i have two lifts that are doing the same thing but it comes and goes. its happening on two lifts. 7FBCU55 models.
what about the strainer on the return side? if there is one? i wouldnt suspect its su ck ing (had to edit hmm) air
maybe a pinched return hose causing a cavitation?
try taking off and cleaning the hydraulic cap and breather element
run it with out the cap (if you can)
heres a slightly different situation but im sure it can apply in reverse
i had a customer with a diesel that would die on occasion
he had the pump and injectors done with no success b4 calling me in
the 1st thing i did was open the tank and i got a huge "whoosh" of air
he had replaced a vented cap with a nonvented cap and the vacuum buildup was enough to overcome the lift pump pressure with half a tank
new cap no problem
maybe the tank is having issues venting the air pressure as the cylinder lowers and the fluid level rises
far out but sounds like you looked at everything else already
We've eliminated the mast as the problem. We have determined that it is a hydraulic problem, possibly in the return side of the hydraulic system somewhere in the control valve. Since the problem only occurs while the main lift cylinder is lowering, we determined it to be not the mast by taking another machine and using it's hydraulic system, and found the mast to be operating perfectly. So we have determined that there is a problem with the hydraulic system in this Toyota model. Ironically, there are two machines having the same problem, so we have determined that Toyota may have a problem with this particular model. Due to budget constraints, we were not allowed to take the hydraulic control valve and associated parts off for inspection. As the machine is operating fine otherwise, we returned the machine to the customer and put it back into service. Still, if anyone knows of any other problems with this particular model, note that this hydraulic problem will literally shake you off the seat of the forklift. Has anyone else had this problem with this particular model of Toyota? This is an electric forklift.
try a light coat of grease on the mast rails too
Have you checked the carriage rollers?