89 YJ deal of the century, now i have alot of work to do! - Page 2 - JeepForum.com

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post #16 of 24 Old 04-12-2010, 07:31 PM Thread Starter
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1989 YJ Wrangler 
Join Date: Apr 2010
Location: kenosha, WI
Posts: 15
ok, so let me get this straight, because the 19 pages on this thread about posi lock are turning my brain to mush.
this will make both tires spin all the time when in 4wheel
this WILL NOT make my 4wheel engage when i put it in 4H or 4L

so i need to make my 4 wheel engage somehow, and THEN do this mod to make both front tires spin together when in 4wheel?

where is the actuator for the 4wheel part then?
my drive shaft turns when i put it in 4h or 4L but the hubs wont engage

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post #17 of 24 Old 04-12-2010, 07:59 PM
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1990 YJ Wrangler 
Join Date: May 2007
Location: Westminster, MD
Posts: 599
Posilock only replaces the vacuum actuator that connects the 2 halves of the passenger side front axle. It is a simple cable arangement that eliminates all the parts associated with the vacuum system. The actuator is located on the passenger side front axle housing. It has vacuum lines that are connected to a mechanical vacuum "switch" on the transfer case, a vacuum operated electrical switch on the firewall (for the dash indicator light), and a vacuum source on the engine. When you shift to 4wd, vacuum is supplied to one side of the actuator which slides an engagement fork and collar in the axle housing to lock the halves of the passenger side axle shaft together. It also closes the circuit on that firewall switch to turn on the indicator light. When you shift back to 2WD, vacuum is applied to the other side of the actuator and the collar disengages the halves of the passenger side axle shaft. The electrical circuit opens and the indicator light goes out. This arrangement replaces the manual hubs found on other 4X4s and allows the front wheels to spin without spinning the front driveshaft when in 2WD.Check out this link. http://www.jeepforum.com/forum/f12/4x4-actuator-940031/ Scroll down to post #11 for a diagram of the system and explanation of how to trouble shoot.

'90 YJ Wrangler - 4.3L Chevy
'91 GMC 3500 Bus - Tow Vehicle
'87 MBenz 300D Turbo
'02 MBenz E55 AMG
'55 Piper Apache

Last edited by stu1021; 04-12-2010 at 08:10 PM.
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post #18 of 24 Old 04-12-2010, 08:03 PM
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1996 ZJ 
Join Date: Oct 2006
Location: Vernon, NJ
Posts: 4,758
In 4 wd (hi or Lo) the Jeep is really only 2 wheel drive. Stock Jeeps have open differentials. Power is directed to the wheel with least resistance because of the spider gears in the differential. If you want true 4wd you need to install locking differentials. There are basically 2 types, Automatic, Aussie locker,Powertrac, Lincoln etc. They automaticaly lock the axle shafts together when the axles start to spin at different speeds. Then there are selectable lockers that you can lock and unlock from the cab.ARB,E locker ect. You pick your price. the stock Dana 35 rear axles have a tendency to break when a locker is installed.
The stock front axle on the YJ uses vacuum operated disconnect system that basically splits the passenger side axle in 2 so the outer axle stub shaft spins free and because of the open differential the driver side shaft just spins the spider gears. The front drive shaft does not spin in 2wd and helps boost MPG slightly. The Posilock thing that's got your head mushy removes the vacuum lines and uses a cable that enables you to engage and disengage that axle disconnect ONLY. It won't make both front tires spin with equal poer. Only a locker will.
Buy a Chilton or Haynes manual. The Chilton will have more info on the carb and vacuum lines under the hood of your Jeep. There is also a FAQ at the top of this forum. There is a ton of axle disconnect answers and I believe there is info about axle strength. Most here swap in a Ford 8.8 rear axle to replace the Dana 35.

