Aug
04
Scotty’s Safety Scoop – Throttle Linkages
By
I know it’s been a while, but I’m back with a new safety article. I’m sorry it’s been so long, but I’ve just been busy down here with work and building some new cars for next season. I don’t want to write you guys something half-ass, so I like to sit down and spend a good four hours on an article. Lately, it’s been hard to find a spare four hours. This article is one that has been on my list for months. I feel it has to be one of the most important mechanical parts on any racecar, it is the throttle linkage. I’m sure we all have at one time seen one stick or have seen the remains of what used to be a racecar from one sticking. I had it happen to me in 1998. I had a compression fracture in my spine, and let me tell you, it hurt. Looking back though, I’m glad that is all that happened.
There are two basic types of throttle systems used in sprint cars. They are either going to be a throttle cable or a throttle linkage. The throttle cable is basically a cable that moves inside of a flexible housing. Throttle linkages are composed of small rods, heim joints, and bell cranks. Both of these systems are designed to move the throttle input on the carb or fuel injection when the gas pedal is pressed.
First, let’s go over throttle cables. Throttle cables are very universal. They can easily be switched from motor to motor, or carb to fuel injection. They are very beneficial in a hard wreck. In a hard frontal impact the motor will move forward, when it does this with a linkage system that is mounted to the car, it reacts as if the pedal is being applied. With a cable system that is mounted to the motor, it doesn’t affect the throttle position. This is good after a wreck; the motor is not going wide open while you’re knocked out. That’s the good things about throttle cables. A bad side to them is they do require a bit of up keep. It is a good idea to take them off often and clean them thoroughly. After cleaning, they should be well lubed and checked for damage. If you don’t, dirt and track grime build up inside the housing causing the cable to bind. This leads us to the other problem with throttle cables, binding. This can be caused by grime build-up, sharp bends, or high heat. It is a good idea to use only as long of a cable as needed. To long of a cable leaves it open to get snagged on something or cause a bind from a sharp bend. High heat situations will cause the outer housing to melt causing it to bind up also. When the cable binds, this is a possibility for a stuck throttle. Another tip is to spend time on your mounting brackets for the cable. Use quality parts and if you don’t know how to weld, don’t use anything in this system to learn how to.
Throttle linkages work a little differently. They use a system of rods and bell cranks to mechanically actuate the throttle on the carb or fuel injection. They are fairly simple in design, and can be adjusted easily, for different driving styles. If a driver like very little pedal movement from idle to wide open or vice versa, the timing in the bell cranks can be adjusted in minutes, unlike a cables system that is pretty much set by the throw on the carb or fuel injection linkage. The biggest problem is that they are mounted to the car. Like I said earlier, when the motor moves and the throttle systems stays put, it’s like the driver is pulling the throttle linkage open. It is very hard to get help to a driver in need when the motor is revving wide open. Another problem I see is people not getting all the binds out of the system during construction. The system should operate smooth as glass without any assistance or tight spots. If it has any, at the shop is where they should be taken care of. All the heim joints should work freely and be lubed weekly. If they are not, they will stick and potentially bind. Another downside to the linkage system is that the entire system is exposed. All of the moving pieces are open to getting caught by breathers, hose clamps, spark plug wires, and even dash panels. Any one of these things can cause the throttle to hang up. It is a good idea to imagine a three inch radius around the entire system. Anything in that radius should either be moved or secured so not to come near the linkages.
Something new to keep throttle linkages from sticking in a wreck are aluminum rods. Normally, the rods are made of steel or stainless material. In a frontal impact when the motor moves forward, the rods are designed to break, this causes the motor to go straight to an idle. If the motor’s throttle is stuck after an accident, it can cause further damage to people and racecars sharing the racetrack. These rods can be bought from your local speed shop relatively cheap.
Another hazard to the throttle system is the air cleaner system. If the hose clamps on the air breathers are loose and let the breather fall down, they can sit on the barrel valve. If this happens going down the straightaway, it holds the throttle in a wide open position. This can also happen the other way. The stacks can come loose from the injection system and get caught in the throttle. It is always a good idea to check the stack clamps often and the hose clamps on the breathers to prevent this from happening.
Carb users also have problems with air cleaners. On the deep dish air cleaner bottoms, they can snag the throttle linkage in a wide open scenario. Always check this before you leave the shop or after changing anything in the fuel system. If it doesn’t work 100% while testing it at the shop, then make it right. If you make any mistakes in this area it will easily cost you a racecar.
I hope giving you these tips will give you something to look at next time you’re working on your ride. I make it a point to handle the throttle linkage system of anything I drive myself, especially if I didn’t build it. The point is no matter which system it is, is to make sure it works freely, it is well maintained, and has a clear area around the entire system. By doing this you ensure that you won’t be buying a racecar because of a stuck throttle. As a driver, I’m trying to make it stick even while I’m waiting to get fired off. I would rather it stick in the pits than on the racetrack any day.
I don’t like doing safety articles on a lot of mechanical things, because everybody has their own way of doing it. These are just a few tips that have worked for me and if somebody gets something out of it, then mission accomplished. Remember, our goal is to keep you guys as safe as possible, and have fun in the process. If you readers have any suggestions, please leave a comment, any helpful info is great. The fewer the times this problem occurs, the less an opportunity of someone getting hurt.
As always, thanks for reading, and sorry about the wait. If you have any questions or comments, get a hold of me or the web-site and we’ll get you the info. Come back to FloridaSprintCarFans.com, the safest website in sprint car racing, for all the latest news.
Be Safe and Have Fun!
Scotty 67