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Thread: Th400 not shifting ??? Speed question at 3K RPM

  1. #1
    Join Date
    Dec 2006
    Location
    Oxford, Ohio 45056
    Posts
    175

    Default Th400 not shifting ??? Speed question at 3K RPM

    I drove the M715 down the road today. The 502 runs great. However, the TH400 doesnt seem to be shifting. It seems stuck in a gear. I hope its sticking in second, I no its not low gear. It aint going to go very fast if its stuck in high.

    IT is a new rebuilt tranny.
    Goes into reverse, Neutral, and drive just fine.
    Will NOT shift when starting in low and trying to shift up in gears.
    Vaccum at modulator valve is 15lbs.
    Fluid is new synthetic and full

    A few times it did shift down when I pulled shifter from 2nd. to low.

    1) Anyone have any suggestions?

    2) Also can someone tell me what speed you will be running at 3000 RPM ,46" tires in 3rd gear ?? I have seen a calculator somewhere.

    Thanks
    Chris

  2. #2
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default

    You can use the spreadsheet I have linked below to play with:

    Tire diameter
    Gear ratio in trans
    Gear ratio in tcase
    Gear ratio in axle

    The rest will be figured for you.

    I can add columns if you like as well...just ask.

    Heres the link...right click...save:

    http://www.m715zone.com/jonmisc/RPM_Calc.xls

  3. #3
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default

    I think your 3rd gear is 1:1...so that and 46 inch tires with stock 5.87 axles gears is 69.9 mph...not accounting for the 5-7% slippage of a non lockup converter...66.4 mph taking the slippage into account.

  4. #4
    Join Date
    Mar 2004
    Location
    northern Arizona
    Posts
    1,025

    Default

    Well, by your chart, at 60 mph with my proposed setup, i'll be turning 1600 rpm - much better than the 3000 I do now.
    67 M725 67 M715 68 M715

  5. #5

    Default

    Sounds like the govenor might be stuck. Pull the 4 bolt cover off the right side of the trans, pull the govenor out. The valves should move up and down inside it as you squeeze the weights on the side. Hard to explain, but if you have a problem, have your local trans shop take a look at it for you.

  6. #6
    Join Date
    Jan 2004
    Location
    Northern Colorado
    Posts
    324

    Default

    If you vac modulator is installed with the elbow fitting, make sure you have the linkage that goes INSIDE the elbow. The tranny will not like it if that part is missing. It will eventually stop working and puke fluid out the the fill hole and leave you stranded on the side of the road in the dark.

  7. #7
    Join Date
    Jan 2004
    Location
    NorthEast Texas
    Posts
    261

    Default

    You could also have a governor gear stripped.

  8. #8
    Join Date
    Dec 2006
    Location
    Oxford, Ohio 45056
    Posts
    175

    Default

    I pulled the governor, it looks and seems to work fine. I am taking to the tranny shop Sat.

    Thanks for your help.

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