FixaForklift.com

i am working on a Caterpillar DP45 forklift and the truck has a slow and very weak hydraulics. All mast functions are effected by the slow hydraulics but the steering is good. To use lift, tilt or even side shift you have to floor the engine but it still moves very slow. The truck is a 9000l lb. capacity but will barley lift 4000 lb. It just statred happening about 6 month ago. The truck has good pressure input to the spool valve assembly. I changed out the main pressure relief valve with a new part and problem went away.

Then about a month ago the truck lost all hydraulics. The pump seals were blown out. So i replaced the hydro pump and hydraulic service was once again fine. Now about a week ago the truck again started to have slow and weak lifting again. I adjusted main relief valve with no change. Next i swapped out the valve from another truck but still have the same problem. Also switched out spool valves and still have the problem.

Hello and welcome to fixaforklift.com

This question is minor tricky to answer but I think I can help.

Since you have stated pressure is where it should be I won't have you check pressure again, but I will say that there is a possibility that while swapping out the main hydraulic valve a "poppett" might have fell out, this poppett looks like a small round plastic piece, it is what separates the main hydro valve to the auxiliary spool,

There is a breakdown diagram that shows all the spools and hydraulic valve assembly,