HydroGear Pump unit -- any one open one up?

[pfrederi 18,593]

I have spent a lot of time recently working on piston to piston sundstrand units. I have a Charger and Electro 12 that have the older Hydrogear unit.. The sundstrand manual you can download gives extensive info on rebuilding the piston to piston units. For hydro gear you are pretty much limited to the push valve and the acceleration valves. I have never found a parts breakdown of the pump or the gearmotor.

I has always assumed (and we all know what that means) that if the motor portion was a gear unit so was the pump. Looking at the schematic in the Wheelamatic service manual (which provides no info or part number for inside the unit) it is apparent the pump portion is piston unit. The schematic looks just like the piston bloc with slippers and valve plate found in newer units. Has anyone opened up a hydrogear pump??? Does the piston block look like it would interchange with later models??? If it was interchangeable it would be another source of parts to fix up a weak later model sundstrand unit.

[Hodge71 665]

I'm not 100% positive Paul but for some reason I remember being told Sundstrand Hydrogear units are not serviceable. The only serviceable parts are the push valve and acceleration valves. I also do recall that they are interchangeable. You can take replace a hydrogear with a piston to piston unit. I actually believe that was S.O.P back in the day when a dealer had a bad hydrogear unit come in, they swapped it out with a piston-piston unit. Maybe we have another area we both can learn about here....

[pfrederi 18,593]

The " Non-Serviceability" is what I have read and probably explains the lack of info on part # etc.., That schematic has me interested because it sure looks like the piston block with slippers we are getting too familiar with.

[can whlvr 994]

commandomayo just posted a topic about fixing a hydrogear,maybe he can shed some light on your situation

[refracman 167]

The piston to piston and the hydro gear have the same type pump, different valve body and motor. Motor on hydrogear is gear and piston to piston is a piston, hence the names. I'll have to check with my pump man on if the swash plates and pistons interchange.

And yes the piston to piston was a replacement with the correct kit( internal trans drive gear) for which tractor it went on

[pfrederi 18,593]

The piston to piston and the hydro gear have the same type pump, different valve body and motor. Motor on hydrogear is gear and piston to piston is a piston, hence the names. I'll have to check with my pump man on if the swash plates and pistons interchange.

And yes the piston to piston was a replacement with the correct kit( internal trans drive gear) for which tractor it went on

Thankyou that is some good info.