Bobcat 743

[HorseDoc]

Thanks in advance for any help ya'll can provide. I aquired a 743 last week from an individual. At the time of purchase the machine was working well. However, after running it for around 30 minutes it began to make a horrible gear grinding sound that seems to come from the area where the engine connects to the pump. I immediately shut the motor down and pulled the machine into the shop. I then allowed the machine to cool down for 24 hours. During this time I changed the hydraulic filter located in the engine compartment. After the cool down period, I restarted the machine briefly. The grinding noise was not as bad while the engine was cold but got progressively worse as things warmed up. The lift arms, wheels and bucket still works though noticably sluggish. I am not familiar with the how power is transmitted from the engine to the pump ie spline drive, belts etc... Was wondering if others may have seen this problem before. Again, I appreciate any and all info....

 

[Fishfiles]

The pump to engne connection on a 743 is a splined shaft with a yoke on one side and a yoke bolted to the flywheel on the other side with a double u joint vlocity ring in between , I have seen the splines strip out and still work sluggishly but mae a terrible growl

 

[Tazza]

The pump to engne connection on a 743 is a splined shaft with a yoke on one side and a yoke bolted to the flywheel on the other side with a double u joint vlocity ring in between , I have seen the splines strip out and still work sluggishly but mae a terrible growl

It still makes the noise when you simply sit on one place with the engine running and park brake off? or does it only make noise when you try and move? I have had a noise like that when the park brake is engaged, unsure its kicked back towards you when you operate the machine. Forward is locked, backwards in unlocked.
As Fishfiles said, the engine is linked to the pumps via 2 universal joints to a splined shaft. I have never seen it cause noise before, but i have not worked on THAT many of them.
Lift the cab, is there a square block on top of the hydraulic pump with about 5 hoses going into it? or just one large one that connects the the left side of the chassis? If so, there is a hidden filter on the right side where the 3 hoses connect, its behind the middle fitting. This only applies if your machine has the square block on the pump.

 

[HorseDoc]

It still makes the noise when you simply sit on one place with the engine running and park brake off? or does it only make noise when you try and move? I have had a noise like that when the park brake is engaged, unsure its kicked back towards you when you operate the machine. Forward is locked, backwards in unlocked.
As Fishfiles said, the engine is linked to the pumps via 2 universal joints to a splined shaft. I have never seen it cause noise before, but i have not worked on THAT many of them.
Lift the cab, is there a square block on top of the hydraulic pump with about 5 hoses going into it? or just one large one that connects the the left side of the chassis? If so, there is a hidden filter on the right side where the 3 hoses connect, its behind the middle fitting. This only applies if your machine has the square block on the pump.

It makes noise whenever the engine is running. The growling gets worse as the motor warms up. The pedal in the middle ( brake? ) doesn't seem to affect the noise at all. In fact, it doesn't seem to do anything at all. Suspect adjustment problem. I will check the filter on the top of that block next. However, I am thinking along the same lines about the universal jts. Is there an easy way to get to and checkout this area or do you need to separate the pump from the motor.

 

[Fishfiles]

It makes noise whenever the engine is running. The growling gets worse as the motor warms up. The pedal in the middle ( brake? ) doesn't seem to affect the noise at all. In fact, it doesn't seem to do anything at all. Suspect adjustment problem. I will check the filter on the top of that block next. However, I am thinking along the same lines about the universal jts. Is there an easy way to get to and checkout this area or do you need to separate the pump from the motor.

Do you know that there are some grease fittings on the u joints , and that could be the problem , try and locate ad repair asap , for it the u joints fail it can cause some damage when they let loose , a grease gun with a long hose on it , or two 12 " hose coupled together will get in there , they may be already ruined but some grease may quiet them down so that you can pin point it , a remote starter button helps to line them up , they can be seen but not very clearly , if the splines are slipping on the shaft , after running the machine for a minute or so and killing it you can touch the splined yoke collar and the u joints and you may be able to feel a heat build heat , it's easier to pull the motor than it is to pull the pump if that is where your problem is --------is the machine trying to move while sitting there running as the growl you mention does occur when the steering nutraul is out of adjustment

 

[Tazza]

Do you know that there are some grease fittings on the u joints , and that could be the problem , try and locate ad repair asap , for it the u joints fail it can cause some damage when they let loose , a grease gun with a long hose on it , or two 12 " hose coupled together will get in there , they may be already ruined but some grease may quiet them down so that you can pin point it , a remote starter button helps to line them up , they can be seen but not very clearly , if the splines are slipping on the shaft , after running the machine for a minute or so and killing it you can touch the splined yoke collar and the u joints and you may be able to feel a heat build heat , it's easier to pull the motor than it is to pull the pump if that is where your problem is --------is the machine trying to move while sitting there running as the growl you mention does occur when the steering nutraul is out of adjustment

Thats a good point. Block the loader so the wheels are off the ground, start it up and see if it still growls. The brake pedal should tilt back towards you. The wheels should not turn, if they do, this *could* be whats causing the growl.
With the wheels off the ground there is no reason for it to growl, if it still does you may need to check your Uni-Joints.
Pulling the engine isn't hard at all. As mentioned if the uni-joints go bad they can cause you a lot of grief. It can take out the oil cooler, radiator or fins off the fly wheel. If you keep running it with bad joints you will eventually cause pump damage.
Hopefully its something simple that is easy and cheap to repair.

