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Desiel Transmission

Discussion in 'Truck & Equipment Repair' started by Langlois Enterprise, Jun 26, 2009.

  1. Langlois Enterprise

    Langlois Enterprise Junior Member
    Messages: 24

    I have a 1985 GMC 1 ton, desiel 4 wd dump truck automatic transmission. I am having problems with 3rd gear. I have a transmission from a gas 1 ton, I was told that they are not the same. The throttle body is different ? Anybody have experance with desiel transmissions.:confused:
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    As long as they're both Turbo 400's then they're physically the same and will interchange...BUT you have to use the valve body, governor, and the torque converter from the diesel trans or it won't shift/operate correctly. Everything else is the same...

    Make sure if you swap the components that you check them over and clean them thoroughly or else you run the risk of transfering any contaminants/debris from the old trans to the replacment one. This doesn't include the converter, don't attempt to reuse it as it can't be easily or properly cleaned internally, replace it with a reman unit.

    Note: Thread needs moved out of the pic forum.
  3. Langlois Enterprise

    Langlois Enterprise Junior Member
    Messages: 24

    Transmissions desiel

    Thanks for the info on the transmissions desiel.:salute:
  4. 80sturgisrider

    80sturgisrider Member
    Messages: 55

    I disagree with having to do all the changing over to a new valve body, torque convertor, etc. I have done MANY gas to diesel conversions using the 6.2 and 6.5 diesel with the TH400 automatic transmission. The ONLY issue I have had to deal with was adjusting the modulator. It has a little teeny tiny screw inside of the hole where the vacuum line connects. As long as the TPS on your injection pump is adjusted and working (which means your vacuum pump must also be working), you will not have any trouible with the TH400 (unless you actually have a problem with the inards in the trans).
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    And so to have I. And cranking on the modulator is a poor way to compensate for the differences in the various part that are different between the gas and diesels. It simply crutches the differences.

    Will it work? Depends on what one would call acceptable. IMO no it doesn't. WOT shifts are incorrect and so to is the stall speed (neither of which the modulator adjustment have any bearing on). Still needs the valve body (or at the least the 1-2 and 2-3 shift and shuttle valves) and converter changed to work as its intended.
  6. JDiepstra

    JDiepstra PlowSite.com Addict
    Messages: 1,780


    Right. You don't want your diesel shifting at gasser RPM's.
  7. towpro570

    towpro570 Senior Member
    Messages: 241

    I have a th 400 out of a 89 chevy 1 ton that had a 6.2 in it 2wd for sale