Dual circuit master cylinder

[Errol62]

Dragging up an old topic, I picked up a master cylinder amongst some parts I stumbled on via gumtree this morning.
It’s a PBR 12C8 P6612, 69 - 72 LC Torana part, $192 on Allparts website.The mount face has a protruding snout which I assume mates to a booster vessel. Mentioned in an earlier post by Trev the firewall hole needed to be enlarged so seems to be consistent with what he may have used. I’m hoping to use this on the van in conjunction with vh40 on front disc circuit only. Anyway it came with a bunch of other stuff for bugger all.

[Harv]

Looks to be the HT/G booster from the part number (6612). Rares sells these new for $276.

Looks like the guts have had a leak at some stage. If it's been stored in the open, the internals may not be salvageable. Strip it down and see if you can get away with a kit.

Cheers,
Harv

[Errol62]

Thanks Harv
Haven’t tried to free the piston but opened it up and didn’t look bad.


FB ute fixer upper, EK van on rotisserie

[mph]

Is there a benefit of running a remote vh44 booster for just front disk with rear drums still , do drums not need to be boosted,
? or is this just done to eliminate trying to mod and fit a booster to the fire wall to have boosted duel circuit brakes?
Id like to go to dual circuit for safety reasons but don't think I would like to loose the booster more so now I'm going to front disks not to sure if you can even run disks with out a booster .
I see wilwood dual master cylinder is quite popular with older holden now but no booster or are they made to also feel like and replicate a booster?

[Mick]

Is there a benefit of running a remote vh44 booster for just front disk with rear drums still , do drums not need to be boosted,
? or is this just done to eliminate trying to mod and fit a booster to the fire wall to have boosted duel circuit brakes?
Id like to go to dual circuit for safety reasons but don't think I would like to loose the booster more so now I'm going to front disks not to sure if you can even run disks with out a booster .
I see wilwood dual master cylinder is quite popular with older holden now but no booster or are they made to also feel like and replicate a booster?

i've done a few mounting a holden master straight to firewall i think there is an adapter but i just made the hole bigger drilled new holes to bolt master on i run VH40 (The bigger of the 2) on front only i then used unboosted drum brake compatible rear brakes, the last one i did needed to be brake tested for an engineers report the people that did it was a brake shop and they were quite impressed with how they worked
i'm thinking of trying the unboosted willwood set up

[Errol62]

Like mick says the ubiquitous Holden &*#@ etc dual circuit bolts up with minor firewall mods. There is also a Nissan unit that bolts up without any mods. Gledges car on here runs unboosted four wheel discs.


FB ute fixer upper, EK van on rotisserie

[FireKraka]

Hey Clint speak to Gazza he is fitting non boosted wilwood master to the shed find ute I think or have a look at his build.
Neil

[mph]

interesting guys,the boosted front disk and std drums sounds like a goer, im doing plenty of reading on forums and the net about the setup also trying to work out what bore size to use , seems like 5 different sizes can be used ,i think ill end up with a dual circuit master cylinder on the fire wall and remote booster for the fronts unless i end up with a set of Brodie's ve bonnet hinges and can fit a firewall booster with not many major mods, i seen some on ebay small boosters to master cylinder for around $400 probs rubbish.

[gpi]

perhaps look at it this way:

A brake booster is an enhanced master cylinder setup used to reduce the amount of pedal pressure needed for braking:
https://en.wikipedia.org/wiki/Vacuum_servo

fitting a booster is not a requirement of VSB14:
https://www.infrastructure.gov.au/vehic ... an2011.pdf

you can waste a lot of money in this space when you concentrate on aesthetics rather than requirements.

[Harv]

interesting guys,the boosted front disk and std drums sounds like a goer, im doing plenty of reading on forums and the net about the setup also trying to work out what bore size to use , seems like 5 different sizes can be used ,i think ill end up with a dual circuit master cylinder on the fire wall and remote booster for the fronts unless i end up with a set of Brodie's ve bonnet hinges and can fit a firewall booster with not many major mods, i seen some on ebay small boosters to master cylinder for around $400 probs rubbish.

Small boosters (like the Gemini 7" one) are a pain. They fit into a small space, but have very little volume. When you are dancing on the brakes, they run out of vacuum real quick. You can then need a vacuum tank, or vacuum pump. The idea of the Willwood system is very attractive - low pedal effort without a vacuum booster. There must be some real magic in getting the pedal effort low without needing to have a high pedal travel, otherwise OEMs would have done this a long time ago.

Cheers,
Harv

[ardiesse]

Harv,

The magic lies largely in reducing the bore diameter of the master cylinder (and it goes inversely as the square of the bore diameter too). A dual-circuit master cylinder has two compensating ports, and so has double the "wasted" travel of a single-circuit master cylinder. The compensating port's maybe 0.020" diameter, but it adds up. Then there's the clearance of the booster pushrod to the rear master cylinder piston. Then there's the pushrod travel at the booster's input which is required to actuate the booster itself.

The HR disc/drum setup I had in my EK had bugger-all pedal travel. I could bring the car to a halt without the brake light coming on. In contrast, my Monaro's brake pedal goes to a hand's thickness of the floor before the brakes engage. And it has the same caliper and rear wheel cylinder piston sizes as the HR setup. The extra pedal travel has to come from somewhere.

I reckon that if you could make a dual-circuit master cylinder with say 9/16" or 5/8" bore diameter, with the dimensions carefully controlled so that the lips of the rubbers are right at the edge of the compensating ports, the pedal travel would be manageable and you wouldn't need to boost the brakes.

Argument in favour: Clutch master and slave cylinders in the mid-2000s Honda CR-Vs. Tiny bores, bugger-all swept volume, but stroke similar to the Holden equivalents.

Rob

[Harv]

Agree - pressure is simply force (from your leg) divided by area (from the bore of the cylinder). Less cylinder area (smaller bore) = more force = no need for a booster. The smaller bore though means less fluid gets pumped to drive the brakes. You could:
a) tighten up all the slop in the master
b) run smaller bore slaves (calipers) with multiple pistons
c) increase pedal travel

I wonder if Willwood take option b), and reccomend some of their fancy calipers to go with their no-booster slave?

Cheers,
Harv

[mph]

Has anyone looked into running a side offset hk booster in their fb ek

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[EK283]

I did try this but for the life of me I can't remember why I didn't pursue it.

I know I ended up cutting the bracket and I sort of think the angle was wrong to fit the V8 or something like that.

It would work with a 6 cylinder I imagine

Greg

[mph]

I bolted a HG dual circuit directly to my firewall, had to enlarge the hole and flatten the pressings but it went on no problem.
Then used a remote booster.


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Did you have any picks of this Trev

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