Owatonna / Mustang 770 wheel loader weak hydrostatic drive

[DoubleO7]

I didn't see any metal shavings in the filter. It was pretty clean.

If it is a spin-on filter, did you cut it open or just look into the center hole?
If yes, you need to cut the can off in order to see the crud on the filter inside.

How is the hydro unit driven from the clutch? A splined shaft in the drive disc? going out of the bellhousing via a flanged pillow block bearing. Then a u-joint or shaft coupler of what type? Which is then connected to the hydro unit input shaft?
If yes, is it possible there is a key on the input shaft that has sheared?
I have seen where a keyed shaft breaks the key and will still transmit enough power to spin the hydro enough to provide slow movement when there is little resistance to moving. Then as moving gets more difficult like going uphill or up onto a trailer or over a curb, the broken key is inefficient to transmit power and the input shaft spins in the coupler. Progressively getting worse as chewing itself to slip more easily.
Until it eventually won't wont move the machine at all.

I don't use the clutch at all because the cable is shot.

As used red mentioned, is the bad clutch cable even installed?

You also mentioned this slow moving creep was going on BEFORE the engine change?
Was the diesel bad and needed replacing or you thought that the "no power" was an engine problem?

 

[Woodtractor1]

Having a mechanical clutch in front of a hydrostat isn't common and will make diagnosing the problem harder since there are more factors in play.

One quick and easy test for the motor is to check the case leakage. There will be a hose coming off the motor housing that leads to the cooler and return filter and this is the case drain. Take this hose from the motor and direct it into a bucket (just plug off the connection it was attached to on the other end.) When the machine is in neutral you should have a case drain flow of around 3 gpm maximum, ideally quite a bit less than that. If you have more flow than that it would suggest a worn-out rotating group that is allowing too much oil to escape around the pistons.

You can't check the pump this way because the pump leakage is combined with the oil going over the charge relief valve and comes out the case drain port all together.

I found a video of a Sundstrand pump undergoing tests on youtube. Does the picture below look like the back of your pump? If so the tee fittings coming out towards you in the picture are the gauge ports, the ones right close to the system ports. You really need two gauges capable of taking full system pressure to diagnose a hydrostatic pump. When the hydro is in neutral both ports should show charge pressure which is generally in the 200 to 400 psi ballpark, depending on how the hydro is configured for that application. When the hydro is stroked in one direction or the other the high pressure side of the loop will increase while the low pressure side will remain at charge pressure. It is critical that the entire loop remains at charge pressure or higher to avoid destroying the pistons and swashplate. The peak pressure on the high side will depend on the relief valve setting but it will be at least 3000 psi if not higher.

One way to determine if it is the clutch slipping rather than a faulty hydrostat would be to plumb a flow meter into the outlet of your auxiliary function pump. If this flow drops when the machine stalls out you will know that it is the clutch slipping since this flow would not be impacted by anything the hydrostat is doing.

View attachment 67758

I will check the pump for the connectors.

Once I receive and install the filter, I'm going to try driving up to a curb and stall the machine while trying to pick up 4000 or 5000 lbs and see if it will pick it up while I'm stalled. I would assume it wouldn't pick it up if it's the clutch slipping. By the way, this wheel loader has a forklift mast on it, not a loader assembly.

 

[Woodtractor1]

Not sure if this shows to others or not.
…”The engine revs high and does not bog or stall when I am trying to go over a small bump or incline, but there's just no power.” This tells me you are not using all the engine power that is available. Fact 2.. you didn’t pull the clutch off the used engine to check its condition tells the story to me. You’re going to have to get back to the clutch to check it out. The only saving grace you may have is that the the clutch free play is set incorrectly. Or the bad actuating cable may possibly be holding the clutch partially disengaged. Disconnect the cable end from the lever it operates down by the clutch. If it requires force to remove the pin that operates the lever and it springs to a different location away from the cable then that was likely your problem. That was holding the clutch partially released. All my terminology is based on a general idea of what the clutch cable layout is like in most machinery so equipped. Between non turbocharged gas and diesel engines of the same size the gas engine will make the most horsepower.

I'll feel pretty foolish if it's the clutch and I didn't check it before I installed the engine. This was not an easy install.

 

[used red MN]

I'll feel pretty foolish if it's the clutch and I didn't check it before I installed the engine. This was not an easy install.

You do understand the the checks I have suggested can be and should be done before you condemn the clutch as the possible problem? I don’t know if there is an access cover to see the throwout brg but what I am suggesting is that the clutch needs free play on the TO brg. You say the cable is bad I am thinking that may mean it is very stiff and is not letting the TO bearing back away from the clutch plate TO bearing. If the clutch is bad don’t worry about it that is just a way to learn how to do it bettter next time.

 

[used red MN]

Many Sundstrand hydros have a thru put output shaft directly connected to the input shaft.

