I have a Bobcat 743B (not sure what year) that is making a loud growling sound that appears to be coming from below the operators seat. At the same time I have no forward or reverse or lift/tilt, in other words, no hydraulics. I double checked the hydraulic fluid level and it took about 1/2 gallon and once it was topped off I did have some hydraulics, able to move the machine slowly and lift and tilt slowly but the loud growling sound was still there. When this first started I checked in the engine compartment and found the alternator/water pump belt was broken. I replaced it but that did not help. Any insight on what the issue could be would be greatly appreciated.
743B Hydraulics problem
- Thread starter Rtoddhess
- Start date
polishpete
Well-known member
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- Oct 15, 2023
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- 282
the plate that goes between engine and pump
Could be the U-joint connecting the engine to the pump has failed. Most people don’t grease this and so they will fail which can lead to destroying the pump.
Thanks for the response! Does that require pulling the engine? If so, I would like to move it into my shop but when I tried to tow it the wheels wouldn't move. Is there some way to get the wheels to turn so I can tow it about 50 yards to my shop?
If you push the levers in the direction you want to tow the machine, it should allow the motors to turn. You can either have someone in the cab or tie them in possition.
If that does not work you will have to disconnect the motor hoses. Just make sure to clean around them real well and have a way to plug or cap the hoses. Do not plug or cap the motors. The big thing is to make sure no dirt gets in the motors. Some oil will come out of the motors with the hoses off. You can wrap the motors with thick garbage bags and bungee them on to contain the oil and help to keep dirt out.
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Hi Rtoddhess,
Welcome to the forum. You will need to pull the engine to get to the u-joint coupler. Sounds like the splines on the input to the hydraulic pump have either stripped or the splines in the coupler have if you're still getting some limited movement. Definitely DO NOT run it like this! Sounds like your u-joint itself is still relatively intact but if it does let go completely it WILL cause catastrophic damage. Ask me how I know!
To pull/tow the machine into your shop like Brdgbldr says the easiest thing you can do is disconnect the hydraulic lines going into the drive motors, they are under some small covers between the wheels on the bottom of your machine. You will lose a small amount of hydraulic oil but this will allow the motors to turn relatively freely. The other option is to remove the travel relief valves on the main pump body but this is a pain in the rear end. Unfortunately on these machines moving the travel levers will not allow the machine to move as they just stroke the pumps; this won't allow any fluid to circulate unless the pump is actually turning...
To pull the engine is actually really easy. It is mounted to a subframe within the machine and held in place by 4 bolts. All you need to do is disconnect the wires and fluid lines going to your engine, undo the exhaust and intake and the throttle connection, pull the 4 bolts and slide the engine backwards out of the engine room. You can have the engine out in about 30 minutes to an hour, surprisingly easy procedure. Getting it back in it is best if you have a helper to align the coupler to the pump shaft while the other person slowly and gently pushes the engine back in.
Welcome to the forum. You will need to pull the engine to get to the u-joint coupler. Sounds like the splines on the input to the hydraulic pump have either stripped or the splines in the coupler have if you're still getting some limited movement. Definitely DO NOT run it like this! Sounds like your u-joint itself is still relatively intact but if it does let go completely it WILL cause catastrophic damage. Ask me how I know!
To pull/tow the machine into your shop like Brdgbldr says the easiest thing you can do is disconnect the hydraulic lines going into the drive motors, they are under some small covers between the wheels on the bottom of your machine. You will lose a small amount of hydraulic oil but this will allow the motors to turn relatively freely. The other option is to remove the travel relief valves on the main pump body but this is a pain in the rear end. Unfortunately on these machines moving the travel levers will not allow the machine to move as they just stroke the pumps; this won't allow any fluid to circulate unless the pump is actually turning...
To pull the engine is actually really easy. It is mounted to a subframe within the machine and held in place by 4 bolts. All you need to do is disconnect the wires and fluid lines going to your engine, undo the exhaust and intake and the throttle connection, pull the 4 bolts and slide the engine backwards out of the engine room. You can have the engine out in about 30 minutes to an hour, surprisingly easy procedure. Getting it back in it is best if you have a helper to align the coupler to the pump shaft while the other person slowly and gently pushes the engine back in.
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Thank you for the detailed information! That was exactly what it was. I pulled the engine out and found the power transfer yoke that attaches to the u-joint was completely stripped and the shaft adapter that attaches to the hydrostatic pump shaft and goes inside the yoke was also damaged. Hearing all the problems that can happen if the u-joint goes bad made me bite the bullet and order a new one of those too. I am having trouble getting the shaft adapter off the hydrostatic pump shaft. I removed the bolt and tried to get a gear puller on it but there wasn’t enough room on the back side of it. I bought a smaller one that fit but it just bent under the pressure and slipped off. I ordered another gear puller from Amazon that looks like it will fit and be strong enough to do the job but I just want to be sure I’m not missing something that I still need to remove before trying to get it off. Like I said I already removed the bolt from the center of the shaft
- Joined
- Dec 17, 2009
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That drive spline coupler is on a taper on the shaft if I recall correctly so it will take some force to pop it off. A good quality puller will get the job done. That center bolt is all that holds it on, unless some enterprising individual before you put loctite or something like that on the shaft before they installed the coupler... Whatever you do BE VERY CAREFUL if you apply any heat to it so as you don't cook the pump seals. Another thing that could work is if you can get in there with a very thin (think Dremel tool) cutting wheel and carefully cut a slot along one of the splines to split the coupler and then it will come off pretty easy. I had one that was cracked right down the middle along one of the splines and it came off with no effort.
