gearbox wont shift into 4th

[cardwielder]

i have a 92 legacy l wagon rhd(postal wagon) and i recently had to swap the gearbox out due to the diff taking a dump. i was lucky enough to find another postal wagon of the same year and got a gearbox, tc and a spare engine for 350. i got the gearbox and tc installed and everything works perfect, except the it wont shift into 4th while driving. idk why it wont fluids are good and that stuff. the only way it shift up to 4th is if i let of the gas completely while driving, but if i put the slightest bit of pressure on the gas it goes back into 3rd. could that other wagon i got the gearbox from have had a 3spd? i thought 3spd's would only have 1 2 D and 1 2 3 D. the gearbox that's in now has seven positions which would lead me to believe that it is a 4spd just as i had before. i can also go from D to 3 at 40mph and there is no rpm change, but there is in 1 and 2. does anyone have any ideas what could be causing it not shift into 4th. or if will become a serious problem driving around town w/3rd as my final gear? i'm not really worried about driving around town just if for some reason i have to get on the highway to go anywhere because i wont have the extra gear. to be honest i don't even think i could reach the speed limit of 75 in 3rd anyways lol

[Platinum_Racing]

Both cars have 4 speed transmissions.

 

They also have a locking torque converter. The converter in mine locks at anything 45 and over after its warmed up. If you apply enough throttle the converter will unlock. To the untrained eye this can seem like a gear change, but it's not. This may or may not be what you are experiencing. Since there is no change in RPM's when you put the gear lever in "3" chances are there is a problem within the transmission.

 

Usually when a transmission cannot shift into 4th gear the problem is with the main pump. the main pump is what creates pressure within the transmission. It takes the highest amount of pressure to shift into 4th and reverse. If the pump has failed and is causing inconsistent pressure the car will eventually refuse to shift into reverse and 3rd gear.

 

Automatic transmissions can be very tricky things. Honestly, I hardly ever tell people to go to repair shops for automotive repairs, but in your case you want to take the car to a transmission shop and have them drive it and see what its doing wrong. If the pump is bad the only course of action is to tear it apart and do a complete overhaul.

[cardwielder]

if i dont have any problems with reverse now could the pump still be a concern? or wil it already be having issues if its bad? and how long do you think it takes for the tc to warm up. i drive normally to work and back which is only 10-15 max and its not very warm out, normally 11pm and 8am is when im driving.

[ehsnils]

Since you mention that it do shift into 4th if you really tweak it I would suspect that there is a problem with the throttle position or a sensor controlling the gearbox.

 

How about the other gears - are they "long" and shifting at a relatively high rpm? That can also be an indication that it's an issue of adjusting rather than a major fault.

 

Of course - I hope that you have checked the oil level.

[cardwielder]

the other gears shift like normal at low rpms. it just keeps going in third. my old gearbox cruised around 1500revs @ 40mph. now its almost @ 2500-3k. as far oil level goes. i did all of my fluids when i changed gearboxes. so fluid levels shouldnt be a problem.

[ehsnils]

Just check the level again in case it dropped due to an air pocket.

 

But it sounds a bit weird. Anyway - the 4EAT is controlled by electronics so I suggest that you check the control unit and related sensors to see what it "thinks".