Need a little hydraulic assistance/troubleshooting on FMTV Wrecker

[PowerstrokeNC]

I am having an unusual problem with the Grove crane on the FMTV wrecker.

When I first go to use the crane, naturally I activate the PTO switch on dash, system fires up and all is good.
However for some reason the crane 'lift' operation and the boom lift operation will sometimes not work.

So since the crane is folded, you need the lift circuit to bring it out of its folded state, as well as the boom lift function to get the boom at the right angle.

A couple of notes; ALL the other functions work 100% boom lower/hoist up down/rotate etc. Also all the wrecker functions work 100% too.
So what I have done recently is shut off the PTO, let the rpms settle back to idle count to 10 and re engage. Count to 10 and disengage. Then after 10 secs & re engage again.

After this little sequence the lift and boom lift work no problem as they should, so I am scratching my head.

I thought well maybe its the valves that supply those functions, but the opposite function works i.e. boom raise doesn't work or works very slightly, but boom lower works fine. Same with the crane lift function, won't work, but the crane lower seems to work fine.

Also in case it helps the functions are partially working, they sort of 'start' to move but then stop. Almost like they don't have full pressure.

Nevertheless though once I go through the PTO engagement cycling everything works fine.

Any thoughts?

 

[NDT]

Going off my industrial experience here, I would say the solenoid actuated spool valves for the functions in question are sticking.

 

[PowerstrokeNC]

Going off my industrial experience here, I would say the solenoid actuated spool valves for the functions in question are sticking.

Is this a serviceable problem? Is there something I can check/troubleshoot? Thanks for the help.

 

[PowerstrokeNC]

Also for what its worth, this wrecker has a 2 or 3 stage pump on it. So when you activate a circuit it starts slow and then 'speeds up'. When I pull the control I hear the typical noise change in the hydraulic circuit, but then it sound like it almost releases or stops working. This is hard to explain in written form
Maybe like it applies pressure then a relief valve lets go and allows it to bypass is the scenario I am imagining in my head and also what it sounds like is happening listening to the hydraulics.

 

[NDT]

If your hydraulic multi-stage pump was flaky, it would likely do the same with all functions, not just one or two. Back to the spool valve diagnosis, I seem to remember the wrecker has a control pendant with electric switches. The switches power soleniods that are mounted on top of a bank of valves. Usually the solenoid will have a light that indicates power to it. Find the one in question. Usually, the spool can be manually pushed in the end with a screwdriver. Try that and see if the function works normally.

 

[M920]

I have worked for a month on a Grove crane, that had very similar symptoms, last spring. It was mounted on a PLS M1074. These trucks are equipped with a variable output hydraulic system, that turned out to be the source of my problems!
The reason the functions are all weird and erratic is because there is a 'Idle Pressure' of about 120psi that is always present when the PTO is engaged. Once one of the functions on the spool valve is activated, a small additional port opens and sends a pilot pressure signal to the variable output pumps. They in turn will throttle up and supply full system pressure to operate the respective hydraulic function.
Sounds to me like you could maybe research the TMs and see if your vehicle has a variable output hydraulic system.
If so, can be several reasons why the system has trouble throttling up sometimes. It is to extensive of a subject for me to go in to here on SS, but if you like to talk by phone to me about it, feel free to PM me your phone number and I will be happy to call you.

Soni

 

[glassk]

I am having an unusual problem with the Grove crane on the FMTV wrecker.

When I first go to use the crane, naturally I activate the PTO switch on dash, system fires up and all is good.
However for some reason the crane 'lift' operation and the boom lift operation will sometimes not work.

So since the crane is folded, you need the lift circuit to bring it out of its folded state, as well as the boom lift function to get the boom at the right angle.

A couple of notes; ALL the other functions work 100% boom lower/hoist up down/rotate etc. Also all the wrecker functions work 100% too.
So what I have done recently is shut off the PTO, let the rpms settle back to idle count to 10 and re engage. Count to 10 and disengage. Then after 10 secs & re engage again.

After this little sequence the lift and boom lift work no problem as they should, so I am scratching my head.

I thought well maybe its the valves that supply those functions, but the opposite function works i.e. boom raise doesn't work or works very slightly, but boom lower works fine. Same with the crane lift function, won't work, but the crane lower seems to work fine.

Also in case it helps the functions are partially working, they sort of 'start' to move but then stop. Almost like they don't have full pressure.

Nevertheless though once I go through the PTO engagement cycling everything works fine.

Any thoughts?

Relief Valve, broken spring or leakage is something to check out,

 

[PowerstrokeNC]

Thanks for all the input and suggestions this far.

 

[PowerstrokeNC]

I have worked for a month on a Grove crane, that had very similar symptoms, last spring. It was mounted on a PLS M1074. These trucks are equipped with a variable output hydraulic system, that turned out to be the source of my problems!
The reason the functions are all weird and erratic is because there is a 'Idle Pressure' of about 120psi that is always present when the PTO is engaged. Once one of the functions on the spool valve is activated, a small additional port opens and sends a pilot pressure signal to the variable output pumps. They in turn will throttle up and supply full system pressure to operate the respective hydraulic function.
Sounds to me like you could maybe research the TMs and see if your vehicle has a variable output hydraulic system.
If so, can be several reasons why the system has trouble throttling up sometimes. It is to extensive of a subject for me to go in to here on SS, but if you like to talk by phone to me about it, feel free to PM me your phone number and I will be happy to call you.

Soni

Soni, I will PM you my number, this system does have a variable output from what I can tell. What you are describing sounds close to the symptom. When I activate the circuit the cylinder moves slightly but doesn't have enough pressure to fully function. I can also hear the second stage start to kick in but stop, whereas when it actually works I can hear the 2nd stage kick in and stay on.