Author Topic: 75 truck throttle sticking  (Read 4740 times)

Offline entropy454

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75 truck throttle sticking
« on: August 24, 2005, 04:57:00 PM »
I have a 75 camper special 2wd 454.  Last night while test driving it around the block after replacing a u-joint, the throttle on the carb seemed to get stuck.

The engine was revving pretty high and it made the brakes weaken to the point I was pushing the pedal to the floor to get the truck to stop. It kinda felt like the brakes were going out or the booster was losing vacuum.

I got back to the house barely, the exhasust was smoking and when I shut off the truck, it backfired out the exhust.

I looked at the carb, I noticed the throttle was stuck and all I had to do was pull on it to free it.
When I tried to restart it, it ran perfectly fine. Just like it has in the past.

Later that night I ran it around the block again and sure enough it got stuck again.  I barely made it back and shut it off before it tried to blow the engine.  When I tried to restart it after wiggling loose the linkage, it acted like it was way out of time.  It kinda backfired in the carb and let loose what looked like smoke to me.
I messed with the throttle again and started it and it idled perfect.  When I drive it around the block it runs great and the brakes work good. It is just when the idle gets stuck that the truck acts dangerous and out of time.

Ok here is where it gets complicated.  The day before I was using carb cleaner on it. I also had used starter fluid to get it started cause the battery was low.
This truck also has an aftermarket cruise control which im sure doesnt work.  

I noticed when I looked at how the gas pedal was connected to the carburator. I noticed that at the fire wall was a round rubber diaphram looking item with a spring in it that was about 4 inches in diamater or slightly bigger.

The throttle cable goes through it. The throttle cable looked completetly different than anything I have ever seen. It looks like a chain. The kind of chain that is a series of silver balls like you see on a drain plug for an old bathtub. This chain goes through a tube near the carb. Im suspicious that maybe some of my cleaning some how effected how well that chain goes through the tube.

Does anyone know if this chain is a common item for chevy trucks or is possibly some kind of aftermarket setup for the non working cruise control?

Does anyones truck also have the rubber diaphram/spring setup that I mentioned on the firewall also?

I cant take any pictures yet because I have lost my cable to my camera so I dont have any pictures so I tried to be as thorough as possible.

Thanks for any help.
jim


Offline entropy454

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Re: 75 truck throttle sticking
« Reply #1 on: August 24, 2005, 05:59:00 PM »
I just checked it better int he daylight.
It looks like the chain device has to be part of the old cruise control. This is because I found the normal throttle cable underneath it. It looks just like what I would expect.
I am going to try to disconnect the supposed cruise control 'chain'. It may have been causing the pbolem by binding up when I stepped on the gas.
Hopefully it will fix the problem.


Offline RSBAD454

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Re: 75 truck throttle sticking
« Reply #2 on: August 24, 2005, 09:33:00 PM »
sounds like the problem......who uses Cruise Control anyways?:hat  

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Offline boll213

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Re: 75 truck throttle sticking
« Reply #3 on: August 24, 2005, 09:49:00 PM »
Sort of sounds like the choke is sticking.  When the choke is engaged, it will run at fast idle.  That may also explain the rough condition and smoke (was it black?) you described in your initial post.  You might check this linkage and make sure when you were cleaning, you didn't knock anything loose or "jam" any part of this linkage.


Offline entropy454

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Re: 75 truck throttle sticking
« Reply #4 on: August 25, 2005, 09:10:00 AM »
The smoke was white.
I removed the 'chain' last night and drove it around the block with out the air cleaner on it.
It seemed to be ok now, though it did run a little hesistant. I think that is because of the vacuum hoses that were unplugged with out the air cleaner on.


Offline roundedline

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Re: 75 truck throttle sticking
« Reply #5 on: August 25, 2005, 11:12:00 AM »
If you had the chain hooked to the throttle then that is definitely a problem.  Glad you got that fixed.  If you have any kind of vacuum leak, it is going to hesitate some, but anything going to the air cleaner wouldn't cause that much trouble.  Put it all back together and let us know.

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