[DeTomaso] Booster talk
Thomas Tornblom
Thomas.Tornblom at hax.se
Sat Jul 18 15:18:05 EDT 2009
When you look at how the prop valves work, you realize that they have no
place at all in the front circuit. Check the tilton link I sent before.
The problem is that they are not linear.
Thomas
Julian Kift skrev:
> I'm far from an expert on braking, but have been reading enough to be
> dangerous in regard to putting together a brake system for the '74.
>
> Someone feel free to call me on anything irrational in the following;
>
> The Pantera has an almost 50/50 front/rear weight split and low center
> of gravity, thus should be fairly 'neutral', hence one would expect that
> the brakes would be of almost equivalent size front to rear, yes? Stock
> they are far from that with larger fronts and hence that is the reason
> for the proportioning valve in the front system (whether the reported
> 70/30 split in the proportioning valve is optimal is another question).
>
> Intuition and reading says that proportioning valves are normally
> installed in the rear circuit to limit rear brake lock up, however, I
> think the Pantera's rear barkes are so undersized that that thinking is
> null and void. By installing the prop. valve in the front circuit what
> you are effectively doing is making up for inadequate rear brakes by
> limiting the front efficiency, thus reducing overall braking
> efficiency. Rationale (at least mine) would say installing larger rear
> brakes in combination with stock proportioning valve removal (or
> replacement with an adjustable unit for fine tuning) is the best way to
> a brake upgrade.
>
> To make things worse, many aftermarket brake upgrades disproportionately
> add more braking capacity to the front(vented rotors, larger calipers),
> that in combination with all the experts advocating removal of the stock
> proportioning valve, ending up very biased to front braking. Unless you
> have added significantly more rear braking capacity, I still see any
> aftermarket proportioniong valve installation being in the front circuit.
>
> How many people have actually driven their Pantera down the road and
> tested whether they can lock up their rear brakes?
>
> In reality the braking efficiency depends on many fatcors like
> suspension, weight et.c and particularly tire type. There is no one
> solution and to do it properly wheel strain gauges or a four wheel
> rolling road are required (the latter being far more common in the UK
> for MOT testing where they actually annually test your braking
> efficiency front to back and side to side, plus the e-brake has to be
> able to stop the car on the rolling road!!)
>
> Julian
>
> > Date: Sat, 18 Jul 2009 20:16:40 +0200
> > From: Thomas.Tornblom at hax.se
> > To: MikeLDrew at aol.com
> > CC: Thomas.Tornblom at hax.se; detomaso at realbig.com
> > Subject: Re: [DeTomaso] Booster talk
> >
> > Giving it a new try...
> > ---
> >
> > MikeLDrew at aol.com skrev:
> > > In a message dated 7/17/09 23 33 47, Thomas.Tornblom at Hax.SE writes:
> > >
> > >
> > >> It will still require a fair amount of pressure before it starts
> > reducing the pressure.
> > >>
> > >>>> What makes you say that? I was under the impression that a
> > > proportioning valve does just that--convert X amount of inlet
> > pressure into Y amount of outlet pressure.
> >
> > There is a knee after which it begins to reduce the pressure. Initially
> > the output pressure is the same as the input pressure.
> >
> > See:
> > http://www.tiltonracing.com/pdfs/98-1261_Prop_valves.pdf
> >
> > >
> > >
> > >> It will have too much pressure on the fronts until that happens. I
> > want well balanced brakes throughout the entire range.
> > >>
> > >>>> Which is exactly what you should get. You wouldn't want a
> > non-linear
> > > system where you got equal pressure until some threshold is reached
> > and then the pressure reduces from there. You'd want the reduction to
> > be constant.
> > >> Come to think of it, having the prop valve in the front cirquit is a
> > stupid idea. During hard braking you get weight shift to the front, and
> > what you need then is to reduce the force on the now lighter loaded
> > rears to avoid having them lock up.
> > >>>> The weight transfer is so instantaneous that you wouldn't gain
> > anything
> > > by having increased pressure to the rears initially, then dropping
> > down to 'proper' balance. You'd want them to be proper all the time.
> >
> > Yes, but the harder you brake, the more weight is transfered to the
> > fronts, so you would want proportionally more brake up front then, which
> > is what you'd get with a prop valve in the rear cirquit.
> >
> > >
> > >
> > >> With the improperly balanced brakes of at least my car the fronts
> > will have locked up before you get to this point.
> > >>>>> And you should be able to dial them in so that they lock up just
> > a bit
> > > later than they do now (which is to say, the rear brakes would
> > contribute more to the total stopping cause).
> > >
> > > Mike
> >
> > Thomas
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