Cruise Control Throttle Bracket
I made a custom throttle bracket for my 1975 Suburban so that I could hookup the factory cruise control even though I had added an aftermarket intake manifold and carb setup to it. This is a fairly uncommon thing to do for some reason, but it was a fairly easy project and one of my first successful custom metalworking tasks. I am documenting this well after the work was done as a result of needing to use this basic design on my project to create a TV cable bracket based on this design.
What's so cool about this bracket design?
I got the basic idea from another commercially available bracket made out of machined aluminum that I had bought for another car. It did the job nicely for just my throttle cable, but I couldn't hook up my cruise control and it's annoying to have one simple connection stand between you and having cruise control when you are about to go off on a 500 mile drive. I searched and found a few brackets that purported to allow me to hook up my cruise control, but none of them really seemed to be what I wanted, so my brain came up with the nifty idea of just extending the existing bracket design to accommodate another slot and L-bracket for the cruise control cable, and voila - the idea for this project was born.
Along the way I came up with the idea for making the throttle return spring tension adjustable by adding a second L-bracket for the springs so you could change the "at rest" length of the springs to be snug, but not stretched so much as to create too strong of a pull holding the throttle closed. This design idea came about because my wife complained that the gas pedal was too hard for her to push. In her defense, it really was tough to push, even for me! This is why the base plate on mine has the same notch as the original in the back corner - it's where the springs originally hooked in at.
Here are the pictures of the original throttle bracket. It is available in various designs through many places such as Jegs. It is a fine design, and is a nicely machined and anodized piece.
The first diagram below shows the basic structure of the bracket base and the L-brackets you will need to build. It intentionally does not include dimensions - your carb and throttle cables may be different than mine and if you decide to build this, it's much more important that it fit your application than knowing how big mine was. The second diagram shows how to construct an attachment point for both the throttle cable and the cruise control cable to a single point on the throttle linkage on the carb, as well as the type of end you need to have on the two cables to make this work.
When sizing the bracket for your vehicle, the considerations you have are 1) the two main mounting holes need to fit your carb's mounting studs/bolts, 2) the offset of the bracket between the two main mounting holes must clear the throttle linkage attached and anything else (accelerator pump, etc.) attached to the carb in this area, and 3) the slots must roughly line up with the attachment points on the throttle linkage on the carb. In my case, I copied the existing bracket dimensions for the mounting holes and offset, the simply enlarged the area where the slot was to accommodate a second slot next to the first one. The original bracket mounting holes are 23/64" in diameter (just shy of 3/8") and the holes are 5 5/8" apart from center to center. The inside edge of the outer mounting arm is 2 1/8" away from the centerline of the mounting holes to the side and 1 7/8" to the front - this gives clearance for the linkage on the carb.
The L-brackets are pretty straightforward - two mounting holes in line in the long side of the "L" and the short side of the "L" should contain either a small hole to hook the throttle springs into, or a larger hole suitable for the attaching mechanism for your throttle cable. Some throttle cables need a roughly square hole and they simply "snap in" for attachment, others need a round hole and attachment is via two nuts to lock the cable into place. Note that if you have adjustment in all of your cable ends, then you have one more thing to adjust to get everything "just right" when you get done.
One other design improvement I have thought up after building my original bracket is a way to make it easier to adjust the throttle linkage L brackets and the throttle spring mount point. The original bracket used a milled aluminum piece that fit into the adjustment slot and only one screw to hold it snug, installed from the bottom. While this made on-car adjustments difficult, it did look snazzy when done because the screw was not exposed. You could incorporate this design idea with a thicker base piece on the L-bracket - for example by welding a small piece of 1/4" plate steel to the bottom of the piece - and by drilling and taping two blind holes in the underside. That way the two screws would enter from the bottom and be largely hidden once on the car. The spring mounting plate would have to mount from the top, but you could make the screw less visible by using black cap-head mounting bolts all around.
The picture below is a scan of the two base plates side by side with a ruler in the middle so you can get some idea of the scale.
The bracket base and the L-brackets are constructed out of simple plate steel - 1/8" should work fine and still be easy to work with. I built my original bracket with a thinner piece of sheet metal (around 1/16" thick) and it was quite flimsy. It worked, but it flexed quite a bit and I think it will eventually break from metal fatigue. Slightly thicker metal should cure this, and if you want even more durability, you could weld a piece of 1/8" square stock to the bottom of the bracket down the "arm" that goes to the forward mounting point, between the two slots, and in the area in front of both slots that connects to the rear mounting point. I solved most of my flex problem when I made my spring tension adjustable - the original design stretched the springs all the way to the back of the slots and it put a lot of strain on the metal. Moving them in added another L-bracket to help stabilize the base and reduced the tension in the springs. It's held up for a few years now with no ill effects.
The throttle cable hookup is made out of a few small bits and pieces that you should be able to get at any decent hardware and/or auto-parts store. You need a piece of all-thread in a relatively small size - it has to fit the holes in your throttle cable ends snugly enough to not have too much slop, but not so tight it will bind. You can cut the head off a suitably long machine screw if you need to and use a small file to clean up the thread end. Washers and lock washers are both needed, as are two nuts. The spacers are simply tubes that fit over the threads - mine were small brass pipes cut to length. Short lengths of steel brake line would work as well.
