Four-wheel-drive on the fritz - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-01-2001, 04:33 PM Thread Starter
 
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Four-wheel-drive on the fritz

Ok, I posted about this before and have done some tests but first I will explain the problem again. Just recently my front axle has been disconecting(no 4x4) The thing is it doesn't do it all the time. It only does it at highway speeds (50mph) and when I am climbing a hill. It has never gone out under 50. Here are the tests I have done. Pulled the vac lines at axle and shifted from 2h to 4h. Vacuum switches from one line to another so the vac switch is good. Put a vac line on shifter assembly sucked on it untill shifting fork engaged and after it engaged I couldn't suck anymore so the diaphram is good. I hooked a vac gauge onto the lines and got 17 for the one that keeps it in 2 wheel drive. Put it one the one that engages 4 wheel drive and got 4 untill I pluged the one that turns one the light in the dash then I got 17. Now, with the harness off the axle and its engage in 4 wheel drive, Is it supposed to suck from both lines(four wheel drive and the indicator). Other than that Everything works perfect. I am really stumped on this one and if anybody could help me It would greatly appreciated. Thanks. OH one more thing. when it disengages it only does it for a second or two then it slams back into four wheel drive.Very scary on an icy road.

I need to get a girlfriend I'm getting to close to my jeep.
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post #2 of (permalink) Old 01-01-2001, 04:57 PM
 
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Re: Four-wheel-drive on the fritz

Myabe you are going too fast for the 4wd, I know jeep says something like it's good at all high way speeds but I'd slow down, why do you need at 50mph, if the conditions are that bad do you really need to be going fast.
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post #3 of (permalink) Old 01-01-2001, 05:02 PM Thread Starter
 
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Re: Four-wheel-drive on the fritz

I have driven two other 4x4s with a similer system at highway speeds for a couple of years and have yet to have a problem.Remember this has started to happen recently it worked perfectly before.

I need to get a girlfriend I'm getting to close to my jeep.
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post #4 of (permalink) Old 01-01-2001, 05:37 PM
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Re: Four-wheel-drive on the fritz

Check your vac when you are at highway speeds. Also check to see if your system will hold a vac. Is there a
vibration in the front end?

post #5 of (permalink) Old 01-01-2001, 07:33 PM Thread Starter
 
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Re: Four-wheel-drive on the fritz

thanks for the advice but you never really answered my question. Are you supposed to have vac at the 4 wheel drive line and the indicator line.And like I said I put a guage on the 4x4 one and only got 4 untill I plugged the one for the indicator light, then I got 17. Which means i am pulling vac at both of them, is this or is this not normal and if not what is the problem. Thanks

I need to get a girlfriend I'm getting to close to my jeep.
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post #6 of (permalink) Old 01-01-2001, 07:54 PM
 
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Re: Four-wheel-drive on the fritz

Sounds like your vacum lines are a-okay. I've had to replace 2 of them on my old wrangler. BOTH times they had moisture in them and as soon as it got cold they would freeze up. The first one I took in the house too warm up and it started working again. But as soon as it got cold it would freeze up. Same with the second one. If you decide to replace it buy from 4wheelhardware, they are only like 30 bucks compared to the 120 something you will pay at the dealership.

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post #7 of (permalink) Old 01-02-2001, 07:14 AM
 
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Re: Four-wheel-drive on the fritz

Pull the shift motor off the axle and check to see if the collar and shift fork are ok. Be ready to catch some fluid when you take the motor off but it won't be too much. Check the condition of the shift fork; they are known for weak castings in the early years for both YJs and XJs. Try to move the collar back and forth by hand; if the halfshaft splines don't line up, turn the front driveshaft by hand until they do. If it doesn't move freely, slather a good amount of axle grease on the splines and work the grease under the collar by moving it back and forth. When you put the shift motor back on the tube, make sure the fork rides in the collar center groove. You can use RTV to make a gasket if the orginal one is not reuseable.

While the motor is off the axle, give it the "suck" test again and see if the fork moves back anfd forth. Good Luck!![img]/wwwthreads_images/icons/smile.gif[/img]

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post #8 of (permalink) Old 01-02-2001, 08:54 AM
 
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Re: Four-wheel-drive on the fritz

<font color=blue>Are you supposed to have vac at the 4 wheel drive line and the indicator line.</font color=blue>
To answer that question: Yes the 4x4 light is a vacuum switch that indicates you have vacuum to the system when 4 wheel drive is engaged. If one or the other line is off you will not have enough vacuum to hold or even operate the shift motor. Wet lines, (freeze up) cracked tubing, and loss of engine vacuum are some of the causes. Also if the splines are worn on the axle shaft or shift yoke or slide. You could even have a build up of dirt or sludge causing the yoke to not fully engage. The shift motor could have a bad diaphram.
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