96 ZJ.
05' Grand Cherokee Limited, 2"OME lift
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post #19 of 24 Old 04-12-2010, 08:32 PM Thread Starter
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1989 YJ Wrangler 
Join Date: Apr 2010
Location: kenosha, WI
Posts: 15
Thanks so much guys
the part about:
"locks the passenger shaft to the blah blah blah"
is what was screwin me up
so the fork (whatever it does) when engaged puts you in 4wheel
and thats all there is to it
the transfer case selector just engages the front driveshaft and applies vacuum to the fork in the axle
the fork is what makes the power coming from the driveaxle actually transfer to the wheels
so basically
my drive shafts are spinning,
i engage the fork manually,
NOW i am in 4wheel drive?
should be able to do this before the weekend
now if the rain will stop for a couple hours!

89 yj I6 5 speed
4" suspension 3" body 35x12.5x15
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post #20 of 24 Old 04-13-2010, 03:57 AM
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1987 YJ Wrangler 
Join Date: Aug 2006
Location: grafton ohio
Posts: 3,286
It does look nice for the north. You might as well drop the stock carter carb like a bad habit before you end up shooting it. Throw on a motorcraft as they work really well on the 258. "Heat", you don't need no stinkin heat, after all, it's a jeep for Pete's sake. Besides, thats what the girlfriends for ha ha!!

1987 wrangler, 258 I-6, 5-speed.
2007 liberty sport 4X4, automatic
2009 ford ranger 4x4 FX4 OFF/ROAD, 5-speed
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post #21 of 24 Old 04-13-2010, 04:31 AM
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1995 YJ Wrangler 
Join Date: Jul 2007
Location: Fayette County WV
Posts: 1,050
Originally Posted by turkish View Post
Thanks so much guys
the part about:
"locks the passenger shaft to the blah blah blah"
is what was screwin me up...
It's all in relation to the axles being OPEN. The tire with the least resistance will be the one that gets power. Think of it this way, one tire is in a grease pit and the other is on good solid ground. Even with everything working and in 4WD the tire in the grease pit will spin and the one you would think you want to turn (get power) just sits there doing nothing. So... when your passenger side axle (broken in two pieces) is not "engaged" all the power will be applied to that little stub of an axle because it's not connected to anything. The fork and collar actuate and make it one unbroken axle.

A stock setup even in 4WD is still could be thought of as a 2WD because for it to be 4WD all four tires would have to have equal resistance. How often does that happen when out in the mud and terrain? Not often or at all. Scenario: you're going up a paved hill of black ice, the shoulder of the road looks like it has some good gravel on it so you drop it in 4 low and put the passenger side tires over on the shoulder so you can make it up the hill. But the driver's side tires (one front and one back) get the power and sit there and spin. Thus 2WD.

I hope this helps and not make it worse for ya.
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post #22 of 24 Old 04-13-2010, 09:56 AM
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Join Date: Mar 2010
Location: Vernal
Posts: 2,787
The axle disconnect system, a.k.a. CAD (center axle disconnect) Was an answer tothe consumer as well as the the Mileage Standards imposed by the Federal Government. The average consumer did not like getting out of their Jeep to lock/unlock the hubs, but at the same time Jeep wanted to improve the fuel efficiency. The CAD system was a happy medium for both parties.

Check out this article on JP Magazines answer to the CAD.
Dana 30 Vacuum Disconnect - Jp Magazine

I personally don't mind the CAD, I don't mind getting out and locking/unlocking my hubs either. Keep this in mind. The CAD only disconnects one side of the axle, the left side is still affected by parasitic drag on the carrier and the axle shaft.

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post #23 of 24 Old 04-13-2010, 01:57 PM
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Join Date: Mar 2010
Location: Vernal
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[QUOTE=turkish;9270149]oh lol,
hows she like the garage?
i mean the jeep.

that would be a funny thread tho about the wifeys ideas and comments.
i saw a couple girls in the build section who do good work.
sure they would get a kick out of it.QUOTE]

She would spend much more time in the garage if her Jeep was in there, but then again, it won't clear the low door height!

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post #24 of 24 Old 04-13-2010, 02:36 PM Thread Starter
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1989 YJ Wrangler 
Join Date: Apr 2010
Location: kenosha, WI
Posts: 15
i feel ya there!
mine wont fit in any garage!

89 yj I6 5 speed
4" suspension 3" body 35x12.5x15
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