Manual Throttle Question

[Love 70 Chevys]

Finally finishing one of my "winter" mini projects of rebuilding/replacing my instrument cluster. The truck has the K31 manual throttle option. I am cutting a hole in my new bezel so I can keep the option, as I think it's pretty cool. The cable is still present, but is frozen up. I will soak it in Evaporust tonight to try and free it. The question I have, is it a push-pull cable or does it move by a turning action? The shaft the knob mounts to has a "D" so it looks like it is meant to turn. I'm sure the cable has to move only slightly to change the position of the carburetor throttle linkage, I'm just not sure how this works. Is the upper portion of the cable internally threaded to turn rotary motion into linear, or do you just pull on the knob?

[LockDoc]

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If memory serves me correctly you turn it to engage it but you can push it in "or" turn it to disengage it.

LockDoc

[chevy71super]

The 72 throttle cable unit I installed in my 71 truck is strictly pull out. I took the inner cable out to inspect and lubricate it and there is no turning mechanism. Just "stops" in the form of small bumps on the upper end to hold different positions. Twisting it back and forth a little bit may help each stop release but its not necessary. Mine is very, very tight to pull out. Depressing the throttle to the desired RPM helps.

[Love 70 Chevys]

Interesting. Appreciate the help you guys. How did you get the inner cable out? Just give it a good yank from the knob end using vice grips? There really is not anything to disassemble. Mine is still soaking.

[LockDoc]

Originally Posted by Love 70 Chevys

Interesting. Appreciate the help you guys. How did you get the inner cable out? Just give it a good yank from the knob end using vice grips? There really is not anything to disassemble. Mine is still soaking.

If you try and pull the inner cable out of your factory unit you will probably ruin it.....

LockDoc

[Love 70 Chevys]

Would really not want to ruin it. Here is hoping that evaporust works its usual magic and things free up! The fact that it has a "D" makes me think it is designed to be turned. The knob interface is the same as the windshield washer knob, and that is meant to turn. ("D" with a setscrew.) The headlight knob is meant to be pulled, and it is a different design where the shaft is molded right into the knob. Mine is factory for sure. Pretty much everything on the truck is. It's a real time capsule.

[clay68c10]

It is a push/pull to adjust. Like a manual choke.
You turn it one way (right?) to lock in the adjustment and the opposite to unlock.
It's been a long time since I've had one, but that's the basic operation.

[CS1972]

I've never tried to operate mine as I could not find any directions in literature or on the web. Like most of you state, the knob can turn left of right AND pull in and out. I may have to try this out in a big parking lot to see how this is supposed to work.

And BTW, I noticed on your picture that you Manual Throttle is on the left side of your dash bezel, mine is mounted on the right side below the windshield washer. Did they put it in different places over the years? Mine is a 1972, listed on the SPID and has all the parts as I checked when I had the dash all apart.

[Love 70 Chevys]

Yes, mine is on the left. Can't wait to hear the report from your parking lot test! Here is a pic that helps explain a little more how it works. The cable on the other end attaches to the gas pedal "teeter-tawter" on the other side of the firewall. It is secured at a hole just below where the teeter-tawter attaches to the carb linkage. (Carb linkage removed and cable not secured in this pic)

[CS1972]

OK, now I'm on a mission to figure this out. Since I had out my dash cluster bezel I followed the cable and found that it was just stuffed up into an area above the gas pedal and wasn't connected to anything. Which is why the one time I did try to operate nothing happened. Mine routes straight down the a bracket connected to the gas pedal and the end cable connects literally right beside the cable that routes out to the carb. So # 1 is where the manual throttle cable connects, # 2 is where the gas pedal cable connects and # 3 is where the manual throttle should be connected to (but was not).
I took my cable completely out to see if by using pliers how far the cable really pulls out, seems to only be about a 1/2", and as stated in a earlier post, it was hard to pull out. Once out the inside looks like a worm gear and although you can pull it out, it really works by the "righty tighty, lefty loosey" rule (right completely off, left completely on). I simply turned the knob and it went smoothly back into the mechanism. Now I just need to hook it up and test it out.

[Love 70 Chevys]

So cool! Thank you for update and pictures. I am on the same mission and also have had some success! I took my cable out of the soak (coiled up in the black plastic bin) and it looks and acts like it is brand new!!! I did not pull on mine though. Mine turns very smoothly now and the internal cable has about 1/4 inch of travel until you get to the end of the outward turn and it pops into a very pleasing spring detent. Seems like it is supposed to stay and end there. I am now starting to understand how it works. (Will take more pictures soon to help with the explanation.) The external cable on the firewall end has a clip on it that dictates how much of it sticks out beyond the firewall to create some slack. Under normal throttle/gas pedal operation this slack just moves with the mechanism. I think the manual throttle is intended to work only at low RPM to just tweak the throttle open a little more than idle. If your foot were off the gas and you turned the knob, the motor would speed up a bit. My truck (1970 K10 250 SWB) is a four speed with a granny gear, so you can imagine how this might be useful for a farmer out in a field who just wanted the truck to putter beside a combine or trailer. This forum is so great for exchanging information!

