743 Major Repairs

[Tazza]

gonna check whether its the same pressure.. but my mechanics told me that the flow wouldn't budge because of the other line. it should be less. nut unless i have a bad control valve. or my charge pressure is high

Seems odd....
I can't see your charge pressure being an issue for this, as if it was high enough to prevent the oil returning to the other coupling you would blow your seals in the pump, blow the hydraulic filter off and potentially split your oil cooler.
Your charge pressure should be around 100PSI
If the oil isn't returning, its almost as if something is blocking its return path to the control block. I can't see the spool causing this, its one piece and the ports it slides back and forth in are pretty large and would take something substantial to block up. Does it lock into detent? i'm only curious because if the spool was actually broken inside the control block, it would not disengage. It should pull to the right and POP into place and hold there. You need to pull it to the left to get it to pop back out.
I can't believe how many bugs you have had to deal with in this machine! But i must admit, you are doing an amazing job of sorting them all out!!! and quickly. A 743 i had with masses of problems took me about 12 months to get all sorted out, that included painting too.

 

[bluthunder]

Seems odd....
I can't see your charge pressure being an issue for this, as if it was high enough to prevent the oil returning to the other coupling you would blow your seals in the pump, blow the hydraulic filter off and potentially split your oil cooler.
Your charge pressure should be around 100PSI
If the oil isn't returning, its almost as if something is blocking its return path to the control block. I can't see the spool causing this, its one piece and the ports it slides back and forth in are pretty large and would take something substantial to block up. Does it lock into detent? i'm only curious because if the spool was actually broken inside the control block, it would not disengage. It should pull to the right and POP into place and hold there. You need to pull it to the left to get it to pop back out.
I can't believe how many bugs you have had to deal with in this machine! But i must admit, you are doing an amazing job of sorting them all out!!! and quickly. A 743 i had with masses of problems took me about 12 months to get all sorted out, that included painting too.

well i just realized when i push it to the right to detent position it locks in to place and doesn't release back.. i have to pull it back in place. is that right or i got a problem with the spool? Lol... good thing you have 12 months for that i got only a few days left to get it working.. i'm already delayed with my project. and i badly need this machine to get it work.. as a recall. when you pull to detent position. both hoses have hydraulic oil coming out. i think its about the same pressure.. same thing when you push it to the right.. im not sure whether the pressure is the same... an this is the last problem i have to face before i could get the thing done. everythings seems to be working great except for the auxiliary attachment though.

 

[jerry]

well i just realized when i push it to the right to detent position it locks in to place and doesn't release back.. i have to pull it back in place. is that right or i got a problem with the spool? Lol... good thing you have 12 months for that i got only a few days left to get it working.. i'm already delayed with my project. and i badly need this machine to get it work.. as a recall. when you pull to detent position. both hoses have hydraulic oil coming out. i think its about the same pressure.. same thing when you push it to the right.. im not sure whether the pressure is the same... an this is the last problem i have to face before i could get the thing done. everythings seems to be working great except for the auxiliary attachment though.

That is right with the detent, it will stay in position till you manually move the stick back to the middle. The oil from both lines sounds odd though. Can you connect it to something to try it?

 

[bluthunder]

That is right with the detent, it will stay in position till you manually move the stick back to the middle. The oil from both lines sounds odd though. Can you connect it to something to try it?

ive connected a hydrauilc breaker with it and it doesn't work.. and what happened was when i disconnected the return side of the breaker and leaving it open the breaker is full force and is working great. the problem is the return side of the auxiliary. i think this could be a damage in the spool. maybe some scratches that pressure passes and blocks the return of the second auxiliary hose.. i will try tomorrow determining the problem. my options are reversing the connection. - hoping to have a good psi rating on the other side.. but if not i may have to connect the auxiliary hose to the other spool that have no connection because i have 4 stages of spool.. only three are connected to the hydrauilc lines one is not used.

 

[bluthunder]

ive connected a hydrauilc breaker with it and it doesn't work.. and what happened was when i disconnected the return side of the breaker and leaving it open the breaker is full force and is working great. the problem is the return side of the auxiliary. i think this could be a damage in the spool. maybe some scratches that pressure passes and blocks the return of the second auxiliary hose.. i will try tomorrow determining the problem. my options are reversing the connection. - hoping to have a good psi rating on the other side.. but if not i may have to connect the auxiliary hose to the other spool that have no connection because i have 4 stages of spool.. only three are connected to the hydrauilc lines one is not used.

I have checked the control valve and when we tested it, it is working properly. my guess is that there is pressure on the outlet side of the control valve.. is this the charged pressure? how can i control the charge pressure. The control valve that i have is not the same as the ones in the manual explained. i think its an old 4 spool contol valve w/ cavities.. need help guys

 

[Tazza]

I have checked the control valve and when we tested it, it is working properly. my guess is that there is pressure on the outlet side of the control valve.. is this the charged pressure? how can i control the charge pressure. The control valve that i have is not the same as the ones in the manual explained. i think its an old 4 spool contol valve w/ cavities.. need help guys

Charge pressure is generated as far as i am aware, with the returning oil from the cylinders/attachments when it returns from the oil cooler/filter. Its adjusted with shims in the main hydrostatic pump. I don't know off hand what port it is though, but naturally, it will be in a hard to get to place.
I wouyld stick a gauge on the filter housing to see what your pressure is, if its 100'ish PSI its right.

