721 Pressure Problem

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bugs0617

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I am new here, looks like the place to be to get answers to Q's . I have a 721 with Hydrostatic Pump when I got it pressure was very weak 30 pounds according to my repair manual it should be 75 pounds right side would not move left side would move but very noisy I bought another one just like mine for parts changed Hydrostatic Pump and motors pressure came up to 50 pounds so I had the orignal pump and motor rebulit pressure came up to 75 pounds just as manual suggest but heres my problem now when I'm using it the bucket jerks and is some what noisey when lifting steering is still a little noisy as your using it the pressure will drop to 25 pounds and the right lsteering lever will lose all pressure you can shut engine off or keep working bucket and steering at same time and the pressure wil come back up any help would be appeciated. Thanks
 

Tazza

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How long since you changed the pump over? you may still have air trapped in the system. It does take a bit of time to clear the air from the cylinders, mine took weeks of use it for a few mins then shut it down. The hydraulics were jittery for some time till all the air was gone.
That problem originally sounded like a suction line filter. It should be in the square block on the hydro pump. Middle hose on the left side behind the hose fitting. These filters almost never got changed because no one knew they were there!
I'd check the filter first. They may not have replaced it.
 

Tazza

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How long since you changed the pump over? you may still have air trapped in the system. It does take a bit of time to clear the air from the cylinders, mine took weeks of use it for a few mins then shut it down. The hydraulics were jittery for some time till all the air was gone.
That problem originally sounded like a suction line filter. It should be in the square block on the hydro pump. Middle hose on the left side behind the hose fitting. These filters almost never got changed because no one knew they were there!
I'd check the filter first. They may not have replaced it.
I am assuming this machine runs a vickers TA1919 pump. I'm pretty sure all the early machines up to the 743 series ran the same pump setup. The only difference was in the later models the block was not on top of the hydraulic pump but was moved to just near the throttle linkage on the chassis and only had 3 or 4 hoses attached. The port block filter was also removed. That filter caused so many dramas!!
 

bugs0617

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I am assuming this machine runs a vickers TA1919 pump. I'm pretty sure all the early machines up to the 743 series ran the same pump setup. The only difference was in the later models the block was not on top of the hydraulic pump but was moved to just near the throttle linkage on the chassis and only had 3 or 4 hoses attached. The port block filter was also removed. That filter caused so many dramas!!
Yes it does have the vickers hydrostatic pump and motors I will give it a look over to see if I can locate this filter I know theres a filter that is right before hydrostatic pump its like a car oil filter have changed it twice. It screws on a block that has the pressure sending unit on it is this the one your talking about.
 

sterlclan

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Yes it does have the vickers hydrostatic pump and motors I will give it a look over to see if I can locate this filter I know theres a filter that is right before hydrostatic pump its like a car oil filter have changed it twice. It screws on a block that has the pressure sending unit on it is this the one your talking about.
if your machine has a charge filter similar to mine it would be in the port block that is mounted right on the pump it has 3 hoses down the side its the middle one that has the filter some machines have the block mounted to the side of the chassis a service manual is worth every penny......good luck Jeff
 

Tazza

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if your machine has a charge filter similar to mine it would be in the port block that is mounted right on the pump it has 3 hoses down the side its the middle one that has the filter some machines have the block mounted to the side of the chassis a service manual is worth every penny......good luck Jeff
This filter does not screw in, its held in place with a spring. Its more like a bronze screen than a *normal* filter. The charge pressure sender is mounted to the port block, this is the same square block the filter is hidden in.
http://users.tpg.com.au/tazza_/731 hydrostatics.jpg
Look at that picture, the right side of the port block in the center. Its hiding behind fitting labeled 10.
See if thats any help, if not i may have more details here somewhere.
 

bugs0617

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This filter does not screw in, its held in place with a spring. Its more like a bronze screen than a *normal* filter. The charge pressure sender is mounted to the port block, this is the same square block the filter is hidden in.
http://users.tpg.com.au/tazza_/731%20hydrostatics.jpg
Look at that picture, the right side of the port block in the center. Its hiding behind fitting labeled 10.
See if thats any help, if not i may have more details here somewhere.
All 4 of my lines for the motors come out from the top of hydostatic pump.My vane pump bolts on front of hydro pump fa line comes off of vane pump to a valve (forgot what its called) then from there T's off to control valve and and to the filter I was talking about then to the hydro pump. I looked today I didnt see any other filters. Coluld it possibly be the pressure release vale the reason I say that is because the right side loses everything and the pressure release valve is located on same side as the feed lines for right side.
 

Tazza

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All 4 of my lines for the motors come out from the top of hydostatic pump.My vane pump bolts on front of hydro pump fa line comes off of vane pump to a valve (forgot what its called) then from there T's off to control valve and and to the filter I was talking about then to the hydro pump. I looked today I didnt see any other filters. Coluld it possibly be the pressure release vale the reason I say that is because the right side loses everything and the pressure release valve is located on same side as the feed lines for right side.
From the top of the pump? odd setup....
Most come from the sides, the rear 2 go to the right hand motor the front 2 goto the left. The vane pump attaches to the front with the high pressure hose going to the control block. The port block that sits on the pump connects to the “supercharge” port of the hydro pump. The filter hides in this block if your machine has this fitted.
Are you able to take a picture of the pump and post it? this way i have a better idea if what pump setup you have. If you can't pist it here, you can send it to my e-mail address
“taz38sup at yahoo.com.au” replace the at with an @ of course.
The lack of drive on one side could be low charge pressure due to a restriction in the suction line filter. The spin on filter you are refering to i believe is a return line, this is under charge pressure not negative pressure like the suction line filter. One side is pulling the oil through instead of it being pushed at 70 odd PSI like the spin on type does.
If that makes any sense.....
 

bugs0617

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From the top of the pump? odd setup....
Most come from the sides, the rear 2 go to the right hand motor the front 2 goto the left. The vane pump attaches to the front with the high pressure hose going to the control block. The port block that sits on the pump connects to the “supercharge” port of the hydro pump. The filter hides in this block if your machine has this fitted.
Are you able to take a picture of the pump and post it? this way i have a better idea if what pump setup you have. If you can't pist it here, you can send it to my e-mail address
“taz38sup at yahoo.com.au” replace the at with an @ of course.
The lack of drive on one side could be low charge pressure due to a restriction in the suction line filter. The spin on filter you are refering to i believe is a return line, this is under charge pressure not negative pressure like the suction line filter. One side is pulling the oil through instead of it being pushed at 70 odd PSI like the spin on type does.
If that makes any sense.....
Got you a picture out of my service manual see if you can get it if not I will e-mail it to you. http://www.flickr.com/photos/[email protected]/
 

Tazza

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Just sent it to your e-mail sorry that you couldnt get from the website. Let me know if you get it and what you . Thanks
I can sort of make it all out, you really needed to scan it in a higher rez.
From what i can see, its plumbed differently to the 731/743 machines. The pump and motors appear the same though.
Any change of a better scan so i can get a bit more detail?
I think i can make out 2 seperate filters, are they both spin on? i'm pretty sure the one shown near the oil cooler on the return line will be spin on but the other one thats shown in the botton picture running off the “T” piece thats coming off the control block then goes to the hydrostatic pump. I'm pretty sure this is the filter you want. This should suply oil to the charge port on the pump.
Its a shame i don't have a picture of my 731 to show what i mean, i will do a search on my pc at home for a pic. I may have one showing you what you need to look for.
 
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