Question about 1990 GMC S-15 Jimmy

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Vacuum hoses for transfer case

Need hose connections diagram for 1990 GMC S-15 pickup 4 wheel drive. From transfer case to engine. New vacuum hose line connection was installed but no one knows where all the hoses go.

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Posted on Jan 02, 2017

  • 186 Answers

SOURCE: not sure where 4WD vacuum hoses hook up at

Isn't that an electronic motor on the case? If so then it's just a vent for the T-case. If not then it would go to a round ball canister on the fender.

Posted on Aug 02, 2009

  • 507 Answers

SOURCE: 1990 GMC Sierra 4x4 1500

the connections near the front axle that activate the motor to engage the system aren't melted? That's a comon problem for that body style. If there good, sounds like it could be that motor itself. To figure out if it's you motor or transfercase, jack up the rear end, have a friend inside shift into 4 wheel drive, or try to, and put it in gear and apply some gas. If the front driveshaft is turning then it's something with the front end. If not, farther back in the system.

Posted on Sep 22, 2008

  • 6 Answers

SOURCE: Front drive, 4 Wheel drive won't engage

Check the switch on the transfercase remove the vacume lines if there is oil in them the switch has to be replaced and the lines should be cleaned out you should also check under the battery tray to make sure the boot is not ripped that controls the leaver to engage the front axel

Posted on Feb 16, 2009

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SOURCE: i need a 1987 chevy S10 vacuum hose routing diagram

Go to, become member, will give you repair manual,location of parts,diagrams.

Posted on Apr 09, 2009

  • 383 Answers

SOURCE: oil seal leaking on 1999 gmc half ton 4w/d on front of transfere case do i need special tools or can I drop drive line and replace seal

billbohman: Unless GMC has had some change I am not aware of and that has not been published in service manuals for the repair of these units, the procedures are the same as any seal replacement and require no special tool. There are some universal seal installation tools which I would venture the majority of techs don't have because they substitute other tools in their place most of the time. Most techs will have a special tool designed from removing seals. However, the seal can be removed without it.
Just use a little common sense when removing a seal. Don't damage the casing.
Good Luck.

Posted on May 10, 2009

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I have a 96 gmc jimmy i have changed the actuator,actuator cable,all the vac lines,vac switch and switch on differential and still the front tires dont engage,the transfer case is locking in and so is the...

on your Jimmy you need to put it in 4 hi and up under the battery tray is the actuator for the front dif. make sure the vac hose going up to it has vacuum. if it doesn't then start tracking the hoses going down to the transfer case. one goes to the actuator, one to the vents on the transfer case and transmission and one goes back up to the vacuum canister, it's located on the hood on the drivers side. if the canister isn't getting vacuum then nothing is going to work. i just had to repair the hoses in the truck i put the trans in. the 4 wheel drive now works in it. i would have never know this, the hoses drop over by the exhaust and get hot and burnt and start cracking and breaking up and leaking. this can also cause some minor running problems. also. one last note. where the hoses attach on the transfer case. that connector has to go on correctly. it has a pin hole in it to line up on. if you put in on wrong things won't work.

Apr 22, 2012 | 1996 GMC Jimmy

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Need vacuum hose diagram for a 1997 gmc jimmy, have hose that appears to be coming from the transmission/transfer case area. It is hanging out right next to the brake fluid reservoir. I don't think it

Hmmm, go down and look at that transfer case: that same hose should connect somewhere there (that's what activates the 2WD shift out): either that, or it should go through the solenoid, and then to the transfer case. The best place to find such a diagram would be a Chilton or Haye's manual, either are invaluable to vehicle service.

Dec 03, 2011 | 1997 GMC Jimmy

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1995 gmc jimmy...won't go into 4 wheel easily...took me about 45 minutes today to get it to engage, going back and forth and it seemed to engage and then "pop" out. finally engaged and stayed...

