A while back I asked if early 40's brakes would stop good and the response was yes..so now, I need to get mine to do so. Here's the deal- I took a 1950 Ford Master cylinder and mounted it under the floorboards facing backwards. I put a T-fitting in the line and plumbed the front off one side and the back off the other. I use the pedal to pull a rod, which pulls a flat plate that is pivoted in the middle and then the bottom pushes the master cylinder rod to work the brakes. You can see it in the pic. Front of car is to the right. Mashing the pedal can produce 1.25" of travel up top, which translates to 1.5" of travel at the m/c rod...so there is plenty of travel to work with. Right now, when I mash the pedal, there is hardly any pedal movement and I can physically STAND on the pedal and the brakes just scrub the car to a stop...and it takes a LOOOONG time. No such thing as a 'panic stop'. Dose anyone see any flaws in my linkage arrangement? All the wheel linings are good and adjusted snugly. I don't want a lot of pedal travel, but it should stop the car better than this.
Judging by the photo, it appears that your mechanical advantage (pedal ratio) is ziltch (1:1). I'd say your problem is in the pedal geometry, you need to create a better pedal ratio.
Man, I don't know... the arm of the pedal pulls on a app 5" flat bar (seen in the upper right of the pic) and that goes to the top of the flat pivot bar. the top hole is about 2" above the pivot, the bottom hole is about 1.75 below the pivot.
According to your measurements my original thought is off so it is probably due to issues in the hydraulic system it's self or the way the brakes were set up. Brakes adjusted correctly? all lines in good shape with no kinks or smashed spots? How quick and straight does the car actually stop? Those of us who have driven with drum brakes - power for years may think that the brakes are working ok but a guy coming from cars/trucks with four wheel power disks may not.
Your going to need a 6:1 ratio with manual brakes, also, what is the size of your MC. A 1" bore or smaller should give you enough line pressure---
I agree with the rest . There is just not enough swing on that arm . You need the pivot point closer to the shaft . If you look at your picture you will see a white line on the plate , now if you move the pivot point over there , you will have more peddle . As for stopping , what size MC do you have and is it a single or dual bowl MC ? What size brakes & drums do you have ? If you have small skinny brakes that won't stop a thing very well . You need better brakes up front . That takes most of the stopping of the car . Have you turned the brake drums and installed new brake linings ? Retro Jim
IF the cars is under 2500 Lbs early Ford brakes correctly rebuilt and installed will stop the car just fine. If I under stood your post correctly your pedal ratio is a WAY off. The pedal in the car should travel 6-7 inches to move the MC piston 1 inch aprox. The rocker link in the end of the MC should be a 1 to 1 ratio ,same distance to either hole from the center. Just looking at what I can see of the arm on the pedal it looks to be way to long pivot to hole for pullrod.
The arm from the pedal was only ~2.5" long, but I increased it to about 5", with the idea that I could get more 'throw' from the pedal. I thought I might be running out of pedal travel and that was preventing me from being able to mash the brakes far enough to get them to engage tightly. Would going back to a shorter arm on the pedal improve my ratio? The m/c is a stock 1950 ford unit. The drums are good, the linings new. Would it help to go a little shorter on the m/c side of the pivot bar? The brakes don't actually 'lock down', they just sort of 'drag' the car to a stop...over time. and that's with me standing up on the pedal... My 'panic stop' would consist of ramming the car in front of me. It's really not safe as it is...so I'm trying to figure out a way to fix it.
when they say pedal ratio. they mean you want the brake pedal to travel 6in for every 1in the master cylinder piston moves. thus giving you a 6:1 ratio you may can get away with 5:1 but nothing less.what is your ratio?
Also remember that your plunger in your master should bottom out before your pedal hits the floor. Easily checked by just opening one your bleeders and pushing on the pedal. If your plunger in the master isn't moving much than you will not build up any reasonable amount of pressure to your brakes.
If you go to ECI barkes website-Ralph has a good explanation of pedal ratio with a nice diagram to illustrate the concept.
yes, shorten the rod to the stock length, and on a side note,, why all the work to put a crappy single mc in the car? its the same amount of work to put a good dual circuit master in the car. Brakes are not an area to be playing mad scientist. also it would be a good idea to move the tab on the pedal to the bottom side of the pedal and use a straight push to the mc and get rid of the rube goldberg apparatus you have now.
Wrong on short shoe to the front ! OP is running early Ford brakes Lockhead style . If any of the shoes have short lining they go to the rear,not all aftermarket relines have long and short lining, many are alllong. Old single cylinders really don't suffer damage from bottoming out ,but dual cylinders can be hurt by bottoming forcefully depending on internal design.
V8 Bob : You WILL note I said JUST before bottoming out !! When I design/fab up a system I determine the max stroke of the MC and set the pedal/linkage to stop about a 1/16 " before the cylinder bottoms. Respectively, John
I hope that everyone who replied will see this post, but with ya'll's help and guidence, I have got it to the point that I can leave a skid mark in the grass!!! I KNOW that sounds lame, but you have no idea how bad this was...it would not do that. Anyway, someone asked for a better picture: included. you kinda have to look beyond the wishbone and e-brake setup and you can see the flat rod coming in from the left and it attached to the arm that then went up to the top of the pivot plate. That is what I am getting rid of. It was the best I thought of back in '95 when I converted to Hyd brakes. Someone asked why use the '50 m/c? I have a '50 and was familier with it, back in '95..that's all. Now, here's what I'm doing. I am eliminating the first junction and making a rod that will go all the way from the pedal to the top of the pivot plate. I jury-rigged it first and the change was unbelievable, so I know I'm on the right track. Thanks VERY much guys...I have learned something and my car is the better/SAFER for it.
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