Bobcat 743 making noise and hardly moving

[Peter M]

I just rebuilt my lift cylinders and tilt cylinder. I started it up and backed out of the garage. It was making lots of noise and I thought it was air in the lines and it would work it's way out. Up down and tilt work perfect. Forward, reverse, left , right are something else. I drove it down the hill it was making loud noises the idea was if there was air in the lines it would work its way out.
Sometimes I have nothing when I move the levers and no noise. It rolls down the hill fine. Other times the levers fight me as I move them. It is now at the bottom of the hill and not going to make it back up the hill. I hope it is just in need of bleeding the system. Help. The noise is similar to when you overload the drive system and it is just about to stall. Help.

 

[isb cornbinder]

Are any hoses reverse installed?

 

[Pen & Wrench]

This is probably a dumb question but did you shut it down and re-check fluid levels, maybe it was low after it purged air out of the system?

 

[Peter M]

I filled it several times after doing the rebuilds. Ran it and moved it outside. then lifted the arms and tilt. turned it off and refilled, then repeat. So hydraulics are filled. It probably took a 6 quarts to fill it.

 

[Peter M]

Only hoses are on the tilt cylinder and they only fit one way and the tilt cylinder is operating properly.

 

[zkdiesel]

Check hydro level. Check charge pressure.
Possible you got debris stuck in relief valve holding it open having the lines off

 

[Nthill93]

Is the parking brake stuck on? No noise when you lift the arms or tilt the bucket? If the brake is off jack up all 4 wheels and go forward reverse left right and try to bleed the air out. Open the hydraulic tank cap and see how much pressure is in the tank when it’s running. Should just be the return line so low pressure

 

[Firebrick43]

I was taught and have seen many references that you never drive a hydro machine to purge the air but Jack it up off the ground as Nthill93 mentioned.

 

[gizardlizard]

I was taught and have seen many references that you never drive a hydro machine to purge the air but Jack it up off the ground as Nthill93 mentioned.

Agree 100%. Wheels off the ground to minimize the load to the hydros while purging air.

 

[zkdiesel]

You guys are missing the point. He worked in the boom, not the drice
All he has to do was cycle the booms before driving and refill

 

[crewchief888]

Start and run at idle, raise the boom and hold over relief for 5-10 seconds, repeat at necessary to purge air. Repeat with tilt.
Check the tank for foaming oil. May have to let the machine idle for a while to clear up the foamy oil.
You may want to raise the cab, and tighten hose clamps on all the suction hoses.
You may have a plugged charge filter in the port block on top or side of the hydrostat.

 

[gizardlizard]

You guys are missing the point. He worked in the boom, not the drice
All he has to do was cycle the booms before driving and refill

Does this machine have separate reservoirs for the drives and the lift? If yes, you’re right. If they share one reservoir, air ingested into the tank must be worked out from each hydraulic circuit. Thought 743 machines are 80’s vintage.

 

[racecougar]

Does this machine have separate reservoirs for the drives and the lift? If yes, you’re right. If they share one reservoir, air ingested into the tank must be worked out from each hydraulic circuit. Thought 743 machines are 80’s vintage.

No, a 743 would have a single reservoir. If the OP allowed it to run low enough to pull air into the pump, that's no bueno.

 

[zkdiesel]

Does this machine have separate reservoirs for the drives and the lift? If yes, you’re right. If they share one reservoir, air ingested into the tank must be worked out from each hydraulic circuit. Thought 743 machines are 80’s vintage.

How does the air get into the drive motor and pump circuits? Yes it could have airaited fluid circulating in the pump circuits but with pumps neutral position it won’t get compressed or moved into the drive motor. You and down with cylinders, too fluid, away you go. Again, people over thinking everything
I have skidsteer hydraulics apart everyday
Working on the boom circuits I never have to worry about pump/drive problems....

 

[Peter M]

The brake is definitely not on. It rolls down hill fine and if I try to go up hill and let off of the drive levers it rolls back.
It only squeals when it is trying to move.
Tilt and lift work and have enough power to lift the machine.
There is a red light on the right hand column in front of the operator
One reply said "You may have a plugged charge filter in the port block on top or side of the hydrostat." how would I check that?
Another reply said, "Possible you got debris stuck in relief valve holding it open having the lines off" where is the relief valve and how do I check it?
This is a 1987 model
I hopped on the skid steer this morning before leaving for work and started it up hoping that it would like me this morning. Nope pretty much nothing. I moved the levers almost full any direction and nothing. Then she built up pressure and started to squeal at full stick. I think when I get home today I will try and get one side off the ground at a time and run that side without a load on it to try and purge air out of it.

