Modifying a brake pedal for more leverage?

[Kern Dog]

Who has modified a brake pedal for MORE leverage?
I have a mismatched brake system in my 70 Charger. It started out out in 2000 as an experiment to see what parts I could use from various A body cars in wrecking yards. I found that the 73-76 A body brake booster and MC fits, so I used that along with 11" rotors. It was a great improvement over the original 4 wheel drums so I stayed with it.
I currently have 12" front rotors with 2.75" calipers. The rear is a disc kit offered by Dr Diff consisting of 10.7" Toyota rotors and 1.75" Mustang calipers. The car stops okay but not as quickly as a non power front disc A body. Years ago I tried a switch to manual brakes and had bad results. I tried 4 different master cylinders and each one gave me a hard pedal with poor stopping ability. It was very confusing because in theory, everything made sense for it to work. I looked at brake pedal ratio calculations and found that the manual brake A body had a 6.92 to 1 ratio and the B body had a 6.6 to one. The B body ratio should have the advantage yet my brakes were not reacting enough when I stood on the pedal. I gave up after awhile and put the power equipment back on. Braking is again "okay" but still below what I want. I added a vacuum pump since the lumpy cam I have produces about 5 lbs of vacuum at idle in gear.
I've read that some people suggest to drill a new mounting hole in the brake pedal lever above the stock hole. I found that the center-to-center of the brake pushrod hole to the mounting point is 1 7/8". A move to 1 1/2" changes the ratio from 6.6 to 8.125.
I have a spare brake pedal assembly and am considering giving this a try. I figure that I'd try seeing if this helps with the power booster still in place. In reality I'd prefer to eliminate the power equipment for a simpler system but I'm still gun-shy since I had terrible luck before.

[tan top]

 not got any  first hand experience  , but have read about it somewhere , think it might have been on here or moparts , sure it was a guy with the SSBC disc set up , it did increase stopping power , ie more line pressure , as you have already mentioned  
IMO depending where your going to drill the  hole , think I would weld a couple of thick washers to the  hole in the pedel too , for strength  

[John_Kunkel]

8-1 is a way high pedal ratio for power brakes.

[Kern Dog]

Looking at the linkage again, the A body parts I have include a reduction in the linkage between the firewall and the booster. My ability to calculate ratios on top of ratios isn't so good. If the pedal to pushrod is 6.6 and the booster linkage is 1.5 to 1, (Just a guess) where does that leave me?
Regardless, I did drill another brake pedal assembly and install it. The original hole is 1 7/8" down, the new hole is 1 1/2" This does change the under-dash linkage from 6.6 to 8.125, but I need to determine how the rest of the linkage affects the total ratio.
The brakes are a little better but I still can't get them to skid. Oddly, the car slows okay but under 20 it still feels wrong.

[chargerbr549]

On my 69 charger with 11.75 front rotors and 11 rear drums and manual brakes seems to work pretty well but from what I read and not saying this from experience, it seems when you goto a disc front and disc rear the manual brake setups for some people just don't work out very well and they end up going to a hydroboost or a very good vacuum brake setup to get the stopping power they are looking for.

[c00nhunterjoe]

Increasing your ratio is masking another problem. Increasing your line pressure could and probably will, end up with bad results and blown parts. You have another issue somewhere. Verify good vaccum source to the booster and/or switch to hydroboost. Could be a bad proportioning valve.

[Kern Dog]

It is quite possible that the performance is poor due to this: Last night I looked again and saw that I have a disc/drum proportioning valve in the car. Years ago when I was swapping parts around trying to get a manual system to work, I must have left the proportioning valve in there. 4 wheel disc Cars with properly sized calipers need no additional proportioning. I am going to swap in a 4 wheel drum distribution block. The ir function is to merely allow a point of connection of the lines from the master cylinder to the individual brake lines. NO proportioning at all.
A member elsewhere also mentioned that the Mustang calipers need to be "adjusted" since they are not like a traditional piston type caliper. They can have excessive clearance resulting in slow reaction to pressing the pedal.

[c00nhunterjoe]

Ive never heard of mustang calipers needing adjustment. Thats ridiculous. And IF they were somehow out of adjustment and too slack, you would have a very low pedal similar to what drums that are very loose feels like. It would be easy enough to check by simply looking at the air gap

[Kern Dog]

Good news: Step by step, things are improving.
First up, I swapped IN the drum/drum distribution block. The system was bled. I looked at the rear calipers and it seemed that they have very little slack/clearance. I took the car for a drive and was quite happy to find that while initial free-play was more than I'd like, the brakes do work much better once I take up the slack. I may need to REbleed the system. The pedal is firm once the brakes engage and does not sink.
I removed the MC from the booster and adjusted the length of the pushrod. OEM A body systems have a threaded insert at the end of the pushrod that fits between the MC and the booster diaphragm. On the test drive, the brakes felt better than ever! The pedal free-play was gone and the car stopped great....THEN the brakes started to smoke. I had to get back home QUICK! The brakes were engaged all the time and dragging. It would slow and stop when I put it in neutral.
I pulled the MC and adjusted the pushrod again. I set it about halfway back to where it was originally. The car was able to roll freely but the pedal free-play was back. I think if I rebleed the system and maybe fine tune the adjustable pushrod, I should be able to call it good. Maybe I'll even try engaging the parking brake slightly to see if the rear calipers do need to be adjusted out a bit.
Thanks guys!

[c00nhunterjoe]

sounds like you are on the right track. i dont think there is an adjustment on the calipers though. double check your pushrod length again.

[A383Wing]

not to sound stoopid here, nut also make sure your bleeder screws are at the highest point as well...I can't tell you how many people put calipers on wrong side...not saying that you did this.....just saying

[Kern Dog]

That is a good point, 383wing. The rear disc kit was from Dr Diff and came without any instructions. For 5 years I had them on wrong yet they fit and worked okay. They are now mounted with the bleeders at the highest possible point. The rear caliper pistons are not the traditional type that just push out with pressure. They rotate as they move. I looked online and found other calipers that are the same type, some Honda models have the same feature. To adjust them, the extended portion of the piston is actually spun clockwise to retract the piston and clockwise to extend it. I know... it sounds strange to ME too. This was news to me until this morning when a member on Moparts told me about it.

[A383Wing]

a lot of calipers are like that, Caddy had them also..that's because the e-brake was incorporated into the rear calipers...you have to wind them back in to put new pads in

[Kern Dog]

Yeah, thats right about the parking brake. Kinda strange to keep learning stuff at the ripe age of 48, huh?   

[c00nhunterjoe]

They are not "adjustable" screw piston calipers are nothing new.you simply put them on and pump the pedal like any other caliper. Dont try to screw them in or out to adjust them. It doesnt work that way.

[John_Kunkel]

Pump the emergency brake handle, not the brake pedal; those rear calipers adjust by the emergency brake...each application of the emergency brake handle moves the piston in one notch.

[A383Wing]

They are not "adjustable" screw piston calipers are nothing new.you simply put them on and pump the pedal like any other caliper. Dont try to screw them in or out to adjust them. It doesnt work that way.

^^ This...