Transfer case help

[Kevin Martin]

I have a 95 3.0 auto trans (rebuilt) 4x4. I have bypassed the ADD system and installed manual hubs. The issue I have even before the trans rebuild and the ADD bypass is once in a while when i put it in drive or reverse the trans locks in the transfer case and puts in 4 wheel drive low gear?? Is there a sensor that "turns on" the transfer case?? Im at a loss here Ive done everything I can think of.. PLEASE HELP

 

[KidVermicious]

Um, don't think that tcase has an electronic actuator, I'm pretty sure there's a manual shift linkage on the tcase selector. There's no way for the tcase to know you just shifted to D or R and decide to spontaneously pop into low range, so let's back up...

1) Do you know it's going into low range for sure? Are your RPMs a little over double what they should be while you're rolling in D?

2) And are you definitely in 4WD? With the tcase selector in 2hi? Next time it does it, sit there with your foot on the brakes and have somebody try and spin the front DS with their hands (make sure the hubs are unlocked first).

 

[Kevin Martin]

Thanks Ill try that and get back to you

 

[Kevin Martin]

Um, don't think that tcase has an electronic actuator, I'm pretty sure there's a manual shift linkage on the tcase selector. There's no way for the tcase to know you just shifted to D or R and decide to spontaneously pop into low range, so let's back up...

1) Do you know it's going into low range for sure? Are your RPMs a little over double what they should be while you're rolling in D?

2) And are you definitely in 4WD? With the tcase selector in 2hi? Next time it does it, sit there with your foot on the brakes and have somebody try and spin the front DS with their hands (make sure the hubs are unlocked first).

Okay it finally messed up again and the front drive shaft will not rotate, I made sure the hubs were unlocked (jacked it up and the wheels spun) and the shifter is in 2H. when it does this the runner will only run about 40 mph at a high rpm and you can hear the front end whine

 

[KidVermicious]

Okay it finally messed up again and the front drive shaft will not rotate, I made sure the hubs were unlocked (jacked it up and the wheels spun) and the shifter is in 2H. when it does this the runner will only run about 40 mph at a high rpm and you can hear the front end whine

Well heck. It's definitely going into low range then, and it sounds like 4wd too. That's really odd.

I wonder if the transmission shift linkage is somehow fouled with the tcase shift linkage. Or if maybe the tcase shift rails are disconnected and just flopping around in there. Are you handy enough to take your center console apart and have a look at the shifters?

 

[Kevin Martin]

yes Im pertty good with stuff. Ive never owned a 4X4 so Im a little lost but I can build chevy engines all day long lol. The prob I have is I dont know much about Transmissions so just tell me what to look for if you can and i should be able to do something....

 

[fourwd1]

You should have an A340H trans which has an integral t-case.
It's controlled both electronically and hydraulically.
There's a brake and 2 clutches inside that control 2wd/4wd and Hi/Lo range.
Signals from shift selector, park/neutral sw, T-case postition sensor, TPS, and VSS feed the ECM. So yes it can be an electrical problem.
The trans ECM has a diagnostic procedure similar to the CEL, counting flashes of the O/D light. If you google you can find it, it might help you narrow it down.

 

[Kevin Martin]

if its throwing a trans code would the O/D light come on like the check engine light? Reason I ask is it has never come on when having the issue or any other time unless I turn off the O/D. The check engine light is on and its a Knock sensor which Im fixing to tackle with a new harness and sensor.

 

[fourwd1]

IIRC it would flash to let you know of a problem.
I'll try to check the manual when I get home.

 

[Kevin Martin]

I found a Trans diagnosis form and did the throttle postion sensor test by hooking the volt meter to E1 and TT. it said with the switch on it should read diffrent volt levels as the gas pedal is pressed. well I got 0 volts all the way to the floor. now I'm no master tech but this sheet said it could be the ECU??
what you think by the way I hate electronic controled stuff lol

 

[Kevin Martin]

I'm still fighting the trans case engaging on its own after an hour of driving. I've replaced the TPS, ECS and added a trans cooler with a build in fan... The only things this solved is the trans doesn't overheat anymore. Something is telling or making the transfer case after I drive for a while and put in park and then into drive. I'm about to give up

 

[penbergm]

I think the solenoid in the transfer case tells it to go to 4lo. maybe it is getting energized somehow.
I ran across your post cause I'm in process of doing a a340h swap and my donor tranny has 2 solenoids in the transfer case. I can't find anything that tells me what its for.