Charlies Brakes with stock mastercylinder

[james curl]

Those of you who have installed Charlies Disc Brakes with the stock master cylinder did you have any trouble with the front brakes not releasing. I have disconnected the master cylinder push rod from the brake pedal and the front wheels still will not release. When I installed the kit I installed a 2lbs residule valve in the front line and a 10 lbs in the rear. I removrd the 2lbs in the front line and the front brakes released while the brake line was out. I installed the front line in the master cylinder without the 2 lbs residsule valve and the front brakes still will not release all the way. Do I need to remove the stock residule valve from the master cylinder?

[rearview]

The stock master has an internal 10lb valve. You'll need to disable that and run the externals.... I've been thinking of cutting the spring, and only running 10 in the rear??? Need to see schematic first though. I have the same thing with my ECI brakes, but it clears up in a second on the street

Bob

[Norm's Coupe]

I'm using the ECI system with the same type residual valves. I'm not having a problem. I would not mess with the MC. Should be the same with any of the disc brake systems, ECI, Charlie's or any other. They are really the same system other than maybe the calipers and rotors.

[Norm's Coupe]

On second thought, you may want to look at the MC after all. Check to make sure the vent hole in the cap is not clogged. I'm using a new cap I took from the extra NOS MC I had as a spare, so I know mine isn't clogged or stopped up.

[James_Douglas]

James,

See the photo for my set up. I had ECI custom make a set of front disks. My Desoto is like the Chrysler 8 and has huge hubs.

I did my tubing & valving by the book.

1. I use a RED 10# residual valve on the rear for the drum brakes.

2. I use a BLUE 2# residual valve on the front disk brakes.

3. I use a metering valve on the line to the front brakes.

4. I use an adjustable proportioning valve on the line to the rear brakes.

Not everyone uses all the above. You can get away without the metering valve and the proportioning valve. HOWEVER, any disk/drum system without them is not going to function optimally. (I don't care what anyone says, you just wrong on this one if you think otherwise.)

In my case the car is heavy and can seat 9 people so I wanted that last little bit of optimization in my braking. If the auto companies did not think the stuff was not necessary they would have surly dropped it from every disk/drum car they make to save money. All of them us them, built into a single valve called a combination valve.

Best, James

[Suddensix]

Had the same problem with my car. Removed the residual valve from inside the master cylinder and no more problem.

[grey beard]

Gents,

Residual valves are seldom if ever required for disc brake applicarions.What keeps the piston against the pad is a square-cut piston seal that makes for a self-adjusting feature on all disc brakes made in the past few decades.

This is the reason why the original drum master cylinder usually will not usually work well with a disc conversion up front. You will look long and hard to find a modern auomotive application that uses residual pressure on a disc circuit. Check this out.

Residual pressure is used only with drum brake applications. Its purpose is to keep a slight pressure on the wheel cylinder piston cups so they don't leak when at rest. Much of the advice dispensed by street rod and resto rod sources is designed to sell additional parts that are not needed. JMHO:)

[James_Douglas]

Please note the issue of the MC being BELOW the calipers...

" The two pound valve is used in disc brake applications where the master cylinder is mounted below the horizontal plane of the calipers and fluid drain back occurs from gravity and vibration, thereby causing excessive caliper piston retraction and a longer brake pedal stroke. The minimal two pound residual pressure prevents fluid from flowing back without causing the brakes to drag. With drum brakes, a ten pound valve is used to compensate for return spring tension in the drums." ---Wilwood Engineering.

Most of the cars on this forum have low mounted MC's. As I said in my first post, you don't need all that stuff, but the system built will not be optimum.

Best, James

[Norm's Coupe]

James,

I agree with you on why the residual valves are needed. ECI says the same thing about when the MC is lower than the brakes.

That said, I also agree with part of what Dave said about disc brake drag due to the self adjusting feature. They even drag on your modern car if you inspect it closely.

In your modern car, after it has sat for awhile jack the front wheel off the ground. You can probably turn the wheel by hand. Now, apply the brakes and let off them. Chances are you will not be able to turn the front wheel now, unless you use lots of force. Once you get it moving it will move freely again. The same thing happens with our disc brake conversions. It's all due to the self adjusting feature of the disc brake.

Now, more than likely your modern car is an automatic. So......if you stop and let off the brake, yes the car will roll a little. That's because it's being forced to because the car is in gear. If you put the car in neutral it doesn't roll that easily when you let off the brake. Once the you take off from a stop the brake releases fully like it should.

As mentioned, mine will drag too until I let out the clutch to go, then they release fully without a problem. It's normal.

As an added note about our conversions. Most of the disc brake conversions tell you to use GM calipers and rotors. GM calipers seem to keep the pad very close to the rotor even when released. So much so that the least amount of distortion to the rotor due to warping or not being seated correctly will cause the pads to drag on the rotor. I know this for a fact due to my Lumina Van. At about 30,000 miles I had a squeaking noise in the front brakes on every rotation of the rotor. I assumed it was a hard spot in the pad because the pads were only about half worn. Changed pads and the problem stopped for a few days then came back right away. Took the van in 3 times and they replaced the pads that many times and still had the problem. Then the 4th time they turned the rotors. I now have put about 40,000 miles on since then and they still do not squeak. The rotor was evidently slightly out of round or something. I've heard other GM cars going down the road with the same noise. That's why I think it has something to do with how the GM calipers adjust their self.

[Plymouthy Adams]

On another note abut the square cut o-ring..its job is basically three fold,

1 seal

2 allow piston adjust by sliding through the seal

3 it is the single one device that pulls the piston off the pad for your pad to

rotor clearance. (seal roll just a tad under the applied pressure and its returning to its natural shape is the action)

This was taught by National Institute for Automotive Service Excellence back in the mid 70's when I was a certified mechanic through their organization.

[James_Douglas]

Norm,

I don't have any drag on my front disks after a good hard application. I tried it in the garage today, after reading your note, and when I release it, both sides spin free.

James

[Paul Beard]

I put disc brakes on the front of my B4B newer reaxle on the rear.

I didnot use any residual valves on the truck as the M/C has a one way valve and will not let fluid back into the M/C.

I have a good so;id pedal and haven't had any problems.