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Hydrostatic Transmission Problem


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#1 kiddpitt OFFLINE  

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Posted April 24, 2012 - 06:35 PM

Hi, I had a problem with my '73 LGT 145 blowing the transmission filter apart. Thinking it was clogged, I took off the lines from the transmission to the filter, from the filter to the lift valve, & from the lift valve to the transmission. Cleaned everything and blew compressed air through, put it all back together and the fitler blew apart again.

I don't know much about these transmissions. Is there another part that could be clogged/not working, like a pressure relief valve? I downloaded the service manual from here, but I'm hoping someone that understands this sytem could chime in.

A little history, I ran the tractor last year and it gave me some blow by problems. I recently relapped the valves and did the head gasket, while it was down, I flushed the tranny fluid and filled it woth kerosene for a couple days. Then I drained the kerosene, new fluid & filter and now this problem. Also, the lift cylinder was leaking, so I removed it, capped the hose to & from the lift cylinder, & have a manual lift handle.

Thanks in advance.

Edited by kiddpitt, April 24, 2012 - 07:35 PM.


#2 JDBrian OFFLINE  

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Posted April 24, 2012 - 07:05 PM

It sounds like you have a pressure buildup in the return side of the hydraulics. I've never heard of using kerosene to flush a hydrostatic drive. Not sure what else to tell you except to check very carefully that you didn't cap something that needed to have flow when you removed the cylinder. Also there should be a vent in the hydro system some where. Make sure it's not plugged off.

#3 Russ OFFLINE  

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Posted April 24, 2012 - 07:19 PM

Just wondering if maybe you had cross any of the lines an makeing if back flush or something to make it blow the filter,, Thats a lot of pressuer to blow a filter or could it have just been a bad filter,,,

#4 kiddpitt OFFLINE  

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Posted April 24, 2012 - 07:46 PM

It sounds like you have a pressure buildup in the return side of the hydraulics. I've never heard of using kerosene to flush a hydrostatic drive. Not sure what else to tell you except to check very carefully that you didn't cap something that needed to have flow when you removed the cylinder. Also there should be a vent in the hydro system some where. Make sure it's not plugged off.


The kerosene came right from the service manual. I'm thinking I loosened some sludge/gunk up and moved it to where its clogging the system. At first, I thought it was a bad filter, but it's happened multiple times.

I'm not sure where the pressure relief/vent is at. If anyone knows, I'd appreciate a heads up.

Edited by kiddpitt, April 24, 2012 - 07:47 PM.


#5 Alc ONLINE  

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Posted April 24, 2012 - 08:31 PM

I can't help you but I remember another member having a filter problem like yours ,did you do a " search" ?

#6 MH81 ONLINE  

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Posted April 24, 2012 - 08:44 PM

I know very little about Ford hydrostatic, but I'm wondering if the lines that went to the lift should be joined, not capped.

Another thought, are these filters OEM? If not, I know there can be problems, but it's been a negative pressure problem for me in the past. Can will collapse if not for the purpose. Seems odd that the canister is seeing those kinds of pressures without a feedback, blockage (cap) or plugged return into the tranny.

#7 Kyocum OFFLINE  

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Posted April 24, 2012 - 08:57 PM

Al you hit the nail on the head. The lines for the lift will need to be joined together somehow. There is pressure present when the engine is running and the oil is flowing through the lift valve and back to the tank when the handle is in the nuetral position. Blocking that oil path to tank is the issue.

#8 olcowhand OFFLINE  

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Posted April 24, 2012 - 09:02 PM

But he said he capped the lines to the cylinder, which wouldn't affect anything unless the control lever was moved up or down. Besides, I think the filter is on the return side of things.

#9 Cvans OFFLINE  

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Posted April 24, 2012 - 09:24 PM

Sounds to me like the internal relief valve is stuck open and your dumping the full volume from your pump through the filter.
There, now I've said more than I know but that's where I would start if you have the correct filter installed and the plumbing is correct.

#10 JDBrian OFFLINE  

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Posted April 25, 2012 - 05:07 AM

Some musings: Since filter is in the return line to the fluid reservoir I'm thinking there is an obstruction preventing flow through the filter. If the entire reservoir is being pressurized to the point of blowing up the filter then you would think oil would be coming out of all the seals as they would be a weaker point then the filter. If the full flow of the pump is being diverted through the filter as others have suggested then the pressurre could build up very quickly and blow the filter. If there is a venting problem or a slow buildup of pressure then that might be a clue as to what is wrong. I'm not an expert on these systems so I'm just supposing here. I'm thinking it may have to come apart to find the problem. Is there a way to monitor the case pressure?

#11 KennyP ONLINE  

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Posted April 25, 2012 - 05:15 AM

Here's a pic of the Hydraulic valves used from the service manual:
HydraulicValves.jpg

Could be the kerosene dumped something into the pressure relief area. There is one more valve used as it is what I have on my GTV/16 and came from a Ford:
Image002.jpg
I haven't found a parts breakdown for this one.
  • Sawdust said thank you

#12 kiddpitt OFFLINE  

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Posted April 25, 2012 - 06:16 AM

I really appreciate everybody trying to help me out.

If the full flow of the pump is being diverted through the filter as others have suggested then the pressurre could build up very quickly and blow the filter...Is there a way to monitor the case pressure?


I'm not going to be able to test pressure because the filter is blowing almost immediately, I'd say within 10 seconds of starting the tractor.

Here's a pic of the Hydraulic valves used from the service manual:
HydraulicValves.jpg

Could be the kerosene dumped something into the pressure relief area. There is one more valve used as it is what I have on my GTV/16 and came from a Ford:

I haven't found a parts breakdown for this one.


I downloaded that manual last night and was reading thru it. I think it was subsection 3A (I may be mistaken, I'm going off memory) shows a diagram of the system and it has the pressure relief valve on seperate line. The page of the manual you posted shows the pressure relief as part of the control valve. I do not have a seperate line on my system, so I am guessing the pressure relief for my system is in the control valve.

For those concerned about the lift cylinder lines being capped, I ran it that way last year. Even when I ran it in February, I didn't have this pressure problem. The only thing that has changed between now and then was the kerosene to clean the system, which leads me to also believe I jammed up the relief valve.

#13 KennyP ONLINE  

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Posted April 25, 2012 - 06:50 AM

There is a relief valve in the pump. Below is from the Eaton 11 service manual. Not sure if you have the Eaton 11 or ?
Eaton11.jpg Eaton11a.jpg

The full manual can be found here:
http://gardentractor...del-11-service/

#14 Alc ONLINE  

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Posted April 25, 2012 - 07:54 AM

Boy you have a head scratcher there ! If it was me I would get the correct hyd. diagram , then double check everything even as far as hooking up all the lines including whatever cylinder was leaking , myself I've never had a hydro problem like yours the only thing was on the engine of my Ford utilty tractor , I installed a oil pump kit and the new kit had a little plug behind the pressure reliefe spring that didn't have a hole in the center like the old plug , well that little hole was to let the oil back to the pan and as soon as I started the engine the oil filter puffed up and started leaking , had to split the front axle ( attaches to the oil pan ) and drill a little hole :wallbanging: , Don't know enough about your hydro but maybe sludge plugged something up , Al

#15 KennyP ONLINE  

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Posted April 25, 2012 - 08:15 AM

Found some more on the pump. Since it has a JAC # I'm not sure which it is.
HyrdroGear.jpg

HyrdroGearA.jpg HyrdroGearB.jpg

There is a relief in there, could be the spring broke or something has it letting full pressure thru.




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