Bobcat 773G lift / tilt problem

[Bruceinhealy]

Hi all,
I have a 773G model with ACS (Advanced Control System). It has AHC (advanced hand controls), no foot controls. It’s got the BICS system on it. No seat switch.
I was out plowing snow the other day and when I finished I brought the 773 in my shop and let it thaw overnight. Next day I find a decent sized puddle of hydraulic fluid under it. I tracked it down and found it was leaking from the Oring where the solenoid valve threads into the BICS valve. I was relieved and thought great an easy fix. (Yeah right) Replaced the Oring (old one was shot, intact but small areas eroded or missing that oil could leak by), checked for leaks, all good. I did not have new Orings and back-up rings for the stem of the solenoid valve itself but they looked good and it had been working flawlessly.
I fired it up to move it out and couldn’t lift the boom or tilt the bucket. When I try to lift or lower the boom it does load the engine but will not move the boom. When I tilt the bucket down it loads the engine and it will tilt down just a hair and take some weight off the front tires but won’t pick them up. When I tilt the bucket up it loads the engine but won’t tilt the bucket up. I do hear a hissing noise like hydraulic fluid flowing internally in the valve. Kinda the same sound of hydraulic fluid flowing thru a relief valve or flowing by a partially opened valve.

Here’s what I have done so far:

* checked and have all 4 green LED’s lit up on the BICS controller in the cab

* when I had the solenoid valve out the second time I applied 12v to the coil and the valve appeared to be moving as it should…clicking in and out.

* checked the wiring harness and had 14v to the connection where the solenoid valve plugs in.

* fired it up, hit the operate button, had all 4 green BICS LED’s lit up and stuck a screwdriver down by the solenoid coil. Had some magnetic pull but it felt pretty weak. Not sure how strong that should feel with a screwdriver??? It’s been awhile since I have messed around with any solenoid valves.

* checked the resistance on the solenoid coil. It was 10 ohms. Specs say 8.7-10.7 ohms


Has anybody had an experience like this, or these symptoms? Any ideas would be greatly appreciated. Hydraulics are not my strong point.

Thanks,
Bruce

 

[Sapientoni]

sounds like something in the solenoid was disconnected while you had it apart, if that is possible. Take the coil off and put the screwdriver inside it before hitting the button. Do NOT hit the button without anything ferrous inside the coil. That will burn them out almost instantaneously to check without taking it back apart, put the screwdriver beside another coil for comparison.

 

[Bruceinhealy]

sounds like something in the solenoid was disconnected while you had it apart, if that is possible. Take the coil off and put the screwdriver inside it before hitting the button. Do NOT hit the button without anything ferrous inside the coil. That will burn them out almost instantaneously to check without taking it back apart, put the screwdriver beside another coil for comparison.

I’ll see if I can find another coil to compare with the screwdriver, that’s a good idea. I don’t think anything happened to the solenoid but that’s the only thing I have messed with so who knows. The solenoid looks exactly the same as the service manual shows in the disassembly instructions.
Just want to try and make sure it is the problem, don’t want to start throwing parts at it as they are kinda speedy.

 

[Bruceinhealy]

Update:

* I welded up some fittings and hooked up to the auxiliary hydraulics and checked the hydraulic pressure. idle=2500 psi. About 1/2 throttle=2800 psi and I didn’t go any higher as the machine was in my shop and not warmed up. 3000 psi is the spec. I engaged the auxiliaries and ran them in each direction and had the same pressures in both directions. That tells me the pump is working, the main relief is not stuck open, oil is making its way through the main control valve, and the auxiliary spool is moving correctly.

* I pulled the solenoid valve out again. Grabbed my air nozzle with a rubber tip and blew air through the end of the valve stem and it was coming out one port on the valve. I energized the coil and it came out the other port on the valve stem. I could visually see the plunger was moving and the air confirmed it was moving from port to port. As I said in an earlier post the Orings and back up rings on the valve stem are not damaged and look fine. Also looked into the bore where the solenoid valve threads in on the BICS valve and it looks good/clean.

