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Thread: Accelerator linkage adjustment

  1. #1
    Senior Member frederik's Avatar
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    Accelerator linkage adjustment

    I’m suspecting that my (MFI) throttles don’t open up completely when the accelerator pedal is completely depressed. The rod at the accelerator pedal is at its longest and the stop is at the bottom of the pedal board, but there’s not that much travel on the pedal. If I put a weight on it to keep it at the bottom, I can move the throttles at the engine quite a bit further still.

    1. Should the linkage be adjusted such that the throttles at the engines are just at their maximum stop position when the accelerator is fully depressed? Or could this be beyond the maximum opening?

    2. It looks like the linkage needs to be adjusted so the pedal ends up higher, so it has more travel and can therefore fully open the throttles. Is this achieved by adjusting the rods to the left side of the gearbox underneath the car?

    What I’m reading is that this can be very hard to set up correctly, so any tips would be highly appreciated!
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

  2. #2
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    Frederik, you might also check the condition of the accelerator linkage lever on the driver's side throttle body...on my car the plastic bushing had deteriorated and wasn't allowing full movement of the linkage
    Mike O'Meara
    Reg #1043
    72 911T
    56,59 356s gone
    67,68 912s gone

  3. #3
    Most cars I see don't have full throttle. There are three bellcranks that all must have good bushings as Mike said above. Start by removing the pedal floor board, often that bell crank gets bent over. You will need to study bellcrank leverage to understand how to do the adjustments. Bellcranks can only operate with a straight pull that makes max usage of the travel of the other arm on the crank. Look closely at the movement and you'll see what is needed.
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  4. #4
    Senior Member frederik's Avatar
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    Thanks Mike and Ed. It's a shame to not have full throttle so I definitely want to spend some effort here to make sure this is set up correctly.

    So my assumption is correct that the accelerator pedal should allow full throttle movement at the engine? Or is it possible that the "fully open" position of the throttle butterflies is reached earlier? I guess the best way to find out is to remove the airbox and check how the butterflies are opening.
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

  5. #5
    Senior Member frederik's Avatar
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    OK. Removed the airbox and the butterfly is not even completely vertical when the throttle is pushed all the way to the stop at the engine. I was worried that it would be over the maximum position but this is not the case. So it's definitely a good idea to go for complete movement of the throttle lever at the engine (how do you call this?).

    I checked all the bellcranks and the levers and there's definitely around a mm play on the snap-on levers at the engine end, connecting the pull rod to the big "axis" that connects the left and right throttle bodies. Should these be really tight or is it normal to have a little bit of play here?

    The low-hanging fruit is here though:

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    The bell crank needs to move around 5 mm before it starts to pull the pull rod, so that's what I'm going to work on first. I think I need to shorten the lever on top of the engine to get the pull rod a bit higher.
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

  6. #6
    My advice is you always start at the pedal bell crank. Notice the welded on tab which forms the return stop for the bell crank. This MUST be at 90 degrees to centerline of car, if it is bent back you will never get the linkage adjusted correctly. After verifying that go to trans bell crank and adjust the tunnel linkage to attach to bell crank arm so arm is at about a 20 degree angle towards rear of car. That should make the arm with the pull rod at about horizontal. So the straight pull of the tunnel rod gets maximum travel of that horizontal arm. Now go to the bell crank on the engine. The forward facing arm should be vertical. When all is adjusted set the throttle stop so the pedal hits the stop just as the butterflies go vertical.
    Early S Registry member #90
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  7. #7
    Moderator Chuck Miller's Avatar
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    Ed,

    I just copied that word for word and put it in my '911 Tech' folder....

    As always... You'da'man...
    Chuck Miller
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  8. #8
    Senior Member Scott A's Avatar
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    Is there a drawing of this somewhere...perhaps seen from the left of the car?
    It seems the bell cranks and levers would/should be the same angle for similar year cars?

    Current long term ownership: 63 Cab, 71 911, 74 914

  9. #9
    There is one for the trans bell crank in the 356 shop manual.
    Early S Registry member #90
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  10. #10
    Senior Member frederik's Avatar
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    Thanks Ed, I'll follow your advice. I noticed my transmission bell crank was not as far backward as in your pictures (more vertical than 20 degrees to the rear) so there's some leverage to be gained here too. And will check at the pedal end first.

    I was just happy to see that the pull rod has about 5 mm of play which is obviously an easy win.
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

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