Neil,
Even though the brakes are hissy, you probably still have 90% of the power boost still working. If you want to see the difference, either disconnect the vacuum hose and plug it. Or just switch off the engine (in neutral, in a safe straight line place) while doing 60, apply the brakes a few times to bleed off any residual vacuum stored, and try a fast stop. This simulates engine failure and its effect on braking.
The amount of brake power needed to lock up the tires also depends on the tires. Skinny bias tires of the 50s with hard rubber will lock up much easier than a modern grippier radial tire of a wider size and better traction rubber.
Making the factory brakes more powerful than that required to lock up the original tires of the 50s, would have been considered overkill and excess cost by the factory. If you have bigger tires now, then bigger brakes will work better.
The ForwardLook brakes were designed so that the pedal operated directly on the master cylinder and the booster only added force to the top of the pedal. This should give plenty of road feel. All modern power brakes operate the pedal through the booster unit to the master cylinder, which has a large spring inside. This spring has 2 drawbacks: 1. less feedback for road feel, 2. with the loss of vacuum, the spring also needs to be compressed, making pedal force requirements much higher.
Experiments have show that in the hands of an experienced driver, the car can be slowed faster with non-ABS brakes than with ABS. The driver needs to control the brakes at the edge of lockup. The reason is that ABS temporarily turns off the brake on any wheel that locks up, thus reducing braking. Unfortunately, the vast majority of drivers are not experienced or practiced for 4 wheel skids, and panic in a skid, so they benefit from ABS.
Dave Homstad
56 Dodge D500
---- Eastern Sierra Adjustment Svc <esierraadj@xxxxxxxxxxx> wrote:
> OK: fuggedaboutit---I hear you, thanks;....I was hoping that the pedal-swap
> might have been a simple procedure/experiment (NOT-)....
>
> But, FWIW, the "manual-braking" effort, when the power assist has been lost,
> is not any major effort or ordeal to endure, and absolutely nothing to
> be feared
> (like a complete loss of brake fluid is).
>
> Kinda-really looking Forward to the full power braking effect of that
> reconditioned
> booster assembly, as compared to what's happening now, with the reportedly
> full-manual-braking effort that is required.
>
> The major stopping difference will probably be felt during a concerted
> braking effort.
>
> And, that's a scary thought, because the 11x3" Bendix's on Horrie, now,
> are plenty
> powerful enuf---it would be neat to see how well they could perform,
> when controlled
> by an ABS system, because 'you' can lock them up, with an OEM power
> brake system.
>
> Thinking back, now, I don't recall that I have been able to lock up the
> Bendix's, in the
> full-manual mode--altho I never had to try an expedited stop maneuver...
>
> I was kind of hoping that the manual-pedal might have allowed for more
> brake pedal feel
> or modulation.
>
> Neil Vedder
>
>
>
>
>
>
>
> jrawa@xxxxxxx wrote:
> > 57-59, just as earlier hung pedal assemblies- requires an entire
> > hanging pedal assembly- so.. plan on steering column removal and
> > unbolting the lower half of the dash from the side jambs to wing it
> > out- i usually swap in the power assembly when the body is still a
> > shell.. on the way back together- if i opt to do so.... the pedal has
> > a lever above the lower swinging arm- the carrier/support has an
> > elongation where it pivitos up and through, im pretty sure the fulcrum
> > point is also a little different- aiding in the advantage ratio change
> >
> >
> >
> > -----Original Message-----
> > From: Eastern Sierra Adjustment Svc <esierraadj@xxxxxxxxxxx>
> > To: L-FORWARDLOOK@xxxxxxxxxxxxx
> > Sent: Thu, Feb 11, 2010 11:20 am
> > Subject: Re: [FWDLK] Hissy-fitting brake booster
> >
> > So, what do you think about the mechanical advantage of installing a
> > manual pedal to my P/B system,
> > assuming that the pedal may be a bolt on replacement deal?
> >
> > Should I try to find one, anyway???
> >
> > Neil Vedder
> >
> >
> > Dave Homstad wrote:
> > > On my car, I converted the non-power brakes to PB. I bought my car
> > with non-power brakes. Then I rebuilt the original wheel cylinders and
> > linings, turned the drums slightly, and replaced the linings and
> > hoses. Everything worked OK, but the car required more pedal pressure
> > to stop than before. A hard stop took both feet. I concluded that
> > modern off-the-shelf lining materials are designed for power brakes,
> > which seem to be standard on most everything, and these require more
> > pressure. >
> > > Then I installed a factory power brake set up from a parts car. I
> > thought I could just install the PB pedal, but it didn't fit the old
> > support structure. So the entire structure got replaced. The master
> > cylinder didn't even need to be disconnected from the hose, so no
> > bleeding was necessary. Wth the power brakes, the car now needs half
> > the pedal pressure to get twice the stopping power of the old system.
