4HI doesnt engage

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tylers88

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Hey guys, my 88 doesn't engage the front axle in 4HI. Accuator has been replaced and if I hook it up to the battery directly it does engage the axle. Case itself does go into gear also. I wondered if the the "switch" in the top of the case would be my problem or if I have bigger issues somewhere. I would like to have this truck running and driving good for next winter so we have 2 4wd trucks when snow flies next year, funny thing a V8 FWD car does horrible in the snow :roflsquared:. I would prefer to not get the posi lock cable system because I would like to keep a clean look to the interior when its done.

Also when I rebuilt the trans I was pulling the tcase and forgot the shift linkage hooked up, :banghead: this was some where between 2 and 3 am when I did the trans, and I think I bent where the linkage hooks up to the case itself. I does still lock into each gear but I tried to adjust the linkage because the shifter would hit the stop before it would lock into 4 HI when pulling it back and I broke it so I need to pick one up from a junk yard. I wondered if this could effect anything if it still goes into gear, I would assume not but this truck seems to have an aditude. It would not engage the front axle before this happened
 

volunteerff21

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I know this is a month late but I figure I'll still try and help you out. When mine wouldn't engage it was a bad dash switch. A friend of mine had the same problem and again it was a bad dash switch. There's a chance there's a broken wire somewhere in your harness as well. You need to find out if the switch is sending power to the wires when you push the 4 HI button. If the switch is sending power but it's not reaching the actuator you have a broken wire. If no power is leaving the switch at all I'd suspect a bad switch. As far as you linkage goes, It is my understanding that as long as it goes into gear 4wd should work.
 

great white

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If it's an 88, there is no dash switch.

The transfer case is manual, it's in gear or not.

The front axle actuator is triggered by a switch to engage. I believe that's what he is referring to.

You are quite correct though, the dash switch on the electric transfer cases are very often the culprit. Cold solder joints are usually the problem.

Cold solder joints have been a problem with GM's since the late 80's/early 90's.

That's what you get with "hencho en mexico".

I had the same issue. I opened up the switch, retouched the solder joints at the connector, put it back together and its been working fine ever since. That was about 2 years ago....

To the OP: put it in 4Hi and meter the Pins at the TLA for 12v. No power = bad switch.
 

Kyle97GMC

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Mine does the same thing. 4hi doesn even blink but 4lo works flawlessly. I have switched my dash switch with three other ones from junkyards and its the same thing. I also just replaced my actuator. Any other ideas of what it could be?
 

great white

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Mine does the same thing. 4hi doesn even blink but 4lo works flawlessly. I have switched my dash switch with three other ones from junkyards and its the same thing. I also just replaced my actuator. Any other ideas of what it could be?

Only things left are the rotary encoder, the actuator, module or maybe a wiring/connector issue.

Prepare to open thy wallet...







I'd still bet on the dash switch though. With cold solder joints on the board, simply pulling the connector on and off is enough to break the connection at the board.

Hmm, I've got an extra in the glove box, maybe I should do a "how to".

Although it's a pretty simple simon task to start with....
 

Kyle97GMC

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Only things left are the rotary encoder, the actuator, module or maybe a wiring/connector issue.

Prepare to open thy wallet...







I'd still bet on the dash switch though. With cold solder joints on the board, simply pulling the connector on and off is enough to break the connection at the board.

Hmm, I've got an extra in the glove box, maybe I should do a "how to".

Although it's a pretty simple simon task to start with....

Where is the encoder located? How do you check that? A write up would be awesome! If you just explain it im sure I could do it, What would I hve to solder? I already pulled it apart haha
 
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great white

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Where is the encoder located? How do you check that? A write up would be awesome! If you just explain it im sure I could do it, What would I hve to solder? I already pulled it apart haha

Rotary encoder is on the transfer case and it's part of the motor assembly that shifts the box.

The cold joints are where the pins are attached to the pcb. It has to do with improper soldering techniques.

In these cases, it caused by essentially unskilled workers.

Proper technique is to heat the pad and pin with a solder bridge and then apply solder from the opposite side allowing the heat to draw the solder into the joint.

Poor fluxing technique or disturbing the joint before it has cooled are also causes.

Dirty components are another cause, usually a thin film of corrosion that prevent proper solder bonding. This happens if components sit around too long before assembly without proper storage precautions ie: sealed containers with dessicant, etc

Too much or too little heat is another cause.

Soldering sounds like a very simple task, but its not as easy as one may think...
 

Kyle97GMC

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Do you have any pics of where exactly you soldered? I wouldnt do it my dads friend knows how to do it nice
 

volunteerff21

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OOps my bad for missing the 88 part :banghead:. But I'm also interested in seeing how you re-solder the board. Like you said it's a common problem with these trucks so I'm sure I'll come across it again. And if I can save myself $70 bucks each time that'd be fantastic!!!
 
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