4EAT, AWD does not work, then 'bangs in' at 3000 rpm

[CNY_Dave]

96,000 mile used trans, from a 2004 LL Bean H6.

Got it bolted in, trans is filled to the mark on the stick, on the jackstands the rear wheels do spin in all gears.

Took it for a test run, by chance it was snowing.

1, 2, 3, D, the rear wheels do not drive until I get the revs up to about 3000 with the fronts spinning, then the AWD kicks in, and there is a bit of a groaning while it operates. Revs drop below 2500 or so and then it's just the fronts again.

This wouldn't seem to be a grooved clutch basket, or any other post-torque-bind symptom, based on what I have read for the past few years.

Any thoughts?

Is the duty-c external? In the pan? in the rear case?

[ntippet]

Could be:
-weak transfer solenoid that won't engage properly until it receives a DC above 40-50%.
-MPC material has worn down too much or is gone all together, requiring too much movement to engage or metal on metal plates
-sticking transfer clutch valve

The only way to find out for sure whats happening is to dig into it and have a look.
Good news is you can do it with the transmission still in the vehicle.
http://opposedforces.com/parts/legac...llustration_1/
Pull the extension housing off the back & the transfer solenoid should be right in front of the assembly you pull out.
http://opposedforces.com/parts/legac...llustration_3/

[plain OM]

My first thought was line pressure, but if it otherwise seems to run and shift properly (albeit with the front wheels only) in normal driving, low line pressure isn't likely.

Some measurements might help isolate the issue, if you are able to do them; here I'm thinking: duty cycle signal to the AWD solenoid and AWD clutch hydraulic pressure. The first would confirm whether or not the TCM AWD electronic control system is working, and the pressure test would indicate if the AWD solenoid and transfer valve are responding to the TCM commands.

There's always the possibility that the AWD clutch plates are worn out.

But, double check that the rear drive train (drive shaft, rear differential, rear axles) is intact and properly engaged. For example, a rear axle that isn't fully inserted into the differential could give those symptoms.

The duty C (AWD solenoid) on that tranny should be in the rear extension case.

[CNY_Dave]

Everything other than the trans guts is exactly as before the trans swap, and my 200,000 mile transfer clutch worked perfectly.

[plain OM]

Originally Posted by CNY_Dave

Everything other than the trans guts is exactly as before the trans swap, and my 200,000 mile transfer clutch worked perfectly.

Not sure I understand what parts of the AWD system are from your original transmission and which came with and were retained with the "new" one. Did you move just the clutch from the "old" to the "new" or the complete extension section?

If you're using the "new" transmission's extension case, then the solenoid/transfer valve and transfer pipe that are mounted in the extension housing could be malfunctioning.

In addition to ntippet's links, see 4eat tail section rebuild without removing transmission. There's good photos of the clutch, as well as the solenoid and transfer pipe area.

[CNY_Dave]

Complete transmission swap, is what I meant.

[ntippet]

Yeah I didn't quite understand what you were saying either CNY, thought you had swapped over a completely "new" tranny.

[CNY_Dave]

The road test was at 1:30 AM at the end of a full day of wrenching, then I was up a little before 8 to get ready for work, it's a wonder I'm coherent at all.

[ntippet]

If you have FreeSSM running, there is something else you can try real quick.

[CNY_Dave]

Don't even know what that is... I'm going to see if it has trans codes on my way home tonight.