Did you ever wonder "What the heck is a Bell-Crank?"

All of you older guys will already know what it is. My friend Gord just came back from the sunny south (Florida) and while there he purchased one of those nifty 90 degree under dash brake pedal/master cyinder set-ups, and brought it over to my house to model in Solidworks.---Anyhoo----A bell-crank is a very simple mechanical device that can turn a "push" or "pull" force through a 90 degree corner. In this case, the bell crank is the elbow shaped peice in the lower right corner of the picture, with a spherical rod end attached to the end of the top arm and a clevis attached to the end of the other arm. When the rod with a spherical rod end on both ends moves from left to right, the bell-crank pivots, and pushes the yellow rod into the master cylinder to operate it. (and yes, the yellow rod is an old pencil that I broke off and stuck in there for illustration purposes.) This simple mechanism has saved the day for many a hotrodder, over the years, when they had to operate a carburetor, clutch, or brake pedal and the plane of motion was not in line with the plane of motion that could be applied to it, and a flexible cable was either to light or not suitable. Simple tech, yes, but still has a lot of good applications in the hotrod world.---Brian

 

Hey Brian... could i get some more detailed shots of that brake setup? Tried making my own and its a pain, i overcomplicated things and this one seems nice and simple.

Email me pics to monstergarage87@aol.com

Thanks,
John

 

Monstergarage87---I sent you a bunch of email pic's.---Brian

 

Thats super cool. Ive never seen or noticed anything like that before. Thanks for posting this.

 

Hello..Throttle shafts have a bell-crank..Look at the stromberg 97..
YUP..
Duane

 

Is that a commercially available setup? If so, who makes it?

 

This one I made using a cut down brake pedal as the bell crank-





or- http://www.kugelkomponents.com/index.html

http://www.ecihotrodbrakes.com/master_cylinder_systems.html

 

If you are after a set up to run behind your dash from the wreckers have a look at cab over small trucks, especially from japanese makers. Most have them. The only h***le is access to the master cyclinder to add fluid. Chopperman's hinged dash may well be a great solution.

 

ford vans and some dodges from the 69'-74' era had these bellcrank setups. spark that one you made is killer, great fab work dude!

 

Kirk---it is commercially available, but I don't know where my friend bought it. I will find out and let you know---brian

 

http://ecihotrodbrakes.com/hanging_pedal_***emblies.html

http://www.kugelkomponents.com/products/brake_systems/brakesystem.html







.

 

Hey Nick,
Mike has used that set-up on a couple of his cars.
DD

 

Cool,

Thanks Brian. I think this info will help me with my truck. It's getting tight in there and I don't want to mount the master cylinder on the outside of the fire wall

 

Thanks Brian, I am considering the same kinda setup. Can you be so graceous as to emial me a bunch of pics, too.
Thanks man...............
bigken069@yahoo.com

 

That's very clever! I have seen a setup like that before but just last night I tried to think how it works! Thanks. --mika

 

Nice setups. Yeah, bellcranks are pretty neat. I think the name goes way back to the old days to the levers they used to swing church bells.

If you're designing something from scratch, I'd add that it's a good idea to mount the bellcrank in "double shear", which means that whatever axle the bellcrank is pivoting on is supported from both sides. If it's in "single shear" (supported only at one side of the pivot pin), just make sure the pivot point is extra sturdy because the arms of the bellcrank give leverage to whatever force is on the ends of the two arms to try to bend the pivot shaft.

Also, the joints at the ends of the arms should be in "double shear" if you can. A clevis is supported equally on both sides of the pivot, so it doesn't try to bend the bolt that acts as a pivot point. But if you use a spherical heim joint and it's bolted to something only on one side, the force against the heim joint tends to try to bend or break the bolt especially if the bolt is loose. If it has to be in single shear like that, it's better to bolt the spherical part of it solidly to the arm (using spacers if needed for clearance). If it's bolted solidly, then the sphere of the joint becomes like part of the bolt to stiffen the bolt up against bending, but if it's loose, there is more bending force on the bolt. They sell small spacer tubes that allow you to bolt up the spherical part tightly without losing too much movement of the outer part of the joint when things aren't perfectly aligned anglewise. You can also make U-shaped forks to go around the spherical ball joint so that it puts the support bolt back into double shear instead of single shear.

In spherical ball joints, the ball turns against the outer race part, usually with a teflon to metal joint for low friction. That's where you want the joint to move. You don't want the rotational movement to take place in between the axle bolt or pin and the inside of the ball. The axle or pin should be "as one" with the ball. I hope that makes sense.

 

For another awesome setup check Kruzer63 for his owner fabricated one.

 

RustyBolts, thanks for giving my setup the once over, I agree with all the points you have raised.

The long bolt –hem to bellcrank will be replaced with one with more thread so the head and nut will hold the hem firm,
the bottom nut will be nylock, as will the pedal to hem, locknuts on the hem to hem.The bolts fit tightly in the holes in the bell and pedal, the hems do sit on the unthreaded hilt of the bolts and fit the ball of the hem well (just need to get a bolt with slightly more thread for the hem to bell).

All bolts are grade 8, I used the original bolts for the bell shaft, brake pedal and brake booster,
I will also fit new spring washers.

The photo was when I first put it together, using what I had on hand- all just finger tight because
I will be cleaning it up and painting before final ***embly and fitting.

Apart from the bell crank support braket, no brake parts have been welded.

 

A friend on mine used the Kugel Komponents piece on his 27 T roadster and the master cylinder resivior lined right up with the original cowl vent for filling.

All of these are great looking pieces in my opinion.

 

Another couple of points to ponder, (for those who don't already know this).
You can lengthen or shorten one of the two "arms" on the bellcrank and gain or reduce physical output force over applied input force. (You do, however, give up some linear throw.)

BTW....Kudos to Brian for bringing a subject like this. It might be a rather simple mechanism, but the applications are almost endless. Damn good tech refresher post.

Roger

 

GTS225 You are correct, and that is called the inverse force/distance ratio. Basically what it means is that by monkeying with the length of the arms, you can get it so that by moving one of the arms 1/2", you can get the other arm to move 1"---BUT---when you do that, it will take twice as much force to move that first arm the 1/2". Likewise, if you set it up in the reverse of that, so that by moving the first arm 1" the second arm travels 1/2", then it only takes half as much force to move the first arm. Fun stuff---right!!!

 

a bellcrank on a railroad freight car is part of the hand brake system

 

Really great thread. I noticed that the ECI and Kugel kits also have a single shear point.....should I be worried? I'd like to just buy a kit rather than taking the time to build my own...

Thanks.
Gary

 

No !

 

Kirk Hanning here on the HAMB built his own for his '34 truck. I'll bug him to post some pics.

 

Not sure how you guys take to "foreign" cars but here's one I made for my VW Rabbit. There was no room at the top of the pedal pivot so I had to switch things up a bit. I didn't have cash for fancy joints so I used modified sway bar end links.

 

one of my sprint cars had a master setup with a bell crank. it mounted the master between the firewall and the steering box. gave you more room for your thighs.

 

Way to jump right in! No matter what car that is on, the same idea would apply. Any details on how you modified the swaybar links, or more photos of construction?

 

I've got a couple more pics but none really clearly illustrate what is going on. It went together pretty easy. I set up the angles within some square tubing so I could get it put together on the bench. Once that was squared away I had to tie it in with the pedal somehow. I looked at fancy joints at the speed shops but figured a sway bar link was basically two universal joints. All I had to do was cut and reweld at my desired length. I'm sure there are simpler ways of doing it but this is just what I came up with. I think I have like $12 into it.