Newbie CAD dif 4x4 questions.


RyanC

New Member
Joined
Nov 23, 2021
Messages
2
Location
West of Denver
Hey All-

New to the YJ/Wrangler world- picked up a manual 1990 4.2, the 4x4 doesn't seem to be working, which I assume is the vac/CAD issue. Also the heater/fan has been re-wired to a electronic switch and nothing seems to change with the damper lever- which from reading some threads, I understand is (was?) also based on the vac system. I do intend to dig into this a little more- but it seems a good bet that some of the vac control system has been deleted.

So my first question is- assuming the spline isn't getting engaged- should I still be able to 'feel' it go into 4hi? Right now, both 2hi and 4low 'feel' like gears, 4hi just seems like it's kinda floating around over there.

Other question is, I mostly plan to use this for some light-duty snow plowing, winter driving (snow or just cold) and some 4x4. Maybe 2k miles a year max. In this scenario, would it even make sense to do a posi-lock (or replace vac), or just do the 180 fork hack?

Last question- she doesn't like to startup in the cold, which is probably 80% of my use/need. I'm going to throw some 5w-30 syn in (no idea what's in there now), but was also curious if anyone recommends a frost plug block heater or other type?


Thanks!
 

machoheadgames

Certified YJ Researcher
Supporting Member
Joined
May 19, 2020
Messages
950
Location
Dallas, TX
You should feel a physical engagement of the transfer case when you shift to 4 hi. The shifting of the transfer case is real and it sends power out the front driveshaft immediately, it's just that the power doesn't get to the wheels until the CAD engages the front right axle shaft. So yes you should feel something. The vacuum switch gets pressed as soon as you go into 4hi or 4lo, which is when the vacuum motor begins moving the fork.

The heater control lever controls the vents, the floor or defrost air positon, pushes a button on a vacuum switch to open or close the cowl gate, and pushes the blower motor switch to cut the blower motor off (and lets go to let it run). The blower motor switch is normally closed and is momentary. So when heater is in off or vent, it holds the button down on the switch to cut off the motor. When you go into defrost or heat, it lets go of the switch and the motor runs. What speed it runs depends on the left lever which routes the power through the blower motor resistor to slow the fan down. The only vacuum based portion of the heater is the upper cowl gate which lets air into the heater system. The cowl gate is held closed by vacuum when heater is set to OFF. In all other positions (defrost, heat, vent), the vacuum switch is pushed by the heater lever which cuts off vacuum supply and the flap springs open. The lever should be operating the cowl, the two vents, and the floor/defrost flap. If it is not, you have something to fix if desired.

My recommendation for the 4wd is to get a TJ shaft but you can do the 180 flip or whatever else. I wouldn't go the cable route. It can be finicky and a pain in the ass at times.

Not sure why it's hard to start cold, don't have that problem so I don't really have a block heater to recommend.
 
OP
RyanC

RyanC

New Member
Joined
Nov 23, 2021
Messages
2
Location
West of Denver
Great thanks-

I rigged the fork to hold the collar over the spline (small hose clamp holding fork on the shaft, plus put caps vac seals- the pod is still good). I'm pretty sure both 4hi and 4lo are working now. It was a lot more jerky in a tight circle...but I was just in the yard on some dirt so it should be easy to tell in a circle when I get a chance.

Also changed the oil, which was pretty bad, put some Mobile1 5w30 in and so far it seems to start much easier. I will have to try when it's all the way cold, but I think I can get just a stick-on oil pan heater for really cold starts. It's running much better now though.

1 Question-

When I pulled off the cover of the CAD, two of the heads broke off of the bolts (both driver side). I got 2 new bolts for the other side, and tightened them down pretty good- is it reasonable to assume that will hold up for a few months? I'm going to have a garage here soon and would rather wait until then to try to get the bolt shanks out- or if not, rig it with some make-gasket and a big hose clamp or something. It looked like I would need a grinder or wire-wheel to get the old gasket off...

Thanks for the help- man this thing is fun to drive, I took it to a little ungraded part of a parking area at a green belt and messed around for a minute. It was this or a 2d late 90s blazer- I'm glad I got the YJ!
 

Gilaguy23

YJ Enthusiast
Joined
Apr 12, 2021
Messages
432
Location
Q town New Mexico
Take a center punch and dimple the center of the broken bolts. The striking will help loosen them. get a left hand drill bit of the correct size and see if they'll come on out when you start to drill. Ive had good success this way myself.
 

machoheadgames

Certified YJ Researcher
Supporting Member
Joined
May 19, 2020
Messages
950
Location
Dallas, TX
I would say no, just two bolts is not going to cut it. The first time I took apart my CAD I cross threaded one of the bolts going back in and it snapped. I think it was the bottom left. Anyways, with a nice new thick gasket and all the other bolts tight, I was leaking. That’s one benefit of doing the TJ shaft is it seals at the diff so you don’t have fluid going to the CAD, which makes the CAD bolts matter a bit less.

Is there any part of the bolt sticking out that you could grab with vise grips? You might be able to make it with some RTV or something like you said but I’m not sure.

Hope you enjoy the YJ. I think you made the right choice over the Blazer, but get ready to work. I’m sure the blazer probably would have been some work anyways, everything from the 90s needs it by now.