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Discussion Starter · #1 ·
I'm at that place where most YJ owners have been at some point.

You guessed it, the 4wd isn't engaging. It could be the switch on the t case. It could be the actuator. It could be a failed vacuum hose.

It could be time for either a cable kit or just a permanent vac delete kit.

What are the pros and cons of the vac delete plate?

On my last YJ I went with the cable kit, but it was a real pain in the butt to use.

If I do go with the vac delete kit, are there any negatives to it?
 

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On my last YJ I went with the cable kit, but it was a real pain in the butt to use
Agreed. I had a cable, liked 2WD Lo, but it would sometimes freeze in the winter, and needed adjustment now and again.

My 89 currently runs a CAD but it stopped working recently because the vac motor rusted through with pinholes.

The brand new Crown vac hose assembly was like $28, the vac motor $25, and the tcase switch $12 or $15 or something.
The new vac motor came with new phosphated grade eight bolts, new CAD fork shoes, E-clips, o-ring, and a gasket.

Fixing it with all new parts is not expensive. It can be expensive if you buy from Morrisse or another place thst charges more than commodity resources. Like three or four times as expensive for identical-looking parts.
Shimmed mine over about fifteen years ago. No problems. If you lift enough without regard to pinion angle, then you can have the driveline vibes
The fact is that lift isn’t the issue: IF the front driveshaft happens to be unbalanced from the factory (some happened to have balance, some did not happen to have balance- by chance) you didn’t get lucky. AMC /Chryco didn’t balance YJ front driveshafts when they made them.
 

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Discussion Starter · #6 ·
Just fix what's broken. It's likely just a vacuum issue with the old hoses.
So I got at it and I did find a vacuum leak.
Plugged it in to the only other hose that fit that was open and all of a sudden 4wd works again. Now the issue is that the light won't come off when I shift the t case into 2wd. I'm going to need someone to shift in and out for me while I lay underneath and observe if the mechanism is working or not. Whoever owned this before me has made a bit of a mess with things. A lot of mystery hoses with plugs in them
 

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Now the issue is that the light won't come off when I shift the t case into 2wd.
What year is this jeep?
I’d like to help but there’s a couple or three different ways the light gets triggered- PLUS sometimes the switch won’t quit until you move the jeep and the coupler can let go of the axle shaft splines.
 

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Discussion Starter · #9 ·
What year is this jeep?
I’d like to help but there’s a couple or three different ways the light gets triggered- PLUS sometimes the switch won’t quit until you move the jeep and the coupler can let go of the axle shaft splines.
It's an 89. I did disengage and try ripping around, over dirt obstacles ect. Can't get the light to come off. My concern is that the fork isn't actually being moved over.
It ought to be audible if you're beside it eh? I was hoping to get someone to shift the t case for me while I observe it from underneath
 

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Discussion Starter · #11 ·
89 has a vac switch on the firewall.
This is good info. I'll look for that. I think you may be into something with the switch. I'll go pick one up tomorrow and start there. I'll just do the auto parts store parking lot shop thing and sit out front replacing parts till it works. Haha.

I vape so what I did was blow smoke through the vacuum lines and the only place any came out was out the carb. So I'm thinking I don't have any leaks, but I can very well have the connections set up in the wrong places.

I wonder if there's a good place to find a schematic diagram of the vac system on these old jeeps? I was looking earlier but I ran short of time
 

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think you may be into something with the switch. I'll go pick one up tomorrow and start there.
I wasn’t saying it was the firewall switch (it could be) I was saying that if the vacuum lines have another flaw or the hose connector to tcase vacuum valve is plugged in wrong or if the vacuum line routing isn’t correct the vacuum light switch won’t turn off.

How many vacuum lines are at the CAD; two or three? That it went in to 4WD and locked the passenger axle shaft shows that the vac motor works. That it won’t turn the light switch off says that that circuit either isn’t putting vacuum on the opposite side of the vac motor (and thereby the light switch) because the vac hoses are wrong; or that there is a leak in the hoses, tcase vac switch is messed up, or the vac diaphragm housing is leaking.
You can remove the vac motor and with engine running operate the tcase lever to see if the vac motor works both directions. That will save a lot of time.

If vac motor operated both directions then you can suspect the vac light switch.
Human body Jaw Gesture Rectangle Font

The tcase vac switch is ‘keyed’ and the hose connector has two recesses to make sure it is plugged in correctly as in picture. If the triangle keys are broken off (like mine is) it is possible to plug it in wrong and you’ll need to rotate 90* to get proper operation.
 

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I picked up a cable actuator for my D30 when I was doing my build. After doing some research, it seems that the only thing the CAD does is engage/disengage the RF wheel. Seemed like a lot of weak points for something that isn’t really needed. So I put the cable kit on the shelf (happy to sell it if anyone wants it) and bought a CAD delete kit.
I will say, I don’t do much/any highway driving in the Jeep, and typically drive under 55mph on road.
 

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Seemed like a lot of weak points for something that isn’t really needed.
It’s nice with a front locker.

And it’s not weak- more positive power with vacuum than the cable imho. Plus think about it: we put lockers in every day with tiny pins and use ujoints with less cross section than the cad collar and think nothing of it.
 

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It’s nice with a front locker.

And it’s not weak- more positive power with vacuum than the cable imho. Plus think about it: we put lockers in every day with tiny pins and use ujoints with less cross section than the cad collar and think nothing of it.
Oh I’m not claiming that the cable option is better than the vacuum driven CAD.

I’m saying the cable and the vacuum options have more that can malfunction or break, that is why I decided to eliminate the CAD function and lock the shafts together.
 

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Discussion Starter · #17 ·
I wasn’t saying it was the firewall switch (it could be) I was saying that if the vacuum lines have another flaw or the hose connector to tcase vacuum valve is plugged in wrong or if the vacuum line routing isn’t correct the vacuum light switch won’t turn off.

How many vacuum lines are at the CAD; two or three? That it went in to 4WD and locked the passenger axle shaft shows that the vac motor works. That it won’t turn the light switch off says that that circuit either isn’t putting vacuum on the opposite side of the vac motor (and thereby the light switch) because the vac hoses are wrong; or that there is a leak in the hoses, tcase vac switch is messed up, or the vac diaphragm housing is leaking.
You can remove the vac motor and with engine running operate the tcase lever to see if the vac motor works both directions. That will save a lot of time.

If vac motor operated both directions then you can suspect the vac light switch.
View attachment 4159938
The tcase vac switch is ‘keyed’ and the hose connector has two recesses to make sure it is plugged in correctly as in picture. If the triangle keys are broken off (like mine is) it is possible to plug it in wrong and you’ll need to rotate 90* to get proper operation.
Dude thank you. That's extremely helpful. I'll let you know how it goes after I get at it.
 

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Dude thank you. That's extremely helpful. I'll let you know how it goes after I get at it.
No problem.
The funny thing is that I just played CAD Roulette for the first time in a while just last week. The only part (I bought) that was not needed was the tcase vac switch. The rubber vacuum harness parts and the vac motor were all that were needed.
 

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just to put things in perspective in the keep vs delete debate:

Chrysler decided to do away with any kind of CAD or locking hub system for both the TJ and JK. so it's pretty easy to argue that it's a mostly pointless system.
 
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