Stuck Accelerator?
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Tuned
Joined: Jun 2005
Posts: 372
Likes: 1
From: Walnut Creek, CA
Stuck Accelerator?
I have a 312 engine with a Holley 4 bbl carb in a '56 with an automatic transmission. Recently when I put it into reverse and press down even a bit on the gas pedal, the RPM's shoot way up and off she goes. I don't think the linkage is stuck to the carb but don't know what else it could be. Any suggestions? Could it be a vacuum problem? It never happens when the trans is in drive-forward that is.
Cargo Master
Joined: Apr 2007
Posts: 2,063
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From: Valley Center, California
Disconnect the linkage at the Carb and ensure Carb isn't binding someplace. If it's cool, start looking at the linkage. The broken motor mount is a good call also to check.
I started using heim-joints every place possible with Carb linkage.
I started using heim-joints every place possible with Carb linkage.
Roast em' if you got 'em
Joined: Mar 2005
Posts: 21,955
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From: Rio Rancho, NM
Does the transmission have a vacuum modulator or any kind of vacuum line running to it? If so and the above suggestions don't reveal the problem then try disconnecting the vacuum line to the tranny (make sure and plug the vacuum port) and try putting it in reverse again.
If it does have a vacuum modulator/govenor/etc it might be leaking when in reverse and causing a vacuum leak
Bobby
If it does have a vacuum modulator/govenor/etc it might be leaking when in reverse and causing a vacuum leak
Bobby
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Tuned
Joined: Jun 2005
Posts: 372
Likes: 1
From: Walnut Creek, CA
The motor mounts are good but there is a vacuum line connected to the carb. I don't know what a modulator or governor looks like so I need a bit more explanation. I think that is likely the problem since tapping the pedal doesn't "unstick" it, it just makes it go faster!
Roast em' if you got 'em
Joined: Mar 2005
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From: Rio Rancho, NM
The modulator adjust the tranny shift points in relation to the load on the engine. It does this by sensing the vacuum.
Basically what you have to look for is a small diameter can on the side of the tranny with a vacuum line going to it. It should be about 2 to 3 inches in diameter (it should look similar to a vacuum advance on the side of a distributor)
Unplug the vacuum line that you see and plug it off at the carb and try the truck and see how it acts. A vacuum leak will cause a high idle.
Bobby
Basically what you have to look for is a small diameter can on the side of the tranny with a vacuum line going to it. It should be about 2 to 3 inches in diameter (it should look similar to a vacuum advance on the side of a distributor)
Unplug the vacuum line that you see and plug it off at the carb and try the truck and see how it acts. A vacuum leak will cause a high idle.
Bobby
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Tuned
Joined: Jun 2005
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From: Walnut Creek, CA
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Roast em' if you got 'em
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Joined: Oct 2002
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From: Valley Center, CA
Just to be different, I'm going to say that there is a conflict between the kick-down rod and the shift linkage. If those are touching when you you are in reverse, then the kickdown might be holding the throttle open. 
Good luck, Jag
Good luck, Jag
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Tuned
Joined: Jun 2005
Posts: 372
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From: Walnut Creek, CA
Well despite my protestations to the contrary, it was the linkage. The two "plates" that slide against each other when you press down on the gas pedal don't slide easily. A little spray from teflon and bingo it's better but not totally fixed. I guess I need to take it apart and derust them and see what happens. I also found that the accelerator doesn't return to the stop on the carb when I let off the gas so the idle is too fast. Any idea how to solve that issue. A stronger spring might do the trick but that doesn't seem like the appropriate way to solve the issue.
Roast em' if you got 'em
Joined: Mar 2005
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From: Rio Rancho, NM
Cool!!
It sounds like a little elbow grease is in your future. Get it all cleeaned up and see how it all works then. That will probably take care of it not returning all the way back to idle.
I wouldn't go to a heavier return spring unless you absolutley had to. While its an easy fix it will hasten the wear on the base plate of the carb around the throttle shaft which will eventually lead to a hard to fix vacuum leak (this was a huge problem on quadrajet carbs)
Good luck, at least its not an expensive fix
Bobby
It sounds like a little elbow grease is in your future. Get it all cleeaned up and see how it all works then. That will probably take care of it not returning all the way back to idle.
I wouldn't go to a heavier return spring unless you absolutley had to. While its an easy fix it will hasten the wear on the base plate of the carb around the throttle shaft which will eventually lead to a hard to fix vacuum leak (this was a huge problem on quadrajet carbs)
Good luck, at least its not an expensive fix
Bobby
Cargo Master
Joined: Apr 2007
Posts: 2,063
Likes: 38
From: Valley Center, California
Just my two cents.....
Like Bobby said, time for some elbow grease. When it comes to Brakes and Throttle Linkage, good isn't good enough. It's gotta be perfect or overkill perfect. From my racing days, I always use two return springs which the rules require.
Replace anything worn, clean and lube everything. "When in doubt, throw it out".
Does the Carb return to the stop with the Linkage Disconnected ? If it isn't returning, something's wrong or out of adjustment. Do you have a Dashpot ?
The thing is, it was designed to function a specific way. Don't settle for less than correct.
Good luck and keep us up to date.
Like Bobby said, time for some elbow grease. When it comes to Brakes and Throttle Linkage, good isn't good enough. It's gotta be perfect or overkill perfect. From my racing days, I always use two return springs which the rules require.
Replace anything worn, clean and lube everything. "When in doubt, throw it out".
Does the Carb return to the stop with the Linkage Disconnected ? If it isn't returning, something's wrong or out of adjustment. Do you have a Dashpot ?
The thing is, it was designed to function a specific way. Don't settle for less than correct.
Good luck and keep us up to date.