etd66ss
Senior Member
I'm hoping maybe someone here has exp rebuilding variable displacement pumps/hydrostatic units.
5 years ago I bought a Ford 1620 HST, the first spring I was using the tractor with a mid pto mounted mower, I accidentally left the parking brake on part way and mowed for 1.5 hours. The tractor started dumping hyd oil out of the case drain. I proceeded to pull the tractor apart to inspect the HST unit: http://imgur.com/a/fKOQF
It turned out there was a torn gasket from one of the variable displacement pump housings to the main plate. I thought it was a manufacturer defect when I saw it, like someone bumped & tore the gasket during assembly. I never thought I'd have to mess with the HST unit again. Here are the re-assembly pictures from back in 2012: http://imgur.com/a/KH5gQ
Fast forward 4 years to almost the day, and the HST unit started dumping oil again. I once again split the tractor and went right to the gasket that gave me troubles the last time, sure enough, the gasket was deformed: http://i.imgur.com/1JjirKg.jpg
In that picture, the vertical sides of the gasket are supposed to be straight. They both seemed to be sucked into the housing, far enough that the left side started leaking. New Holland wants $70 for this single gasket. Last time around I paid $270 for a full HST rebuild kit. (A few gaskets, seals and O-rings, it was a rip-off)
I guess my first question is, if the housing surface is flat (I checked it last time, it was not warped), what would cause this gasket to shimmy its way into the housing like that? On a pump like this is a suction created, is that why the gasket is being sucked in?
I'm hoping someone with variable displacement pump rebuilding experience can help me out a bit.
I decided this morning to design a new, more sturdy, gasket in AutoCAD and laser cut it here at work: http://i.imgur.com/D575K3l.jpg http://i.imgur.com/02KzuGX.jpg
I am unable to find gasket material that is identical thickness to the OEM gasket. Considering that the variable displacement drum is pressed against a wear plate via a die spring, I am unsure if using a custom thickness gasket is a bad idea, it will change the distance the housing is off the main center plate by like ~0.010" I hate to damage the actual HST unit, as they are $6500 new, and from what I can tell, no shop wants to touch them, so I am forced to rebuild this myself.
The shop manual I have states to not use gasket sealer on the gaskets, but instead to use a light coating of grease.
I really don't want to have to do this repair again. I am wondering if anyone here has exp/ideas on how to solve this issue?
5 years ago I bought a Ford 1620 HST, the first spring I was using the tractor with a mid pto mounted mower, I accidentally left the parking brake on part way and mowed for 1.5 hours. The tractor started dumping hyd oil out of the case drain. I proceeded to pull the tractor apart to inspect the HST unit: http://imgur.com/a/fKOQF
It turned out there was a torn gasket from one of the variable displacement pump housings to the main plate. I thought it was a manufacturer defect when I saw it, like someone bumped & tore the gasket during assembly. I never thought I'd have to mess with the HST unit again. Here are the re-assembly pictures from back in 2012: http://imgur.com/a/KH5gQ
Fast forward 4 years to almost the day, and the HST unit started dumping oil again. I once again split the tractor and went right to the gasket that gave me troubles the last time, sure enough, the gasket was deformed: http://i.imgur.com/1JjirKg.jpg
In that picture, the vertical sides of the gasket are supposed to be straight. They both seemed to be sucked into the housing, far enough that the left side started leaking. New Holland wants $70 for this single gasket. Last time around I paid $270 for a full HST rebuild kit. (A few gaskets, seals and O-rings, it was a rip-off)
I guess my first question is, if the housing surface is flat (I checked it last time, it was not warped), what would cause this gasket to shimmy its way into the housing like that? On a pump like this is a suction created, is that why the gasket is being sucked in?
I'm hoping someone with variable displacement pump rebuilding experience can help me out a bit.
I decided this morning to design a new, more sturdy, gasket in AutoCAD and laser cut it here at work: http://i.imgur.com/D575K3l.jpg http://i.imgur.com/02KzuGX.jpg
I am unable to find gasket material that is identical thickness to the OEM gasket. Considering that the variable displacement drum is pressed against a wear plate via a die spring, I am unsure if using a custom thickness gasket is a bad idea, it will change the distance the housing is off the main center plate by like ~0.010" I hate to damage the actual HST unit, as they are $6500 new, and from what I can tell, no shop wants to touch them, so I am forced to rebuild this myself.
The shop manual I have states to not use gasket sealer on the gaskets, but instead to use a light coating of grease.
I really don't want to have to do this repair again. I am wondering if anyone here has exp/ideas on how to solve this issue?