4 wheel not engaging - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-01-2000, 01:36 AM
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4 wheel not engaging

Hi, my bro has a '95 YJ, stock driveline, etc. untill recently ran like a clock, except now the 4 wheel isn't working. I noticed the front driveshaft does turn in four wheel, and I have concluded that it must be the automatic locking hubs since they are computer controlled. Also the dash light that shows when you are in 4 wheel also is not showing up. If it is the auto hubs, how about do we fix this? My personal thoughts were that the Jeep wanted manual hubs, but I dont think my brother wants to go thru that. Thanks in advance.

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post #2 of (permalink) Old 05-01-2000, 02:04 AM
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Re: 4 wheel not engaging

That is a very common problem I think. I have a 91 YJ, had the smae problem last year. Its the vaccum operated 4 wheel drive device located on the front axle pasenger side. You can buy the part for about $100 bucks I think. Easy to replace, 4 bolts I think. This was known as one of the weak links of the Jeep YJ, just about every YJ owner has to replace this part sooner or later. I believe the new TJ's fixed this problem by using a mechanical system. There are kits available that change the vacuum operated system to mechanical, I remember seeing the kits, not sure where.

post #3 of (permalink) Old 05-01-2000, 07:05 AM
 
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Re: 4 wheel not engaging

It could be a number of causes but the 3 most common are: broken or disconnected vacuum lines to the shift motor, a bad motor diaphram and a shift collar that is stuck on the splines due to lack of lubrication. Check to be sure there is vacuum at the shift motor in both 2wd and 4wd. If there is none, then trace the lines back to their sources to find out where the breakage is.

When you remove the shift motor to check the diaphram, some old lube will ooze out so be ready to catch it with a small container. Check the diaphram for leaks by applying vacuum to the ports and see if the shift fork moves back and forth. Check the shift collar to make sure that it moves freely on the axle halfshaft splines from the unlocked (2wd) to locked (4wd) position. If it is stuck, a few gentile taps with a hammer and screwdriver will free it. Apply a good coat of axle grease to the splines while moving the collar back and forth to work the grease under the collar. If the splines don't line up allowing full collar range of motion, rotate the front driveshaft by hand until they do.

When you put it all back together, make sure that the shift fork rides in the collar center groove. If you need a new shift motor, the kit you get from the dealer will have a new gasket. You can also order a gasket separately from the dealer but I use some RTV blue to make a gasket seal. After you get it all back together, check the level of differential fluid and add some if it is low.

A quick way to check if the front axle disconnect system is working is to raise the passenger tire off the ground. With the engine idling, shift the transfer case into 4wd and try to spin the tire by hand. If all is working properly, the tire will NOT spin and the front axle is locked (4wd). Shift into the 2wd mode and the tire should now spin by hand and the axle is unlocked (2wd). If you fnd that the collar is stuck on the splines, then it might be a good idea to re grease the splines as part of a preventative maintenance procedure once or twice per year. Good Luck!! [img]/wwwthreads_images/icons/smile.gif[/img]

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post #4 of (permalink) Old 05-01-2000, 08:37 AM
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Re: 4 wheel not engaging

First things, first.
Get someone to look under Jeep to see if front driveshaft is turnig when you have it in 4wd, if the front driveshaft isn't turning then there's something wrong with the transfer case or the shi
ft linkage.
9 times out of 10 if there is a problem with the front axle disconnects, it is a vacuum line problem and not the shift motor.
Start with the transfer case and work your way forward. To properly diagnose front axle vacuum disconnct problems easily, get yourself a hand vacuum pump, about $35, and a service manual. I cannot believe the number of people on this board who try to work on thier vehicles without a service manual. It is the single most important TOOL you can buy. The very first thing I buy when I get a new piece of machinery, whether it's a Jeep or a bike or a quad,or a lawn mower, or a weedwacker, is a service manual.
The factory manuals are the best, but a Chiltons or Haynes will work.
Personally, I maintain 30-40 internal combustion engines, and I have a service manual for every one of them!!!
CTjeenut

Funny thing is, the more I practice, the luckier I get
post #5 of (permalink) Old 05-01-2000, 09:21 AM
 
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Re: 4 wheel not engaging

CTjeep,
Good advice concerning the aquisition of service/maintenance manuals, but if you read the original post over, you will notice that he said the front drive shaft is turning when in 4wd.

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post #6 of (permalink) Old 05-01-2000, 10:30 AM
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Re: 4 wheel not engaging

I just wanted to thank everyone for their quick and informative responses. I'll keep you posted as I plan on fixing the problem this weekend.

post #7 of (permalink) Old 05-01-2000, 11:06 AM
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Re: 4 wheel not engaging

Go with what xyj173 has to say. The last thing you want to do is buy a new shift motor. If you need the colors of the lines and where they go xyj173 or I can help. I had the same problem with my 88 YJ a few months ago. Cost me about $35 in parts(vacuum harness and some soft windsheild washer tubing) to totally cure the problem.
Good luck.
Bryan[img]/wwwthreads_images/icons/crazy.gif[/img]

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post #8 of (permalink) Old 05-01-2000, 12:22 PM
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Re: 4 wheel not engaging

Ooops, must be reading too fast, or I'm needing glasses. LOL
CTjeepnut

Funny thing is, the more I practice, the luckier I get
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