There are vacuum lines at the rear of the engine that t-off into different directions. These can become deteriorated with age and get mushy and collapse. The main culprit is underneath the battery tray. You'll have to remove the battery and the tray to get t it. The hose is connected to a vacuum actuator that controls the front axle engagement. It is always coming loose because of the sharp bend in the hose where it hooks up to the actuator. There is also a hose that runs down to the transfer case. While you're under there checking those vacuum hoses, go ahead and check the electrical connections at he front axle and the transfer case.

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Were is the vac switch on the transfer case for the 4 wheel drive

Hi, the vacuum switch is located in the top of the transfer case, in the area where the front drve shaft goes out. There is a 3 vacuum hose connector that attaches to it. Good luck...Coop

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The vent hose on my 1990 k1500 is disconnected from the engine side, and i cannot figure out where is came from. I can follow the hose from the transfer case all the way to the engine bay. I haven't been...


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4 wheel drive will not engage

A frequent problem with these trucks is the vacuum switch on the transfer case.It is a three port switch screwed in above where the shift lever comes out of the t/case.The switch just screws in,7/8 wrench if I remember correctly.When you remove the vacuum hose connector from the switch,you should hear a vacuum noise for a few seconds.If you don't check for a defective vacuum check valve near the firewall behind the engine,or a cracked vacuum resevoir.One other area to inspect is below the battery. Sometimes battery acid will leak onto the vacuum hose that goes to the actuator causing a leak in the hose,which will disable the four wheel drive.To check for a broken actuator cable,jack a front wheel,put your t/case in 4wd, move the diaphragm manually you should feel the axle lock in...the front tire should not turn by hand

Apr 09, 2010 | 1986 GMC Jimmy

1 Answer

1998 gmc sonoma 4 wheel drive not working. Front axles clink when button pushed. Transfer drive shaft not turning when jacked up . Don't see any vacume leaks on switch and vacume lines not filled with...

Watch what clinks?
You should see the vacuum servo move the linkage. The servo could have a leak. You can connect your own hose to the servo temporarily, and simply **** on it, then plug it with your tongue. After about 15 seconds, if it holds that vacuum, then no leaks.
The linkage could also be binding. Transfer case could also be binding. Try helping the servo by hand. Careful when under the vehicle. Chock wheels and make sure in neutral while underneath.

Mar 04, 2010 | 1999 GMC Sonoma

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4 wheel drive will not engage on my 1989 gmc sierra 2500?

actually that first soultion is wrong it is correct on smaller pickups but on the full size pick ups they use a differnet sytem
there a electric actuator on front axle
there be two elctrical plugs on front axle u want the bigger of the two other one is just to turn the 4 wheel drive light on
un plug actuator then remove actuator after it removed plug it back in but leave it out of axle turn key on and shift down to 4 wheel drive the actuator should move out if it dont that your problem if i does move this isnt your problem it either the tranfer case or in front axle

Jan 07, 2010 | 1989 GMC Sierra

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Does my pickup have a 700r4

Yes it is a 700R4. They went to a 4L60E in 1993. Good Luck

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1998 gmc jimmy has no 4x4 anymore

Hi there. under your battery is the 4x4 actuator. there should be a vacuum hose that is connected to it. this actuator is the one that will lock your front diff in 4x4. this hose could fall off and you will not have 4 wheel drive without it connected.If that hose is connected, there is another hose which comes from the vacuum switch up the back of the engine and over toward the driver side of the engine compartment. it tees off and one end goes to a little resevoir on the engine hood. with the engine running, check to see if you have vacuum to this hose. also with thye engine running press the 4x4 switch and make sure that the actuator os working. the vacuum should **** the diaphram in and hold it in. If there is vacuum to the diaphram when 4x4 is engaged but the diaphram doesn't hold, you will need a new actuator. Hope this helps you.

Dec 29, 2008 | 1998 GMC Jimmy

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