 

[HorseDoc]

Thats a good point. Block the loader so the wheels are off the ground, start it up and see if it still growls. The brake pedal should tilt back towards you. The wheels should not turn, if they do, this *could* be whats causing the growl.
With the wheels off the ground there is no reason for it to growl, if it still does you may need to check your Uni-Joints.
Pulling the engine isn't hard at all. As mentioned if the uni-joints go bad they can cause you a lot of grief. It can take out the oil cooler, radiator or fins off the fly wheel. If you keep running it with bad joints you will eventually cause pump damage.
Hopefully its something simple that is easy and cheap to repair.

Looking at engine removal, it doesn't look difficult. However just to be clear, could someone post a step by step that hits the highlights of engine removal. Thanks...

 

[Tazza]

Looking at engine removal, it doesn't look difficult. However just to be clear, could someone post a step by step that hits the highlights of engine removal. Thanks...

In simple terms remove the following:
4 bolts that hold the engine down.
Air intake hose at the manifold, plug both ends.
Fuel line at the lift pump, plug BOTH ends of this line. Also remove the tap off line at the back of the engine on number 4 injector, rite where the blower housing is.
Remove all wiring to the engine.
Remove the shutdown cable and throttle linkage.
Exhaust line from the exhaust manifold must be removed, depending on how rusted the 4 bolts are at the manifold you may want to leave it attached and remove it where it enters the muffler.
I think thats about it.... Just use a car hoist or black and tackle through the lift points on the cylinder head lift and pull the engine back. Do the reverse to put it back but don't push it all the way in. Sit it on the back of the engine bay, have 2 people, one will lay on the hydro pump with the cab in the air the other uses bars to SLOWLY push the engine forward. You need to hold the coupling up on the end of the U-Joints to line up with the pump. Be careful not to put a finger between the spline and coupler when moving the engine, it could be nasty!
When the engine is in place, re-prime the fuel line and you are set!.
If anything is not clear just yell.

 

[HorseDoc]

In simple terms remove the following:
4 bolts that hold the engine down.
Air intake hose at the manifold, plug both ends.
Fuel line at the lift pump, plug BOTH ends of this line. Also remove the tap off line at the back of the engine on number 4 injector, rite where the blower housing is.
Remove all wiring to the engine.
Remove the shutdown cable and throttle linkage.
Exhaust line from the exhaust manifold must be removed, depending on how rusted the 4 bolts are at the manifold you may want to leave it attached and remove it where it enters the muffler.
I think thats about it.... Just use a car hoist or black and tackle through the lift points on the cylinder head lift and pull the engine back. Do the reverse to put it back but don't push it all the way in. Sit it on the back of the engine bay, have 2 people, one will lay on the hydro pump with the cab in the air the other uses bars to SLOWLY push the engine forward. You need to hold the coupling up on the end of the U-Joints to line up with the pump. Be careful not to put a finger between the spline and coupler when moving the engine, it could be nasty!
When the engine is in place, re-prime the fuel line and you are set!.
If anything is not clear just yell.

Good news, considering all the alternatives. It is indeed a stripped power transfer yoke and spline adapter. This appears to be a relatively easy fix. Called Bobcat for parts and its about $500. I was wondering if there are other options for new parts other than the dealer? Thanks again Tazza and Fishfiles.

 

[eddyseptichands]

Good news, considering all the alternatives. It is indeed a stripped power transfer yoke and spline adapter. This appears to be a relatively easy fix. Called Bobcat for parts and its about $500. I was wondering if there are other options for new parts other than the dealer? Thanks again Tazza and Fishfiles.

I don't think you'll get that anywhere else but bobcat, on the good side if you maintain it it will last a long time. You should also replace the motor mounts, as they age and sag it wears on that very same spline. While youve got the engine out look at increasing the size of the drain hole on the plastic air shroud it always clogs up and fills with rainwater which blows up through the rad on startup.And check all those steel lines for wear some of them are easy to replace now rather then later.The 743 is one of the best machines of that size around,cheap to run and easy to maintain . Good Luck

 

[Tazza]

I don't think you'll get that anywhere else but bobcat, on the good side if you maintain it it will last a long time. You should also replace the motor mounts, as they age and sag it wears on that very same spline. While youve got the engine out look at increasing the size of the drain hole on the plastic air shroud it always clogs up and fills with rainwater which blows up through the rad on startup.And check all those steel lines for wear some of them are easy to replace now rather then later.The 743 is one of the best machines of that size around,cheap to run and easy to maintain . Good Luck

I would also check your u-joints, if they are worn make sure you replace them too.
The drive splines you will have to buy from Bobcat..... It will be specially made for them.

 

[Fishfiles]

I would also check your u-joints, if they are worn make sure you replace them too.
The drive splines you will have to buy from Bobcat..... It will be specially made for them.

Did you disassemble it yet and inspect the splines on the input shaft of the pump , there may be damaged there as well , also might try bringing the spined yoke to a machine shop and see if they could get that size splined shaft and weld a piece to the yoke cheaper than a new one cost if time isn't an issue , I have not priced one of those in quite a few years but almost wonder if the price you quoted (around $500 ) is for the entire assembly , which would include the u-joints , velocity ring and spline yoke

 

[Joby]

Did you disassemble it yet and inspect the splines on the input shaft of the pump , there may be damaged there as well , also might try bringing the spined yoke to a machine shop and see if they could get that size splined shaft and weld a piece to the yoke cheaper than a new one cost if time isn't an issue , I have not priced one of those in quite a few years but almost wonder if the price you quoted (around $500 ) is for the entire assembly , which would include the u-joints , velocity ring and spline yoke

You should be able to buy what is called a 'splined hub' that conforms to your yoke spline style from any major hydraulics supplier and then get it welded onto your yoke (your yoke may need machining to take the hub) but any machine shop should be able to do the work. You can also buy the universal joints from an auto supplier at little cost, some GM universals are identical to the 743, I know, I've used them myself.