Sundstrand Hydrogear and piston to piston

[pfrederi 17,893]

learned something new to me the last couple days.  I have always been curious about the fact that the Sundstrand Hydrogear (and its immediate predecessor Wheelamatic) were designated by WH as non repairable (Repair by replacement) other than fixing acceleration valves.  I have successfully overhauled a couple piston to piston units and have been thinking about why not do the same to a weak hydrogear.  I understand the gear motor art is completely different but when you read the description of the piston pump parts of the unit, variable swash plate and 9 slippers sounded like the same thing as the units I had fixed.  Figured I would take a stab at it and found out some interesting things..

 

The finned aluminum pup housing look the same but that is about where the similarities end.  The georotor pump housing is a much different shape and height. The hydrogear uses a sleeve bearing instead of a needle bearing  to support the input shaft. See picture one and two.    Next look at the size difference between the piston block (Pic 3 ) the hydrogear is the larger one.  Piston to piston units have a separate brass valveplate  which you can resurface or buy if it is really bad off. .  The hydrogear's  is aluminum (i guess not magnetic) and an integral part of the piston block.  Given the deep scratches i would thin resurfacing it would almost erase the relief/ bypass passages. see picture 4

 

 

So bottom line unless you can find a reasonably priced piston block (very unlikely) Wheelamatics and hydrogears are probably not really repairable.

[Sarge 3,463]

I found the same thing years ago on the 1277 when the original self-destructed suddenly - it destroyed nearly all those internal parts and couldn't be saved . Got lucky and swapped it out for one from an 876 which is the same hydrogear/axle setup - still running perfect and powerful enough to break it's frame 3 times now....lol . When they work , they work - when they don't - it's done .

 

I haven't personally tried it , but pretty sure the later model piston to piston pump will bolt in place of the hydrogear and everything else will fit - getting one out of a C series would be a great swap and easy enough . I think I remember seeing a service bulletin about dealers should just do that very thing on older units that gave up...

 

Sarge

[953 nut 55,860]

       Thanks for sharing that info.     

Several years ago I swapped the pump and drive from a Charger into my GT-14. All I changed was the output gear. The acceleration valves and springs on the GT-14 were hammered so hard the valves couldn't be removed. I was told the piston to piston could not be swapped onto the axle of the GT-14 and looking at the differences I agree.

[Sarge 3,463]

So , the only one that is different is the GT14....just trying to be clear . I'm sure the hydro section on the older '67 automatics can be swapped out for the later model piston to piston style...?

 

Sarge

[pfrederi 17,893]

A piston to piston hydro can be put on an older Wheelamatic or Hydro gear transaxle.  I think in the case of a GT-14 you have to change the output gear on the hydro gear motor to match the GT14 transaxle gears.

[Sarge 3,463]

Ok....that's what I thought . I know somewhere around here was the dealer bulletin about swapping in the later unit - wish now I could find it .

 

Sarge

[953 nut 55,860]

8 minutes ago, pfrederi said:

in the case of a GT-14 you have to change the output gear on the hydro gear motor to match the GT14 transaxle gears.

That is what I did a few years back.

 

This was one of my first posts and I made a few errors including calling the donor a Ranger, but the process worked well.