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Modifying Full Throttle Upshifts BW M12 |
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sweatlock
AMC Addicted Joined: Apr/28/2014 Location: Largo, FL Status: Offline Points: 3285 |
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Posted: Jun/10/2022 at 3:19pm |
I’m sure someone back in the day had the specifics of this exact governor modification nailed down, but it’s since been lost in the mists of time and would need to be gone through all over again. Which is a shame, because I doubt anyone would bother with these transmissions since everyone is convinced they’re boat anchors. So the external modulator adjustment is the de facto way to go.
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george w
Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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I agree but the modulator is readily and easily externally adjustable with a small screwdriver. Modifying the governor requires some disassembly and then some experimentation with the governor’s internals. Typically with an M-11 or M-12 modification of the governor isn’t needed to get the full throttle upshift points close to the engine’s stock redline.
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16591 |
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george w
Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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Sorry to hear that the set screw stripped out. It may be possible to back it out all the way and replace it. I’m wondering if your tach is reading accurately. By manually using first or second gear will the engine rev to at least 5000 rpm or a little beyond ? I will say that as you turn up the pressure the set screw is pressing against a spring so the effort to turn it increases. I’m surprised it stripped out though. Maybe just the slot got a little messed up so maybe a slightly larger screwdriver blade may get you another turn or two.
Just as a thought, is the electric kick down switch above the gas pedal in proper adjustment ? It has a ratcheting type of self adjusting mechanism. The TSM details the procedure. It only takes a few seconds to reset it. No tools required. |
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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DAMX
AMC Apprentice Joined: Nov/13/2017 Location: Silicon Valley Status: Offline Points: 194 |
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I got 1 more turn in, and the screw slot stripped. The transmission shifts nice and tight. The car feels much more sporty, as it holds 2nd gear longer. It still won't go into 1st above 18mph, and full throttle shifts at 4000rpm (much better than 3500rpm). I'm much happier with it. I was almost ready to go to a manual. I'll put that off for awhile: ) Thanks!
Regards Dono
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george w
Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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Yes, crank in a few more turns. As you go in you’ll find that the pressure and shift points will move up more quickly as you turn the adjustment screw inward. If you go too far you’ll know it as the shift points will be too high. If that becomes the case then back out one turn at a time until you get to a full throttle upshift at about 4900 rpm assuming you gave a stock cam. There will be a world of difference in the performance of the car and you’ll be materially extending the life of the transmission as well. There will be little to no slippage during the shifts. It will shift like you installed a shift kit !
Edited by george w - Jun/09/2022 at 9:56am |
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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DAMX
AMC Apprentice Joined: Nov/13/2017 Location: Silicon Valley Status: Offline Points: 194 |
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Added 2 more turns in. Now the full throttle upshifts occur at 4000 rpm. I must have been mistaken about the 4700rpm shift at the last iteration. Shifts are tighter now. So far I've gone in 6 turns. Maybe need 3 more? I'm getting really good at disconnecting the crossmember.
Regards Dono
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george w
Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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Did you get a chance to do any additional tweaking, or did you reach a happy place setting ?
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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george w
Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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I want to correct a mistake that I made in my post of the 21st. The transmission’s upshifts occur when the governor pressure exceeds the modulator pressure, not the other way around as I stated earlier. Governor pressure is directly related to the transmission’s output shaft rpm so it’s proportional to road speed. Modulator pressure is varied by manifold vacuum with maximum vacuum providing the lowest modulator pressure. This is why upshift points and shift “firmness” increases as the throttle is opened wider.
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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george w
Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
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Try another couple of turns. You’ll want to move the full throttle upshift point up another 200-250 rpm’s. You’ll know if you’ve gone too far. The improvement will be significant. You’ll also note that the full throttle 2-1 kick down speed will go up a little but you’ll be able to drop the shifter down manually into first gear at a little higher speed than the kick down will allow.
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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