Weak front brakes, air in the line or were the brakes this bad?

[Triple Black 73]

The '73 Charger is back on the road but I'm not exactly happy with the front brakes. The front brakes feels, well, weak. They slow the car down but they aren't strong enough to lockup the front wheels under hard braking.

I don't know if there's air in the master cylinder, something else is off, or if the brakes really were that bad in the '70s. I guess you can say I've grown accustomed to the wife's sport car like stopping power in her '16 Journey R/T 13" rotors and the heavy duty stopping power of my '02 Ram 2500.

All the braking components are brand new: brake booster, master cylinder, Wilwood 260-11179 proportioning valve, Right Stuff stainless steel line, flex lines, Raybestos reman brake calipers (pin type), Raybestos 7032R 11" rotors, and Raybestos SGD39M brake pads.

Beside bleeding the master cylinder again, what are some other things I can do to make sure I'm getting max braking?

Also, are the 12" Cordoba brakes worth the upgrade?

 

[MarPar]

 

[Yatzee]

Verify the clearance between the tip of pin of the booster and master cylinder, reduce the bore size of the master to 15/16 or even 7/8 if possible, readjust your prop valve to 80% front, 20% rear, readjust your rear shoes to be closer to the drum surface ( if applicable), re-bleed your entire brake system ( threes a charm). You can literally close off the rear brakes completely with that prop valve to see how well the car stops on only the front system. And, if you've done a conversion of any type from original you'll have to check your pedal ratio to make sure you're stroking the master the right distance with the right amount of pedal force.

 

[AMX364]

However on pedal ratio if changing from manual to a power booster setup you can get a "over-boost". I left it like that, you could slam on the brakes and anything on the seats went to the floor.

Was it power brakes before? If not what was it, how is it different then from now(other then crap stops)?
edit: mainly details about master and booster, which I think is where the issue is.

 

[Triple Black 73]

Verify the clearance between the tip of pin of the booster and master cylinder, reduce the bore size of the master to 15/16 or even 7/8 if possible, readjust your prop valve to 80% front, 20% rear, readjust your rear shoes to be closer to the drum surface ( if applicable), re-bleed your entire brake system ( threes a charm). You can literally close off the rear brakes completely with that prop valve to see how well the car stops on only the front system. And, if you've done a conversion of any type from original you'll have to check your pedal ratio to make sure you're stroking the master the right distance with the right amount of pedal force.

Oh yeah! I read about that in an old Mopar Action rag years ago. Rock Auto has the bore listed at 1-1/32. Where would I find a 7/8 MC?

The Wilwood prop valve is pretty cool. I have it cranked down right now to test the front brakes. Installation was a bit of pain as I had to bend all the new SS line to get them to route correctly, then bend a 8" SS line to go to the front of the MC to rear of the PV. I bought the Wilwood bracket but only used the short line from the kit. I bought a hand full of fittings and ended up only using one 7/16 fitting to block of the rear line as the 9/16 fitting I bought was 18 thread instead of 20, so, then I had to going to hydraulic shop for one $10 fitting (9/16-20 to 3/8-24) and $15 to have them cut my new $70 rear SS line to put a 3/8-24 fitting to match up to the prop valve. Oh it was a pain, but I think it will all be worth it in the end. Plus, I think the stock prop valve mounted too close to the headers for comfort. I mounted the prop valve directly under the master cylinder. I'm thinking of building a heat shield around the whole mess.

However on pedal ratio if changing from manual to a power booster setup you can get a "over-boost". I left it like that, you could slam on the brakes and anything on the seats went to the floor.

Was it power brakes before? If not what was it, how is it different then from now(other then crap stops)?
edit: mainly details about master and booster, which I think is where the issue is.

It was power before. Is there anyway to adjust the pedal ratio? I didn't see anything in the service manual.

I think I'll bleed the master cylinder and the rest of the system... again.... This would be like the 8th time. Really. 7 times:

1) The old rear line was leaking at the fitting.
2) Found out the old rear line was clogged and the fitting was 9/16-18 instead of 9/16-20. Blocked off the rear line with the 7/16 fitting and a bolt.
3) Found out I had the front and rear line swapped and the mild steel lines I made was leaking.
4) Right front was leaking.
5) Quick bleed as the shop before dragging it home
6) Right front still leaking, replaced the crush washers
7) Bleed the front lines again.

 

[Billccm]

If you read the end of my Dr Diff conversion thread, we bled the system 11 times yesterday. It was difficult to get the front to flow and purge air. The rears were straightforward and easy to bleed and purge. I do not have an explanation for as to why the front was so difficult, and it was stumping my mechanic.

 

[Sixpactogo]

I'm not sure which booster you have there but from all I've learned about upgrading to front discs, you need a dual ballast booster. I had the same problem with a single ballast booster.

 

[Triple Black 73]

I'm not sure which booster you have there but from all I've learned about upgrading to front discs, you need a dual ballast booster. I had the same problem with a single ballast booster.

Not a upgrade. The brake booster looked the same as the original so we ran with it.

 

[HT413]

Whoa there. How's about confirming the pressure that the MC is producing before things get too haywire.

I has the zak same problem and it turned out to be a bad MC.

 

[Triple Black 73]

If you read the end of my Dr Diff conversion thread, we bled the system 11 times yesterday. It was difficult to get the front to flow and purge air. The rears were straightforward and easy to bleed and purge. I do not have an explanation for as to why the front was so difficult, and it was stumping my mechanic.

Dang. That's crazy. I was given a '01 Durango that we've been chasing brake issues for the last 6 years. We've replaced everything related to the brake system on that car and the rear still locks up way before the front ever do and the left front caliper will lock down if the brake fluid gets too hot. My dad and I can drive it but we won't let anyone drive it. Then we have my Ram 2500 or my dad's 3500 that never gives us any brake problems. Go figure.

 

[HT413]

The solution for me was a new MC. I was getting 500 psi on the bad one, 1700 psi on the new.

http://www.forbbodiesonly.com/moparforum/threads/damn-brakes-suck.105377/

 

[AMX364]

Verify the clearance between the tip of pin of the booster and master cylinder,

.
Since you can not see the clearance, you can check if it giving you issues. Loosen the 4 bolts holding the master cylinder to the booster. With the lines still connected and the master cylinder cover off, with a strong flashlight looking at the bleed hole inside the master cylinder, remove the nuts enough to see IF THE PISTON is moving, when master is loosened. IT should not, IF the piston did move then it is slightly too long and causes all sorts of weird problems. If it is too long, just lightly remove some metal from the rod.

This is not a Mopar only problem. It is a issue of different parts and related clearances.

 

[Triple Black 73]

Whoa there. How's about confirming the pressure that the MC is producing before things get too haywire.

The solution for me was a new MC. I was getting 500 psi on the bad one, 1700 psi on the new.

http://www.forbbodiesonly.com/moparforum/threads/damn-brakes-suck.105377/

Yup. Theory, test, evaluate, re-test, then act.

Btw, is the MC you bough? Looks modern. Yuck. But if it works...
http://www.doctordiff.com/aluminum-master-cylinder-kit.html

 

[HT413]

Btw, is the MC you bough? Looks modern. Yuck. But if it works...

Lol yeah it's a Dr Diff MC. Cheap, light weight and it works. I'm not a factory original kinda guy.

 

[Bruzilla]

My question would be did you do a bench bleed before installing? If you didn't, you're gonna be doing a LOT of bleeds. Also, what's your vacuum looking like? I had braking issues as well after installing a new booster and it turned out there was a open port on the booster vacuum port I had missed.