743 steering issue

[bunkbe]

Hi all, Got my 743 up and running. Lift and bucket all working, forwards and backwards work too, however its making a crazy loud noise when trying to steer in either direction and only turns a little before the noise gets to loud and seems to slow up. I was wondering where to start looking first. Pump, drive motor or could it be a linkage issue? Cheers

 

[brdgbldr]

Hi all, Got my 743 up and running. Lift and bucket all working, forwards and backwards work too, however its making a crazy loud noise when trying to steer in either direction and only turns a little before the noise gets to loud and seems to slow up. I was wondering where to start looking first. Pump, drive motor or could it be a linkage issue? Cheers

My first thought is a weak bypass valve.

 

[laurencen]

have you tried putting it on stands and see if there is creep, next try each side forward and backwards and see if any noise, then try steer both directions and see if its noisy one way or the other, you may have a bad axle bearing or loose, it would show up more when on ground turning but not so much off the ground

 

[bunkbe]

have you tried putting it on stands and see if there is creep, next try each side forward and backwards and see if any noise, then try steer both directions and see if its noisy one way or the other, you may have a bad axle bearing or loose, it would show up more when on ground turning but not so much off the ground

ok thanks will try this after i check the bypass valve. I did notice that one of the axle seals was leaking a bit, The noise sounds very high pressure, almost like something not flowing well.

 

[Markle]

Check that aux hydraulics is not stuck on. My 743 screamed and took pressure from drive when I bumped the aux hydraulics, stuck on, and I did not realize it…duh! Also, my drive motors make noise, kind of a whine, both sides, but absolutely no issue with function. For whatever it's worth, a bobcat mechanic told me that to check the hst pump, he removes the main hydrostatic fluid supply hose that supplies a drive motor from the pump, caps it at the pump, starts machine and then pushes the stick on the capped side. If pump is good, machine will try to stall til relief kicks in. Just sayin and sharing. It's your call how to proceed.

 

[bunkbe]

Check that aux hydraulics is not stuck on. My 743 screamed and took pressure from drive when I bumped the aux hydraulics, stuck on, and I did not realize it…duh! Also, my drive motors make noise, kind of a whine, both sides, but absolutely no issue with function. For whatever it's worth, a bobcat mechanic told me that to check the hst pump, he removes the main hydrostatic fluid supply hose that supplies a drive motor from the pump, caps it at the pump, starts machine and then pushes the stick on the capped side. If pump is good, machine will try to stall til relief kicks in. Just sayin and sharing. It's your call how to proceed.

Ok thanks for the reply. I checked the aux and seems fine. Will try the block off drive motor at pump method as soon as i get a chance. cheers

My first thought is a weak bypass valve.

ok thanks. where is the block off valve located? Im also searching for a bronze filter that might be blocked but i can't seem to find it on my model serial 50673xxxx

 

[bunkbe]

My first thought is a weak bypass valve.

is this the bypass valve you were referring to?

 

[bunkbe]

Anyone know how to test this pressure switch? Its part of the hydraulic filter unit on the above pic.

 

[brdgbldr]

No, I should have said relief valve not bypass.

It would be in the hydrostatic pump. There should be one for each drive side. You should check the parts catalog for your specific machine.

Bobcat Parts Catalog - Find Diagrams for Your Equipment - Bobcat Company

Locate all parts and component information about your Bobcat equipment with detailed visual diagrams and illustrations with parts numbers and add to your list.

partscatalog.bobcat.com

 

[bunkbe]

No, I should have said relief valve not bypass.

It would be in the hydrostatic pump. There should be one for each drive side. You should check the parts catalog for your specific machine.

Bobcat Parts Catalog - Find Diagrams for Your Equipment - Bobcat Company

Locate all parts and component information about your Bobcat equipment with detailed visual diagrams and illustrations with parts numbers and add to your list.

partscatalog.bobcat.com

ok no worries. i'll check those relief valves out next.

 

[Markle]

Ok thanks for the reply. I checked the aux and seems fine. Will try the block off drive motor at pump method as soon as i get a chance. cheers

ok thanks. where is the block off valve located? Im also searching for a bronze filter that might be blocked but i can't seem to find it on my model serial 50673xxxx

Bronze filter location on top of hyd/hst pump, from my 743. see pic

 

[Markle]

Anyone know how to test this pressure switch? It's part of the hydraulic filter unit on the above pic.

I suspect you could test it on the machine, key on engine off, take voltage. Then repeat when running. There should be a range of voltage results. If no change in VDC, probably bad.

 

[spitzair]

How fast are you running your engine while all of this is going on? These machines will make all sorts of noise and feel weak if you're just running the engine at idle or lower RPM, they need to be revved up some. They will whine a bit with the engine running at higher rpm and that is normal but at low rpm they will sound very unhappy. Also check your hydraulic fluid level. You say you just got it up and running, is this a new to you machine? If it's been sitting for some time or it's been all apart there could be air in they hydraulic system and that can take a bit of time to work itself out.
Another thing, that pressure switch on your filter is there to warn you if the filter is getting plugged up and it will only turn on your warning light when the filter goes into bypass. It looks for a difference in pressure between the inlet and outlet side of your filter and once that pressure hits a certain value it will activate the switch. You may be able to test it by hooking a multimeter to it, one lead on the body and another to the screw on top and then compressing the spring, once compressed enough your ohm reading should drop from infinite to zero.

 

[bunkbe]

How fast are you running your engine while all of this is going on? These machines will make all sorts of noise and feel weak if you're just running the engine at idle or lower RPM, they need to be revved up some. They will whine a bit with the engine running at higher rpm and that is normal but at low rpm they will sound very unhappy. Also check your hydraulic fluid level. You say you just got it up and running, is this a new to you machine? If it's been sitting for some time or it's been all apart there could be air in they hydraulic system and that can take a bit of time to work itself out.
Another thing, that pressure switch on your filter is there to warn you if the filter is getting plugged up and it will only turn on your warning light when the filter goes into bypass. It looks for a difference in pressure between the inlet and outlet side of your filter and once that pressure hits a certain value it will activate the switch. You may be able to test it by hooking a multimeter to it, one lead on the body and another to the screw on top and then compressing the spring, once compressed enough your ohm reading should drop from infinite to zero.

Ok thank you for the reply. The machine is new to me, I got it off a friend who said it wasnt steering. I got it running after it had been sitting for a few years and when i tried to steer it revving full, half or idle it screams really loud, but moves backwards and forwards fine.

 

[bunkbe]

I suspect you could test it on the machine, key on engine off, take voltage. Then repeat when running. There should be a range of voltage results. If no change in VDC, probably bad.

Thankyou ill check it out

 

[bunkbe]

Bronze filter location on top of hyd/hst pump, from my 743. see pic

ok thanks. My pump seems to be different see attached

 

[Markle]

I checked on line parts diagram and only sn 501914999 and below used that bronze filter. And it was only in the place I showed you in my pic. So I guess scratch that off your list.

 

[ward]

THe real question is how does it dig or push will it spin the wheels or does one side spin and the other does not, from the sounds of it the pupms are worn out, the above picture shows the lift pump and the right hand side drive pump the left is further up in under the crossmember, it is using a common center housing for the left and right hand side of the drive, ie the high pressure.

 

[ward]

IF the tires wont spin or almost kill the engine then you have bad drive pumps is the most likly issue.

 

[oiu789]

Check that the parking brakes are releasing.