Komatsu 450-3 transmission shifting issues

I recently bought and put a new engine in my friends 450-3MC loader. The machine has 13,500 hours on and it has been sitting with no engine for 8-10 years. when it was parked back in 2010ish everything ran fine I know because i remember running th e machine. I've had 4 of these 450-3 over the years so I'm pretty familiar with them.

So on Friday i threw the engine in and got it started. runs great and hydraulics are strong. Im having some issues when the tranny though. it always goes right into forward. but when you shift to reverse sometimes the transmission will just do nothing and sometimes even go forward, and sometimes reserve will actually work. the dash indicator works fine and says its goin into gear.

Ive tried it with the converter cut out on and off doesn't seem to make a difference.

When in forward. you can put it into first with the lever and it will go to first and then shift to second as soon as you give it gas. then won't return back to first till you stop and go into neutral. it digs into a pile very strongly in second though.
so far all i have done is topped off the tranny and hydraulic fluids with Komatsu TO10 and a new tranny filter.

Any help is greatly appreciated,
Thank You,
Jake Harrington

I haven't worked on a Komatsu loader that new but all that I have worked on were electrically shifted. I've seen plenty of issues with harness connectors being corroded and insulation going bad inside the harness between the control box on the transmission and going up to the cab. Did you drain and replace all the oils and filters when you got the machine running again?

I topped of all the fluids and changed all the filters. Havent changed the tranny fluid yet though.
Im heading over to my shop now. Ill pull the connectors and clean them up today.

also anyone know of a good place to get radiator cores for these machines. Mine is in rough shape

if the dash is displaying what your selecting its an issue from the controler down, like john said eletrical issues, the shift diodes on the ground side of the harness are very well known for causing head aches. clean and apply di-eletric grease and test.

i cleaned and dielectric greased every connector from the cab down. they all looked perfect but greased them any way.

I really feels like an electrical problem. what exactly is the computer that controls the tranny. do all the signals come from the dash board/gauge assembly?

i found a good one out of a 470-3 that i want to try hooking up into it, any thoughts on that?

Also does anyone have a service manual for a 450-3?

I have the full paper owner and parts binder, just need a service manual now

I finally changed the tranny oil and the filter and cleaned the strainer. The old oil looked perfect and the strainer was clean.

my buddy had a parts machine laying around so i stole the dash monitor and the shift levers assembly and tried plugging them into my machine to eliminate a lever problem or a computer problem. Still the same problems.
After everything ive done so far there is absolutely no improvements.

does anyone have any more advice?

thanks in advance for all your help.

I would suggest checking the electrical harness between the transmission up into the cab.

Sounds stupid but wiggle the tranny fuses. I’ve seen a few -3 loaders where the fuse box corroded and caused funny issues.

Might be due to.
1)Defective reverse solenoid valve
2)Defective relay of reverse solenoid valve

You can interchange above with forward and observe if the problem shifts to FORWARD
3)Contact in the wiring harness. (especially need to check F/R solenoids and F/R relays related cables).

It almost sounds as if your forward solenoid is sticking. When you go to reverse you are applying pressure to forward and reverse.