You may opt for a cotter pin so you can cross-drill the very end of the all-thread and slide in the cotter pin for worry-free retention of all the little hardware in the throttle cable hookup. I strongly recommend this as it's a easy to do and it prevents the linkage for falling apart on you should stuff vibrate loose. For the record, I did not do this originally, and my linkage did vibrate loose until one day I pressed the throttle and heard a "twang" noise under the hood and nothing happened. I spend a good bit of time finding all the little pieces in the dark in the rain by the side of the road and then I had to reassemble them on a hot engine. I added the cotter pin as soon as I got home, and my throttle linkage has been worry-free ever since.
The L-brackets are each held down to the base with two mounting bolts, lock washers, and nuts. If you have a throttle cable, cruise control cable, and a spring bracket - you will need 6 sets of "bolt, lock washer, and nut". The exact size isn't important so long as they are all the same and you have a way to loosen and tighten them down later once the bracket is mounted on the car. You may wish to use black cap head bolts (the kind that uses an Allen key to loosen it) for a nicer appearance. Make sure they length is appropriate, especially if using my idea for drilled and tapped mounting holes in the bottom of the L-bracket base pieces.
Lastly, you will probably want extra washers to go above and below the bracket on the two main mounting studs. If you needed new washers above and below on both mounting points, then you would need 4 washers. I believe most 4-bbl carbs use 3/8" mounting studs, so you would typically need 3/8" washers.
If you desired, you could substitute aluminum for steel throughout this project. If you do, you will need to increase the metal thickness enough to be sure the bracket has enough strength to do the job. I'll leave it up to your judgment on how much "enough" is. For reference, the original bracket I based this idea on was made out of aluminum and was approx 1/4" thick. My replacement was made out of a piece of sheet metal I had laying around in the garage and it was a bit thin for my tastes. It had a good deal of flex in it, and although I never had a problem with cracking or breakage, I think that was only a matter of time given the flexing each time I pressed the gas pedal. Thicker metal - say 1/8" plate steel - or perhaps some small stiffening braces welded to the underside of the base piece would have fixed this quite nicely and given more piece of mind. I would recommend using slightly thicker metal for the base piece because it's easier that welding. For the L-brackets, I would recommend using the sheet metal and then forming side "angle" pieces that welded to the base to provide stability if needed. It's much harder to bend 1/8" steel plate than it is to bend sheet metal, especially with hand tools working at home.
You will need a file, drill, jigsaw with a metal cutting blade in it (or your metal cutting tool of choice), a small bench vice, and optionally, a grinder of some kind - Dremel tool, bench grinder, air powered cutter/grinder - whatever you feel comfortable with. A center-punch for marking holes to be drilled is also recommended.
First, cut out the metal for the L-brackets. Cut out three strips of metal of the desired width and length. How wide? The mounting point of the throttle and cruise control cables will determine how wide you need to make these pieces. How long? The length should be enough to form the upright portion of the "L" with enough left to have a mounting point a bit longer than the upright. Something on the order of 1/3 and 2/3 sizing should be about right. Make sure you mark your anticipated "bend point" on the L-bracket, I would suggest somewhere around the 1/3 mark and take note of what will be the "upright" (1/3) and "mounting" (2/3) parts later on.
Next, make the proper holes in what will become the "upright" portion of the L-brackets. The spring mount is easy - just drill a hole big enough to slip the spring ends into somewhere near the top middle of the upright section. If you need a round hole for your throttle or cruise control cables, then mark and drill a hole of the proper size that is roughly centered in the upright section. If you need square holes, then mark and drill a roughly centered hole that is about the same diameter as the smallest width you need for the final square hole. Then use the jigsaw and a small file to open up the corners of the hole until they are suitably square. Test fit the cables and springs before moving on to be sure all is well.
Next, drill the mounting holes in what will become the "mounting" portion of the L-brackets. They should be centered side to side, and in line with each other. I would place them at roughly the 1/4 and 3/4 mark in the "mounting" portion of the bracket. These holes need to be big enough for your L-bracket mounting bolts to slide through easily without excessive play. If using my idea of a thicket mounting base, drill and tap them in the mounting base piece so they do not go all the way through to the top. If using my original idea, drill them all the way through.
Using your bench vice, bend the strips of metal into an "L" shape. Insert what will be the upright portion of the "L" into the bench vice so that the line you made previously is right at the top of the vice. Then, using a hammer and perhaps a heat source applied at the point of the bend, make a 90 degree bench in each of the metal strips.
Before creating the base, I would suggest going through the layout steps for the base using some thin cardboard as a mock-up first to validate your basic shape and dimensions will work the way you think they will. Cutting cardboard with scissors is much easier and faster than cutting metal.
The first step is to lay out the dimensions of the base piece on your chosen piece of steel. Consider the mounting studs, clearance for linkages, and the location and layout of the slots for the L-brackets. Make sure that your slots are far enough apart so that the L-brackets don't touch if side-by side (1/16" clearance is fine), and that the slots are long enough for the adjustments you will need to make later on.