If the hydraulic filter was plugged I would not have lift or tilt. Is that correct?

 

[zkdiesel]

Depends on restriction. Checking charge pressure is next check
You can have low charge psi from stuck relief and boom will work but not be strong.

 

[Firebrick43]

How does the air get into the drive motor and pump circuits? Yes it could have airaited fluid circulating in the pump circuits but with pumps neutral position it won’t get compressed or moved into the drive motor. You and down with cylinders, too fluid, away you go. Again, people over thinking everything
I have skidsteer hydraulics apart everyday
Working on the boom circuits I never have to worry about pump/drive problems....

Post 4 he said he moved it outside first then started moving the lift and tilt cylinders. Indubitably he lifted the bucket a little before backing it out. That is how it pulls air into the drives.

If he moved the cylinders up and down multiple times first then I would agree with you.

Start and run at idle, raise the boom and hold over relief for 5-10 seconds, repeat at necessary to purge air. Repeat with tilt.
Check the tank for foaming oil. May have to let the machine idle for a while to clear up the foamy oil.
You may want to raise the cab, and tighten hose clamps on all the suction hoses.
You may have a plugged charge filter in the port block on top or side of the hydrostat.

Running over the relief can damage the relief valve if it has air in it. Cavitation is very destructive

 

[Peter M]

Start and run at idle, raise the boom and hold over relief for 5-10 seconds, repeat at necessary to purge air. Repeat with tilt.
Check the tank for foaming oil. May have to let the machine idle for a while to clear up the foamy oil.
You may want to raise the cab, and tighten hose clamps on all the suction hoses.
You may have a plugged charge filter in the port block on top or side of the hydrostat.

I am not sure what or where I would find this. I assume it would be under a big nut. I could check under me - I am a nut.
I tried to attach a picture of the pump from my phone.

 

[Peter M]

I am not sure what or where I would find this. I assume it would be under a big nut. I could check under me - I am a nut.
I tried to attach a picture of the pump from my phone.

 

[4x4Pete]

I think it's under the seat/cab. The whole chain case is the tank. It holds a **** ton of fluid.

 

[Peter M]

 

[crewchief888]

Yours is a later 743, port block is off to the rh side of the frame.
You can go to bobcat.com and pull up parts diagrams.
If the machine is rolling downhill. I'd guess either your drives have no oil in them. Or they are extremely worn. The hyd tank supplies oil to both the hydraulic system and hydrostats. The chain case is a separate reservoir that lubes the chains and axle bearings only

 

[Peter M]

Yours is a later 743, port block is off to the rh side of the frame.
You can go to bobcat.com and pull up parts diagrams.
If the machine is rolling downhill. I'd guess either your drives have no oil in them. Or they are extremely worn. The hyd tank supplies oil to both the hydraulic system and hydrostats. The chain case is a separate reservoir that lubes the chains and axle bearings only

I hope you are not telling me the charge filter is in the piece I circled.

 

[Peter M]

I lifted each side off the ground and ran the wheels forward and reverse. Right side first then the left side. and repeated 2 more times for 5 minutes a side. Wheels spin fine. lifted the arms up and down half a dozen times and then the tilt the same. Set it down on the ground and it refuses to go up an incline. its now starting to whine all the time. so now it whines and squeals when it tries to move. sure rolls down the hill nice. At this point I have been fighting it so much to get it up the hill that I may have done real damage to something. Oil has some small air bubbles in it which dissipate in 5 minutes. ( looking through the site glass)

 

[crewchief888]

if bubbles keep coming back after you run the machine, you are sucking air into the system someplace.
the control valve is back in the area you circled in red

 

[2gslse]

Dumb question but is the aux port being activated? Can't remember but I think it's the left stick that will move side to side and will sometimes stick if not used regularly maybe it's engaged and the relief is doing its job to save you. I vaugly remember something like that with my unit and afterward I put a locking bolt in to prevent future accidental use.
Keep us posted

 

[crewchief888]

Dumb question but is the aux port being activated? Can't remember but I think it's the left stick that will move side to side and will sometimes stick if not used regularly maybe it's engaged and the relief is doing its job to save you. I vaugly remember something like that with my unit and afterward I put a locking bolt in to prevent future accidental use.
Keep us posted

That would affect the hydraulics, and make the engine hard to start, if it would start at all

 

[Peter M]

Yes it has the auxiliary and has not been used for some time. I fired it up and gave that a try . No change other than the whine would go when I shifted it.