This may be a way to test the clutch if the hydro has no dependence on the output of that auxiliary pump. You could pull it back and then see if the thru shaft slows down. Even how the other hydraulic respond during the suspected time the clutch is slipping could verify this. If they slow down this probably means the shaft driving it is slowing down.

 

[used red MN]

If it is a spin-on filter, did you cut it open or just look into the center hole?
If yes, you need to cut the can off in order to see the crud on the filter inside.

How is the hydro unit driven from the clutch? A splined shaft in the drive disc? going out of the bellhousing via a flanged pillow block bearing. Then a u-joint or shaft coupler of what type? Which is then connected to the hydro unit input shaft?
If yes, is it possible there is a key on the input shaft that has sheared?
I have seen where a keyed shaft breaks the key and will still transmit enough power to spin the hydro enough to provide slow movement when there is little resistance to moving. Then as moving gets more difficult like going uphill or up onto a trailer or over a curb, the broken key is inefficient to transmit power and the input shaft spins in the coupler. Progressively getting worse as chewing itself to slip more easily.
Until it eventually won't wont move the machine at all.

As used red mentioned, is the bad clutch cable even installed?

You also mentioned this slow moving creep was going on BEFORE the engine change?
Was the diesel bad and needed replacing or you thought that the "no power" was an engine problem?

…Was the diesel bad and needed replacing..
This is the squeaking 172 lost oil and knocked the bearings out. Installing the used running gas engine was the cheapest alternative.
https://forums.yesterdaystractors.c...-smoke-out-of-breather.1755443/#post-11441498

 

[Woodtractor1]

If it is a spin-on filter, did you cut it open or just look into the center hole?
If yes, you need to cut the can off in order to see the crud on the filter inside.

How is the hydro unit driven from the clutch? A splined shaft in the drive disc? going out of the bellhousing via a flanged pillow block bearing. Then a u-joint or shaft coupler of what type? Which is then connected to the hydro unit input shaft?
If yes, is it possible there is a key on the input shaft that has sheared?
I have seen where a keyed shaft breaks the key and will still transmit enough power to spin the hydro enough to provide slow movement when there is little resistance to moving. Then as moving gets more difficult like going uphill or up onto a trailer or over a curb, the broken key is inefficient to transmit power and the input shaft spins in the coupler. Progressively getting worse as chewing itself to slip more easily.
Until it eventually won't wont move the machine at all.

As used red mentioned, is the bad clutch cable even installed?

You also mentioned this slow moving creep was going on BEFORE the engine change?
Was the diesel bad and needed replacing or you thought that the "no power" was an engine problem?

I put the old filter in a coffee can and plan to cut it open (it's a canister filter element) when the replacement filter arrives. I need to make sure it fits before I destroy the old one.

I inspected the clutch cable operation when the engine was out. It's basically in an "always engaged" position. Meaning in it will not push the pressure plate and disengage the clutch. I don't think it's the throw out bearing pushing up against the pressure place based on what I saw when the engine was out.

There is a splined shaft that goes into the clutch. It was in great shape.

I am leaning toward it being the hydrostatic pump or hydrostatic motor. This sounds like it's going to be a nightmare trying to figure out which one it is. I don't have a flow meter or gauges. I suppose I can buy these tools

 

[Jim.ME]

I put the old filter in a coffee can and plan to cut it open (it's a canister filter element) when the replacement filter arrives. I need to make sure it fits before I destroy the old one.

I inspected the clutch cable operation when the engine was out. It's basically in an "always engaged" position. Meaning in it will not push the pressure plate and disengage the clutch. I don't think it's the throw out bearing pushing up against the pressure place based on what I saw when the engine was out.

There is a splined shaft that goes into the clutch. It was in great shape.

I am leaning toward it being the hydrostatic pump or hydrostatic motor. This sounds like it's going to be a nightmare trying to figure out which one it is. I don't have a flow meter or gauges. I suppose I can buy these tools

You may want to search out a hydraulic shop that works on Sundstrand pumps and motors. It may cost to have them check it; however, it may be less expensive in the end. And there may be issues/wear in both the pump and motor. JMHO

 

[used red MN]

I put the old filter in a coffee can and plan to cut it open (it's a canister filter element) when the replacement filter arrives. I need to make sure it fits before I destroy the old one.

I inspected the clutch cable operation when the engine was out. It's basically in an "always engaged" position. Meaning in it will not push the pressure plate and disengage the clutch. I don't think it's the throw out bearing pushing up against the pressure place based on what I saw when the engine was out.

There is a splined shaft that goes into the clutch. It was in great shape.

