YJ Front axle lock, how/when does it work ??

[yeehaa]

1056569

I have a 94' Wrangler with 2.5/ 5-spd. I am curious about how the front axle vacuum lock works. What signals the vacuum to connect the RF axle? Does it only work in 4 Low? Does the front axle have a limited slip/posi differential so that when the axle is locked both front wheels turn? Thanks for any help.

Ryan[addsig]

 

[far_right]

1056570

chrysler would like to know how it works too....j/k...um im not quite sure how it works, i know it has problems, but there are several ways to fix it.... [addsig]

 

[dingus]

1056571

lol, yeah... if you solve it, chrysler is paying top dollar for the information lol[addsig]

 

[yeehaa]

1056573

OK, how about this. If I get the cable operated system well I have both front wheels turning (4L & 4H) when it is locked in? Or well i still only have one front wheel spinning?[addsig]

 

[far_right]

1056574

no i dont think posi-lock works like limited slip/posi or a locker, it just replaces the vacume opperated front axle engager[addsig]

 

[Snitty]

1056577

The front axle has a basic open differental... at the vacuum shifter, there is a break in the axle, and the connection is much like a slip collar connection, like in your front drive shaft that allows it to lengthen... when in 2wd, the differental will allow the driver side wheel and the opposite half shaft to spin freely in opposite directions, much like if you put your vehicle on a lift and spin one wheel... the opposite will spin the opposite way... when you engage 4x4, there is a vacuum switch in the Tcase that changes the vacuum properties in the shift motor...The shift motor is a pneumatic pump that slides the collar over the shaft to complete the drive connection... instead of the driver wheel and the half shaft working with the differential, the two wheels are now working with each other. With the front drive shaft now turning, the power will be transfered to one or both of the front wheels... if they have equal traction, they will both be driven... if they have different traction, it will drive the wheel which requires the least amount of torque to drive. If you replace it with a cable, you are simply removing the vacuum system and not affecting the mechanics of the differential. If you want both wheels to spin under unequal traction, you must use a locker or similar device. It is not a good idea to weld the differental in the front axle if you do not have manual locking hubs... because the driver wheel is connected to the axle shaft at all times, an open differential will allow the front drive shaft to stay still... if the diff is welded shut, then every time the driver wheel is spinning, the front driveshaft will be as well, and thats too many parts to be constantly running.... wow.. that was a lot of typing... sorry if i confused anyone... but i think its all in there[addsig]

 

[far_right]

1056579

good explanation snitty, thanks[addsig]

 

[Bounty__Hunter]

1056580

Snitty, paragraphs are your friend :-O Makes info much easier to follow if it's broken up a little.

I disagree on one point, that it's not a good idea to weld the front diff without manual hubs. Mine is welded, and the driver's wheel spins the front driveshaft constantly with no ill effects. The front driveshaft on a TJ spins constantly, and that is a factory design. Installing any locker in the front of a YJ will consantly spin the front driveshaft, Lincoln Locker or otherwise.

Of course, I have a manual vacuum switch so I can disconnect the pass. side axle when in 4wd, this makes tight turns on the trail so much easier being able to put it in 3wd.

It is not a good idea to weld the differental in the front axle if you do not have manual locking hubs... because the driver wheel is connected to the axle shaft at all times, an open differential will allow the front drive shaft to stay still... if the diff is welded shut, then every time the driver wheel is spinning, the front driveshaft will be as well, and thats too many parts to be constantly running

[addsig]

 

[Bounty__Hunter]

1056581

Snitty hit the nail on the head with most of his post. The front axle does have an open diff, so torque goes to the axleshaft with the least resistance. When the pass. side shaft is disconnected in 2wd, that is the path of least resistance.

There is a vacuum switch in the transfer case that switches intake manifold vacuum to one of two vacuum lines going to the front axle. One line for 2wd, the other for 4wd hi and lo. The vacuum diaphram in the front axle moves a shift fork, which slides a collar locking two splined axleshafts together for 4wd.

In older YJ's, the shift fork also activates a vacuum switch that controls the 4wd dash light. In newer YJ's, this is electrical from the axle.

Of course it's not true 4wd when you have stock open diffs in each axle, it's really 2wd. One front wheel and one rear wheel receiving the most torque when traction is needed most. This is why most open diff vehicles get stuck easily with one front and one rear wheel spinning.

[addsig]

 

[JP]

1056605

Bounty,

How did you rig up a vacuum disconnect? does someone manufacture toggles for this? or do you run a length of hose into the cab and crimp it when you dont need it ? hehe... I'm being serious, but I have this mental image of a hose popping out of the dash! :-O :-O :-O :lol:
-JP[addsig]

 

[Bounty__Hunter]

1056612

The vacuum switch comes from an older Jeep equipped with the full-time Quadratrac 4wd. The switch is usually in the glove box of CJ's and SJ's. It has one input and two outputs.

Mount it on the dash and splice it into the stock vacuum system. The red intake vacuum line from the manifold goes to the input. Run the two outputs to the pass. side frame rail next to the engine and splice into the two black vacuum lines running from the transfer case to the front axle.

That's it. Now you can manually switch the vacuum. Allowed me to weld the front diff for the ultimate in traction.

Total cost: about $20 :-O depending on where you find the switch.[addsig]

 

[Snitty]

1056624

that is true... a manual disconnect will allow for better handling offroad. I was unaware that the TJ's had all-time engaged front shafts. I'm a YJ man... I guess I never cared to look for the difference. Yeah.. sorry about the billion word paragraph... When I wrote that, I just got done watching monster garage and had different things on my mind. Bounty... with that front driveline engaged all the time... did the drag from that affect your gas mileage? I would have thought that the extra moving parts would kill top top speed and fuel economy... but... I guess if its ok with the TJ's, then it should be alright[addsig]

 

[Bounty__Hunter]

1056637

It's only the R&P and front drivehaft turning, I don't think it's that much more parasitic drag to noticably reduce mpg and top end. Use synthetic in the diffs and it'd be greatly reduced.[addsig]

 

[Snitty]

1056722

thanks much.. i might have to consider it[addsig]