Changed my '31 Tudor (Banger powered) over to the '48 Lincoln Bendix brake system front and rear. Due to some linkage ratio issues, and thinking that the 1" MC was too small, I changed to a 1 1/8" MC. While the brakes work OK, it requires a lot of pedal pressure, more than I would consider normal. Pedal ratio is verified to provide the 1 1/2" of travel required. So............would a 1" MC provide sufficient volume, along with more pressure, to operate this system? BTW, I have correctly installed RSV's, and both MCs are a dual chamber design. No leaks, adjusted brake shoes, etc. As I still have the 1" MC in stock, I'm considering changing back. Comments? Thanks Ken
The 1" is a much better choice, as it will provide more psi with less effort, but with more travel, so be sure the pedal can still bottom the master fully.
I'm using a modified stock pedal. It has a fabricated link arm welded to the pedal to provide a "pushing" action. I did'nt like the bellcrank style setups that are out there. Ken
Do the math a 1-1/8 MC has a ****load more surface area than the 1" . Put the 1" back on and tweek the linkage a bit if need for full travel.Most of the the early Ford brand car ran no more than 1-1/16 bore cylinders.
had a problem like that. what is the lenght of your pedal to the pivot point? and from pivot point to the push rod what is that measurement? there is math involved in that area. JAN i believe from pivot point to connecting push rod that arm needs to go 7 times to whatever the lenght of the pedal arm is.
do you have pix of your pedal ? i cant seem to get mine to work right ........ also i have a wilwood composite m/c 4 sale $25 ....... shipped kzsteve@yahoo.com
Being able to travel full stroke is important; but the correct pedal ratio is the first step. In the range 6 or 7 to 1 is what is needed, just like Jan said. The wrong ratio even with the correct travel will still be like pushing on a brick wall to stop.
Get the pivot as close as possible to the axis point I think this will provide more leverage. ? Just a thought Hard to say without seeing the whole setup
Update: Installed the 1" MC, pressure bled the system. Better, but still excessive pressure required. I can see now, that the pedal ratio is not correct. I don't see any way to change it, while still using the stock pedal, with a lever arm welded to the bottom to provide the pushing motion. Any ideas on how to get the needed ratio, and still use the stock pedal? The stock pedal pivot is 12" from C/L of the pivot, to the center of the pedal pad. My current setup has the pushrod lever C/L 3 1/8" from that pivot. Not quite a 4:1 ratio. As I'm writing this, it looks like a bellcrank setup is the only way to get the right ratios. Thanks for all the comments, very helpful steering me in the right direction. Ken
Rally 1 heres mine in mock-up. stock model a pedal. i took the pull part from the stock pedal cut it short, and welded it to the bottom to push. if yours is longer then this, with a model a pedal u need to cut it short. mine is no longer than 1 1/2" shorter if u can.
I see how the leverage is gained, but what did you do to gain the piston stroke needed for the MC to bottom? Ken
that comes in were u weld the part to the bottom of your pedal. i would pull your pedal up all the way, and weld it at about 7 o'clock or a little more.
as soon as i push my pedal i'm pushing the push rod i don't know about that 1 1/2" play your talking about. i do have that play on my clutch pedal not my brakes. JAN
Rereading the instructions for the Wilwood MC. It states under the bleeding procedure, "Pedal must allow full travel (stroke) of master cylinder for complete bleeding". This is where I am looking for the 1 1/2" travel. I have a much shorter lever arm available, plan to install it this morning. As I can pressure bleed this system, maybe the 1 1/2" travel isn't required. Keep tuned. Everyone, thanks for the responses. Ken
Update: Installed the shortest of the link arms. No pedal at all, goes right to the floor. Piston travel at full pedal is less than an inch. The pedal ratio is 3.8:1. I then reinstalled my medium length lever, much better, but requires a lot of pedal pressure. The pedal ratio with this arm is 4:1 I checked both of the other MCs I have, Strange 1 1/8", and another Wilwood 1", both require 1 1/2" of travel to function correctly. Looking at some type of bellcrank setup. I really wanted to stay away from all that linkage. Searching through the forum, I found some drawings of bellcrank linkages.
You can have less than full travel of the MC and have properly operating brakes. Part of the idea of having full MC stroke available was so if you let your brakes get WAY out of adjustment [old style manual adjusters] you still could get the thing stopped. I would try for at least 1" of MC travel however. Back in the early 60s when I worked part time in a gas station people would let their brake adjustments go till the #*$%^ pedal was right on the ****** floor. Full stroke does make bleeding easier as you are moving more fluid/air with each pedal stroke. Edit: Just read your last post . Are your brakes corectly adjusted? And some modern lining is very hard[low friction] made to work with power brakes for long life,****s on manual systems sometimes. But you really need your 6-1 ratio and at least 1" on the MC. Edit 2 loose the prop valve as with a drum system you really don't need such. And you did install the shoes with the short lining to the front?? And if those backing plates have adjustable anchors did you do the correct full adjustment procedure?
John, Thanks for the response. Yes, the shoes are installed correctly. I went back and checked adjustment again, some minor tightening required, only on the fronts. Rears are fine. Double checked for any leaks, found none. Looks like the pedal ratio is the achilles heel in this application. I drew up some sketches, and built a prototype of a lever ***ist device. with 1" of travel from the pedal lever, it allows for 1 1/2" at the MC, giving me a 6.5:1 to 7:1 overall ratio. Looks like it will work. I need to order some rod ends, and do some more fabrication. I installed the bias control valve,thinking that I would need to reduce rear brake. It has zero effect unless I adjust it differently. I would agree, it is probably not needed. I'll post some more pics after I get my lever ***ist built. Thanks again. Ken
Update....... I had to take time off this project to finish a customer car rewire. Back to the brake setup. Attached are several pics of the "lever ***ist" I fabbed. The actual modified pedal ratio is 4.4:1, lever ***ist multiplies that by 1 1/2, overall ratio is now 6.6:1. Substantial improvement, the car is actually driveable. The lever ***embly uses 3/8 rod ends, sealed ball bearings. Some additional tweaking should get me to a 7:1 ratio.
As far as the ratio goes the tex smith ch***is building book he has helped me out the most! Looks like your p*** that stage but something to keep in mind for next time
how much "actual" master cyl travel ?? leverage is great but you have to have m/c piston travel . nice work !
I currently have 1 3/8"" travel at the master cylinder with the current adjustment. I plan to move some of the adjustments to obtain a 7:1 ratio. FYI, the link bars are .625" 4130, with welded in thread inserts. Rod ends are 3/8" with reducing sleeves for a 5/16" bolt, in double shear. The "lever ***ist" bolts in. Thanks for all the help. Ken
that should be good enuff on the travel . i really like your linkage , hope it works for you . ps. dont believe all the bs on line size & m/c size . hydraulics require volume ... i use 1/4" line & 1" m/c ... no power & all is good ..................
One aspect of linkage fabrication that is sometimes overlooked is the geometry of the linkage. All the pivots should be at 90 degrees at the mid point of travel. Quite a bit of usable travel can be lost if the movement only occurs before or after center instead of being balanced on both sides of center. I have found this to be especially critical on brake pedal set up and getting full stroke on the master.
Rich B. Thanks for that tip, something I overlooked when I installed the lever arm. I'll definitely adjust accordingly. I built in additional adjustment when I machined the arms and linkage. Ken
The Jalopy Journal
