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post #1 of (permalink) Old 04-28-2000, 10:40 AM
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vacuum shift motor

I own an 87 wrangler with a vacuum actuated shift motor. I know that they are a real problem but I really don't want to spend two hundred dollars for the Roc Lock from BDS Suspension. I checked all the vacuum hoses and they look alright. If you have any suggestions please reply. Its been broken for about six months and I'm losing my patients.

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post #2 of (permalink) Old 04-28-2000, 11:36 AM
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Re: vacuum shift motor

My 1986 Cherokee XJ has the same Dana30 disconnect as does your Wrangler.

Check the vacuum at the shift motor with the engine idling; there should be vacuum at the motor in 2wd and 4wd transfer case positions. The third vacuum tube is for the vacuum to electric switch for the dash 4wd light. If there is no vacuum in 2wd, 4wd or both; you will have to trace the vac lines back to find out if they are missing or broken.

If you have vacuum present, then the problem is either a stuck shift collar or a bad vacuum motor diaphram. Remove the shift motor from the axle tube; be ready to catch the old liquid grease that will ooze out. Try to move the shift collar by hand; if it is stuck, some gentile taps with a hammer and long screwdirver will free it. Then take some axle grease and lube the splines real good, moving the collar back and forth in order to get the grease under the collar. You can rotate the front driveshaft by hand in order to get the splines to line up, allowing you to move the collar thru its full range of motion.

Check the vacuum motor diaphram by applying vacuum to each port and seeing if the shift fork moves back and forth. If the diaphram leaks air, then you'll have to replace the motor; you can order one from the Jeep dealer. Put everything back together; you can get a gasket for the shift motor from the dealer as well but I use some RTV Blue. Make sure the shift fork rides in the center groove of the collar. Just to be safe, check the front differential fluid level.

A way to check if the entire front disconnect assembly is working is to raise the passenger tire off the ground, start the engine and shift into 4wd. Try to rotate the tire by hand. If the axle is locked (4wd position), the tire should not spin; if you now shift the transfer case into 2wd it should spin freely.

Good Luck!![img]/wwwthreads_images/icons/smile.gif[/img]

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