TH200 Trans

Discussion in 'The "Juice Box"' started by Blurredman, Apr 24, 2018.

  1. Blurredman

    Blurredman Well-Known Member

    Hi guys,

    Is there any way I can tune slightly the shift points for the TH200 transmission. It has a connector on the left hand side above the pan which I believe is a lockup. This didn't seem to be working recently until I realised the torque converter had come loose a tad, identified by a knocking on startup and in reverse. Anyway, I have torqued up the bolts for this and it seems like the clutch wants to engage. So that will save my economy a little bit. Though it does seem to engage quite quickly, almost instantly from entering into third gear.

    Where does the wire from the transmission go to? Is it Electronically controlled or a combination of electrical and connected to a vaccum diaphram or to an intake vaccum? Every few months I find I am replacing a vaccum line here, or a vaccum line there.
    Totally factory standard 1980 350 and th200 with the huge amount of spaghetti vaccum lines cris-crossing ontop of the engine..
    Transmission pan says "METRIC" on it.

    But I have two things besides:

    1) When cold and on choke, the engine doesn't want to shift up to 2nd until around 18 to low 20's mph, and then to third at 35-40.
    When warm it does shift much better (at a lower speed), but it often doesn't like to shift up automatically unless I am accelarating decisively (not aggressively- but firmly on a part throttle, as if I was to get to motorway speeds). It feels smooth when doing the shifts, however.

    2) Part throttle shifts around town can seem to be delayed unless manually implemented by releasing the throttle and waiting for the shift and engaging the pedal again. Sometimes, the engine can hang onto first gear at 15mph and won't change to second unless I command it with the above proceedure.

    Both above points have been apparent in the car since I purchased it with original 23k miles. It now has 30k, and nothing about the above has changed at all and none are a new 'problem'.

    Any way I can change this? Is this just a design of this transmission, and non-adjustable. I don't know anything of this transmission, so any help would be greatly appreciated.

    I'm likely thinking that I want to implement a manual switch on the lockup so that it doesn't keep enging and disengaging in a loop during certain situations. But with a switch that will 'throw' off (like a breaker) the same way as when the brake is applied for ease of use, but more of a control over it, for example in the above situation. The connector only has one (brown?) wire going to the trans.

    Thanks in advance.
    Last edited: Apr 24, 2018
  2. TexasT

    TexasT Texas, where are you from

    To be clear, this is a three speed th200c? Not a 2004r wth od?
    The governor could be "gummed up" or have spit its spring on the gov weight out.
    Is the fluid nice and cherry red and not burnt smelling? Are the shifts at least crisp? Seeing as this unit is 37yrs old, I would think there is some(or even a lot) internal leakage not allowing the unit to build the needed pressure to command a shift at the tv angle until you change it by moving the accelerator pedal.
    A pressure gauge in the trans might give some insight to its condition.

    BRUCE ROE Well-Known Member

    I had that setup in my 80, the clutch would drive me crazy. Another owner
    added a switch to keep it from engaging in some situations. I blew mine in
    9000 miles and put in a switch pitch TH400, problem solved. Bruce Roe
  4. Blurredman

    Blurredman Well-Known Member

    I always thought I had a 350 until I did a transmission filter change, I wish I did have a 350.. :)

    Anyway. Yes it is the 3speed with lock up converter.

    The fluid is nice actually. It's not bubbly, it's not burnt, just smells of standard cat piss ATF smell.
    When the car is shifting when I am driving decisively, the shifts can be incredibly smooth. Around town, when the speed gets to 20mph and then it changes up, it can be quite a jump. And sometimes getting into third at around 35 it can make a bit of a metal on metal sound clunk. Don't get me wrong, it does shift nicely though when accelerating briskly, but I don't really like it to be shifting at 15-20mph when i'm driving around town.. Doesn't seem economical, nor good, mechanically.

    I have never opened up the governor unit and, Where would I put the pressure system?
    Last edited: Apr 27, 2018
  5. Bigpig455

    Bigpig455 Fastest of the slow....

    it doesnt sound like a governor issue unless we're talking full throttle shifts... I'd recalibrate (perhaps replace) the vacuum modulator first. thats what controls part throttle shifts .
  6. Blurredman

    Blurredman Well-Known Member

    I don't believe TH200's have vaccuum modulators.
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The TV cable adjustment is critical on the THM 200, 2004R, 7004R transmissions. Have you tried adjusting it?
    Mark Demko likes this.
  8. Mark Demko

    Mark Demko Well-Known Member

    Yup, a messed up throttle valve cable will ruin the trans. in short order.
    Too loose an adjustment will cause late, hard upshifts, IIRC
  9. Blurredman

    Blurredman Well-Known Member

    Hi guys. TV cable is good adjustment.

    I've decided to change my driving style a little and let the car shift when it wants to. I feel much better in this as I can confirm that shifts are good.
    The only reason I had a problem was that the pressure seemed to take a while to balance to allow upshifts on part throttle. It is just me being pedantic.

    But, is there any real increase in economy to be had cruising at 30mph in 3rd instead of 2nd (on level ground)?
    I have a feeling that, perhaps the lower rpm doesn't necessarily mean decreased consumption, as the engine could be countering by actually requiring more fuel to keep a lower rpm in a higher gear, in certain situations.. as opposed to a lower gear and therefore higher rpm, but not being strained.

    For example, I didn't notice all that much of a decrease in fuel consumtion with torque converter lockup disconnected.. It was there, but not too bad. I am aware that the lockup is not a fourth gear or overdrive, but the theory in regards to the above is relavent to make the same connection?>


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