87 YJ 4WD engage/disengage vacuum problems.
 

I am having troubles with my 87 YJ engaging 4WD.

At first it wouldn't do it at all. After a few tests I found that
one of the vacuum nipples had rotted away from the front axle
shift motor.

So I bought a new one from my friendly Jeep dealer. $280.50
(beyond ouch, for a thing that's little more than an EGR valve)

I installed it. Nothing happened. Still no 4WD. But the 4WD lamp
would now light. It would not go out though until I disconnected one of the
vacuum lines.

Now the strange part. I disconnected the green line that supplies vacuum
in 2WD but not 4WD and plugged it. It plugs into the front face of the
shift motor (not the top two nipples). Now almost everything works well.
In and out of 4WD drive on the fly. This tells me the shift motor is
mechanically okay, it moves the axle collar.

The 4WD light still stays on once in 4WD until I disconnect one of the
shift motor lines though.

What do I have wrong?

Also...

Looking at it from under the hood, there is a blue line that comes from the
rear and terminates in what looks like an inline check valve. Is it
supposed
to go somewhere?

Does anybody have/know-of a schematic for the vacuum line routing?


Thanks,
Charlie

Re: 87 YJ 4WD engage/disengage vacuum problems.
 

There are different flavors of shift motors with different vacuum
routings...

That blue one is a vent.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Charlie Dellacona wrote:
>
> I am having troubles with my 87 YJ engaging 4WD.
>
> At first it wouldn't do it at all. After a few tests I found that
> one of the vacuum nipples had rotted away from the front axle
> shift motor.
>
> So I bought a new one from my friendly Jeep dealer. $280.50
> (beyond ouch, for a thing that's little more than an EGR valve)
>
> I installed it. Nothing happened. Still no 4WD. But the 4WD lamp
> would now light. It would not go out though until I disconnected one of the
> vacuum lines.
>
> Now the strange part. I disconnected the green line that supplies vacuum
> in 2WD but not 4WD and plugged it. It plugs into the front face of the
> shift motor (not the top two nipples). Now almost everything works well.
> In and out of 4WD drive on the fly. This tells me the shift motor is
> mechanically okay, it moves the axle collar.
>
> The 4WD light still stays on once in 4WD until I disconnect one of the
> shift motor lines though.
>
> What do I have wrong?
>
> Also...
>
> Looking at it from under the hood, there is a blue line that comes from the
> rear and terminates in what looks like an inline check valve. Is it
> supposed
> to go somewhere?
>
> Does anybody have/know-of a schematic for the vacuum line routing?
>
> Thanks,
> Charlie

Re: 87 YJ 4WD engage/disengage vacuum problems.
 

There are different flavors of shift motors with different vacuum
routings...

That blue one is a vent.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Charlie Dellacona wrote:
>
> I am having troubles with my 87 YJ engaging 4WD.
>
> At first it wouldn't do it at all. After a few tests I found that
> one of the vacuum nipples had rotted away from the front axle
> shift motor.
>
> So I bought a new one from my friendly Jeep dealer. $280.50
> (beyond ouch, for a thing that's little more than an EGR valve)
>
> I installed it. Nothing happened. Still no 4WD. But the 4WD lamp
> would now light. It would not go out though until I disconnected one of the
> vacuum lines.
>
> Now the strange part. I disconnected the green line that supplies vacuum
> in 2WD but not 4WD and plugged it. It plugs into the front face of the
> shift motor (not the top two nipples). Now almost everything works well.
> In and out of 4WD drive on the fly. This tells me the shift motor is
> mechanically okay, it moves the axle collar.
>
> The 4WD light still stays on once in 4WD until I disconnect one of the
> shift motor lines though.
>
> What do I have wrong?
>
> Also...
>
> Looking at it from under the hood, there is a blue line that comes from the
> rear and terminates in what looks like an inline check valve. Is it
> supposed
> to go somewhere?
>
> Does anybody have/know-of a schematic for the vacuum line routing?
>
> Thanks,
> Charlie

Re: 87 YJ 4WD engage/disengage vacuum problems.
 

for next time, you might also consider a cable shifter. a little cheaper
i think, and a lot more reliable.
--
Ben Jerew
ASE Master Technician
New Country Lexus of Latham, NY
Amateur Off-Roader

Re: 87 YJ 4WD engage/disengage vacuum problems.
 

for next time, you might also consider a cable shifter. a little cheaper
i think, and a lot more reliable.
--
Ben Jerew
ASE Master Technician
New Country Lexus of Latham, NY
Amateur Off-Roader

Re: 87 YJ 4WD engage/disengage vacuum problems.
 

Charlie Dellacona wrote:

> I am having troubles with my 87 YJ engaging 4WD.
>
> At first it wouldn't do it at all. After a few tests I found that
> one of the vacuum nipples had rotted away from the front axle
> shift motor.
>
> So I bought a new one from my friendly Jeep dealer. $280.50
> (beyond ouch, for a thing that's little more than an EGR valve)
>
> I installed it. Nothing happened. Still no 4WD. But the 4WD lamp
> would now light. It would not go out though until I disconnected one of the
> vacuum lines.
>
> Now the strange part. I disconnected the green line that supplies vacuum
> in 2WD but not 4WD and plugged it. It plugs into the front face of the
> shift motor (not the top two nipples). Now almost everything works well.
> In and out of 4WD drive on the fly. This tells me the shift motor is
> mechanically okay, it moves the axle collar.
>
> The 4WD light still stays on once in 4WD until I disconnect one of the
> shift motor lines though.
>
> What do I have wrong?
>
> Also...
>
> Looking at it from under the hood, there is a blue line that comes from the
> rear and terminates in what looks like an inline check valve. Is it
> supposed
> to go somewhere?
>
> Does anybody have/know-of a schematic for the vacuum line routing?


Not addressing your request, but a bit of advice; look into the 4x4
Posi-Lok or a similar cable-actuated front axle engager. You could have
spent a hundred bucks less and gotten something a lot more dependable.
>

Re: 87 YJ 4WD engage/disengage vacuum problems.
 

Charlie Dellacona wrote:

> I am having troubles with my 87 YJ engaging 4WD.
>
> At first it wouldn't do it at all. After a few tests I found that
> one of the vacuum nipples had rotted away from the front axle
> shift motor.
>
> So I bought a new one from my friendly Jeep dealer. $280.50
> (beyond ouch, for a thing that's little more than an EGR valve)
>
> I installed it. Nothing happened. Still no 4WD. But the 4WD lamp
> would now light. It would not go out though until I disconnected one of the
> vacuum lines.
>
> Now the strange part. I disconnected the green line that supplies vacuum
> in 2WD but not 4WD and plugged it. It plugs into the front face of the
> shift motor (not the top two nipples). Now almost everything works well.
> In and out of 4WD drive on the fly. This tells me the shift motor is
> mechanically okay, it moves the axle collar.
>
> The 4WD light still stays on once in 4WD until I disconnect one of the
> shift motor lines though.
>
> What do I have wrong?
>
> Also...
>
> Looking at it from under the hood, there is a blue line that comes from the
> rear and terminates in what looks like an inline check valve. Is it
> supposed
> to go somewhere?
>
> Does anybody have/know-of a schematic for the vacuum line routing?


Not addressing your request, but a bit of advice; look into the 4x4
Posi-Lok or a similar cable-actuated front axle engager. You could have
spent a hundred bucks less and gotten something a lot more dependable.
>