TH400 3 speed

Discussion in 'The "Juice Box"' started by 1969briviera, May 25, 2020.

  1. 1969briviera

    1969briviera Antique Gold Poly

    Original 1969 Riviera with TH400 3 speed.
    The manual says that L2 and L1 may be used when going down a hill which helps braking the car.
    Is it okay to use L2 and L1 for take off (race the car) and shift manual to drive or is it not designed for this originally? When i take off part throttle in L2 it shifts stronger/faster between the gears.

    Thanks.
     
    Last edited: May 27, 2020
  2. Bens99gtp

    Bens99gtp Well-Known Member

    As long as you dont down shift at too much speed the trans shouldn't be hurt
     
  3. 1969briviera

    1969briviera Antique Gold Poly

    Thanks!
     
  4. Bens99gtp

    Bens99gtp Well-Known Member

    Upshifting manually isn't an issue, most ppl racing do this anyways. The line pressures get changed when in manual gears
     
  5. 1969briviera

    1969briviera Antique Gold Poly

    Okay. I don't have an rpm tach installed but i am not pushing it to the limit anyway, just a cruiser. Was wondering how to use the L1 and L2 and using them manually. Good to know it can be used without hurting the trans.
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Cruiser? I have a different opinion. I was told a long time ago, by a respected transmission re builder that manually shifting a THM400 can wear it prematurely. He explained that the shifts are accomplished differently when shifting manually vs. automatic (leaving it in Drive). I don't remember the exact specifics. A properly functioning THM400 with a functioning kick down and properly calibrated modulator and governor, will shift where you want it to, all the time. The more throttle you give it, the higher RPM shifts you will get. You can modify that yourself if it doesn't shift where you want it to now.
     
  7. Bens99gtp

    Bens99gtp Well-Known Member

    Dont get me wrong I wouldn't tell someone to do it everywhere they go.......but to use for fun from time to time, or to help control load and speed under certain driving conditions it what it was really ment for
     
  8. 1969briviera

    1969briviera Antique Gold Poly

    With cruiser i meant that i have never raced my car from L1 or L2, i have no intentions either. What i did the other day is i used L2 from take off part throttle and i felt that it shifts stronger/faster than using drive range. I have no issues with drive range or whatsoever, kick down and all it works just great and it is all i use. I will leave L1 and L2 for what it is. Maybe from time to time a shift at normal or low speed, that's it. Keeping the trans in good shape.
     
  9. 1969briviera

    1969briviera Antique Gold Poly

    Yes, exactly.
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    As long as you don't make a habit of it. I know what you mean as a cruiser.
     
  11. 1969briviera

    1969briviera Antique Gold Poly

    Exactly...i am not gonna do that for sure. Would like to keep engine and trans untouched as long as possible.
     
  12. BRUCE ROE

    BRUCE ROE Well-Known Member

    Normally a TH400 can free wheel if somehow going down hill with little throttle,
    pulling it into a lower setting engages on of the 2 bands to allow engine braking
    (not breaking). That is, the bands are only for deceleration situations or backing
    up, not high power situations. So there is some difference which you may never
    notice, I do not believe selecting a lower gear causes more wear than the same
    power and automatic shifting. I certainly have done it lots. For example I put
    it in low starting from a turn at a stop sign, then throw on the power when the
    car is straight. In auto the trans at light throttle would get into a higher gear,
    then I would need to downshift again when straight to get going. That extra
    shifting I am sure would do more wear, besides wasting time.

    As for leaving the trans alone, it would be far better to get it apart and replace
    the inexpensive soft parts long before now, so they will not die of old age and
    then cause serious damage to the hard parts. And do replace any original
    timing chain set. good luck, Bruce Roe
     
  13. gs430

    gs430 Well-Known Member

    L1 l2 use the bands and consequently the the front planet/reaction carrier. My th400 had a B&m kit that would shift to 3rd by 20 mph with a 2.73 rear, so I was always downshifting. It was evident when apart with the wear on the reaction carrier.
     
  14. 1969briviera

    1969briviera Antique Gold Poly

    Thanks. I changed breaking to braking. I meant braking ofcourse. The timing set with (nylon) sprocket is still there. No slack. We've replaced a set on another Riviera because of too much slack and far over a 100K miles. Sprocket was just fine. No teeth missing. Timing was all over the place but that was it. Nothing to worry about. Don't know about the trans you mention. Gonna leave it the way it is for now.
     
  15. 1969briviera

    1969briviera Antique Gold Poly

    I understand. Thanks!
     

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