drum brake "display" question

I have a drum brake assembly in my classroom (think back to your school days, basically a spindle attached to a stand with the brake components bolted to it) that we use for discussion and demonstration and the kids take it apart and put it back together. I would like to attach a master cylinder and pedal to it so the kids can see the brake shoes, wheel cylinder etc. in action...is there any problem with applying the brakes without a brake drum in place? Will the pistons in the wheel cylinders push out if there is nothing for the shoes to press against? I dont have a hub or drum for this setup as it is an old shop made piece and not exactly sure what it is...
thanks-

 

If you could make a couple stops on each side so the shoes hit them that should do the trick.

 

I don't see how it would hurt, the springs should keep the shoes from moving far enough to let the pistons come out. If you're really concerned about it you could always make a metal tie bar that slips over the spindle and keeps the shoes from extending. Kinda like a "C" with a hole in the center.

Or use huge zip ties

 

merlin, we must have been typing at the same time, haha

 

I would make a thick c shaped link to go across the shoes near the top to retain/restrain the wheel cylinder afer a small amount of travel. Removeable easily to allow playing with the assembly like you now do.Don't forget, the kids will try and break anything that is weak. Right?

 

Why not cut out some large windows on a drum? dont need to keep much to hold it to the spindle.

 

Ideally I would love to cut some windows in a drum but I will have to find a hub that fits the spindle...in the mean time a "c" shaped bracket like mentioned is a very good idea...
yes they will try to break it if its weak, they also enjoy trying to break it if its strong...

 

...I have had those pistons pop out with no brakedrum on; it's dangerous and makes a mess. Cut windows in the drum or build stops as suggested.

 

Yes they will pop out...

 

I would just put a limiter on the pedal itself, so you can't fully depress it but will travel enough to show the brake action at the shoes.

 

Yes they will pop out, THEN you can't stop, THEN you run thru the front of a local convenience store you were going too, to buy hot dog buns, THEN they get the cops out, THEN you blow in a tube, then they haul your ass to jail, THEN you miss your birthday picnic.

Don't fucking ask.

 

I'd bend up a piece of say 1/8"-3/16" flat stock to the curve of what the drum would be and figure a way to mount that. then when they push the pedal they could see the shoes in action.

 

that is a cool idea...

 

Why not go the easy way and cut a slot out to expose the wheel cylinder and cutouts in the drum to expose the shoes so you can show them how everything works,then you can pull the drum off to explain all the parts.Put a shutoff valve in the line so when you have the drum off you have no brake fluid disasters.

 

have no hub, no drum, dont know what this came off of to get said parts so for now am looking at fabb'ing something...

 

a swim through the parts pile found a hub with the correct bearings but the drum was too small, remove about 1/4" on the lathe and the drum fits, attack with plasma and create a window in the drum...thinks it going to work, thanks for the ideas

 

Most drum brake backing plates since the mid-1960s (yeah, I know, O/T) already have a retainer like the one being talked about here. I just did brakes on my 1984 Olds DD and it's got them. The pistons can't come out even with the drum off.

 

I'm gonna ask...

We're talking about not having drums on and depressing the pedal. The wheel cylinders fly apart. So you didn't have any drums on the car. Which meant the shoes had nothing to press against.

THEN you couldn't have stopped anyway. THEN you should have known long before you nailed the pedal in front of the convenience store that you had no brakes.

I think its time for a story. Was there beer at the picnic?

Adam

 

Joe padavano if you think the little pin with the spring on it to hold the shoes on the backing plate will keep the brake cylinder from popping out without the drum on it you are sadly mistaken.

 

No, I am talking about the C-shaped piece of 5/16" thick steel that surrounds the wheel cylinder and prevents the pistons from coming out. You have to physically remove the wheel cylinder to remove the pistons.

Note the part above the wheel cylinder with the tabs that block the pistons from coming out.

 

It was my Einstein like Brother in Law " Big Ed" working on his truck and my sister (his wife, only slightly smarter) told him they need hot dog buns for the picnic. He throws on the wheels and down the hill in to the grocery store.
Yup we had beer at the picnic he didn't , he didn't get out of jail until the next day.

Like my dad used to say "Ya know , I don't know why she ever married him, he could fuck up an anvil ".

 

wish i could have had this class at my high school!!

 

Can You cut some holes in the face of the drum in between the lugs and the edge. Like the Rocky Mountain Brakes on Modle A's. The mechanicals can be seen and the shoes wont expand out to far to come apart.