curious about these sounds 743

[marko13]

Don't know if you'll be able to make anything out from this clip that I'm wondering about the higher pitched sounds that just makes at certain times.
In other words is something need fixed?
happens more on turns, lower throttle, and I guess what it is is when it's "working harder relative to rpm???"

 

[brdgbldr]

Don't know if you'll be able to make anything out from this clip that I'm wondering about the higher pitched sounds that just makes at certain times.
In other words is something need fixed?
happens more on turns, lower throttle, and I guess what it is is when it's "working harder relative to rpm???"

That sounds like the drive motors. Possibly the bypass valve. That is the sound that these machines make when the parking brake is engaged and you try to drive the machine. In other words not enough power to the motors or a weak relief valve spring.

It should go away at higher rpm. If not there are several things that can cause this….relief valve and or spring worn out, drive motors worn out, just to name a few.

When these machines are in good shape you should be able to drive them up to an unmovable object, and at full throttle, all of the wheels should spin.

 

[marko13]

That sounds like the drive motors. Possibly the bypass valve. That is the sound that these machines make when the parking brake is engaged and you try to drive the machine. In other words not enough power to the motors or a weak relief valve spring.

It should go away at higher rpm. If not there are several things that can cause this….relief valve and or spring worn out, drive motors worn out, just to name a few.

When these machines are in good shape you should be able to drive them up to an unmovable object, and at full throttle, all of the wheels should spin.

okay so I wondered about the parking brake because it doesn't seem to do anything but that's a separate conversation. I haven't taken time to trace out where the linkage goes or how they work because I'm just trying to get this little job done.
so if I run it a higher throttle I'll see if that sound goes away, I think that does help but I've been trying to run a little lower to save fuel if it's not necessary to run full out all the time.
so the other half for the question is am I done some damage when that sound is occurring? meaning I guess I should be running it higher throttle normally than what I've been trying to do.

 

[polishpete]

the parking brake is enguaged u need to relase or change solonid

 

[brdgbldr]

I don't think your doing any damage. With full loads of gravel. You are lifting and moving a lot more weight then most people think so when you hear those sounds throttle up.

The other thing that you should check is the in-line filter. Those machines have a brass filter in an aluminum housing that will get clogged. You can find it in the parts schematics pages:

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

As for the breaks, they consist of two brake pads that when the peddle is engaged compress a steel disk. Most of those older machine the pads are either wore out or just completely loose and need to be adjusted. If when you press the toe of the center peddle there is no resistance, then the brake is not engaging. Just keep the heal of the peddle down when operating the machine. You can also look at the brake system in the parts catalog.

 

[marko13]

Thanks guys
next I want to post a vid of the side play in the bucket to question tolerances. I'd guess I have 1/4" side to side but haven't measured

 

[marko13]

That sounds like the drive motors. Possibly the bypass valve. That is the sound that these machines make when the parking brake is engaged and you try to drive the machine. In other words not enough power to the motors or a weak relief valve spring.

It should go away at higher rpm. If not there are several things that can cause this….relief valve and or spring worn out, drive motors worn out, just to name a few.

When these machines are in good shape you should be able to drive them up to an unmovable object, and at full throttle, all of the wheels should spin.

Yes all four wheels will spin if I just drive straight into the pile, and higher RPM reduces that squeal but then the engine is even louder than the squeal lol.

 

[pondfishr]

My 743 makes the same sounds. Has done it for some time. It's louder at a lower throttle.

 

[Markle]

Ditto what pondfishr said. Mine makes the same sounds. No loss of power. No change in realistic performance. Each side responds as it should. I asked a veteran hydraulic tech about it and he said just run it. The older drives were noisier than new technology drives.

 

[oiu789]

Might not hurt to take a look at the main drive belt, pulleys, and idler. Doesn't sound like it but easy to check it.

 

[Dave1234]

I wonder if what you are hearing at less than full throttle is the sound of the bypass valve cycling open and closed rapidly enough to be described as a frequency or squeal in response to pump volume being only slightly more than what is needed by the drive motors for the speed you are going, with the result that pressure is forming a sine wave above and below bypass pressure, and hence the bypass valve is opening, then pressure drops, it closes, pressure rises, it opens again etc. etc. That might also be accompanied by whistling of the hyd fluid going through a minimal opening in the bypass valve. If you increase the motor speed, then the bypass might be open nearly all the time, and/or cycling at a higher frequency, and/or opening the bypass a little farther eliminating the whistle, thereby collectively producing no or a different sound. I would expect the least noise to be present when "demand" (fluid potentially sent to the drive motors) is greater than "supply" (pump volume) with the result that the bypass valve never opens because under those conditions excess pressure cannot be generated.
Just a thought.

 

[marko13]

I wonder if what you are hearing at less than full throttle is the sound of the bypass valve cycling open and closed rapidly enough to be described as a frequency or squeal in response to pump volume being only slightly more than what is needed by the drive motors for the speed you are going, with the result that pressure is forming a sine wave above and below bypass pressure, and hence the bypass valve is opening, then pressure drops, it closes, pressure rises, it opens again etc. etc. That might also be accompanied by whistling of the hyd fluid going through a minimal opening in the bypass valve. If you increase the motor speed, then the bypass might be open nearly all the time, and/or cycling at a higher frequency, and/or opening the bypass a little farther eliminating the whistle, thereby collectively producing no or a different sound. I would expect the least noise to be present when "demand" (fluid potentially sent to the drive motors) is greater than "supply" (pump volume) with the result that the bypass valve never opens because under those conditions excess pressure cannot be generated.
Just a thought.

wow I guess I forgot to reply to this thread back then. thanks Dave I think that's the ticket if I give it enough throttle the engines a lot louder but the squeal is gone. Guess I should just go find some earplugs lol

 

[mrbb]

wow I guess I forgot to reply to this thread back then. thanks Dave I think that's the ticket if I give it enough throttle the engines a lot louder but the squeal is gone. Guess I should just go find some earplugs lol

yes I always wear ear muff 's anymore as I got older, I started to value my hearing more and more
I keep a set of ear muff inside my cab hanging on a magnetic hook from harbor freight, behind my shoulder out of the , but then there there all the time, so every time I get in machine, there already there for me to put on, and not forget to bring them to use
and I find ear muffs easier to put on/take off to talk someone or?? or do other things, find them easier and cleaner than ear plugs,
as with dirty hands, I rather not be handling things I am sticking in my ear! haha!

 

[MalcolmV8]

My 743 makes those same exact sounds but I find it's a part throttle thing. I really only throttle down when moving around or doing minimal stuff. As soon as I'm doing actual work I crank it to full throttle and those squeals are gone or maybe just so minimal I haven't noticed. I'll pay more attention now lol