I am leaning toward it being the hydrostatic pump or hydrostatic motor. This sounds like it's going to be a nightmare trying to figure out which one it is. I don't have a flow meter or gauges. I suppose I can buy these tools

If indeed the hydraulic pump is driven through the engine clutch as has been proposed then the hydro can’t be blamed until you perform the check you have spoken of in reply #22. An immediate change in the hydros response after the engine change points toward something that was changed when the engine was put in. The hydro is still the same as it was before. The clutch was changed. JMHO

 

[Woodtractor1]

If indeed the hydraulic pump is driven through the engine clutch as has been proposed then the hydro can’t be blamed until you perform the check you have spoken of in reply #22. An immediate change in the hydros response after the engine change points toward something that was changed when the engine was put in. The hydro is still the same as it was before. The clutch was changed. JMHO

I agree.
The hydro unit was drained when I removed the engine. I refilled it with the new engine but didn't change the filter because I couldn't find one anywhere.
I now have a new filter coming.
I wondered if air is in the lines too

 

[used red MN]

I agree.
The hydro unit was drained when I removed the engine. I refilled it with the new engine but didn't change the filter because I couldn't find one anywhere.
I now have a new filter coming.
I wondered if air is in the lines too

Air is doubtful, the fluid in that thing is circulating around like it’s coming out of a fire hose. Well on second thought that is not exactly true. When you have the speed or motion lever to either full forward or full reverse it is. If your controls are not responding properly that may be air. More in the way of say you move the lever half way to move forward. Then it doesn’t respond right away and when it does the speed is erratic, that could be air. I don’t hear you saying that just that it does not have the power to move the machine as it should. Here are videos of what is going on in there.
Fixed swash plate pump
Pump/motor with changeable angle swash plate, @ 2:30
Changeable swash plate
In the exploded views you posted in the upper right is a square cover, then a gasket. Next is an odd looking piece with three holes, two in the same axis crosswise and the 3rd has the (drawn) centerline of the cover going through it. That is the part that pivots to change the swash plate angle. In the case of the motor the swash plate tilts beyond flat and tilts the other direction. When it does that the motor reverses.

 

[Fritz Maurer]

If this is indeed a model 23, the test pressures are taken at the motor, not the pump. The first thing you need to determine before anything else is case pressure. This should be 170-190 PSI.

If the gauge is fluctuating , you have a charge pump suction leak, introducing air into the system which will make it sluggish. Bleeding is not required because the air is released from the oil every time it returns to the reservoir. Except that the air is constantly added to the system, ergo, it never goes away.

Makes sense that it goes worse after engine swap, may have aggravated the leak wiggling the lines around.

If you look at the motor where the pressure lines go into the block, the two test plugs are all alone on the side of the block around the corner from the pressure lines. You will need 7500 PSI gauge to check these, but I’m guessing the problem will become apparent before this is a required purchase. Besides, we already know that there is no pressure here because the machine won’t move. The case pressure test plug is on the end of the pump, near the edge, in the center, on a 90* axis from the high pressure test ports.

A little dirt and no brass in the filter is a good sign. These pumps don’t wear out quietly… they are generally catastrophic failures that don’t leave any doubt .

Should also look for a suction strainer and make sure that’s not blocked.

 

[Brendon-KS]

If this is indeed a model 23, the test pressures are taken at the motor, not the pump. The first thing you need to determine before anything else is case pressure. This should be 170-190 PSI.

I think you meant "charge pressure" instead of "case pressure" here. Case pressure should be in the 20 psi ballpark.

 

[DoubleO7]

Hi,
I have a 1978 omc mustang 770 loader that barely creeps up the slightest incline or up a small curb.

The power was lacking before the engine swap but not nearly as bad as now.

Are these two statements saying the power to climb the slightest incline or up a small curb were present and are still now present after the engine swap?

 

[Woodtractor1]

I got the new filter installed. I didn't see any shaving in the old filter and old oil.

I drove the loader to a curb and tried to go up the curb while lifting a 2k lb log AND while I retracted the tilt cylinders fully which caused the engine to almost stall. The mast still lifted the log while I pressed the accelerator pedal. This leads me to believe it is not the clutch.

When the loader was empty, I barely made it up the curb from a dead stop by full throttling the engine. The gas 172 sounded like it was revving dangerously high. How and where would I hook up a tachometer to the engine?

I am thinking it is the hydrostatic motor. I will try and take some pictures of the motor and post them in hopes that you can tell me where to put the gauges. I didn't quite understand Fritz's post above.

 

[DoubleO7]

When the loader was empty, I barely made it up the curb from a dead stop by full throttling the engine. The gas 172 sounded like it was revving dangerously high. How and where would I hook up a tachometer to the engine?

I am thinking it is the hydrostatic motor. I

Seems to me if it is stalling the engine, the clutch is not slipping.
What is the next thing that could drag the engine down?
A blockage inside the hydro unit?
i.e. not enough fluid flow to move normally and creating too much back pressure causing the engine to bog down