Brake Check / Upgrade

[Chris1966Newport]

Hi Everyone,

I picked up a 1966 Newport a few weeks ago, last night the brake pedal went to the floor so i found my first project. It looks like there is some fluid on the inner rear tire so i assume that wheel cylinder blew.

The car currently has 4 drums, no booster, and a single pot master cylinder.

I bought new wheel cylinders at NAPA. The rears are a 15/16th bore, and the fronts are 1 1/8 bore. Does this sound correct?

I also bought a dual master cylinder to split the brakes. I got a NAPA P1874M (I asked for the part for a 1967 Newport with manual drum brakes) This has a 1 inch bore. Does this sound right? This will use the same brake rod as my current master?

Just hoping someone can spot check this before i take too much apart.

Thanks for all help!
Chris

 

[CBODY67]

There were no upgrades in larger diameter pistons in the brake master cylinder or the wheel cylinders. The difference in brake system "capacity" was in the width of the brake shoes (and related backing plates and drums). And, of course, power assist to help with the pedal input.

1966 was the first year for modern-style power disc/drum brakes on the C-body cars. "Modern style" being the floating caliper design, rather than the "aircraft style" disc brakes that were optional in the middle 1950s.

The difference in the f/r piston diameters is a sort of mechanical leverage in the system, as a way of determining the ultimate pressure differential between the f/r brake axle pairs. In addition to the rear shoes usually being more narrow than the front shoes.

Key thing is to keep the braking power biased toward the front in a hard stop. It was common for the rear wheels to lock-up first, but the narrower shoes on the rear can help to minimize that (although it's hard to totally eliminate it mechanically).

NAPA has a parts lookup website. I also use RockAuto.com for a reference, too, as there usually are specs in the listings/information.

CBODY67

 

[Chris1966Newport]

Thank you for the feedback.

I was concerned that the auto parts store may have mixed up wheel cylinders for a manual brake car with a power brake car, but from what you're saying, it sounds like all drums in 1966 used 15/16 cylinders in the rear and 1 1/8 in the front regardless of the power brake option.

Thanks again for all help.
Chris

 

[CBODY67]

Check the RockAuto website, for confirmation, as they usually list sizes and other specs in their parts listings. It's easier to use than the NAPA website, I believe. Check the NAPA website to confirm what you got, for good measure.

CBODY67

 

[Chris1966Newport]

I replaced the one bad brake cylinder and tried to bleed it without luck. The pedal is now solid even with the rear bleeder open...

It seems like either the rear brake line is blocked, or the rear brake spliter is actually a safety valve that triggered when the rear wheel cylinder blew. Do C bodies have these valves?

Thanks for all help!
Chris

 

[65sporty]

You only changed the one cylinder in the rear? Not sure about the safety valve that would shut off the rear brakes, but if it does it will reset while trying to bleed it.

 

[CBODY67]

NO "safety valve", as you mention. If there was, it could be very troublesome to deal with!

The divider block is just that and nothing more. With the dual reservoir master cylinder, with front disc brakes, it became a "proportioning valve" to put more pressure to the front. It had a switch to signal the loss of one circuit's fluid, which turned on "the light". Later ones were termed "combination valves", for the pressure proportioning function and the warning light function.

An alternative method of bleeding brakes is to do it as the factory does it on the assembly line. Seal the top of the master cylinder and pull a vacuum on the system. This also checks for leaks at the same time. You can do the same with power steering pumps. Once the vacuum is stabilized in the system, then the fluid goes in automatically. In the field, fluid first and then the vacuum. Not quite as messy as the fluid-depress-hold-close valve operation. But sometimes it's best to do things as you know how to do them, no matter what.

If you suspect a blockage, take the rubber hoses off and replace them. During this, use some air pressure to check the metal lines for inner deterioration. That might be the best way to diagnose the situation on an older vehicle.

Keep us updated on what you find, please.

CBODY67

 

[Chris1966Newport]

The rear hose collapsed. My intentions to replace a wheel cylinder turned into brakes all around, new hoses, new brake lines, a rear axle seal. a new master cylinder and replaced those left hand thread lug nuts.

 

[Zymurgy]

I did the same thing just easier to replace it all and not worry about it. Keep your left hand threaded studs you will make someone happy in the future that needs one.