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Vacuum Front Axle Engagement

A

Atownatheist

NAXJA Forum User
Location
Bellingham, WA
I've been lookin around the forums, and haven't had to much luck with finding an answer so I thought I'd try makin a new thread and seenin if that would get any more answers.......

So my problem is: When I engage 4wd, it appears my front wheels dont completely engage (they dont deliever power to the ground) I've heard that the front engagement on the D30's is vacuum powered, and that they tend to go out. So is my problem stemming from a malfunctioning vacuum engagement? Or am I heading in the wrong direction? Any hints/ideas/places to look?

Specs: 1991 xj 4.0 HO, stock axles as far as I know (D30/D35)......

Thanks!
 
if you have the 231 transfercase, i believe the 91 still used the vacuum shift motor on the passenger side of the front axle. crawl under and see if you have vacuum lines running from the transfercase to the pass side of the front axle. first see if there disconnected. if connected, pull them off to see if there is vacuum on the lines. if no vacuum check the vacuum switch on the transfercase(other end of lines from the axle). if there is vacuum, then the shift motor may be bad.

btw, the engine needs to be running and the TC in 4hi.
 
So with the engine running and the tcase in 4hi, disconect the vacuum lines from the front axle (they are connected still) and check for vacuum....

If there is NO vacuum clear the lines to generate vacuum.
If there is vacuum, then the shift motor may be bad?

Is that right? ( I wont be around my jeep til this weekend, so I'm making sure I understand everything before then..... Thanks for putting up with my newbie-ness.
 
Had same problem on my 90 laredo. Felt the transfercase shift but the light wouldnt come on and the axle would lock. got under there just turned out to the vacume line to the shiftter on the axle. got un pluged
 
I also had the vacuum switch stick on me. Its located on the back of the TC its big aluminum switch that 4 vacuum lines go into, it can also cause your 4wd to not work.
 
Search for Vacuum disconnect.
 
Atownatheist said:
How easy/hard are repairs to the vacuum switch? Is it something you can do at home? or is it better to just get a new one?
Click to expand...

easy to replace the vacuum switch on the transfercase. unscrew with wrench and screw new one in. dont know if there is a fix for the switch.
 
Atownatheist said:
How easy/hard are repairs to the vacuum switch? Is it something you can do at home? or is it better to just get a new one?
Click to expand...

Buy a new switch its about $10.00 depending where you buy it. You can remove it and press the round button on the end in and out, also when you push the bottom button in it re-route the the vacuum coming out of the ports on the top to engage your 4wd.
 
So the vacuum lines are not producing suction at both ends. I'm going to replace those with newer unclogged ones, and hope that fixes the problem.

If I still can't shift, would you recommend replacing the vacuum switch or the vacuum motor?
 
You can do a basic test of the motor if you bypass the switch and run a vacuum line straight to the "engage" port of the motor. Of course you won't be able to switch it back and forth while testing, but if the motor shifts and stays shifted, then you can look for problems in lines or switch. For the test you can disconnect the "disengage" port, but leave on the line that runs to the indicator light switch, and it should then tell you if it's engaging. The indicator is also vacuum powered, so if the motor fails to engage or pops out, the light will also go out. Drive up some steep hills with wide open throttle, to make sure that the motor won't pop out under low vacuum conditions. Running with the motor engaged in 2WD will not hurt anything.

If you have a hand vacuum pump, you can do the whole thing more easily, just hooking the pump to the motor. If it holds vacuum, it's good.
 
I got rid of that vac crap and use a posi-lok. Best thing I ever did. Figure it this way with the posi-lok you can use 4 wheel drive low and disengage the posi-lok and end up in 2 wheel low. Can you say help in tight corners when wheeling. Plus if for what ever reason your jeep dies in a stick situation you will not loss 4x4 with a posi-lok. The engine stops you loose vac and hence you lose youe front. Sure it will come back after a minute but if your stuck 9 times outta 10 the front will not move enough to reengage. Just my .02
 
On my '84, I pulled the vacuum actuator off the axle and removed the broken shift fork. I then slid the collar over the axle stubs and installed a hoseclamp to keep it engaged. Reinstalled the vacuum actuator and 4WD works EVERY time. Figure that after 91 they had a solid front axle and the T-Case directed the power to the axles. Been working great ever since for me.
 
Matt is right, the blue is the vent.

And if the engine dies, it doesn't really matter if the axle is engaged, now does it?

Robert
 
The other thing I had was a little water got into the shift motor & froze when it got cold when I needed it most. Pulled it off & let it thaw out & got as much water out of it as I could by moving the fork back & forth to expell the water out of the vacuum ports. Put a drop of alcohol in the ports to keep it defrosted. Then when I could crawl under it when it was warm I changed to the Posilok setup.
 
WrenchMonkey said:
And if the engine dies, it doesn't really matter if the axle is engaged, now does it?

Robert
Click to expand...

Well that came of sounding rude. Not meant that way I'm sure. :jester::jester:
For me, yes it does matter cause when it starts back up I want to know for sure that the front is definitely engaged and not have to worry about it. Going with a newer XJ shaft or a TJ shaft would be nice too, but I like the fact I can use the posi-lok like a twin stick so I can disconnect the front for a tight turn and still be in 4low, effectively giving me 2low.
But my point was if the engine dies the axle will/might /probably disengage the front. Engine will not produce vacuum unless it is running. On pretty much all XJ's,that I am around and deal with, to get it to reengage you have to be able to move the axle forward or backward a little to get the teeth realigned to let the collar to slide over the second part of the shaft so that it can engage.

Sorry didn't mean to hijack the thread to much. But to each there own these are just my findings and personal experiences
 
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