4 wheel disc master cylinder

[oldkimmer]

What’s everyone using for a master cylinder with the factory power brake booster and 4 wheel disc brakes. Wilwoods on the front and Doctor Diff on the rear. The factory master isn’t working worth a darn. Thanks. Kim

 

[Thrashingcows]

Are you running a proper disc brake booster, not the power drum booster?

 

[oldkimmer]

It’s a new replacement for the power disc/drum unit. 1973 car. Kim

 

[Ron H]

To piggy back Thrash's post, since I recently went thru all sorts of hassles with my brake conversion, though I'm only front disks, what are the poor braking symptoms you have? Among the checks as I went thru, was assuring the MC was air-free. You can bleed the brakes all day; but if there's air in the MC it isn't coming out without an MC bleed. Using caution to make for sure no brake fluid gets on any paint, you could do this on the car and a brake re-bleed will need to be done again. This is one thing, other is to check the rod gap between the booster and MC to assure the MC is fully engaging to provide ample brake pressure. Before doing this though...with a buddy, and good light, check the action of the brake pads when depressing the brakes to assure there's no binding - I've come across pads cocking on the caliper guides causing damage requiring refiling the guides, pads, and greasing them. Ok, just some quick stuff tossing over. Yep, I've found bad MC's, boosters (you can check with a vac guage), and binding pads...

 

[oldkimmer]

Honestly I haven’t checked it yet. The car was restored. Now I get to fix all the little things that don’t work properly. He says it has a low pedal and he has to pump the brakes to stop. Kim

 

[Ron H]

If your car has a heppy cam, you should check engine vacuum at idle to make sure you're producing enough vacuum for the booster. In any case checking what vac is - is a check. Also check for other possible vac leaks. Could be the booster should be checked for vacuum leaks, check the hose connections, condition, check valve. If these all seem fine, would do further vac checks if you have a pump up vacuum gauge to see if the booster will hold vacuum. There are 3 simple checks on this using a gauge. I have a mild cam and installed a reserve canister as the vac was borderline enough for me to put one on. They don't do a lot; but add a couple inches especially when using brakes in traffic. If the pedal is 'low' does it pump 'up' after pressing pedal a couple times? Anyway - some quick checks in the hunt. Booster compatibility is important for the system if you find all checking out fine as it may not be ample. Anyway, be sure the pads are sliding well in the calipers if they stick this can create a pedal return issue as well....my two pennies..

 

[oldkimmer]

I haven’t did any checks yet. He says if he pumps the pedal a few times they come up some. He said they led the master cyl and brakes 5 times now with it not being really any better. I seen the car and noticed it had a disc/drum master. He said it’s factory replacement as well as the brake booster. I haven’t worked on this car other than building the 340 for it. I think the cam is 218/224 at .050 .506 lift. Kim

 

[Ron H]

I haven’t did any checks yet. He says if he pumps the pedal a few times they come up some. He said they led the master cyl and brakes 5 times now with it not being really any better. I seen the car and noticed it had a disc/drum master. He said it’s factory replacement as well as the brake booster. Kim

As you know, if you have 4 wheel disks - a disk - drum master isn't compatible (disk/drum would have a larger and smaller reservoir).

 

[chtampa]

I have an OEM Disc/Drum Booster. Removed the shuttle valve from the factory Distribution Block and added an adjustable proportioning valve on the rear of it. Using a Drum/Drum Master Cylinder with the residual valves removed and it works fine on my Disc/Disc system.

 

[themechanic]

I'm using a Wildwood 4 wheel disc MC and the repopped booster. I tried the factory style MC for a newer Dodge but couldn't keep the plastic caps from leaking.

 

[oldkimmer]

I wanted him to go with a hydro boost system. The guy restoring the car said it didn’t need it cause he has done many b4. Everything the restorer guy did I have to do over. Kim

 

[chtampa]

While it is not the answer, Hydro-boost has been used to cover a lot of problems. Why add another system to the car?

 

[oldkimmer]

We also put in an Altercation.it’s if guys recommend the hb. Kim

 

[Thrashingcows]

I have 4 wheel discs on my 68 T/C wagon...originally 4 wheel power drum. I converted to OEM 73 C-body front discs, and scarebird rear disc conversion brackets and related hardware. I run a power disc brake booster and a mid 80's aluminum MC with the front caliper circuit run directly off the MC with no proportioning valve, and the rear circuit has an adjustable proportioning valve....been driving it this way for 7-8 years with no issues.

 

[oldkimmer]

What year is ur brake booster? 4 bolt to 2 adaptor? Thanks. Kim

 

[70chall440]

On the 4 wheel disc conversions I have done (1 manual and 1 power) I use a 15/16 or 7/8 MC along with a disc/disc combination valve; seems to work. Its all about line pressure and there are a lot of factors at play which is part of the reason that a set up one person is using works and the same set up for another person doesn't. Another part is the problem is perception; everyone has a difference idea what "good" brakes are. This is why hydro-boost has become popular; because it overcomes many of the deficiencies a system might have by dramatically increasing line pressure, thus making the brakes more efficient.

You have to look at brakes as a system which includes every component within it; pedal ratio, booster, engine vacuum, MC, various valves, brake lines, piston number and size, caliper condition and efficiency, rotor composition and size, tires and even type of fluid. Changes in any or some of these issues can affect braking or better said how good the brakes stop the car.

What most classic car guys experience is that they have a car that does not stop well (whatever that means to the individual), they make changes of one kind of another and then compare the outcome to what they had, usually by seat of the pants feel. If it is better than they believe they have "fixed" it and move on generally. The point is that what works for one person may not work for another. Sure, there are guidelines that yield decent general results but to be honest very few people actually do any real testing or comparisons. Most who ask me about improving brakes I tell them to get good pads and good tires, then work inward (assuming the general system is sound).

Last point; I would say that 4 wheel discs are more efficient than drums generally, but I would quickly say that a good drum or drum/disc set up that is efficient, in good working order with good tires can perform exceptionally well. This is even more the case with modern performance shoes/pads. In other words, you don't need 4 wheel discs to stop these cars, stock brake systems can work but usually not as drug out of the field or barn, they need to be made efficient even if stock.

 

[Thrashingcows]

What year is ur brake booster? 4 bolt to 2 adaptor? Thanks. Kim

The booster is a Cardone rebuild spec'd for a 1968 Chrysler with disc/drum set up, and yes then running the 4 to 2 bolt adapter. Had to adjust the push rod on the booster a bit to dial the MC in.

 

[Kern Dog]

If your car has a heppy cam,

Where in the world did you come up with THAT term? Heppy ??

 

[Ron H]

Where in the world did you come up with THAT term? Heppy ??

Lol, good question - hepped up, heppy, not in dictionary - hope I haven't insulted anyone in case this word means something bad in another language...

 

[Kern Dog]

I'm still amazed at phrases that people use that I have never heard.
A guy wrote about "whipping shitties" and I had the most confused look on my face. I look at a lot of things in the literal sense.
Why beat on feces?