> > I am sure that with the same pedal pressure, such as one foot as hard
> > as possible, the line hydraulic pressure is much higher. Probably as
> > earlier stated going from 750 psi non-PB to 1100 psi with PB. >
> > >
> > > Dave Homstad > 56 Dodge D500
> > >
> > > ---- jrawa@xxxxxxx <mailto:jrawa@xxxxxxx> wrote: > >> interesting
> > note they published... the line pressures should inevitably be the
> > same to create the same stopping effect- whether manual or power-
> > figuring all master cylinders are 1-1/8 bore as are all 6 wheel
> > cylinders- and, the same amount of fluid [under the same systemic
> > pressure] would have to be displaced from the master to all cylinders
> > to achieve stopping pressure, shoes to drum.... i dont buy into higher
> > line pressure of power brake systems. the position of the pushrod in
> > relation to the point of pivot of the brake pedal arm is different-
> > giving a less advantageous aspect ratio of pedal:master piston travel
> > in a situaution of "manualized" power brakes, the manual ratio has a
> > higher multiplication ration of applied pedal pressure>piston
> > displacement.
> > >>
> > >> i can attest that the instantaneous line pressure may be higher
> > upon brake aplication, but a higher systemic pressure would mean
> > nothing more than the fact that in comparison to pedal pressure- the
> > booster adds that much more applied pressure- raising line pressure-
> > causing the car to stop quicker, giving a more touchy pedal [which i
> > feel in my bellows and cannister booster 57-61s] but by laws of
> > physics, a panic stop would lock all 4 wheels, which i havent had the
> > wonder of experiencing....
> > >>
> > >> my fastest fwdlk cars run manual discs, one with a fully
> > retrofitted gm pedal/booster/master assy. other commonly driven
> > fwdlk's have dual masters in manual and boosted apps... the resto cars
> > all retain single masters, man and power...
> > >>
> > >> so from the fluid dynamic engineering standpoint- the systemic
> > fluid pressure is in proportional relativity to applied stopping
> > power.... so.... back to basics, power brake cars stop "sooner" or
> > easier- using the same components from master to drum, and differ only
> > in pedal apply ratio and have that good old booster making your
> > footwork a little less arduous >>
> > >> >>
> > >>
> > >> >>
> > >> >>
> > >> -----Original Message-----
> > >> From: Eastern Sierra Adjustment Svc <esierraadj@xxxxxxxxxxx
> > <mailto:esierraadj@xxxxxxxxxxx>>
> > >> To: L-FORWARDLOOK@xxxxxxxxxxxxx <mailto:L-FORWARDLOOK@xxxxxxxxxxxxx>
> > >> Sent: Wed, Feb 10, 2010 12:36 pm
> > >> Subject: [FWDLK] Hissy-fitting brake booster
> > >>
> > >>
> > >> Well, for anyone interested, you might recall that my car's
> > canister-type power >> brake booster has been hissing badly, whenever
> > the pedal is depressed, and >> that I'd been quoted O/H prices of
> > several hundreds, and up, for that work. >> >> When this condition
> > occurs, with our cars, a mere reversion to manual- >> braking-effort
> > results, and if so, that is NO big-deal, believe me. Biggest >> PITA
> > is the hissing noise, at red lights (so, don't STOP there, I hear you
> > say). >> >> As I never like risking sending out an essential part with
> > the car remaining >> undriveable, I bought a flea-pay booster, very
> > economically, which was claimed >> to be in working condition, and
> > sent it out to "Booster Dewey", in Portland OR >> for O/H, at the VERY
> > reasonable cost of $175.00. >> >> They just called and will be
> > returning that guy to me; they say that they use a very >> viscous
> > lubricant to seal up the booster's internal compression. >> >> I've
> > asked them to send me some pics of their representative internal work,
> > as I may be >> praising their product to others. They say that my
> > 'new' booster has been tested by >> them to work like a champ! >> >>
> > So, I may be interested in selling my car's canister to someone who
> > might be interested >> in having IT be O/H'ed, and installed in (one
> > of-) your car(s), too. >> >> Anyway: and here's a question for you
> > Engineering-types: the manual brakes apparently >> have a different
> > configuration of the brake pedals/system, from the power brake models
> > (called >> the "aspect ratio"--IIRC) which allow for different p.s.i.
> > line pressure ratings, between the two >> systems. >> >> E.G.:
> > according to the 1957 D501 A.M.A. specs, the manual brakes have a 750
> > p.s.i. >> rating, while the power brakes have a 1,100 p.s.i. rating ;
> > a considerable difference. >> >> (Here it comes: ) so, to what extent
> > would a manual brake car realize an increase in >> braking
> > effort/effect if a power brake's pedal-lever-connections were to be
> > installed >> onto it, and, vice-versa---given, that the master
> > cylinders are identical, which I >> believe that they are???? >> >>
> > Neil Vedder >> >> >>
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