[DeTomaso] Booster talk

Julian Kift julian_kift at hotmail.com
Sat Jul 18 15:11:15 EDT 2009


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
> _______________________________________________
> 
> Detomaso Forum Managed by POCA
> 
> Archive Search Engine Now Available at http://www.realbig.com/detomaso/
> 
> DeTomaso mailing list
> DeTomaso at list.realbig.com
> http://list.realbig.com/mailman/listinfo/detomaso

_________________________________________________________________
Windows Live™ Hotmail®: Celebrate the moment with your favorite sports pics. Check it out.
http://www.windowslive.com/Online/Hotmail/Campaign/QuickAdd?ocid=TXT_TAGLM_WL_QA_HM_sports_photos_072009&cat=sports


More information about the DeTomaso mailing list