1996 GMC Jimmy 4 wheel drive not fully engaging?

[Dan Altmann]

4 wheel drive indicator lights come on solid but 4 wheel drive not engaging. It feels like it tries to engage but as soon as excellerating, it disengages.

 

[Molson02536]

4 wheel drive indicator lights come on solid but 4 wheel drive not engaging. It feels like it tries to engage but as soon as excellerating, it disengages.

Cause could be a low vacuum to your front wheel actuator which is located under your battery is bad and will need to be replaced. The vacuum line could have a crack on it or the actuator it self is damaged.

Remove the left front head light and you can access the actuator vacuum line and inspect the actuator's diaphragm for any signs of tear. Have someone sit in the truck and engage the 4x4 while you watch. If it doesn't move that could be your problem. If it pulls the cable a bit then its fine.That is the simple part, the hard part is to replace the actuator.

If it doesn't move check the black rubber part of it for rips or tears. If there are none then crank the engine, pull off the vacuum line to it, engage the 4x4 and see if the vacuum line has vacuum. If not follow the lines back and try to find any loose fittings, cuts, nicks, or other problems that would cause it to loose vacuum. If you're getting vacuum to the actuator, check the shifting cable to the front pumpkin.

Your going to have to remove the battery and battery tray which is bolted to the inner front fender to access the actuator to remove it. It will take you just under an hour to do the whole job with common tools, and also replace the vacuum switch on top of the transfer-case if you find transmission oil in the vacuum line or in the actuator.

This is what your looking for to replace which is located under the battery tray. http://i20.photobucket.com/albums/b240/Muslhed/Posi-Lok Install Pics/1FactoryVacuumActuator.jpg

#1 is that you need to inspect and replace if damaged, I replaced ,mine once already and picked one up at the Salvage Yard and one from a 2005 Jimmy, Sonoma or Blazer are all the same part for $15.00 there. http://www.compnine.com/index.php?u...delid=6872&capuid=1&majorgroup=06&grouptype=B Good luck and hope it's just a loose vacuum line at the actuator.

 

[DrPablo]

I have the same problem,
I was today working on my car. I removed my grill, the passenger front light and the battery to see the actuator. I plugged the battery again on, so that I can see if the actuator is working.
Luckily it is moving. As I was under the car, I heared a electric motor moving at the transfer case. I found a broken hose, I could hear the vacuum out of this hose.
I followed this hose and it goes into the transfer case. But I don´t find the other end. The broken hose is located at the dip stick from my transmission. Where does it go?
How can I easily get to the hose without taking the engine and transmission out?
Thanks a lot

 

[Molson02536]

I have the same problem,
I was today working on my car. I removed my grill, the passenger front light and the battery to see the actuator. I plugged the battery again on, so that I can see if the actuator is working.
Luckily it is moving. As I was under the car, I heared a electric motor moving at the transfer case. I found a broken hose, I could hear the vacuum out of this hose.
I followed this hose and it goes into the transfer case. But I don´t find the other end. The broken hose is located at the dip stick from my transmission. Where does it go?
How can I easily get to the hose without taking the engine and transmission out?
Thanks a lot

That's the breather hose for the 4wd switch to relieve the vacuum that activates the actuator. Sounds like your 4wd vacuum switch at the transfer case may have gone bad and the actuator under the battery is not fully engaging the front axle .

Simple fix, just a PITA to replace the switch with a open end wrench. http://img824.imageshack.us/img824/4756/55199243.jpg

 

[rolltide5891]

I have a 96 GMC Jimmy and i'm having the same exact problem almost. The only difference is when i hit the button for 4wd the light will come on and i can feel the difference in power but it doesnt lock in. I tried 4 lo and the same thing i had the power of 4 lo but the front didnt lock in. What should i look into?

