1990 2.9L 4x4 Automatic 3 speed w/ OD won't shift while running

[millersir]

Hi everyone,

Like the title says I cannot shift into reverse or any drive gear while the truck is running. When the truck isn't running and the key is in the accessory on position, I can put the truck into neutral and push it. But when I turn the key over and the motor is running I cannot engage any gear. The shifter moves freely through the gears but doesn't engage any shifting. I wasn't having any previous problems with the transmission outside the normal stuff at ~65mph. I typically park in my garage, but last night I was parked downtown while in a rougher neighborhood. Is there something that could have been done for someone to mess with it? Any insight would be greatly appreciated as this is my daily driver and I can't even get it to my mechanic now. Thanks guys!

 

[franklin2]

Check the fluid on the dipstick. If it's really low, put a quart in it and see if it will move. If it does, drive it a little bit and get it warmed up good, and then check the dipstick again with it in park and idling. Top it off if it needs it. If it is low on fluid, you need to take a gander under there and see if there is red oil all over the place, an indication it's leaking somewhere.

 

[RonD]

Does truck roll in Park?
If not the 4x4 transfer case is not in Neutral so not the issue
And if it rolls in any other "gear" then that means shifter on transmission is moving via the column shifter arm

Check transmission dipstick, engine OFF, should see high level on stick
Check again with engine on, should be lower, at "normal" level, that means Pump is working
If fluid level doesn't drop then pump is not working, which would explain the "no gears"
That could be because flexplate has broken(would expect a noise if that happened) or the pump itself has failed

All automatics run on ATF fluid Pressure, 90psi to go forward, 150psi for reverse, this is why people often lose reverse first when there is an internal pressure leak

The pump is connected directly to the torque converter, the pump creates the pressure, so pressure is also engine RPM based
The pumps pressure is sent to the Valve body, the valves route the pressure to engage and disengage clutches and bands(brakes) to select the various ratios(gears)

Torque convert can also fail, its a fluid coupler so full failure(no movement) would be a rare occurrence but that's not never

 

[millersir]

Thanks guys. I'll go try those things right now.

 

[millersir]

I added a 1/2 quart of ATF and was able to get all the gears to engage. Thank you.

The issue now is that the ATF is leaking from the pan at a pretty rapid rate. So we've found the culprit. Does this sound like it's just a pan gasket issue? Are there internal seals that can go bad and cause this whole issue?

I guess what I'm asking is the order of operations to fix this issue. Thanks again for the replies.

 

[franklin2]

Get a can of cheap brake cleaner from the store and clean the bottom of the tranny off really good and let it dry. Then get a light and see if you can tell where the oil is coming from. Around the pan gasket can be one culprit. I don't know about your trans type, but most also have a dipstick tube that enters right above the pan in the tranny, and it has a o-ring that can leak. Both of those will leak all the time, even not running.

There are also tranny cooler lines that run to the radiator. They can be leaking and have rust out pin holes. They will leak more when it's running.

Oil leaks can be difficult to pin point, especially when the oil is blown around by going down the road. That's why you need to clean it up and then try it without moving it.

 

[millersir]

Thank you Franklin2