[Love 70 Chevys]

Still thinking.....Looking at your picture, the 72 setup is different. Must be because the carb is cable operated. Mine is all solid links (except for the manual throttle) and the connections take place on the motor side of the firewall. In 72 it looks like all the connections take place on the passenger side of the firewall. Doesn't matter, we will get both configurations working! Will take more pictures once I get mine 100% hooked up.

[CS1972]

As I was searching around the forum I found this thread which has some great pics of the complete 71 & 72 setup: http://67-72chevytrucks.com/vboard/s...d.php?t=783035

[clay68c10]

I may have used it as a Wyoming country living cruise control when I was younger. I don't think I'd do that in an area with ANY traffic.

[Love 70 Chevys]

Hoping to get some quality time with the truck this weekend and put the manual throttle back in. Will take some pictures to help others out should they need the info. Am learning there are three versions. One used from 67-70, one in 71 and another in 72. Also found a statement from the GM 1960 owners manual on use of a manual throttle:

"Pulling out on the knob opens the carburetor throttle to provide a uniform (constant until knob is pulled further, or pushed in to any position) engine speed above the idle setting. It is generally advisable to pull the hand throttle control out slightly when starting the engine especially if the engine has a tendency to stall a time or two after starting."

Back in the day I owned many 70's vintage cars. They were automatics, but I remember several of them that required one foot on the brake and one foot on the gas at stop lights on cold upstate NY mornings to keep them running. Would have been handy to have a manual throttle on those!

[Love 70 Chevys]

Had a great day working on the truck. Sunny and warm with the garage door open and the tunes on. Installed the manual throttle. I have included three photos in the hopes it may help someone out someday. The first is the overall set-up. The second explains the adjustment and operation. The third is of my dash rebuild that I got done today. The big question was whether I would delete the manual throttle or not as you can't buy one with the third hole. The answer is now definitely not!

[Love 70 Chevys]

OK...we all know restoring one of these trucks is a series of victories and defeats. This whole manual throttle thing was going so darn smoothly that I knew something had to happen! I was so happy when my throttle assembly went from rusted dead stuck to acting liking it was factory fresh just by soaking it. (Which actually happened!) The good news is that this occurred, the bad news is that the first time I tried to actually use it under spring tension, the cable broke inside rendering the whole thing useless!! However, I am determined to snatch victory from defeat. I completely pulled out the threaded portion and discovered that the internal cable had become detached from the threaded portion. There is a small bore and a cross hole where it was secured somehow. Does anyone have any ideas on how this was done? Small tack weld?...dimpling of the cable? The tricky thing is that the internal cable does not rotate, but the threaded portion does. How the heck is that accomplished? I need to get some wire the same size so I can push it by the end and get the attachment portion that broke out where it can be seen. Maybe that will shed some light on it and give me a clue. If anyone knows, please let me know!

[Love 70 Chevys]

Another thing I learned today once I got everything put back together. Those stories of using the manual throttle as an old-fashioned cruise control are not tall tales! On my truck, which has never had the gas pedal to carburetor motion transmission components hacked up or modified, the total travel of the knob is equal to the total travel of the throttle mechanism. You could lock in your gas pedal all the way to the floor!!! I don't know about you, but I am thinking that would be a bit dangerous. One jammed up cable or knob and you would be having one of those no brakes/can't stop the car nightmares for real!

[Love 70 Chevys]

Mystery solved. Victory snatched from defeat! I forced the wire out of the knob end by driving the wire with a long finish nail at the carb end until I could grab it with needle nose at the knob end. Then I could see how it worked. A very cheesy design my probably by now dead GM design engineer! (I have to admit I am in awe of what those guys used to do back in the day....but this one went a little too far on the penny pinching!) The way the connection that allows rotation was done, was to insert the inner wire into the threaded rod and then upset and deform it a bit via a cross hole. Then it theoretically would not pull back out and with a little grease in the hole allow rotation of the threaded rod, but not the cable. I wonder how many of these bit the dust early? I reinserted the wire, ground the ends of two framing nails flat to make my own "tools" and made the dimple in the wire a little bigger. It is a bit fussy because if you try to dimple it too much, the threaded rod won't rotate and the metal left in the wire will be too thin. If you don't dimple it enough, it will pull out if it meets too much resistance. It took me three tries to get it right. Lubricated the snot out of the inner wire, but discovered that any disruptions or slight bends in the inner wire (like mine had near the carb) cause the drag force to go up immensely. In fact, mine probably malfunctioned due to this and not rust and corrosion. I had a lot of fun with this little mini-project and hope what I learned can help others!

[firedemon]

they make a tool to lube cables on motorcycles it clamps on the end and you put the straw from a penetrating lube can in and work it in little at a time . might help with these old cables