* I pulled the pilot actuated locking valves out of the BICS valve. The solenoid directs oil to these valves to open them when you push the ”push to operate” button on the panel. They have to open to allow oil flow from the tilt or lift spools to the cylinders. They were both clean and free of any kind of debris. They moved freely while pushing them with a screwdriver to open and close. The bores both looked clean and free of any kind of debris.

* I turned the key to the on position, hit the push to operate button, had a green light for the lift and tilt on the BICS panel. I moved the lift and tilt controls and I can hear the actuators moving in both directions. Obviously I can’t actually see that the spools are actually moving but can hear that the actuators are working. If I fire up the bobcat and tilt the bucket down it will tilt down a bit and take the weight off the front tires. If I then shut the machine down, turn the key back to the on position without starting it and hit the push to operate button, then tilt the bucket to the up position I can hear the actuator work and the machine settles back down as the bucket tilts up. This tells me the actuator is moving The tilt spool at least a little bit.

Today I’m going find a place to tap in and get some hydraulic pressures after the control valve/BICS valve and before the tilt and lift cylinders just to rule the cylinders out. My machine is fairly basic and doesn’t have a Bob-tach, bucket position valve, or diverter valve for rear auxiliaries. So that eliminates places for internal leakage. Basically I have hard lines or hoses right from the main control valve/BICS valve to the cylinders.

Am I missing something here? Seems like a fairly simple system, but hydraulics are not my strong suit. The machine was operating flawlessly before I pulled the solenoid valve out of the BICS valve and replaced the oring.

 

[Bruceinhealy]

 

[Bruceinhealy]

 

[Sapientoni]

Sounds like you have made some positive progress towards elimination of the problem. The laws of probability always say, "the new problem is the result of the last thing that was worked on." That's not always true, but coincidental failures are surprises that just keep giving unless they are simple and easily identified. That's why you really want to try and do one thing at a time unless it's a bird nest in the middle of the inaccessible area of the machine. Keep up the good reports and make your New Year a great one.

 

[Bruceinhealy]

Another Update:

I tapped in and checked hydraulic pressures after the control valve and BICS valve and before both the lift and tilt cylinders. Pressures were checked with the lines going to the cylinders dead headed. Heres the results at idle:

Tilt up ——— 0 psi
Tilt down ——2500 psi
Boom up ——0 psi
Boom down - 2500 psi

Looking at the hyd. schematic both Tilt up and Boom up oil flow goes thru the control valve, then thru the pilot activated lock valves in the BICS valve, and then onto the cylinders. I’m assuming the lock valves are not opening therefore the 0 psi readings. The Tilt down and Boom down oil flow goes thru the control valve, then to the cylinders, then the return oil from the cylinders goes thru the pilot actuated lock valves in the BICS valve. This side I am getting 2500 psi but assuming the lock valves are not opening I am not getting flow and the cylinders are not moving. So to me this just points back to the solenoid, the only thing I messed with before I had the problem.

Just to make sure the control valve tilt and lift spools were moving as they should, in both directions, I took the end caps off the valve body on the opposite side of the actuators. I measured the spool travel in both directions and they were all the same.

Am I thinking straight here? Anybody have any other ideas?

I ordered some seal kits for the lock valves, a seal kit for the check valve with the screen, Orings, and a solenoid. I’m headed down to America to see my folks and help out around their place. Hope to get back after this the end of the month or early Feb. I’ll let you fellas know what happens.

 

[Bruceinhealy]

Sounds like you have made some positive progress towards elimination of the problem. The laws of probability always say, "the new problem is the result of the last thing that was worked on." That's not always true, but coincidental failures are surprises that just keep giving unless they are simple and easily identified. That's why you really want to try and do one thing at a time unless it's a bird nest in the middle of the inaccessible area of the machine. Keep up the good reports and make your New Year a great one.

I agree. KISS = Keep it simple stupid. Simple things first. That’s how I generally try to go about troubleshooting, but of course I’ve strayed and had it come back to bite me. Haha. But yes, in this case that solenoid is the only thing I messed with to start with. It’s still baffling me that changing that oring, somehow I screwed up that solenoid??? I hope!

 

[Bruceinhealy]

Just incase somebody looks this up down the road. I installed a new solenoid valve stem and a new coil and that fixed the problem. They don’t sell the whole unit. They are sold separately.