Technical Hot Rod Emergency Brake set up question

I am just finishing a model a coupe project . My set up for the Ebrake doesn't seem to work too well. I am running a ford 8" out of a 1966 Mercury Comet. It has the stock emergency brake set up complete with the stainless grab wire running from one wheel to the other. The drum brake set up has been completely rebuilt including the ebrake portion. I set up a pull system mounted to a model A brake handle which is mounted to a flathead heavy duty truck transmission. There were some convenient bosses that i was able to drill out that took bolts nicely. The real problem is that it takes a Russian Weighlifter to pull it back. Really it doesnt come back and engage well at all. Is this something to do with the science of the thing and the amout of force necessary? any good help/advice appreciated

 

Probably has to do with the ratio of the length of the handle, to the distance between the pivot and where it pulls the cable. If that ratio is too low, then you won't get enough leverage to pull the cable with enough force to engage the brakes.

 

I like the Mustang II handle. Like the shifter and front crossmember, is made to adapt to hot rods.

 

thinking about what squirrel wrote above and using the logic....The Model A handle is twice as long as the mustang handle so how will that improve things?

 

You need to compare the ratio of the working lengths; but I think the short lever has a better ratio.

I have put several set-ups together using '35-'36 levers on Model A quadrants. They all worked good; and got better once brake shoes wore in to match the drum ID. If I remember right these levers are an inch or two longer than an A lever; but your set up should still work.

Make sure the brakes are adjusted good; run the star wheel up as tight as you can get it, then back off until very light drag, the adjust the cable so only small pull puts the shoes into the drum, make sure the equalizer let the cable slide so both brake apply evenly, should work then.

 

Same lever principle as a brake pedal. Full travel on handle won't allow sufficient travel and leverage from short side. A longer 'Dim B' will pull the cable more.

 

show us what you have, we can't see it. Where on the lever, does the cable attach?

 

This is where the "tell us more and show us the photos" comes in to play.
Unless you added a lot of length to the bottom lever that pulls the cable I don't see how the leverage ratio would be such that it made it hard to pull. Cables in a bind? The lever assembly it's self in a bind.
The button or lever not releasing the catch far enough so that the lever moves easily? Some have thumb buttons and some have a lever to work the rod that pulls the locking piece out of the teeth.

 

i will be back in a few days with some pictures

 

I hit the wrecking yard and pull E brake handles and mechanisms off newer cars. Some use a roller wheel for the brake cable to roll over as you set the brake, and that gives a better leverage. Usually cost $10-$15 and easy to adapt to most factory rear brake cables.

 

I don't know how to explain it other then to say Picture a Wheel barrow that you use to pick up a load of dirt and move around the yard. A 2nd class simple machine, I learned in Jr High Science Class. Anyway, you need to Fab a simple machine lever under your car. A foot long length of steel that is anchored at one end but allowed to pivot on that end. Pretend that the pivot is the Wheel Barrows wheel. Your cables that go to your brake drums, they are the weight. Like the dirt in the wheel barrow. Those cables must attach to the lever about a third of the way up from the pivot, or Wheel like on the Wheel Barrow example. Now, like your hands grabbing the handles of that Wheel Barrow, down at the far end, away from the pivot, you attach the cable from the lever that you pull on in the cab to engage the E Brake. Like a wheel Barrow your hands grabbing the handles of that wheel barrow. All this is called mechanical advantage. I was laying on my back under my 1985 chevy pickup when I first saw this arrangement and understood the principal. Well, wait, maybe it was my 1964 Econoline Van?

 

The ebrake in the Comet had an equalizer bar mounted under the transmission, the lever under the dash pulled a cable that pulled the bar which in turn pulled the looped rear cable. The equalizer bar generated a lever advantage to make pulling the dash lever easier, I do not believe you have the leverage needed to pull the looped cable tight enough.

 

On my car I use a stock 32 handle, which is like an A handle. Mine is hooked up to a set of 40 Ford brakes so I don't know if the ratio needed is the same as your rear, up maybe.

I have the handle pull straight back on a rod, the rod attaches about 2/3 of the way off an arm pivoting at the inside of the frame rail, right behind the center X member. The other end of the arm (below the driveshaft) pulls the yoke in the middle of the parking cable between the brakes. So basically the arm increases the ratio of pull (more distance of pull) about a third from just the handle itself.

 

Here are some pictures. I did extend the bottom on the brake handle to get it to clear the drive shaft. I did look up the original configuration of the 66 merc and i did see that it uses a lever. Now i am trying to figure out how to salvage this set up and would appreciate any further suggestions. Car is a 29 coupe on deuce rails with heavy duty 3 speed transmission

 

Pics tell all. Your extension has reduced the ratio to almost nothing. It's like you are reaching under the car and pulling the cable directly. Restore the correct ratio and all will be well.

 

Okay here is what I created so far, have not got back to this job yet.
Universal Lokar style cables off rear drum brakes to my leverage pivot.
Pull style underpass cable to lever to actuate, this draw bar.
I'm sure I will be playing with it to get it right.

 

Simple and cheep.

 

You've extended the brake lever, thereby destroying the mechanical advantage, in order to get the linkage to the cross cable below the driveshaft. The 1 800 style solution to this is a Lokar cable setup. Reduce the lever to the correct length and the static end of the twin cables will mount on the underside of the floor. The cables (Bowden type) run just under the floor, above the driveshaft, to the backing plates. I'm assuming Lokar make a cable setup for your style of backing plate. Or you could save the $$$'s and mimic the Lokar stuff with junkyard parts.

Chris

 

By making the lower arm of his handle longer, he created a longer pull on the cables. It will be a harder pull, but it will give you the length needed to make them engage (hopefully). If they are still not engaging they probably need more pull length. Maybe it's time to consider an idler lever with a increased pull ratio.

 

check out pioneer CA-5075 e brake cables they snap into 9 inch backing plates and have worked well for an off topic car i did