My TX has only 2 solenoids, one for Overdrive one for the torque converter lock up. It is a chrysler A-500 from 1989, also called the 42-RH. Basically a 904 with a overdrive housing tacked onto it. The 904 is the venerable 727's baby brother.When the TX is cold, it shifts into OD no problem.Once warm, at 35MPH, it will fall out of overdrive, then back in,out,in, out, quickly, until I hit the OD off button.Speed upto 40 MPH and release OD off button, and sometimes it will go into and stay in OD, other times it will not engage until at a higher speed and will not drop out.I checked most of the wiring harness, not finding anything that cried Eureka, but Got Deoxit on all connectors and cleaned up and wires in split loom and routed cleanly.The Solenoids are controlled by the 1989 ( remanufactured) engine computer.The engine computer decides based on engine speed sensor in distributor, the throttle position sensor, the coolant temp sensor and the Manifold absolute pressure sensor.The TPS could have a flat/intermittent spot on it in that 35 to 40MPH range. Will check tomorrow. It could be original and nearly 30 years old.Trying to figure out a methodology to isolating the issue before dropping the pan and valve body and replacing the two solenoids.Perhaps backprobing the one connector with 3 wires leading to the solenoids and seeing if the voltage is intermittent at that speed, or perhaps feeding 12v or maybee just 5V directly to the solenoid at 35 MPH when it is kicking in and out, and seeing if it still occurs.It could be mechanical in nature too, but I have been rather maintenance minded with this TX, with additional cooling capacity and extra filtering, and regular fluid changes with the proper fluid, and would expect much more mileage on this rebuild before any mechanical issues cropped up. Last June I had the pan down and there was only a slight ferrous sludge on the magnets ands the fluid was still pink and smelled sweet. Only racked up perhaps 3500 Miles since.Any Ideas for diagnosis? Or perhaps somebody familiar with chrysler transmissions from this era. 1989 is the first year the A-500/ 42RH was offered, and lasted to 2004, with some changes regarding the electronics and hydraulics.

Postively superb free forum techs atHttp:www.allpar.comTech ForumEspecially Imperial CrownFussy me --- this is one of the far too scarce expert forums online. It never fails to impress the hell put of me.

A scan tool can't help with OBD1 emissions, but could the issue with working cold be in open loop, and the failure begins when it goes into closed loop? Might give you a clue. Any codes?

Found this link 42 RH trans that may help.

MEXICOWANDERER wrote:Postively superb free forum techs atHttp:www.allpar.comTech ForumEspecially Imperial CrownFussy me --- this is one of the far too scarce expert forums online. It never fails to impress the hell put of me.Allpar is a great site and Imperial Crown always seems to have a great answer.

Allpar.com was one of the first, perhaps the first online forum I joined. Can't remember my username or password though. I think about 10 years back they kept having so many issues with the site I stopped visiting. DO not really remember why.Was in some other Dodge related forums but all it took was one insufferable feminine hygene product and the bag it comes with to get me to remove those bookmarks.The Solenoid wiring has 3 wires. I will assume one is a ground.I am thinking about backprobing the connector at an easy to reach location with some T10 bulb receptacles, that way a steady light bulb will mean the ECM is sending a steady signal, and a flashing light means it is not, and I will not have to drive and hold voltmeter leads at the same time.Replacing the solenoids means dropping the pan and valve body. Never dropped the valve body before, but I do not just want to throw parts at it and pray.Later versions of my transmission have more solenoids and much of the info I find is for them in later model vehicles.So where I am at, is thinking I need to determine if the solenoids are getting a solid or intermittent signal, and go from there.From this forum i was hoping more to understand how solenoids fail, and their behavior when they reach the end of their useful life. I am not going on any roadtrips where overdrive and lockup are required, aI can simply lock it out of overdrive, so I do have some time to deal with this issue. I do fear if it is mechanical in nature that I am grenading the transmission by continuing to drive it though.

Possible transmission Solenoid failure | Good Sam Community

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