Front Axle Disconnects - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 06-06-2000, 10:07 PM Thread Starter
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Front Axle Disconnects

[img]/wwwthreads_images/icons/smile.gif[/img] In response to the question by Jeepnut about the use of electricity as a front axle disconnect; let me just make a comment. FIRST....vacuum has been used as a shift-assist since before WWII. As a kid, I learned to drive trucks equipped with vacuum shift two-speed axles, and my buddy had a Columbia two-speed vacuum shift rear axle in his Model A Ford coupe. The HUGE advantage to vacuum, IS that the power of the vacuum pot is INVERSE to the engine horsepower being applied to the gear train. When the engine is pulling, vacuum is low, so the system will not shift and move a gear or a clutch under power and chip something. When power is minimal, vacuum is at a MAXIMUM, and that's a perfect time for the shift to take place. When you use electric, PRESELECTING is dynamite! You can easily burn out a servo or blow a fuse if you select, then don't let off so the shift can take place. So you see, vacuum is the PERFECT source for something like a shifter. Finally, using a TANK cancels out the effect of the engine vacuum being low under power and high under light pulling, and you will risk damage if the mechanism tries to shift under too much power/torque. This is one time that the factory guys have it right, and have for many years.[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
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post #2 of (permalink) Old 06-06-2000, 10:46 PM
 
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Re: Front Axle Disconnects

As you know, Dave, there have been a fair shair of posts concerning the front vacuum disconnect problems of the Dana 30 front axle on YJs and XJs. This system has gotten a reputation for being troublesome. In fact, I've had some trouble with mine.

I think that one of the biggest problems is the fact that many Jeepers aren't aware that the system exists initally (I was among that number). They are under the mistaken impression that the transfer case alone shifts the Jeep into 4wd. I've have been trying to help other Jeepers out with the disconnect problems since I first logged onto the BBS.

Once you're made aware of the system and you get a good understanding of how it works, it becomes easier to live with it. It does have some disadvantages, one being the lack of a 2wd low range mode, another is that it doesn't behave well in conjunction with an automatic locker.[img]/wwwthreads_images/icons/smile.gif[/img]


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post #3 of (permalink) Old 06-07-2000, 09:29 PM
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Re: Front Axle Disconnects

Let me clarify myself.
I want to throw an electrical switch from the cab of the jeep, something like a 3way 1 line in 2 lines out. I want that switch to opperate a vacuum switch, which would then operate the disconnect shift motor with vacuum.
Simply put I want to replace the mechancally actuated vacuum switch on the T-case, with an electrically actuated vacuum switch.
Hopefully there's already an electrically opperated vacuum switch in service on some vehicle.
With this system in place I could choose 2WD low.
Any Ideas?

CTjeepnut

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post #4 of (permalink) Old 06-07-2000, 09:36 PM Thread Starter
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Re: Front Axle Disconnects

[img]/wwwthreads_images/icons/tongue.gif[/img] Right here on this board you can probably find several Jeep guys who have QUADRA-TRAC vacuum switches from their long-defunct QT that they are no longer using. The QT switch is a dial -type switch that has in...out1...out2...and vent. Just don't mount it in the back of the glove compartment like the factory did[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
Quadra-Trac modified by the crack moonguy[img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/smile.gif[/img][img]/wwwthreads_images/icons/tongue.gif[/img] transfer case team.
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post #5 of (permalink) Old 06-07-2000, 10:27 PM
 
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Re: Front Axle Disconnects

Seems to me, Paul, that the old QT switch that Dave mentioned (I guess one could think of it as a single pole, double throw) could be used to modify a the YJ/XJ front axle disconnect piping system to provide a 2wd low range. Connect the "in" to the 4wd line and then the "1 out" to the 4wd side of the diaphram and "2 out" to a tee connector in the 2wd line.....You would have to add a check valve upstream of the tee on the 2wd line and between the switch and the tee on the crossover. This way when the transfer case is in a 4wd mode you could then select whether the front axle is locked or unlocked thus giving you a 2wd low option. What do you think? [img]/wwwthreads_images/icons/smile.gif[/img]

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post #6 of (permalink) Old 06-07-2000, 10:42 PM
 
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Re: Front Axle Disconnects

You know what? It just might work!![img]/wwwthreads_images/icons/crazy.gif[/img][img]/wwwthreads_images/icons/smile.gif[/img]

Anybody out there want to part with that old QT Switch!???

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post #7 of (permalink) Old 06-08-2000, 12:17 AM
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Re: Front Axle Disconnects

that mechanical switch sounds like the ticket. but if an electrical switch is needed, my 90 mazda 4x has the exact setup to control it via a dash switch. an there are a few of these in the bone yard to grab parts off of.

dan
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post #8 of (permalink) Old 06-08-2000, 06:28 AM
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Re: Front Axle Disconnects

We're on the right track now.
The mechanical QT switch would work but I want to go electric, so I can get the switching device close to the shift motor. This would clean up the engine room of all that delicate vacuum hose.
I've found that 95% of vacuum disconnect problems are in the lines or connections and not the shift motor.
This method would provide more reliability along with allowing me to choose 2WD low for use with a front locker.
Blackjack, I've got a lot of boneyards nearby.
Did Mazda use this type of switch in a lot of applications or just certain models certain years?
If you could tell me what model and year specifically I just might go new, if it ain't too $$$.
Thanks for the input guys, I think this might be of interest to a lot of people.

CTjeepnut

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post #9 of (permalink) Old 06-08-2000, 06:41 AM
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Re: Front Axle Disconnects

when i built a QT jeep a few years back, i moved the switch to the dash where i could reach it, then i even got to lable it "normal" and "deep doo".. seemed like the clear aquarium air line worked better than the black crap for small zip ties on all the connections kept everything working when i wanted it

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it's sort of still a cj thingy....see it at http://www.jeepgod.net
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post #10 of (permalink) Old 06-08-2000, 09:00 AM Thread Starter
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Re: Front Axle Disconnects

[img]/wwwthreads_images/icons/smile.gif[/img] Yeah, elusive, that's what we did too. We even went so far as to design a lamp system that shows: "Normal"(green) Trying to change(yellow) and "Emergency"(red)....that way Jeepchick knows that the system has received her change order....it is trying......it has switched. Believe me, I have spent a lot of time getting the SNOJEEP to where you don't have to be an engineer to run it. Jeepchick does not like to make engineering decisions and have five different levers to work with. She is just horrified at the prospect of driving the FS GM with a SM465 and a 205.[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
Quadra-Trac modified by the crack moonguy[img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/smile.gif[/img][img]/wwwthreads_images/icons/tongue.gif[/img] transfer case team.
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