Right lever to the left for aux. This light is on now. Not sure what it is but am pretty sure it should be off. I may run by bobcat Monday and pick up a filter. I know I changed it 5 years ago.

 

[crewchief888]

if i recall that idiot light is switched by charge pressure, or hyd oil temp, or plugged filter.

 

[Nthill93]

There should be case drain filters under the cab on the return lines from the drive motors. I’d pull those and see if they’re plugged with debris. There should also be one under the hydraulic tank where the return line goes into the tank

 

[Peter M]

Yours is a later 743, port block is off to the rh side of the frame.
You can go to bobcat.com and pull up parts diagrams.
If the machine is rolling downhill. I'd guess either your drives have no oil in them. Or they are extremely worn. The hyd tank supplies oil to both the hydraulic system and hydrostats. The chain case is a separate reservoir that lubes the chains and axle bearings only

I found the spot you are referring to on the right side of the frame. In the middle is a 1" nut and under that would be the charge filter - I did loosen it up and found a spring resistance as I un did it. Then the hydraulic fluid came pouring out from the resivour. I fumbled around trying to get it back in and lost a couple of quarts of fluid before getting it started and in. How do you take the charge filter out without dumping all your hydraulic fluid?

 

[crewchief888]

I found the spot you are referring to on the right side of the frame. In the middle is a 1" nut and under that would be the charge filter - I did loosen it up and found a spring resistance as I un did it. Then the hydraulic fluid came pouring out from the resivour. I fumbled around trying to get it back in and lost a couple of quarts of fluid before getting it started and in. How do you take the charge filter out without dumping all your hydraulic fluid?

you dont.
you'r gonna loose oil
thats the reason it never gets changed

 

[Peter M]

you dont.
you'r gonna loose oil
thats the reason it never gets changed

Bobcat did not find a charge filter on the parts break down so I do not have a spare. I will get a siphoned pump and try and get the fluid out of the resivour before trying to open it again. When I get it out, is it more like a screen that can be cleaned or like a sindered bronze that once plugged is plugged.

 

[crewchief888]

Bobcat did not find a charge filter on the parts break down so I do not have a spare. I will get a siphoned pump and try and get the fluid out of the resivour before trying to open it again. When I get it out, is it more like a screen that can be cleaned or like a sindered bronze that once plugged is plugged.

as far as i remember its a sintered bronze filter, i know the earlier ones were

 

[crewchief888]

Bobcat did not find a charge filter on the parts break down so I do not have a spare. I will get a siphoned pump and try and get the fluid out of the resivour before trying to open it again. When I get it out, is it more like a screen that can be cleaned or like a sindered bronze that once plugged is plugged.

6563995​

this may be the filter you are looking for this one is for a 743B

 

[Peter M]

6563995​

this may be the filter you are looking for this one is for a 743B

 

[Peter M]

Crew chief I wish you were local so you could give me hands on help as I really, really messed this 743 up. Yes it was me who rebuilt the lift cylinder and tilt cylinder and left a paper towel in the cylinder.

As you see I opened up what I think is the charge filter and found pieces of paper towel in there. I did not find a filter element. I included some pictures of the valve.

I have not filled up the hydraulic and tried it as I am sure there is more I need to clean out. Where do I go from here. Thank you for the help.

 

[crewchief888]

keep disassembling and cleaning.
may even want to pull the hyd tank, dump, flush, rinse and repeat.
probably gonna find pieces of that papertowel in everything by now

 

[zkdiesel]

Crew chief I wish you were local so you could give me hands on help as I really, really messed this 743 up. Yes it was me who rebuilt the lift cylinder and tilt cylinder and left a paper towel in the cylinder.

As you see I opened up what I think is the charge filter and found pieces of paper towel in there. I did not find a filter element. I included some pictures of the valve.

I have not filled up the hydraulic and tried it as I am sure there is more I need to clean out. Where do I go from here. Thank you for the help.

Well that explains it
Start cleaning. Take apart your control valve, cylinder lines to and from the effected pair of cylinders. Find the relief valve.


This ***** and will take you several attempts to get right