Brake booster failing?

[vc commodore]

Could also be a vacuum leak somewhere else as well, when the booster requires vacuum and there is a leak somewhere else, it will also affect the idle.

Generally when there is a vacuum leak, you get it revving up, especially when idling....You also have a constant miss...The op only gets this miss under braking, which points directly to the booster, rather than another source...

 

[Fachoo]

Scary advise.....

Nothing scary about it mate
it:s just atmospheric air moving from pedal action, not internal pressured air in booster being lost that your implying and after changing many boosters and master cylinders someone like yourself should know that even if yours was just a straight swap of parts used for different options for disk or drum and different engine sizes.

Boosters are just pumps and storage tanks to aid pedal action transfer of force to the master cylinder through the pushrod, so they don:t operate or interfere with the line fluid pressures for brake performance unless someone fiddles with the pushrod length in conversions or pushrod is too long or short for different master cylinder swaps.

 

[Immortality]

Poor vacuum will cause a long pedal.

I recently drove a car that wasn't firing on all cylinders and the brake pedal was terrible, once the engine warmed up and fired on all cylinders the brake pedal came up as is normal for that type of car.

I've actually experience what the OP mentioned in my old VN. Brakes worked more than adequately so the minor vacuum leak via seal at the push rod didn't bother me, than one day I hit the brakes, the pedal was solid and nothing happened..... something failed in the booster.

 

[Turd Ferguson]

I originally gravity bled brakes, but bear in mind all lines were fully empty due to new hoses and MC bla bla.

Then I got one of those 20 bucks 1 man bleeder jobs from repco ( the little bottle with the 1 way valve and hose you put over bleed nipple.
With that I would give it a few pumps to get fluid through on each corner.

Today I attached the 1 man bleeder but then did the old jam a broom against the pedal and chair and open bleeder / close after a few seconds and then reset pedal and broom

 

[vc commodore]

Nothing scary about it mate
it:s just atmospheric air moving from pedal action, not internal pressured air in booster being lost that your implying and after changing many boosters and master cylinders someone like yourself should know that even if yours was just a straight swap of parts used for different options for disk or drum and different engine sizes.

Boosters are just pumps and storage tanks to aid pedal action transfer of force to the master cylinder through the pushrod, so they don:t operate or interfere with the line fluid pressures for brake performance unless someone fiddles with the pushrod length in conversions or pushrod is too long or short for different master cylinder swaps.

Firstly, disc/drum rear came with both 15/16 and 1" bore masters....No difference with them....Go look at VN to VR....Factory disc rears, and 15/16 masters...1" bore was used on 6 banger cop cars around this era too.....Rellie has a VP ex-cop car with single diaphram booster and 1" bore master....Even early commodores with disc rears had 15/16 masters...The 1" bore masters are the harder ones to find...And yes they were fitted to disc reared cars, rather than drum rears....

Booster..The V8's had the double diaphram one...Not sure if the 6 ever came out from the factory with it....And my swapping had zippo to do with engine changes....

If you hear air escaping when you depress the brake pedal, with the engine running, the booster is stuffed....So giving advise that it is normal, is scary advise....

 

[MikeC]

I originally gravity bled brakes, but bear in mind all lines were fully empty due to new hoses and MC bla bla.

Then I got one of those 20 bucks 1 man bleeder jobs from repco ( the little bottle with the 1 way valve and hose you put over bleed nipple.
With that I would give it a few pumps to get fluid through on each corner.

Today I attached the 1 man bleeder but then did the old jam a broom against the pedal and chair and open bleeder / close after a few seconds and then reset pedal and broom

For years I used the old 2 men- one on the nipple with a tube and jar , one on the pedal pedaling bleeding method then about 20 years ago I bought a one man bleeder to try - bloody miracle device for something so cheap. I haven't needed a mate to help me bleed brakes since.

 

[DavesSV6Tonner]

If you hear air escaping when you depress the brake pedal, with the engine running, the booster is stuffed....

^^^ That's how I knew the Master Vac unit in our VS was stuffed. The continuous sound of air hissing in the cabin the whole time the brake pedal was depressed. Release the brake pedal and the sound stopped.

 

[Not_An_Abba_Fan]

There is a difference between a continuous hiss and the momentary hiss as you hit the brake pedal. I'm referring to the momentary hiss when you push the pedal down, some cars do it, some don't. I've had both a VS and VT do it, booster was fine.

 

[Turd Ferguson]

Another bleed today. Pedal feel is still not what I'd like but maybe I'm expecting too much compared to my Landy.

Braking

Watch "Braking" on Streamable.

streamable.com

Quick stomp from 90 >20 in the wet.

 

[MikeC]

I have an old Triumph TR6 - their brakes are notoriously hard to bleed- it's very difficult to get a full pedal. Some of the blokes jam the brake pedal down hard overnight with a stick then rebleed the next day. The theory is that the pressure and time cause any microbubbles in the fluid to coalesce into bigger bubbles that will bleed out.
I've never needed to do it with a Holden but if your running out of options it might be worth a try.