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Unread 05-24-2010, 09:32 PM   #1
Living_High
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1989 YJ Wrangler 
 
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Four Wheel Drive Indicator Light

First, I've searched the forums and can not find a thread that seems to explain my issue.

My four wheel drive works fine, I can select 4H-4L with no problems and it works in both positions but, my indicator light does not illuminate. I did some troubleshooting...

I connected a vacuum to the indicator switch and the indicator light does indeed illuminate. I disconnected the signal vacuum hose at the vacuum shift motor, with my transfer case selector in 4-HI and no vacuum is present to activate the indicator switch. Vacuum is present for both engaging and disengaging the fork.

Am I correct in the assumption that I have a bad vacuum switch motor? As stated above, my four wheel drive works fine, just my indicator light does not illuminate when I engage my front axle.

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Unread 05-24-2010, 09:46 PM   #2
Djsthe1
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Did you just the bulb itself? If your 4WD works fine, meaning your front axle is going into 4WD your vacuum is fine.
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Unread 05-24-2010, 09:49 PM   #3
ritjobbie
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The bulb might be dead in the dash. Or the switch could be bad.
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Unread 05-24-2010, 09:54 PM   #4
Living_High
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I used a vacuum hose connected straight to the indicator switch and the light illuminated. Hence, the indicator switch and the bulb are fine.
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Unread 05-24-2010, 11:11 PM   #5
ritjobbie
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Quote:
Originally Posted by Living_High View Post
I used a vacuum hose connected straight to the indicator switch and the light illuminated. Hence, the indicator switch and the bulb are fine.
My reading skills suck. At least you got a free bump?

I'd start by taking off the disco housing. Four small bolts, maybe a small spill of gear oil. See if the fork is moving over or if the shift collar is stuck.
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Unread 05-24-2010, 11:34 PM   #6
Living_High
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Quote:
Originally Posted by ritjobbie View Post
My reading skills suck. At least you got a free bump?

I'd start by taking off the disco housing. Four small bolts, maybe a small spill of gear oil. See if the fork is moving over or if the shift collar is stuck.
Thanks for replying. I am certain that my vacuum shift motor is operating, as I can shift into 4H and 4L just fine and can then shift back into 2H just fine as well (by "well", I mean my front axle engages and disengages fine and I have full control over my four wheel drive operation). I read before, sorry no link, that there is a diaphragm in the shift motor, that can/does get sticky and can prevent the shift motor from sending the vacuum to the light switch on the firewall. I am pretty certain it is the shift motor, just looking for other opinions, before I shell out the $$ for a new shift motor.

Edit: I know the lack of the indicator light is a minor issue, I just like having it illuminated when I am in four wheel drive. Since the shift motor is almost half what a posi-lock will run, I may just wait and replace the cheesy shift motor with something much more reliable.
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Unread 05-25-2010, 12:19 AM   #7
MJMPC
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QUOTE=Living_High;9518460]

Edit: I know the lack of the indicator light is a minor issue, I just like having it illuminated when I am in four wheel drive. Since the shift motor is almost half what a posi-lock will run, I may just wait and replace the cheesy shift motor with something much more reliable.[/QUOTE]





How can you call it cheesy and not reliable when it been on there for 21 years?
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Unread 05-25-2010, 12:43 AM   #8
Living_High
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Quote:
Originally Posted by MJMPC View Post
How can you call it cheesy and not reliable when it been on there for 21 years?
Point taken, however, it is susceptible to environmental influences (water, freezing, dirt, etc). If I am looking at spending over $80 for a new shift motor and possibly having more issues with it later on, and not forgetting about vacuum issues that may arise as well, a mechanical lock seems more reliable to me.
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Unread 05-25-2010, 07:33 AM   #9
wanabejeeper
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Not sure if it has anything to do with it but I would check the check valve as well. Honestly as much as I hate things like that not working for the 100 bucks it will cost to replace that vacuum motor I would wait until I couldn't stand it anymore.
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Unread 05-25-2010, 08:03 AM   #10
muddy93
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If the 4wd works fine, and the front axle engages as it should, then I doubt that there is anything wrong with the shift motor. To me, it sounds like a vac line issue. The OP has an 89, which has a vac switch that is seperate from the shift motor. my guess is that the problem is with the line that comes from the shift motor to the vac switch.
here's a diagram that might help,
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Unread 05-25-2010, 08:05 AM   #11
stilllearning6
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I just did a vacuum motor rebuild on a 1988 YJ and this is my input based upon what I learned regarding vacuum control of 4WD light :

I understand that you directly applied vacuum to the firewall switch and result was that it makes the light bulb turn ON . I'd say your issue is prior to the firewall mounted switch .

You said that you can get 4WD so I'd say that your vacuum motor is AOK .
Your diaphragm is AOK .
Your fork shift is AOK .
Your vacuum feed is AOK .

I suspect either the nipple feeding the vacuum to the firewall switch or suspect the black vacuum hose feeding vacuum to the firewall switch, or leaky rubber boot that jointly covers the twin nipples .

Suggest : apply vacuum at the yellow hose input nipple of the 4wd motor which is part of the "TWIN sister nipples rubber boot" , not the one on the outer edge which receives the green vacuum input .

Then you should be getting vacuum out of the nipple that would supply vacuum to the other twin sister nipple closest to center of vehicle , the one that supplies vacuum to the black vacuum hose which in turn feeds vacuum signal to the " firewall mounted indicator switch ".

I suspect that you will get vacuum at the nipple since it shares the chamber with the inner fork shift.
I suspect leaky nipple to vacuum hose or leaky vacuum hose.
My experience was that the nipple rusted partially away , resulting in vacuum leak . No vacuum signal would reach the firewall mounted switch .
My fix was : I drilled out the rusty nipple , tapped new threads , replaced original fitting with a $1.85 brass vacuum fitting that screwed into the newly cut threads. Holds tightly.
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Unread 05-25-2010, 08:11 AM   #12
stilllearning6
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I feel that your switch on the firewall is AOK .

Since direct vacuum applied to the switch makes 4WD dash light turn on --> switch is AOK . It does correctly respond to applied vacuum .
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Unread 05-25-2010, 08:23 AM   #13
Area.3.Fiftyone
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Quote:
Originally Posted by stilllearning6 View Post
I feel that your switch on the firewall is AOK .
Well, all-righty then.
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Unread 05-25-2010, 08:32 AM   #14
Old4X
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Your issues are with the sense line running from the vac motor to the switch on the firewall. Mine has a check valve in it, and it will not light the light if that valve is in backward. Get 5 ft of vac line and hook up the vac motor direct to the switch, if OK, study the diagram above and replace all suspect vac lines. If you place the whole Jeep on jackstands, verifying the 4wd goes much easier.
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Unread 05-25-2010, 10:23 AM   #15
Living_High
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Lots of good suggestions here and I have some stuff to further check. Thanks for the input all.
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