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NP 229 Select Trac

RD84

NAXJA Forum User
Location
Cartersville, GA
I have a 84 Jeep XJ 2.5L SelectTrac with front Axle Disconnect. I have had Jeep since it was new. The 4wd seems to be having problems, works sometimes but does not stay in 4wd. Seems to be a vacuum problem. I think it may be the vacuum motor on the tcase and not the vacuum motor on the front axle. I am thinking of adding a PosiLok to do away with the vacuum system on the front axle, but what do I do on the vacuum system on the Tcase. Does anyone have any suggestions?
 
First of all, determine if the transfer case is engaging. With your 4WD previously engaged on a road test, jack up the front axle. Can you spin the front drive shaft? If so, the transfer case isn't engaging and you need to trace down the vacuum problem causing this. If the front driveshaft doesn't spin, rotate the right front wheel. Does the left wheel rotate the oposite direction? If not, you've got an axle shift motor/vacuum problem. You can easily eliminate the vacuum motor problem by removing the vacuum motor and making a simple mod to leave the front axle engaged all the time, just like the later models were.
 
Getting too old, but as I remember your setup there is a center hump vacuum switch for the transfer case?

Anyway, JP Magazine's take on the D30 CAD axle:

http://www.jpmagazine.com/techarticles/drivetrain/axletech
/154_0904_dana_30_vacume_disconnect/index.html

A different take on the bolt-through the shifting fork fix is to use washers on the fork shaft. Me, I used a shock bolt bushing, a cutoff saw, grinder to make a solid locking sleeve.
 
Thanks for the info from both. I did as you said and checked the tcase. I could spin the front drive shaft and the front axle would not engage. I also checked the wheels by spinning the the front right tire and the left tire would not turn the opposite direction. I tried this test several times. Interesting thing two times the axle would engage, and when tires would spin, however both disengaged fairly quickly and never really seemed to be a strong engagment. I am thinking a I have a vacuum motor problems on both the axle motor and the tcase motor. A local shop I know had a smoke tester the hooked up to find vacuum hose leaks and they did not find any. I think I will bypass the front axle motor by going with a Posilok system or just locking the front axles together using the washers on the vacuum disconnet system. Other than replacing the vacuum motor on the TCase is there away to rig or bypass the TCase's vacuum motor, like with a cable? Since the NP 229 is consider a full time 4wd system is there away to lock the transfer case in 4wd premantely?
 
How's your vacuum reservoir, the one located inside the right front bumper area? Hoses to it that run from the firewall area and under the battery ok? Does your heater/AC system just blow out the defrosters? What I'm getting at is you may have low or no vacuum causing your problem.
 
You maybe correct. I did not even know I had a vacuum reservoir located inside the right front bumper area. I will check on that when I get home tonight.

Yes, The heat and AC are both blow through the defrost only when turned on. The blower motor works, but vacuum motors to adjust the vent doors from the defrost are worn out, I think.
 
You maybe correct. I did not even know I had a vacuum reservoir located inside the right front bumper area. I will check on that when I get home tonight.

Yes, The heat and AC are both blow through the defrost only when turned on. The blower motor works, but vacuum motors to adjust the vent doors from the defrost are worn out, I think.


I'd be willing to bet your life that's what the problem is..........
 
Bet my life??? Not sure about that. Okay I looked for the vacuum reservoir you mentioned, but could not find it or maybe I'm not sure what I'm looking for. What does it look like?
 
It will look either like a large baseball or a pill capsule, behind the front bumper, passengers side. Should be a hard vacuum line running along the passenger's side fenderwell and behind or under the battery and down to the reservoir.

It is common to relocate the reservoir into the engine compartment to shorten the vacuum line and protect the reservoir.
 
black plastic roundish cannister with vac lines going into it. also if your vents dont work and it only blows defrost then its on default, the lever thing to switch a/c heat what ever is actualed by vacuum also and theres lines that go in the firewall on the pass side that send vacuum to the switch, trace those for a fix
 
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