The transmission on my 03 3.0l ranger (250k km 155k mi) is shifting horribly after a combination of a ATF leak in a cooler line and the colder weather. Before I bring in the truck and get the transmission rebuilt I figure I would check here to troubleshoot a couple other options that might be causing the rough shift. First of all there doesn't seem to be any issues with any gears once the truck is at operational temperature (including reverse). When the engine is cold (it's currently ~ -20C outside) it takes about 10 seconds to get in reverse and another 3-5 seconds to get into drive. 3rd gear takes a bit of time to get into and sometimes slips out to a lower gear causing high RPM's. I had the O/D off flash on me once before I got the cooler line fixed and it hasn't happened since. I doubt it is electrical related but I did notice a small clump of corrosion leading into the wiring to my engine bay fuse box. Generally, I haven't had any of these issues in cold weather so to get around it I've been plugging in my block heater to help it get to operating temps faster. Any other suggestions I could try fixing myself before bringing it to a mechanic?

 

Welcome to the forum

All automatics run on ATF fluid pressure, this pressure engages/disengages clutches and bands(brakes)
100psi is need for forward
150psi is needed for reverse

So if there is a pressure issue you notice that in reverse first, it requires higher pressure to engage, its why automatics often lose reverse completely if pressure is really low

The pressure is created by the pump, the front pump(but there is only one, lol)
Pump is connected directly to torque converter housing so spins at engine RPMs, so raising RPMs raises pressure
The fluid, under pressure, is then sent to the Valve Body
The Valve Body is where pressure is routed to the clutches and bands(brakes), this engages and holds the planetary gear sets
Prior to computer control the "valves" in the Valve Body used springs, ball valves and vacuum to change setting of clutches and bands
With computer control, electric solenoids open and close valves to change settings

When you shift in to D or R no solenoids are used, its a mechanical change in Valve Body to put trans "in gear", so lack of firm engagement is most likely a pressure issue, but....

1995 and up Ranger automatics do have an EPC solenoid, electric pressure control valve/solenoid, can fail but not a likely issue

Usual loss of pressure is the Valve Body has gasket/seal leaks or stuck valves allowing pressure to bleed off internally
There are two ports on the outside of automatic transmission's that allow pressure testing, this can help determine, first, if it IS a loss of pressure issue and what area might have the leak

Generally clutches and bands last 250-300k miles, at 150k you are at a point where its a judgement call on just doing the Valve Body(can be done without removing transmission) OR just pulling the trans and do new Valve Body and clutches and bands, MUST do new Ford Pump at that time and also new OD drum, new sprags(one way clutches) is also a good idea unless they look pristine
And new torque converter, so full rebuild adds up