How does a top fuel dragster reverse?

[Cart]

Ok I've been studying top fuel clutches and for the most part I understand how they work. They are five clutches together in a pack with a timer and a centrifugal clutch at the back. I'm just curious how that whole system is able to be put into reverse without a trans?

[Orange65]

To my understanding, they may not have a transmission with a series of gears, but they do have a reverser- a trans like thing that allows them to go backwards.

[Beagle]

hit up Lenco?

[A/Fuel]

That lever pulls a gear back into a sungear, then the tail shaft spins backwards.
They have a centrifugal clutch with 5 disks and 4 floaters against the flywheel, against the fingers on the pressure plate rides a bearing on a tube. It's also attached to a fork then to linkage that connects it to the clutch peddle. When the bearing is pushed forward it pushes the fingers in and it takes the tension off between the last disk and pressure plate.That would be netrual. On the other side of the bearing is a hydrolic ram. It's usually filled with water or somekind of 2w oil. That will control how fast the bearing is allowed to go back and let the finers rotate out. The fingers push against the dough nut in the pressure plate and apply clamping force to the clutch pack. One way to program it would be to have an air activated switch under the gas peddle, it could be converted to an electric signal to a programable timer. It would hold it at a certain point for a certain ammount of time. If you could see it as a line on a computer it would be a serries of little steps. Then it would go back to an air signal to control the ram.
Anyway, you push the clutch peddle in after the burnout and pull the brake, after you stop, reach down with your left hand and push the lever forward. If it doesn't go, you can try to let the clutch peddle out a little and see if you can feel it in the lever. If it's ideling to high and you can't push the clutch all the way in pull the fuel lever back some until the engine comes down some. Once you get it in reverse, let your foot off the clutch. Before you get going to fast push the clutch back in. When you pass the starting line, push the clutch back in, pull the brake and stop, reach down with your left hand and pull the lever back. Now, start pumping the brake, and work the peddle until you light the top light. Then pull the fuel lever back, light the bottom bulb, let your foot off the clutch and wait for the flash of yellow.

[Dignlif]

ok nothing of value to add here but thanks A/Fuel for your description...it was cool imagining the steps happening

[Bamfster]

And I thought my staging routine was complicated! .... Thanks for the in-sight A/Fuel

[greenXpress]

ok nothing of value to add here but thanks A/Fuel for your description...it was cool imagining the steps happening

Ditto !!!!!!!

Was picturing it as I was reading. Thanks.

[Cart]

Thanks A/Fuel! That was the best explanation I have gotten from any where. It was also interesting to visualize the staging.

[A/Fuel]

No problem guys. I love thinking and talking about clutches. It's such a simple yet complicated device that does exactly what you tell it to do. Telling it to do what you really want is a different story though! There seems to be an infinite ammount of adjustments and things you can do.

[DanStokes]

I have an on-going challenge to get mechanical things to do what I want them to do and not what I told them to do. Sounds like one of THOSE things!

And thanks for the insight. Pretty cool.

Dan

[Cart]

So do u need a centrifugal clutch to run a lenco reverse unit with out the rest of the lenco trans or could you use a regular clutch?

[A/Fuel]

You just need an input shaft that will engauge the reverser.

[Caveman Tony]

.... Before you get going to fast push the clutch back in. When you pass the starting line, push the clutch back in, pull the brake and stop, reach down with your left hand and pull the lever back. Now, start pumping the brake, and work the peddle until you light the top light. Then pull the fuel lever back, light the bottom bulb, let your foot off the clutch and wait for the flash of yellow.

Uh, I musta missed something.

If you let off the clutch, doesn't the car start to move? What holds it in place against an idling 8000-hp monster?

[Deaf Bob]

Uh, I musta missed something.

If you let off the clutch, doesn't the car start to move? What holds it in place against an idling 8000-hp monster?

I was thinking trans brake? ... Probably not...

[A/Fuel]

Thats a good question.
There are stall springs that pull the dough-nut to the hat. The fingers, as they rotate try to spread it appart and apply clamping force to the clutch pack. The stall spring tension can be adjusted to counter the fingers to acheive the desired idle. The fingers are what's centrifugal about a centrifugal clutch. As the rpms are raised the fingers will rotate and overcome the stall springs, clamping force increases and the car starts to move. When you let off the clutch peddle the fingers push the bearing back until the stall spring tension is enough to hold it. Now it's starting to heat up and expand taking up the gap between the floaters and disks. You would still have to hold the brake. Thats why it's important to pump the brakes up to about 700psi line pressure before staging.
If you've ever played around with a snowmobile clutch you would find that they work in the same way.

This is an a/fuel clutch but it's similar to a top fuel. In this pic you can see the 6 stall springs and the 12 fingers. The numbers on the fingers tell what radius they are. Or how the lobe is shaped on the underside, .250 long and .265 short is a popular radius for staggered fingers in a/fuel. The nuts and bolts attached to the fingers are the weight, just by looking this clutch appears to have about 516 grams, which would be typical a/fuel starting point.