72' super brake issue

[DPsuper]

On my 72 I replaced all the brakes because I had to pump them up to be able to stop. Well I still have this issue and have bled them several times and they have to be pumped up to build pressure. Anyone have an idea?

[Mitchell]

Had the same issue with a SB a few years ago. someone suggested that I tighten all of the brake pads, then bleed the brakes. Worked like a champ. If all of the pads are resting against the drums and you still have a problem, start looking at the master cylinder and wheel cylinders.

To check the master cylinder I inserted plugs in the ports and bled it. If the master cylinder is out you can bench bleed it to verify it is good.

Mitchell

[DPsuper]

I replaced the master cylinder, wheel cylinders and brake pads. I'll pull it apart and check it all again.

[Ol'fogasaurus]

Mitchel is correct: It is an old trick that does work. If you adjust the brake shoes tight enough to lock both of the brake shoes against the drum they are then centered in the drums which may not happen when trying to adjust the brakes normally. This allow the brakes to be bled with neither of the brake shoes sitting off center/loose which will give you will get a better, more accurate bleeding session.

Once you get the bubbles out of the system you can then back off on the adjuster until you get minimum contact between the brake drums and the brake shoes (you get a soft shush, shush, shush sound as you rotate the wheel) giving a proper gap between shoes and drums. If you later have problems with the brakes going soft then you might need 10# residual pressure valves added to each of the two systems (2# for discs and 10# for drums is the suggested norm). The valves hold line pressure so that when the slave cylinders (wheel cylinders) as sitting higher than the master cylinder which can allow the brake fluid to flow back into the master cylinder reservoir.

Lee

[Marc]

#1 rookie mistake when working on `65-up brakes is orienting the adjuster screw upside-down. `64 and older adjusters had a narrow slot that was uniform in depth, but starting in `65 the slot was widened and "angled" to be deeper at one end. The shoe frames were also revamped to match, so one mustn't mix-n-match adjuster and shoe styles. The purpose of the modification was to enable the shoes to "slide" in the adjusters (and the wheel cylinders - they got wider slots starting in `65 also) to reduce uneven wear.
If you aren't aware of this and install "angled" shoes in "straight" adjusters (or vice-versa) the shoes tend to hang up on the tiny contact point they have with the adjuster which gives you a false adjustment. Late shoes with upside-down late adjusters will make it even worse.

[aussiebug]

And of course every brand new MC should be bench bled before putting it in the car - you can't always get all the air of a new MC with in-the-car bleeding.

[Marc]

Never found it necessary to bench-bleed any M/C with a remote reservoir mounted as high as it is on the `68-up cars, the static head alone is enough to ensure that any air in the master finds its way out the compensating ports and up to the reservoir.