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post #1 of 11 Old 01-16-2002, 10:46 PM Thread Starter
YJ boy
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Vacum lines

I am new to this and have a 90 YJ.

I can not figure out were the blue vacum hose goes to from the transfer. also the vacum shift motor is not working "I think?" there is no vacum from the lines at all!!

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post #2 of 11 Old 01-17-2002, 03:14 PM
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This is just a thought, but you might consider getting a Posi-lok. It is a cable-actuated engagement system that replaces the vacuum-actuated system on the front axle.

However, it is $200. Your call, but I have one, and have had no problems since I got it.

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post #3 of 11 Old 01-17-2002, 05:05 PM
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The vacuum shift motor wears out farily quickly. So if you replace it, plan on doing it again and again. The posi-lock is a nice piece,but it is extremely expensive for what you actually get. The quickest, easiest, and least expensive option is to semi-permanantly lock the inner and outer passenger axles. It takes about 20minutes and costs about a nickel. You'll end up with basically, a standard axle set-up with a solid alxe on each side of the diff. The new tj's did away with the 2 piece axles, probably due to their problems. Another bonus is that the front diff will engage instantly instead of waiting for the vacuum motor to shift the collar.
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post #4 of 11 Old 01-17-2002, 09:13 PM Thread Starter
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First thank you for all your support.

Yea I have been looking at the pos lock but not enough money right now!! also I was told I could put a tj axle in there to eliminate all the worries is this true? if so how.

AJ what was the other method you were talking about?
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post #5 of 11 Old 01-17-2002, 10:19 PM
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Disassemble the vacuum shifter housing. I took a piece of fuel line and slipped it over the shaft that the shift fork slides on. Hard to explain, but if you take off the housing you'll see how simple it is. You end up with a full time locked front end like a TJ. Very minimal increase in wear, very minimal loss of fuel mileage. Way cheaper than conversion to a TJ front end.

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post #6 of 11 Old 01-17-2002, 10:21 PM
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I believe the tj axles should swap straight across. I've never had to change an axle yet, but since folks do it on the trails, it shouldn't be too hard. You should be able to find a couple dozen people on the board that can talk you through it.

What I did is not quite main stream, yet. 1st, a little background on the front axle setup, so that you will forever be knowledgeable in your jeep front axle.

The drivers side axle is 1 piece that connects into the front differential. This axle always turns, which turns the diff, which always turns the front drive-line. But since the transfer case is not supplying power to the drive-line, it freewheels until you lock in 4wd.

The passengers axle is a 2 piece unit. The inner axle is connected to the front diff. and always turns. The outer axle is connected to the inner axle, but it is not a solid connection. The outer axle is also connected to the passenger side wheel, obviously. Since the inner and outer are not directly connected, the outer freewheels inside the inner and they can spin at different rates. I have no idea why jeep did this. The new tjs are 1 piece on each side and they did away with the vacuum motor. That makes perfect sense.

Inside the vacuum housing is a metal fork and a metal collar. The collar is splined to match the axles. When vacuum is applied to the inner side, a rod shifts the fork which slides the collar across the gap, and locks the 2 axles together. Now you basicaly have a solid axle connected to the diff. The transfer case applies power to the front drive-line, and voila! 4wd. That is after a short wait while the axles sync up.

The vacuum motors go down pretty often for a variety of reasons. The posilok replaces the vacuum motor with a cable that slides the fork and collar manually. Much more reliable. My method works for open diffs. I have no idea how it will handle if you have a hard locker up front. If you do have a hard locker, I'd recommend the cable. Air locker or the ox should work fine with mine.

For my method do the following. Jack up the front pass. wheel and put on a jackstand. Chock the rear wheels 1st. Crawl under the jeep and take a look at the pass. axle housing. The vacuum assembly is held on with 4 bolts. Pull the bolts and the housing should come off. You might have to give it a couple taps to loosen the gasket. Some gear oil will come out. Gear oil smells worse than anything I can think of, deal with it.

Once the housing is off you'll be able to see the fork/collar assembly and how it works with the axles. Rotate the pass. wheel while putting a little pressure on the collar. The axles should sync up and the collar will slide across the gap and lock the axles together. You now (for all intents and purposes) have a 1 piece axle, just like the Tj's. Now all you have to do is keep it from sliding back. this is the highly technical part. And the part that is the most expensive.

Slide the fork all the way to the left inside the housing. On the right hand side of the vacuum motor (big round thing)locate the center of the motor and drill a small hole through the outer piece only. Then take a sheet metal screw about 1 1/2" in length (that's the expensive part) and run it in until you feel it connect with the outside of the rod the fork rides on.

This will keep the fork locked to the left and keep the collar from unlocking the axles. Put some gasket maker around the screw to seal the hole. The entire assembly is sealed internally around the rod, but safe is better than sorry.

Then replace the housing, making sure the fork slides back into the groove on the collar and bolt in place. I re-used my gasket, but you might need a new one. You now have a 1 piece axle on each side of the diff. Once you engage your transfer case you'll have instant power to the front end without having to wait for the axles to sync.
I've been running like this for a while, and the only downside I've found is that the 4wd light is always on in the cab. there's been no affect on function or handling in either 2wd or 4wd.

I considered placing something over the rod,but I was worried it would work it's way off and into the gearing.
Good luck.
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post #7 of 11 Old 01-17-2002, 11:37 PM Thread Starter
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Thank you AJ and all I will try that this weekend and let you know how it went !!!!
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post #8 of 11 Old 01-18-2002, 01:59 AM
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I have a color coded vacuum line diagram I made while redoing my 1989 YJ. If you would like it, e-mail me and I'll send it to you. The system is pretty easy to figure out. Most times the problems are caused by age. The plastic vacuum lines up and around the transfer case become brittle with age and break. Usually the culprit is the routing of the lines. Let me know if you want it. Mike
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post #9 of 11 Old 01-20-2002, 08:47 PM Thread Starter
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Well I fixed it for while until I can afford the engagement system. What I did was run the vacum to it self wich inturn created a self vacun and it has worked fine I was in alot of mud and t never sliped or nothing so I will save up and keep my simple fix for now.

Thank you all for your help
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post #10 of 11 Old 01-20-2002, 08:55 PM
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The blue line goes to a check valve and hangs free.
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post #11 of 11 Old 01-20-2002, 09:17 PM
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being a 90 i assume you have the smaller u-joints also. that means a tj shaft will be a big plus because it will be the same used in the 44's. you will need to get the outer spindles including the outer shafts and the inner shafts. that basicaly meens you need to unbolt the rear 3 bolts that hold the outer hubs and take everything that pulls out. then you can pull yours all out and slide the new one in. if i rember right, the inner peice of the pass side is held in by a c clip but im not to sure...its been a while. I already had the larger outer u-joints so i got HD shafts from warn.

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