 

[Molson02536]

I have a 96 GMC Jimmy and i'm having the same exact problem almost. The only difference is when i hit the button for 4wd the light will come on and i can feel the difference in power but it doesnt lock in. I tried 4 lo and the same thing i had the power of 4 lo but the front didnt lock in. What should i look into?

Read post #2 and keep us posted. Good luck and be safe.

 

[DrPablo]

I could find the broken hose and connected it again. I changed some hoses in the engine room, these one which goes from these little black tank on the hood and it goes in the engine.
I saw my vacuum switch on the transfer case, but there is no way I can grab it and replace it. Is there a way to get to this switch?

My 4wd still isn't working. I was on a snowy spot and I tried to switch it to 4hi, the Light came on, but only my rear tires were spinning. Then I pushed 4Lo and both lights were on, 4Hi and 4Lo. During the switching I heard the noise from under the car that it was doing something.

Should I replace the vacuum switch on top of the transfer case?
Should I replace the actuator under the battery?It was moving when I press the 4wd buttons,but only a bit. What are these electronic vacuum switch on top of the engine? How can I check if they are working?

By the way the Clinton Manual is very bad, there is nothing about the vacuum system.

 

[Molson02536]

I could find the broken hose and connected it again. I changed some hoses in the engine room, these one which goes from these little black tank on the hood and it goes in the engine.
I saw my vacuum switch on the transfer case, but there is no way I can grab it and replace it. Is there a way to get to this switch?

My 4wd still isn't working. I was on a snowy spot and I tried to switch it to 4hi, the Light came on, but only my rear tires were spinning. Then I pushed 4Lo and both lights were on, 4Hi and 4Lo. During the switching I heard the noise from under the car that it was doing something.

Should I replace the vacuum switch on top of the transfer case?
Should I replace the actuator under the battery?It was moving when I press the 4wd buttons,but only a bit. What are these electronic vacuum switch on top of the engine? How can I check if they are working?

By the way the Clinton Manual is very bad, there is nothing about the vacuum system.

Pull the vacuum line from the front actuator and check the amount of vacuum it has. If it's weak, then you have a vacuum leak some where. If the vacuum is strong, then inspect the actuator for any rip in the diaphragm or any signs of vacuum leak at the actuator.

If you have a 1999 Jimmy, you cold have a ported vacuum switch (NOTE: this switch is only on 1999 and up vehicles). The drivers side, front axle is always engaged with the front diff -- the passengers side, front axle is controlled by the vacuum switch, actuator and cable. The vacuum switch is a common component to fail.

There are two problems trying to get your vehicle into 4wd with a failed vacuum switch;

1) you can pull on the cable to engage the passengers side hub -- but it will disengage when you release it as vacuum normally holds the diaphragm closed, which holds the cable, which keeps the hub engaged.

2) the vacuum switch also communicates with the TCCM -- no vacuum and your lights will probably flash continually while trying to engage 4wd, but won't engage until all 4wd components, once again, communicate with each other.

You can test the vacuum switch (of course, once you get to it) by removing the two hoses from the switch and connecting them together -- if the cable moves to engage the passengers side hub, the vacuum switch is bad. If you really don't want to replace the switch, you can get a female/female hose adapter and join those hoses together (front hub will ALWAYS lock after doing this).

Unfortunately, getting to the vacuum switch can be a problem, as you will find. I don't want to say "yeah, start ripping stuff apart" as I cannot really answer that question -- only you will know if you have the capability to disassemble things and be able to put them back together. If you feel you can remove a distributor cap, etc. and put them back after, go for it! You'll save yourself a ton of $$$ doing it yourself.

Oh, as a start, the vacuum comes off the drivers side manifold and goes to a reservoir (also on the drivers side), then to the vacuum switch (center firewall), then to the actuator (under the battery).

Well, I'm heading off to work, so I hope this helps -- if I think of anything else, I will post it here. If you have further questions, feel free!
Good luck and keep us posted.

