yj 4wd issues

[tx_country]

So a buddy of mine bought that 91 yj we found some issues... We got the 4wd to engage, but now he can only drive about 5 feet before the front axle locks up... The diff is good... T case maybe? Any. Ideas thoughts or suggestions?

[kirksjeep]

Sounds like the axle disconnect is working .  Can you shift back out of 4wd and put it into 2wd?  When I talked to the P.O. he said it took him a few days to get it back out of 4wd.

If the front axle is locking up it, I am thinking it must be in the gears.  When in 4wd the passenger side shafts become engaged and the differential acts like a open diff just like the rear.  The fact that it rolls about 5 feet with 33" tires would equal 3/4 of a rotation ( 33"x 3.14= 103.62     103.62"/ 12"= 8.64 '   I'm stuck on the couch, and I'm a Nuke).  If it was the transfer case, the largest gear for the 4wd activation is only about 5", so 1 rotation is 15.7" so the math alone points to the differential. 

Pull the front drive shaft and then shift into 4wd.  The axle disconnect will slide and engage.  Try to drive and see if it still locks up.  If it does it is in the gears, if not I would then suspect the transfer case. 

Have you tried shifting in the 4wd low and trying it?  Do not give it much gas, since the lower gearing could cause something to break if it is binding in 4wd Hi. 

The more info you can tell us the better we can keyboard analyze.

[tx_country]

It shifts out of 4wd just fine... Will try your suggestion... Might take a few days tho. We unfortunately went 3 sect duty and a gang went shift work and chris ( the thickness) went on nights. Will post more as I find out more

[kirksjeep]

Shift work sucks!!!!!!!!  But it will end.  Just let us know what you find.

[The_Thickness]

it does the same thing in 4 low. it engages fine no problems with it. shifting out is easy other then the only way to get the front end to unlock is drive in reverse for about 10 ft. when its is in 4 wheel drive about the time it locks up if i remember correctly the drive side tire still wants to rotate or it atleast feels like it.

[PaulW]

it does the same thing in 4 low. it engages fine no problems with it. shifting out is easy other then the only way to get the front end to unlock is drive in reverse for about 10 ft. when its is in 4 wheel drive about the time it locks up if i remember correctly the drive side tire still wants to rotate or it atleast feels like it.

i had an 89 that did the same problem.  ended up having a bad 4wd vacum switch that left the front diff engaged all the time.  my mom knew when i borrow her jeep because it would have bad vibrations on the highway from being stuck engaged. 

[The_Thickness]

we tested out the vaccum it works fine with engaging and disengaging theres no noise from it or vibrations ive almost ran out of ideas on what it could be

[PaulW]

we tested out the vaccum it works fine with engaging and disengaging theres no noise from it or vibrations ive almost ran out of ideas on what it could be

we then that eliminates the shift actuator.  have you pulled the diff cover to look for chunks yet?  or possibly you have a binding u-joint in the front end?

[tx_country]

Pulled the diff last weekend... No chunks... U joint is possible tho... How do you test that? (This is my 1st jeep so I don't know a lot)

[kirksjeep]

 
[/quote]
we then that eliminates the shift actuator.  have you pulled the diff cover to look for chunks yet?  or possibly you have a binding u-joint in the front end?
[/quote]

The U-joints spin all the time since they are directly attached to the hub via the outter axle shaft, how could they cause this only in 4wd?

[Axle]

Definitely not a u-joint.  It has to be something with the shift fork in the axle tube or the transfer case like Kirk said.  It's a bit of work, but if he has the time and tools, he needs to pull his right outer shaft and shine a light down the tube.  If the shift forks are bent or busted, then that's the problem.  Kirk, am I on a good track here? 

[kirksjeep]

Definitely not a u-joint.  It has to be something with the shift fork in the axle tube or the transfer case like Kirk said.  It's a bit of work, but if he has the time and tools, he needs to pull his right outer shaft and shine a light down the tube.  If the shift forks are bent or busted, then that's the problem.  Kirk, am I on a good track here? 

I didn't think about the shift fork being bent, but if it is it could be rotating around and contacting the inner housing.  He wouldn't have to pull the whole axle shaft out since the shift fork assembly can be pulled out the back of the axle with 4 bolts.  Make sure the fork/ pads and collar are all working and are not bent/ nicked etc.. 

The NP231 is a pretty stout transfer case and not very problematic.  The YJ vacuum actuator shift fork is very problematic, just one of the reasons I took mine out.  I would off up my old one but I sold it to a guy in NY for more then a paid for my XJ solid shaft .  If the shift fork is bad, let me know and I can walk you guys through a solid shaft conversion, which is cheaper and stronger. 

I still recommend pulling the front drive shaft, shifting into 4wd and trying to drive it.  I think it would give you less places to look for the problem. 

[Axle]

Definitely not a u-joint.  It has to be something with the shift fork in the axle tube or the transfer case like Kirk said.  It's a bit of work, but if he has the time and tools, he needs to pull his right outer shaft and shine a light down the tube.  If the shift forks are bent or busted, then that's the problem.  Kirk, am I on a good track here? 

I still recommend pulling the front drive shaft, shifting into 4wd and trying to drive it.  I think it would give you less places to look for the problem. 

Right on.  Tim, let me know if you need help.  Other than helping Will with his lift, I don't have much going on.

[calvynandhobbs]

If this ends up being the shift fork actuator and you don't want to convert your axle to non-disconnect let me know. That XJ that I have out at Jeremy's house is a vacuum disconnect style. If it ends up being in the gears, I'm pretty sure the XJ has 3.55s in it if that is what that YJ has.

[kirksjeep]

I checked over on Jeep Forum, since this is a problem I have never delt with and I've been driving YJ's for 14 years now.  I found two other guys that sounded like they had similar problems.  

Guy#1:  Could drive in 4wd but had a lot of binding.  It was also hard to shift into and out of 4wd.  His problem was in the sift fork not sliding far enough over.  It turned out that it was his 4wd actuator swich on the top of the transfer case.  The little ball valve wouldn't allow enough vacuum to pull the fork over.  He also had a bent shift fork and after replacing both, it solved his problems.

Guy#2:  Bought Jeep with a bad transfercase and after replacing it, he could only drive a couple of feet before the Jeep would come to an abrubt stop, like he slammed on the brakes.  Turned out that the P.O. swapped out the rear axle after mostl likely breaking the D35 and replaced it with a D35 that had a differnt gear ratio.  Turn out the front has 3.73 gears and the rear had 4.10.  

It you try the stuff Guy#1 did and you still have problems, you can verify the gear ratios by looking at the numbers on the carrier.
43-14 = 3.07
39-11 = 3.55
41-11 = 3.73
41-10 = 4.10