Sorry nick but I don't agree with what your saying about single piston
calipers and clamping force. My reasoning would be about 1000 words and
would still make me confused. Sorry but I'm no engineer and my physics is
not to flash!
My basic logic is as follows:
two pot simitomo (ie 2 x 4.8cm diameter pistons) - each piston pushes one
pad independantly on either side of caliper towards disk by X force.
Theroretical Single pot sliding caliper with 4.8cm dia piston and same pad
area as above. Ok so given that piston is pushed out of caliper in one
direction by X force. The force at the pad is then halved though as the
caliper is a sliding arrangement.
What I mean is that the pad clamping force in this case is shared equally
between the two pads. Where as the twin pot clamps each pad individually so
the force is greater.
Regards
Trev
-----Original Message-----
From: Andrew Greenbury [mailto:[EMAIL PROTECTED]]
Sent: Monday, 8 January 2001 15:09
To: [EMAIL PROTECTED]
Subject: RE: Brakes - Long
I agree with zac: if you exert force on one side obviously there will
be an equal and opposite force on the other side - this doesnt
equate to twice the effective force/pressure.
if you put scales on a table with 10kg on them, do the scales show
20kg because the table is exerting a 10kg reaction on the scales
too??
andrew
> imagine the disk was "u" shaped so that the a brake piston acted inside
the
> "u" shaped disk, a single piston could be aranged to operate internally,
> pushing outwards against the inside of the "u" and thus the effective
> pressure would indeed be doubled, the piston pushes against one side and
the
> floating cylender pushes on the other side.
> in real life it works the same way but with "levers and brackets" used to
> transfer the pressures against the outside of a disk.
> make sence?
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of Zac Campbell
> Sent: Sunday, January 07, 2001 8:43 PM
> To: [EMAIL PROTECTED]
> Subject: Re: Brakes - Long
>
>
> I'm not entirely convinced that one piston can create the pressure of two
> pistons just by having it push two pads. To me this would mean the
opposite.
> I think that it would then create only a percentage of it's full potential
> pressure on each pad, whereas an opposing twin piston caliper would be
able
> to push 100% on each side.
> Also are we taking into account even pad pressure from both sides created
by
> an opposing piston setup?
> What about pad area!?
> I'm not doubting Terry's setup his obviously works a charm for the reasons
> that Brad Hallett pointed out.
>
> zac
>
> ----- Original Message -----
> From: Ken Abraham <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Saturday, January 06, 2001 5:52 PM
> Subject: Brakes - Long
>
>
> > Errol, Terry, Trevor et. al.
> >
> > Some Notes and questions about brakes resulting from my field trip to
the
> > Wreckers,
> > (some of my recent posts on this have been rejected by the server, so I
> > don't know how much has already got through).
> >
> > 1. Sumitomo twin piston calipers
> > Readily available (i.e choose a good pair and don't pay more than $20
> each)
> > on some Toyota Corona's and Mark 2's (6 cylinder sports coupe), all have
> > braided lines.
> > There are 3 main types, they differ in where the brake line attaches to
> the
> > caliper.
> > The Sumitomo caliper bolts straight onto an early 200b Strut, and I
assume
> > it goes straight onto the 270mm brake-disc 240K struts.
> >
> > 2. Single piston versus twin piston, and four piston - IMPORTANT
> > Previously, we have calculated the effective piston area of a single
> piston
> > caliper as the area of the piston. However, actually the effective area
is
> > slightly more than double the area of the piston since the force exerted
> on
> > the medial chamber wall (the inner face, opposite the piston) is used to
> > press the lateral (outside) pad against the disc.
> > With this new view, compare various calipers below...
> > (Note the greater the effective piston area - the greater the force on
the
> > pads for a given brake line pressure, Pressure=Force/Area)
> > Porsche 993 Turbo caliper has 2x 44mm pistons and 2x 36mm pistons giving
a
> > total area of 50.7681cm sq.
> > By my reckoning the stock 1600 caliper would have 2x 20.43cm sq. =
40.86cm
> > sq.
> > The big 200B caliper would have 45.80cm sq.
> > The poor old Sumitomo would have 36.19cm sq.
> > The Rover 3500/AP Twin pot would have 51.04cm sq.
> > Volvo & Hilux 4 spots 28.27cm sq.
> >
> > As I see it there is no difference in the surface area to volume ratio
> i.e
> > caliper cooling ability) between 1, 2 or 4 or even 10 piston calipers.
> > Perhaps the advantage of 4 spots is that they distribute the clamping
> force
> > over the length of the pad better, hence reducing disc warp and pad hot
> > spots.
> > Perhaps single piston sliding calipers are more prone to flex and pad
> knock
> > off than the opposed-piston fixed type caliper.
> >
> > 3. Sources for brake mods and further research,
> > The Nissan Urvan has large single piston sliding calipers on vented
> rotors,
> > the calipers have the Datto 90mm bolt spacing, but with ~M20 (i.e
large)
> > bolts, and would fit on Bluebird or R31 Struts with slight modification.
> > Approx piston size is 55mm, eff. area = 47.51cm sq.
> > BMW 3.0S calipers are 4 spot vented at the front and twin piston vented
at
> > the rear have 90mm spacing and may fit on Datto 200b, 1600 etc... strut,
> > don't know what type of disc to use though. E28 also has 4 spots and
twin
> > spots. E30 has twin spots up front.
> >
> > 4. Bluebirds/R31
> > The Bluebird is not an 'orphan' or black sheep as people have suggested,
> > parts from it can be good for swaps.
> > The disc brake rear (TRX, LX) is an early version of the R31 rear and
the
> > calipers are interchangeable (internal handbrake on Bluey though),
> similarly
> > up front, the Bluebird brakes are just non-vented R31's
> > There are DBA sport rotors available for the R31.
> > The disc brake rear is basically what is fitted to the VN Commodore!
> > I would like to find a swap for the rear caliper though. I hoped to fit
> > Bluebird front calipers to the rear and fit a Mini pressure regulator,
> > however the bolt and pin spacing is different, any ideas?
> >
> > 5. I made a tactical decision and went for the R31 250mm vented front
> > struts, rather than the 270mm solid 240K struts, I'll just hang onto the
> > Sumitomo's until The brake issue is resolved.
> > I will have to change the spring seat though, or swap all the bits into
my
> > Bluey struts.
> > BTW the R31 struts with vented rotors and finned calipers look SWEET.
> > What car did I get the struts from, it was an R31 skyline, but it was a
> > sports model in Two-tone grey - Not a GTS, they have 270mm discs. A
> > silhouette maybe?
> >
> > Regards,
> > Nick
> >
> >
> >
> >
> >
>
>
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