Who has modified a brake pedal for MORE leverage?

[Kern Dog]

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.

 

[bm02tj]

see if you can find a master with a smaller bore as it will increase pressure to calipers

 

[A383Wing]

you do know that there is a "Z" bar dog-bone ratio piece under the dash for power brakes, right.

do not drill another hole for pedal rod, it must be straight to the pedal, not angled.

Did you get the correct master cylinder firewall mounting plate for power brakes as well?

 

[bigmanjbmopar]

Call Pirate Jack, they use MBM brakes but have all the correct parts for B - bodys I learned the hard way too

http://www.piratejack.net/index.php...category_id=49&option=com_virtuemart&Itemid=6

 

[moperformance]

I tried moving the hole up on the peddle. The mc had to be moved up to keep the rod aligned. A whole lot of work for nothing as I ended up using a 73 A body 340/4 speed front disk w/manual brakes mc back in the original location. You'll need the matching prop valve too.
Hope this helps

 

[AMX364]

The Chevelle forum people found that a hydroboost system would fix the low idle problems and strange brake combinations. Almost as bad as the F+++ word. Often after trying many different systems and not getting the desired results.

I am welding up a brake rod for the Wilwood master cylinder on sister-in-law 66 Barracuda at this time.

 

[Cranky]

see if you can find a master with a smaller bore as it will increase pressure to calipers

But if the bore is too small, your pedal will have a lot of travel and especially so as the pads wear down.

 

[Kern Dog]

I may not have been very clear so I'll add some more info. Thanks though to all who have responded so far.

The firewall plate is the same one the car has had since new. The car was 4 wheel non power 10" drum. I found that the A body power brake booster used the same 4 bolt pattern as the old manual drum MC, so the car is as follows: Inside is the stock brake pedal, the A body brake pushrod that is actually a flat bar, gold anodized. There is no dogbone linkage under the dash since I used the A body stuff. The criss-cross linkage for A body cars is between the firewall and the booster itself. I currently have a drum/drum combination valve in the system.
I know that I have a few options. The best yet most expensive is to buy and install a dual Bendix factory style B body booster, firewall plate and associated linkage. There are several vendors that can help me there. When I tried a manual setup, I used a 15/16" disc/drum MC, a 15/16" disc/disc MC, a 1" MC and an 1 1/8" disc/disc MC. Every one of them sucked: Hard pedal and poor stopping ability. I am not interested in a hydroboost system. I have read from people that have raised the mounting hole and I'd hoped that they might chime in. It would be the cheapest way to go, so of course it is an attractive option.
Thanks again, Greg

 

[Kern Dog]

Yesterday I swapped in a modified pedal. The hole was moved up 3/8". Braking did improve some but it still isn't good enough. I may have found out why though: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.

 

[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!
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!

 

[Kern Dog]

Back again:
I drove the car again today. It was feeling better than ever for the first 1/2 mile or so, then the car started slowing, the engine RPMs went up....The brakes were binding again. I'm going to have to back off the adjuster some more. While more slack isn't ideal, it is better than having them bind up.