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Installing a ZJ Combination Valve


In February, 2002, I finally swapped out the TJ combination valve and installed one from a ZJ, part number 52009061AB.  While not overly difficult to do, I thought I would include a couple of photos from the swap.  Many thanks to Les for stopping by to help with this swap.


I ordered the ZJ combination valve from a local DC dealership ($50).  Note that the brass t-fitting shown in the above picture (the red arrow) does NOT come with the new combination valve.  I picked it up at the local NAPA store for $7.  The t-fitting part number, as can be seen above, is 7900.  They had a handful of them in the brake parts drawer so it appears that this is not a difficult item to find.  (of course, the "dude" at the local Checker auto store told me I would never find one!)  The combination valve comes with the bracket attached to the valve.  It appears to be stamped onto the valve body.  The bracket is not quite the same as the one used on the TJ....some minor bending is needed to get everything to line up.

Note:  This comment is being added after the work and write-up were completed.  I believe there is a way to mount the original TJ bracket on the ZJ valve body.  Doing so would have simplified the install since the only install issue was that of getting the hard lines to bend a bit and line up with the ports on the valve body.


Here is the TJ combination valve.  You can see the slight difference in the mounting bracket.  The t-fitting is needed because the ZJ combination valve does not have the 2nd output port at the back of the valve body like the TJ does in the above picture.


Grab a couple of rags to soak up the brake fluid while you do the swap.  It isn't too bad....one of the two lines from the master cylinder drips brake fluid once you disconnect the metal lines from the combination valve. 


Here is the ZJ valve installed.  By now, you will have noticed that the electrical connector for the pressure differential switch (in the valve body) is not the same as the one you have on your TJ harness.  The differential switch monitors fluid pressure in the separate front / rear brake hydraulic circuits.  A decrease or loss of fluid pressure in either circuit will cause the switch to activate the BRAKE light on the instrument cluster.  I've not changed mine yet.  My plans are for obtaining a ZJ connector from the local junk yard and then cutting off the TJ connector so I may splice the ZJ connector into the harness.  I can detect no other problem with having the connector removed, other than the operation of the BRAKE light in the dash.

The last step was to bleed the brakes.  Les and I did a full bleed at all 4 calipers and then took it for a test drive.  The peddle still felt soft and I was not able to lock up the brakes.  We returned home and did another bleeding session.  That one went better. 

You may be wondering why I swapped the combination valves after having run the o-ring modification for more than a year.  One thing I noticed, since the disc brake conversion, was that my rear wheels were abnormally warm (compared to the front wheels).  This was more prevalent in the warmer months when the air temp did little to help dissipate the heat.  It is my assumption that the TJ combination valve, which was designed for rear drum brakes, was keeping several pounds of residual pressure (normal for drum brakes) on the rear calipers and thus causing just a little bit of friction induced heat.  I could be all wrong about this....time will tell as the summer approaches.  Regardless, the ZJ combination valve is designed for disc brakes front and rear.  The only question now is if the weight difference (between a ZJ and a TJ) will cause any front to rear bias issues for braking pressures. 

So....how does it feel after the swap?.  Pretty good....so far.  I've only taken it down to get some fast food since installing it this morning.  I'll update this in a few weeks or months once I get a chance to really test the brakes.  (I did notice that I could lock up the 35" MT/Rs on the way to McDonalds.  The roads were a little damp from last nights weather so I won't say this was good or bad.....I still need some more behind the wheel time.)

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