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Comments
Things are getting worse and worse! I have some questions but I’ll fill in details first.
1998 GMC Jimmy
3 button 2 Hi - 4 hi - 4 lo
NP01 Transfer case (233?)
Original problem, TCCM needs to be rebooted on a regular basis.
Done so far in this order:
1.Replaced actuator under battery – no change
2.Replaced TC sensor – no change
3.Replaced TCCM with a used one from ebay - no change
4.Replaced at same time –
a.TC fluid
b.Replaced Front Diff oil
c.Replaced TC encoder motor
d.Replaced vacuum lines to TC
Now no 4wd at all, 4 hi and 4 lo flash then back to 2-hi
I am stationed in the Persian Gulf and am unable to do the work myself, physical injury, but, I have a reasonably knowledgeable local mechanic that does what I tell him, that is I supervise!
Questions
1.Is this indeed a 233 TC?
2.I have seen the phrase "firewall solenoid" in the newsgroup, is this the actuator under the battery or is it a different part?
3.When my guy ran the new vacuum lines from the TC sensor, he told me one was a breather. Is this so? If not where do all three 3 hoses go? What did he miss?
4.I have seen repeated comments regarding the encoder motor, 4 hi and 4 low. Before installing the new motor we connected it to the plug and pushed the 4-hi button and it did move. So last and for all, does the TC encoder motor do anything when shifting from 2wd to 4 hi?
HELP
New parts installed:
Vacuum actuator
TC Vacuum switch
TC encoder motor
vacuum hoses from TC vacuum switch
Front Differential oil
TC fluid (Red dexron II)
Checked vacuum at actuator under battery, none!
Hooked up direct vacuum to actuator and it does pull the cable!
So this means no vacuum from 3 port switch on TC to actuator! Further research on vacuum:
I have identified the hoses on the switch on the TC:
1 constant vacuum from intake set up
2 to vacuum actuator under battery
3 is release vent for sifting back to 2wd.
To me, this means that when the ball is pushed or released by something in the TC to either release or send vacuum to the actuator to engage/disengage the front axle. What pushes the Ball? When? I presume something in the TC moves, probably moved by the encoder motor? I hear the TC encoder motor running when pushing the 4-Hi switch.
Is it possible that the hoses were connected incorrectly to the TC vacuum switch? I know it is keyed, so this shouldn't be possible but hose 1 (constant vacuum) and 2 (vent) are the same size and could theoretically be switched and would explain why there is no vacuum to the actuator under the battery. For the sake of argument, which hose should be where, clockwise from the "key" on the switch?
Also, is it possible to install the TC encoder motor in the wrong position, i.e. the motor thinks it's in 4wd but the truck is in 2wd? I hear it run when I push the 4-hi and 4-lo switches, so it's doing something!
Last but not least, I am out here on the fringe of the world so getting parts is a battle! The last one I can think of is the switch on the front axle/diff; anyone have the part number?
Again HELP!!!!!!!!!!!!!!!
thank you
Rod
Any clue to what might me causing this? I would like to get a direction before I start tearing into this thing. And with 6-10 inches of snow in the forecast for tomorrow, I really should go to town on it tonight! Also, is there an easy way to change the transfer case fluid? Thanks!
I took the glove box out and the sound seems to be coming out from behind the back of the wheel well I dont want to disconect any electronics untill I have a better idea what im looking for any idea what im hering ?
When the auto 4wd drive button is pressed, the light stays on, but the front wheels won't turn as needed. ( I tested this in my ice covered driveway) Last week the service 4wd light was on often until I disconnected the battery for .5 hours. Now the 4wd seems ok, but not the auto 4wd.
I've read several posts that mentioned vacuum lines and actuators,but they seemed to be related to the 4wd not working at all, not the auto 4wd .....sooooo. I still don't know what to look for
Please help, Thanks
Yes,4hi does work....I don't use 4lo though. I know this, I was at a traffic light the other day on snow in auto 4wd. When I tried to move, the back wheels were spinning, but the front never engaged so I pressed 4hi. And again it happened in the driveway.
I am afraid to push the dash board 4 buttons :confuse:
prior to working on the hubs - I fixed the vacuum leak at firewall, the buttons would work to engage most times i tried. a few times I had a hard time swithing between the buttons they would engage/disingage but now I replaced hubs and I am so happy the wheels are quiet and the brakes work I am afraid to try the buttons it is now in 2 wheel and cant aford to fix any computer problems at this time
I feel so good about eveerything its like a new truck quiet and tight
should i disconnect battery or pull fuses or cross my fingers and push the buttons???????????
so far we changed both front hubs and inspected front brake pads [lots left] and we changed the rear pads and trued the rotor Thank for your or anyones help I have inspection due april! :confuse:
I tried diconecting bat
4wd check the vac lines under hood first and if 99up with autotrac (as you said auto) then put the case in neutral by pushing the 2 buttons at the same time (marked on 4 button panel), then select 2Hi and it sould work. Then search all the posts on 4wd fixes already posted.
The reason I ask is, I installed it once and when I test drove it, I thought I had something wrong internally. The car dragged in forward and wouldn't back up at all. I now suspect that it was the transfer case. Originally it all worked fine, just reverse was worn out. When I reinstalled the rear drive shaft, the TCase output shaft wouldn't turn, like last time. The transmission itself seems okay.
Thanks
Brad
[email protected]
Things I have tried
disconnected battery for 30 minutes
repaired one disconted vacuum line near the intake manifold
replaced both front wheel bearings/hubs
I have read most posts about this and dont know what to do next
on the front axle to lock it in nothing happens.I tried
to manually put it in but it still doesn't work.Was wondering what couldbe wrong inside the front differential
But amm wondering i had some help from a friends we lifted all 4 wheel up using 1 jack in the front and 2 jacks in the back
got all 4 wheels of the ground i wanted to just see if the 4 wheel drive works still and i dont understand how come the front wheels dont spin is it something that is just because it has to be on the ground will the Front wheels not spin or engage if the jimmy is not on the ground or is something still wrong check the vacuum lines everything seems to be fine cant think of what the problem could be please help thank you
Thanks!
I think its safer, if you pull over, put it in neutral, and change over to 2WD or 4WD.
Mine jimmy's at about 150miles, 250kms, and my truck shifts from 2wd to 4wd to 4wd low perfect, I just keep replacing the trasfercase fluid every summer...its easy and so cheap to do.
When you engage 4WD High, while rolling in 2WD Drive, it has a brief delay and you can "Feel" and hear it engage, but when you go back to 2WD, while rolling in 4WD Drive, it seems to wind out like it's in a Low Gear and seem to hear/feel mechanical "Grinding" then almost a loud bang and it goes back into 2WD and drives normally.
I would almost think whatever engages or disengages the different modes is not doing so completely.
Any ideas?
Thanks everyone
Any suggestions would be greatly appreciated! Thanks in advance.