 

[bluthunder]

Charge pressure is generated as far as i am aware, with the returning oil from the cylinders/attachments when it returns from the oil cooler/filter. Its adjusted with shims in the main hydrostatic pump. I don't know off hand what port it is though, but naturally, it will be in a hard to get to place.
I wouyld stick a gauge on the filter housing to see what your pressure is, if its 100'ish PSI its right.

Is it the main hydrostatic pump? or the main relief valve?

 

[Tazza]

Is it the main hydrostatic pump? or the main relief valve?

Its in the hydrostatic pump housing. The main relief is set to 2,400'ish the charge pressure relief in the pump is set to about 100PSI. It will look like a plug on the centre section of the pump. Underneath it will be a spring, poppet and shims. From memory its a fairly small plug, you will notice a few large ones, especially two large ones per side, these will be you rmain drive pump relief/replenisng valves, you don't need to fiddle with those.
Sorry i can't be more precise.....

 

[bluthunder]

Its in the hydrostatic pump housing. The main relief is set to 2,400'ish the charge pressure relief in the pump is set to about 100PSI. It will look like a plug on the centre section of the pump. Underneath it will be a spring, poppet and shims. From memory its a fairly small plug, you will notice a few large ones, especially two large ones per side, these will be you rmain drive pump relief/replenisng valves, you don't need to fiddle with those.
Sorry i can't be more precise.....

i still can't find where the pressure came from. haven't check the charge pressure yet. could anyone have an experience with control valve that i have well i have a single 4 spool control valve. its a one piece design. two cavity plugs on the aux spool one anti cavity vavle the bob tach, 1 hydro force, and 1 cavity valve at the boom side, there is pressure coming outfrom both aux ocnnnector of the return direction thus giving an equal pressure dat could result in a malfunction of the breaker and restrict flow of hair from the . could i adjust the flow of the oil/ in case that is is the culprit.

 

[OldMachinist]

i still can't find where the pressure came from. haven't check the charge pressure yet. could anyone have an experience with control valve that i have well i have a single 4 spool control valve. its a one piece design. two cavity plugs on the aux spool one anti cavity vavle the bob tach, 1 hydro force, and 1 cavity valve at the boom side, there is pressure coming outfrom both aux ocnnnector of the return direction thus giving an equal pressure dat could result in a malfunction of the breaker and restrict flow of hair from the . could i adjust the flow of the oil/ in case that is is the culprit.

Please post a picture of the control valve I'll compare it to the valves shown in the Bobcat hydraulic control valve repair manual. The valve it shows for the 743 only has 3 spools and looks like this.

 

[bluthunder]

Please post a picture of the control valve I'll compare it to the valves shown in the Bobcat hydraulic control valve repair manual. The valve it shows for the 743 only has 3 spools and looks like this.

I have this one.. 15001 and above type of control valve. OLD MACHINIST can you help me with this? the problem that i have is that when there is a blockage or attachement on the auxiliary connection. the pressure on one side is high and the other one has the same pressure too. but when both have no connection/ no quick couplings and you detent to left hard both hose have the same pressure coming out. but when one is blocked i have a high pressure. could you send mo on how to's so i could determine what is the problem of my control valve? its like there is a bypass going on. because the pressure keeps changing if you also change the one you block. on the same detent left position. do you have a manual for this? i really have a hard time with it..

 

[OldMachinist]

I have this one.. 15001 and above type of control valve. OLD MACHINIST can you help me with this? the problem that i have is that when there is a blockage or attachement on the auxiliary connection. the pressure on one side is high and the other one has the same pressure too. but when both have no connection/ no quick couplings and you detent to left hard both hose have the same pressure coming out. but when one is blocked i have a high pressure. could you send mo on how to's so i could determine what is the problem of my control valve? its like there is a bypass going on. because the pressure keeps changing if you also change the one you block. on the same detent left position. do you have a manual for this? i really have a hard time with it..

Okay so you have the control valve with four spools(lift, tilt, aux. front and aux. rear). Are both the aux. spools activated by the same linkage? If yes is it possible that the plumbing is hooked up wrong(I.E. one of the front aux lines hooked to one side of the rear aux spool and vice versa).

 

[Luthor]

Okay so you have the control valve with four spools(lift, tilt, aux. front and aux. rear). Are both the aux. spools activated by the same linkage? If yes is it possible that the plumbing is hooked up wrong(I.E. one of the front aux lines hooked to one side of the rear aux spool and vice versa).

The rear aux. spool is normally not connected to any linkage unless special rear attachments have been fitted.

 

[bluthunder]

The rear aux. spool is normally not connected to any linkage unless special rear attachments have been fitted.

there is no lingkage for the auxilary spool rear..

 

[bluthunder]

there is no lingkage for the auxilary spool rear..

Just checked the pressure from the filter. there is no pressure/ or the pressure is just too low..