Lift slow and eventually stops as machine warms up

[catmanjan]

Bobcat 753G I've been trying to diagnose this one for a while, I have a pressure valve on a tee on the retraction side of the lift boom With the machine cold, I get 2100 PSI at idle and 2500 PSI full throttle With the machine warm, I get around 1100 PSI at idle and 1500 PSI at full throttle - when the machine is warm it isn't able to lift the boom except for small jerks when I press and release the pedal Tilt seems okay through out this process My mechanic friend suggested this probably means the lift spool valve needs to be rebuilt - does this sound correct? Anything else I can do to diagnose before I attempt?

 

[Tazza]

Can you T in your test gauge into the main hydraulic line from the pump to the control block? Do not dead end it, T in like you have already done.
It will show the pressure on any function you operate, not just on the lift cylinder.
I'm wondering if you have an issue with the aux hydraulics being stuck on, or partially stuck, causing the pressure to be diverted. Even 1,100 PSI, you should still get your lift arms to move.
With the gauge in this location, you can warm the machine up and dead head your hydraulics to see if it still stays at 2,500 PSI or if it lowers that could be the relief or the pump is worn.

 

[catmanjan]

Can you T in your test gauge into the main hydraulic line from the pump to the control block? Do not dead end it, T in like you have already done.
It will show the pressure on any function you operate, not just on the lift cylinder.
I'm wondering if you have an issue with the aux hydraulics being stuck on, or partially stuck, causing the pressure to be diverted. Even 1,100 PSI, you should still get your lift arms to move.
With the gauge in this location, you can warm the machine up and dead head your hydraulics to see if it still stays at 2,500 PSI or if it lowers that could be the relief or the pump is worn.

Thanks for the reply, I'll see if I can fit it anywhere Is there anything I can do to rule out aux hydraulics? e.g. if I disconnect the aux solenoids does that mean it can't be aux? Which relief should I be focussing on? I have a main relief and a port relief

 

[catmanjan]

Thanks for the reply, I'll see if I can fit it anywhere Is there anything I can do to rule out aux hydraulics? e.g. if I disconnect the aux solenoids does that mean it can't be aux? Which relief should I be focussing on? I have a main relief and a port relief

Alright I wasn't able to tee into anything else, the tee I have is a 3/4 JIC which seems to only fit into the lift cylinders... I have both reliefs off at the moment, I noticed a piece missing from the main relief (I think) - see below the CLYD RING is missing https://imgur.com/a/96meDCF Also, the o-ring marked as 18 was split, however this looks like its just to prevent leaks? Could 18 being damaged and 20 being missing be responsible? Either way, I'll get new ones With these reliefs, am I meant to be able to manually actuate the poppets? I am able to press down on the poppet of the main relief and depress the spring with a soft piece of wood (a match), but I can't budge the port relief, even if I try knocking it in with a hammer I'm not sure if the main relief is doing the right thing, or if the port relief is, so I'm not sure if either (or both) just needs to be replaced