Hey ya'll I have a 2000 ranger 4.0 4x4 automatic that recently lost reverse and so i thought the transmission wet bad so we replaced it with another and the exact same problem. took it to the local transmission shop and he checked out the wiring harness to the tranny and found nothing. when driving truck it shifts hard from first gear to second then fine after that, stop then put in reverse there is no reverse, turn off the key and start it up again put it in reverse and it will go fine, but once i drive forward then try reverse again, no reverse till i restart vehicle. could this be some sort of computer issue? its getting frustrating trying to figure this out any suggestions would help thanks. Gabe

 

Welcome to the forum

First off, the computer doesn't have any control of a transmission going into "gear" or not going into "gear"
Engaging a "gear" is done by the shift lever position on drivers side of transmission, its a mechanical selection, not electric

All automatics operating by fluid pressure
In the front of the transmission is the main pump(or front pump), but there is only 1 pump, lol
The pump is powered by the engine directly thru the outside case of torque converter, so engine RPMs are pump RPMs
You need 120psi to engage Drive, you need 160psi to engage Reverse
This is why Reverse is often lost or slow to engage FIRST, while Drive still works OK, because the system is losing pressure somewhere, so can't maintain the higher pressure needed for Reverse

The fact that BOTH transmissions had issues with Reverse has nothing to do with the vehicle its in
Both had issues because both have pressure issues, which is the most common issues with automatics because they ALL operate on fluid pressure

The pump generates this pressure and then sends it to the Valve Body
In the old days(pre-solenoid) there were springs and valves, now-a-days the solenoids control the valves
But the Shifter controls the main routing of the pressure FIRST, it send the pressure back to the pan in Park or Neutral
Shifter sends it to Drive, or to Reverse
If it sends it to Drive then the solenoids get that pressure and can engage the clutches and bands/brakes to select which gear ratio to use, 1st, 2nd, 3rd, ect...
If Reverse is selected then no solenoids are needed, pressure just engages Reverse

Now seals and gaskets in the valve body hold the pressure, so bad seals/gaskets can leak pressure so no Reverse

Then there's the "moving parts" the rotating mass, clutches/bands, planetary gears, one-way clutches any of these can fail or not fully engage if pressure is low
One-way clutches are a common failure in all automatics
If Drive doesn't get you moving but shifting to 1st or 2nd does then its usually a one-way clutch issue, but nothing is 100% on automatics, there are so many interdependent systems in automatics its hard to diagnose an exact problem from just external symptoms
There are pressure test ports on the outside that can be used to get a better idea of whats happening inside

Automatics are not difficult to understand in how they work
They are difficult to diagnose specifically because in the interdependence of the pressure and parts

 

Thanks Ron I will get pressure checks done and see where that leads me

 

Ron, your knowledge is exemplary!!! I re-read you explanation to understand what may be the issue....at least I would start with a pressure check. From the information, it sounds like the pump may be the issue or a seal/gasket. Thank you for sharing your knowledge.