Here's what you're looking for the vacuum switch, located on the firewall.
http://img.photobucket.com/albums/v97/Jigg1300/BlaZeR2/0919-114.jpg

 

[DrPablo]

I am working on the jimmy,I put the battery and actuator out.The actuator looks totaly fine,well I already bought a new one.
If I try to pull the cable by hand it won't move.Is this because my front axle isn't moving or can I do pull the cable also when car isn't moving?

 

[DrPablo]

Where is the indicator for the dashboard 4Hi light?
My light for 4Hi is on, it isn't flashing. I can switch between 2Hi and 4Hi. I saw one indicator directly where the cable from the vacuum actuatorr goes into the front axle/differential. Is this the right indicator?

 

[DrPablo]

hey guys,
I have good news.My 4wd is working again.
So I tried to pull the cable by hand and nothing was moving. I checked the vacuum and the actuator and it was working fine. Then I found out that my actuator cable was so bad corroded that it didn't move at all. I bought a new one at Napa, it cost only $25, I replaced it. I went to the steepest sand hill near my house and stopped. I have to say it is amazing, the Jimmy pulls every hill up. Now I have to get a better suspension.
Thanks for all your help,now I will have fun in the snow again

 

[fathead031984]

Front axle not engaging 1997 gmc jimmy HELP!!

Great thread by the way. i started following this and found no vacuum at the actuator to the front axle . So next the three lines coming off the tranfer case i have pulled offf. At this spot none of the three lines are recieving any suction on the hose end or transfer case end . i am not sure if i should replace this switch ? or should i coontinue to the switch by the firewall ? all of these hoses seem in decent shape where i can reacch them . any input and i will be extremely greatful

 

[DrPablo]

Did you checked if there is a loose vacuum hose in the engine room?
I replaced a hose at the intake system.It is going to the vacuum bowl on the hood.
You can buy the transfer case switch at Napa, it is around $45.

 

[fathead031984]

4X4 not working

Ok sorry i got the 4x4 to work i just bypassed the firewall switch and it works great. but now after tinkering with these vacuum lines my heat is intermittently working and engine is getting hot. as soonb as the engine stars cooling itself correctly the heaT works again and then the engine starts getting too warm and heat stops. Please help what the hell did i break ????? please any ideas would be great no heat + sub freezing temps = no fun thx

 

[DrPablo]

My 4wd quit working again. I parked my car in a sandy spot and when I started the engine again, it is only in 2wd again. Another car had to pull me out and I tried to put it in 4wd again. Now both lights 4Hi and 4Lo are flashing three times and then it is in 2Hi again. What is wrong now?
Is anyone interested in a well maintain GMC Jimmy?

 

[Molson02536]

My 4wd quit working again. I parked my car in a sandy spot and when I started the engine again, it is only in 2wd again. Another car had to pull me out and I tried to put it in 4wd again. Now both lights 4Hi and 4Lo are flashing three times and then it is in 2Hi again. What is wrong now?
Is anyone interested in a well maintain GMC Jimmy?

Don't give up now, recheck everything that was worked on and if you not to far, sure i'll be interested in a well maintained Jimmy

 

[DrPablo]

Hey,
my 4wd is again working.I unplugged the battery for about 5min and then it is engaging again. I went offroading a little bit to try out if it is working the whole time. I found out I can switch from 4hi to 4lo easily. But when I try to switch back to 4hi it won't engage again and it jumps in 2wd.
Is my TCCM bad? I have an extra one in the garage but how do I know if it don't have the same problem?
Where can I look for the problem, it don't want to disconnect the battery everytime.

 

[barks507]

I think you have to be stopped and in Neutral to switch back. Not positive though.

 

[DrPablo]

I have to try it out,right now I am in 4hi all time. When the weather is better again I will try it out.thanks

 

[DrPablo]

i could switch back to 2hi,but i can't get it back into 4hi. both lights 4hi and 4lo are on and it turns back to 2hi. Why can I only switch from 2hi to 4hi but not back?