Cut out the basic shape of the base piece using the jigsaw, file, and grinder. Concentrate on roughing in the shape for now, especially the areas that have to clear linkages and other moving parts on your carb. Remember that you can always cut more metal away later, but if you go too far, you'll have to start over again with a new piece of metal.
Next, you need to mark and drill the two main mounting holes to match the sizes of the mounting studs/bolts on your carb.
Trial fit the base to your carb and look for any places of interference. Fix as needed and get the external dimensions of the part pretty close to final before moving on.
Lay out the location and width of the slots on the base. They should be parallel to the "throw" of the carb, and roughly at the places where you want the cables to be at in the final installation. +/- 1/8" accuracy is fine here. The width should be slightly larger than the bolts you bought to mount the L-brackets to the base. The distance between the slots should allow your L-brackets to be adjusted side-by-side without touching each other - 1/16" clearance is fine here. Be sure the slots are long enough for any adjustments you will need to do later on.
Cut out the slots using your favorite method. You can drill out at the ends, then use the jigsaw to cut out the middle. You can also use a small air powered cut-off wheel to carefully grind out the slots - that's what I did. Focus on keeping them the right width, and as straight as possible so the bracket looks nice and is easy to adjust later on. Clean up any sharp or uneven edges on the base before you get done.
Mount the all-thread to the desired attachment location on the throttle linkage attached to your carb. Use two nuts and two lock washers and snug it down so it won't go anywhere.
Mount the L-brackets to the base using the bolts, washers, and nuts you bought for this, but don't tighten everything yet - leave it loose enough to adjust more once you get it on the car. Note that the spring mount typically goes on the opposite side of the base from the throttle and cruise control cable mounts (in my case, the bottom). Also note that the spring mount typically goes further back than the cable mounts and on the same slot as whichever cable is closest to the center of the carb. That is because the springs should hook to the carb linkage directly and on the opposite side of the linkage pivot point than the cables do.
Mount the bracket on the car so everything can be test fitted and verified to work. As each L-bracket is test fitted and adjusted correctly, tighten it's mounting bolts and move on to the next one. Install the springs first and verify they close the carb linkage without excessive pressure. Then do the throttle cable. Hook it up to the linkage using a washer, the spacer - now is the time to cut it to length - and another washer. Adjust it so that when the gas pedal hits the floor board, the carb reaches wide open throttle (WOT). You want to make sure the carb actually gets to WOT, but you don't want the gas pedal to still be off the floor because it will stretch the cable and could pull the throttle linkage "over center" which is bad. Finally, do the cruise control cable. Hook it up the linkage using another washer, the other spacer - again, cut to length as needed - and another washer. Put a final lock-washer and nut on the end and snug it down enough so there is no slop while making sure nothing binds. Adjust the cruise control L-bracket so there is a slight amount of slack in the cable at idle and make sure there is enough travel in the cable so you can still reach WOT on the carb.
Double check all of your bolts to be sure they're tight, and check to be sure that when you press the gas pedal, it all works like it should, and the carb always returns to idle. Now is the time to adjust the spring tension so the "feel" of the gas pedal is to your liking. Once you're happy with things, fire up the engine and take a test drive to verify it works like you want it to. Make sure to test the cruise control.
If you decided that you want to put a cotter pin in the end of the throttle hookup, now is the time to measure for the location of the hole you need to drill in the all-thread. Disassemble the spacers and washers, remove the all-thread from the carb linkage, and cross-drill a hole big enough for the cotter pin you selected. Re-assemble the throttle hookup and verify the hole is in the proper position. At this point, you may want to use some Loctite on the two nuts that attach the all-thread to the carb linkage to be sure they stay put.
Now it's time to remove everything from the car, do final prep work, clean everything, and paint it all so it looks pretty and doesn't rust. Disconnect the cables from the throttle hookup on the carb, remove the cables and springs from the L-brackets, and remove the entire bracket assembly from the carb. Take careful note of the adjustment positions of the L-brackets my measuring things and possible by taking a picture or two. Remove the L-brackets from the base, and then do any final filing, grinding, and metal prep you need to. Completely clean the pieces (I like to sandblast them), then paint them your favorite color - I prefer a nice semi-gloss black. Note that you may want to clean and paint the spacers and for the throttle hookup as well. Wait for the paint to dry fully before handling the parts again.
After the paint is dry and you're happy with your parts, re-assemble the L-brackets onto the base using your previous measurements as a guide to placing them. Then, mount the bracket to the carb, hookup the throttle linkage, install your cotter pin in the throttle hookup linkage (if you decided to add that) and do your final adjustments. Be careful to not chip the fresh paint and try not to get things too greasy. Repeat all of the previous checks for the cable adjustments, make sure the springs are installed and adjusted to your liking, then do another test drive to verify you're happy with your new throttle cable bracket. Make sure to test the cruise control.
These are the pictures of the original bracket I built along with the individual L-brackets and the adjustable hookup point for the throttle springs. It's a little grungy because it had been in use on my engine for a few years before it was removed for these pictures.
Page last updated 01/02/2009 01:51:39 PM