ST400 switch pitch pump gears

Discussion in 'The "Juice Box"' started by shifter51, Oct 16, 2021.

  1. shifter51

    shifter51 Well-Known Member

    I have a ST400 switch pitch pump that has pump gears that measure .625 thick vs. a normal TH400 .727 thick gear. I’m not sure what this pump with thinner gears is from but I’m wanting to use it for a replacement for a ruined pump that has the thicker gears. I not sure if reduced flow with the thinner gears is an issue that I need to be concerned with. So far I really have not found out much info on what this pump is all about . any input on this would be appreciated.
    Thanks
     
  2. BRUCE ROE

    BRUCE ROE Well-Known Member

    What I have seen, is the TH400 originally used the thinner pump gears, in the switch pitch (65-67)
    transmissions. For about 68 they went to the thicker gears. Other changes were made in the
    67-70 period as well, such as filter and pan, valve body, center shaft spline, center section
    protection ring, clutch pack piston, and 9 element sprag. All of these individual or as sets
    will interchange in all TH400s.

    My transmissions are made of parts from which ever was the best (in my opinion) of these
    parts. Since I am committed to switch pitch transmissions, I must use the thinner pump gears.
    The one exception is the TH425 FWD trans from Toro and Eldo. The pump assembly of these
    may be removed as a set, between the 2. My TH425 switch pitch has the thicker gears.
    Bruce Roe
     
  3. shifter51

    shifter51 Well-Known Member

    Bruce, thanks for the reply. The pump that I have that is destroyed has the thicker gears and oddly the gear set is slightly larger in diameter than the thinner pump gear set. Do you know if this also on one of these 425 pumps?
    Thanks
     
  4. BRUCE ROE

    BRUCE ROE Well-Known Member

    Since I cannot interchange them, I never checked the outer dia. Bruce Roe
     
  5. Matt Knutson

    Matt Knutson Well-Known Member

    "I have a ST400 switch pitch pump that has pump gears that measure .625 thick vs. a normal TH400 .727 thick gear. I’m not sure what this pump with thinner gears is from but I’m wanting to use it for a replacement for a ruined pump that has the thicker gears. I not sure if reduced flow with the thinner gears is an issue that I need to be concerned with. So far I really have not found out much info on what this pump is all about . any input on this would be appreciated.
    Thanks"

    The .625" gear set is from the "fixed" stator TH 400 from '64 & '65. Yours is not variable pitch.
    As per ATSG manual and General Motors Corp.
     
    Last edited: Nov 24, 2021

Share This Page