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Changing Transmission Fluid in a Jeep ZJ Grand Cherokee 42RE Transmission

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Hello, Moses!


Can you guide me on how to change ATF in my 1994 Jeep ZJ Grand Cherokee 4.0L 42RE transmission?  How will I change fluid if I want to also change fluid in the torque converter?  Can I do this thru the line going into the radiator?


How many quarts do i need to change? Thank you...


Mario Bedayo

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Mario...If you disconnect a cooler line, use the special coupler disconnect tool.  You must use this tool or you will wreck the cooler line coupling!  This will only remove a small amount of fluid.  Some run the engine with a cooler line disconnected to pump out extra fluid, but this can be a risky approach...See my cautions.


Caution:  If you disconnect a cooler line and pump out transmission fluid with the engine running, at some point the transmission or converter will run dry.  If you run these parts without lubrication for any time, you will severely damage the transmission.  Here is the coupler tool that must be used to disconnect a transmission cooling line at the radiator: http://www.autozone.com/test-scan-and-specialty-tools/line-disconnect-tool/lisle-a-c-fuel-line-tool-set/222520_0_0/.  This Lisle set comes in handy and is inexpensive.  You can get individual pieces for just the transmission cooler line, but this set covers fuel, A/C and other needs.


If you decide to disconnect a cooler hose and run the engine to pump fluid out, the 42RE transmission must be in neutral (N), and the vehicle must be on level ground, with the parking brake set and wheels chocked for safety.  In "N" (not Park) this will pump fluid from the transmission and converter and increase the amount of fluid you get out.  This is not a flush, though, and if you want to actually flush the transmission and converter, you need a continuous supply of incoming oil while pumping the oil out of the transmission.  This can only be done with an automatic transmission flushing machine.  You cannot flush the torque converter fluid properly without using a commercial transmission flushing machine. 


You may have a local shop capable of flushing the ATF from the transmission and converter with this kind of special "flushing" or "fluid exchange machine".  The commercial flushing machines attach to a cooler line.  Some fluid exchange machines simply pump fluid in and out of the dipstick tube.  Either way, they continue to feed clean fluid into the transmission as they extract old fluid.  Here are two examples of these machines:  http://www.nationaltoolwarehouse.com/TransTech-IV-P180292.aspx and http://www.nationaltoolwarehouse.com/Transmission-Oil-Exchanger-P31246.aspx?gclid=Cj0KEQiA6dGmBRC_3Mi-x_XywKsBEiQA1lcFP7AoMh5QfEaMqBUhyZdZcUU4IaP8htQk47xjs6EDYKgaAj_O8P8HAQ.


If you do not have access to this kind of machine, the common approach is to drain what you can from the transmission pan.  Let the transmission cool down to just warm temperature.  (Make sure the transmission fluid is not hot.)  Drop the transmission pan to change the filter, clean the pan thoroughly, install a new filter and pan gasket, and install the pan. 


Begin by filling the transmission with just a couple of quarts of ATF to bring fluid up to the "Maximum" line.  On level ground, start the engine with the transmission in neutral (N), wheels chocked and parking brake set.  Keep checking the fluid level with the engine running, and add fluid until you reach the "Minimum" line on the dipstick.  Wheels still chocked, hand brake set and your foot on the brake pedal, shift the transmission through all gear positions to circulate fluid.  Place the shifter back in neutral (N) and again check the fluid level.


Keep adding fluid until the level is stable between the "Minimum" and "Maximum" positions on the dipstick, then drive the vehicle to get the transmission hot.  Again park the vehicle on level ground, set the parking brake and chock the wheels, and check the fluid level at the dipstick with the shifter in "N".  If necessary, add fluid to reach the "Maximum" level on the dipstick with the transmission hot and running.  Never overfill the transmission.


Note:  The RE and RH Chrysler transmissions, like the A727 and A904/999 derivative units, must be in "N" (neutral) to pump fluid into the torque converter—unless they have the Sonnax upgrades I describe at this magazine article:  http://www.4wdmechanix.com/Survival-Upgrades-for-Jeep-and-Dodge-Ram-Automatic-Transmissions.html.  You cannot get an accurate fluid level reading in Park (P) position.


Make sure that you use extreme care and do not get dirt inside the transmission, the dipstick tube or on the new filter.  Here is a PDF of factory steps to do a fluid and filter change.  I added specifications and also the details on the factory transmission band adjustment.  If you attempt a band adjustment, make sure you use an inch-pound torque wrench for tightening the bands.  Note the references to inch-pounds, not foot-pounds!  Here's the PDF:


Jeep 42RE Transmission Service and Band Adjust.pdf



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