm going to check those solenoids and all vacuum lines and connectors involved to them. And I ques; leaving tranny in Neutral and t-case selector in "4WD Auto" car should move if I rotate (with my bare hands) axle coming out from front of the t-case?

-eki

 

[gijoecam]

Thanks Joe, this indeed helps me a big time. I'm going to check those solenoids and all vacuum lines and connectors involved to them. And I ques; leaving tranny in Neutral and t-case selector in "4WD Auto" car should move if I rotate (with my bare hands) axle coming out from front of the t-case?

-eki

Hmmm.... that I'm not sure about.... I would think not necessarily though. Under normal operating conditions, the 4wd will engage when the rear driveshaft begins turning faster than the front driveshaft. I'm not sure how the system would interpret the front driveshaft turning faster than the rear.... I suspect it would simply think the vehicle was turning like it would in a parking lot (i.e. where the front wheels have to roll farther than the rear wheels) and would not lock the transfer case. However, I can honestly say that I have no clue what it would do. (I'll have to try it on mine at the next tire rotation and see what it does) I would think that IF you are in 4wd auto, idling in neutral (or park), with the front wheels off the ground, if you turn the front driveshaft by hand, the front wheels should both turn.

Now, if you lock it into 4 LOW, then yes, both driveshafts should turn in neutral.

Another way you could test it would be to jack the vehicle up and support all four corners off the ground.
Then put it in drive. (The back two wheels should drive and the front driveshaft should be stationary or turn very slowly. )
Step on the brakes and stop the wheels.
Engage 4 auto. Give the vacuum solenoids a second or two to engage the hubs locks.
Release the brakes. If the system is working properly, all four wheels should start to spin. If they do, everything sounds fine.

If all four don't spin, take a look at the front driveshaft. Is it turning? If the driveshaft is turning, but the wheels are not, the Center Axle Disconnect may be failing to lock, or there maybe an internal problem with the front diff.

Oh, and for the record, when I was mentioning hubs above, I was mistaken. I should have been referring to the Center Axle Disconnect (I was getting the Ranger and the Explorer confused).... The hubs on the wheel ends are full-time, but there is a center axle disconnect that essentially breaks the passenger side axle shaft between the differential and the CV shaft. It is a vacuum-actuated motor with a yoke and sliding collar that either brakes or unifies the axle shaft (depending on 2wd/4wd mode selected).

-Joe

 

[Eki]

Hi Joe and thanks. I have tested my ex few times. Uphill on loose sand and I'm happy to say that front wheels start digging. Couple days ago we had some snow and again front wheels start digging when rear is slipping. Conclusion: I think all odd behavior was caused by lack of use. In future I will use all wheels more frequently.
-eki