Hydraulic Controlled Joystick Issue - Left - Boom/Arm Slow

[CSS]

Hi,
I have searched for a few hours to find possible causes/fixes for my issue, however I thought I would ask the experts first before I start my trouble-shooting on an old excavator I have bought for farm use.
Machine - 2002 Thomas (NAGANO) TS45-S 4.5 Tonne Excavator, Isuzu motor and Nachi hydraulics. 7500Hrs. (boom, arm and bucket cylinders are good)
Issue: Left Joystick ARM/Boom (Forward <--> Back) weak hydraulics - slow to move. All other hydraulics operate as they should. Switching the joystick controls from ISO to SAE moves the problem from the ARM to the Boom, so I think the issue (low pressure) is in the Pilot line/circuit which goes through the left joystick.

I am thinking I'll test in this order to find the cause:
1. Measure the pilot pump output pressure first and adjust if needed,
2. Measure the pressure coming out of the joystick,
3. Clean the strainer in the pilot line that goes into the joysticks to check,
4. Test the joystick itself ie weak internal springs by swapping the joysticks over to test. (my parts book says the joysticks are the same part number)
5. Change all the hyraulic fluid and filters, or should I do this first?

Am I on the right track, let me know your thoughts, advice etc. thanks in advance

Cheers.

 

[uffex]

Good day
No1 low pressure would effect all circuits otherwise you are right on track, compliments on the diagnostics.
Kind regards
Uffex

 

[funwithfuel]

#3 would be my guess. Going one step further, I would check the hose from your pilot manifold to the RCV to make sure you don't have a flapper on the inside. I believe, on most equipment, the pattern change valve is after the RCVs soI don't think your issue is further down the line.
#2 the pressure only matters if you're Teed into the pilot out. Don't deadhead into a gauge, that will yield false information.
Good luck and be careful

 

[Coy Lancaster]

If like you say the problem is in just that one function of the joystick I would also check for a collapsed or pinched line.

 

[uffex]

Good day
You may find the attached helpful.
Kind regards
Uffex

 

[CSS]

Thanks all for the advice, it's appreciated. I'll be investigating it at the end of the week hopefully, and will update accordingly.
Cheers.
Chris