[DeTomaso] Booster talk

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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