At a loss why my brakes suck

[TonyBolton]

70 cuda....garage kept 50k miles. Stock brakes....disc front drum rear. Parts store brake booster. Dr Diff master cylinder

Large cam in 440 using an electric vacuum pump mounted in trunk.  Works...no leaks...

The car will stop....but you basically have to use both feet to do so.

It seems like initial bite is the worst part. Like if you needed to panic stop....you're ****ed.

If you're gradually slowing down for a stop light...the brakes seems to increasingly get better if you jus keep applying normal pressure to the pedal.

What the heck can be the problem?! No wierd noises from braking....no leaks...pads have material on them.

I'm at a loss.

Any help is appreciated.

[Bullitt-]

Well having learned to drive in a '66 Polara 4-wheel drum car over 40-years ago I'd say things is normal...

[TonyBolton]

No.....it stopped better a few years ago. Not great....but better.

I kept trying to convince myself "that's just how they are ".....but I jus don't believe it.

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[Beekeeper]

When I upgraded the brakes on my Superbee, I decided not to go with vacuum. A guy at the dodge dealership parts counter recommended a master out of a late 80s 1 ton van. It used a larger diameter piston in the body (like 1 1/8" instead of 1" I think) so it provided more pressure at the wheels for the same pedal effort.

I was skeptical but after putting it in, I was blown away with the improvement. No vaccuum and one foot could make it stop a lot more like a modern car. Wasn't quite as soft as a modern car but I liked the firm feel.

[TonyBolton]

The master cylinder I bought from Dr Diff was supposed to be suitable for a stock disc/drum setup as well as with rear disc upgrade.

I'm looking into his 13" front cobra setup along with matching rear. Anyone think this would help?

Would the stock proportioning valve have anything to do with anything?

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[Beekeeper]

The master cylinder I bought from Dr Diff was supposed to be suitable for a stock disc/drum setup as well as with rear disc upgrade.

I'm looking into his 13" front cobra setup along with matching rear. Anyone think this would help?

Would the stock proportioning valve have anything to do with anything?

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Based on what you are describing, I've had better braking with plain stock disc/drum setups. I can't speak for the cobra setup but I wouldn't rush to buy it just yet. As far as the proportioning valve, I can't see that being the issue unless you constantly lock up the rears while the fronts don't seem to bite.

It may be a new dr diff master but I can't help but wonder if something is sticking inside. I've seen the same problem with stock setups on friends cars and simply swapping out the original master with another stock style one from auto zone made a big difference.

[TonyBolton]

Damn....I didn't wanna think that....but I might hafta try it. Damn...

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[Bullitt-]

I'd imagine any front disk would be an improvement over drums, which is the one to go with I'd be searching here for others experience 
Never seen a cobra upgrade, many have done the Viper upgrade.****Careful with Wheel Clearance**** 
  Ck member brads70 has done a bang up job http://www.cuda-challenger.com/cc/index.php?topic=59072.msg745164#msg745164
kit avail http://www.doctordiff.com/viper-caliper-mounting-brackets-for-mopar-drum-knuckles.html
  For something more conventional http://www.manciniracing.com/mbmbebofrdib.html


As to your current setup I'm reminded of how Dad used to back up pumping the brakes for a considerable distance to get the self adjusters to do their thing. I have done the same numerous times with varying results.
A few years ago member sleepychallenger was in town saying his brakes were not working well even though he had just paid a shop to replace all shoes & pads. I traced the problem to inoperative rear adjusters which I was able to correct. That seemed to solve the issue. 

[Mpdlawdog]

Did you check for a vacuum leak and that the pump was working right?  Sounds like there might be an issue there.  I called  My 68 charger brakes two feet and a prayer stopping... I had a vacuum issue found it and the first time I drove the car I about threw me and my son threw the windshield

[73_Cuda_4_Me]

I'd get a brake pressure test... see what kind of fluid pressures you're getting out of the master cylinder, then at the brake cylinders...

[TonyBolton]

The pump comes on/off correctly....but I've never hooked a psi tester to it. Vacuum gauge yes....but not psi gauge .

[1 Wild R/T]

Putting the vacuum pump & reservoir in the trunk means you need to up size the line to the front...  I'd go at least 1/2"....  Or I'd do what most folks do & mount at least the reservoir under the drivers fender.... 

You say parts store booster... Post a picture... Hopefully it's the big Bendix unit...

[73_Cuda_4_Me]

With disc front/drum rear, you should get around 1500-2000 psi front, 800-1000 psi rear...

Front discs could be 'glazed', also... cuts effective braking rate in half... look for blued rotors and heat checking...

I've heard of old brake hoses separating internally, and blocking flow with pcs of rubber... bad rusty lines or really old fluid can also crud up lines as well... normal fluid 'can' asorb water, and if in lines can make brakes mushy (water compresses a lot more than brake fluid does)... an easy check would be to drain all the brake fluid out from the lines and install new fluid and bleed completely...

[TonyBolton]

Putting the vacuum pump & reservoir in the trunk means you need to up size the line to the front...  I'd go at least 1/2"....  Or I'd do what most folks do & mount at least the reservoir under the drivers fender.... 

You say parts store booster... Post a picture... Hopefully it's the big Bendix unit...

Hose is quite large I know....but can't remember exactly size. The system worked fine without the extra can....I just tried that as a cheap fix. Didn't really help/hurt.

The booster is the same size as the one that came off of it (stock).

[TonyBolton]

With disc front/drum rear, you should get around 1500-2000 psi front, 800-1000 psi rear...

Front discs could be 'glazed', also... cuts effective braking rate in half... look for blued rotors and heat checking...

I've heard of old brake hoses separating internally, and blocking flow with pcs of rubber... bad rusty lines or really old fluid can also crud up lines as well... normal fluid 'can' asorb water, and if in lines can make brakes mushy (water compresses a lot more than brake fluid does)... an easy check would be to drain all the brake fluid out from the lines and install new fluid and bleed completely...

All brake lines/hoses have been replaced with new....maybe 5 years old.

Fluid is high end Motul. All was bled out when new booster/master was installed.

Thought about the pads...but didn't think it make that huge of a difference.

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