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Re: [T3] Converting Single MC to Dual MC


On 12 Dec 2002 at 0:40, John Jaranson wrote:

> Actually, we often use an adjustable proportioning valve during the
> development of the braking system.  This lets us tune the front/rear brake
> bias as the suspension is tuned and the weight of the car is still moving
> around some.  Once the development engineer is happy with the brake
> performance the rest of the vehicle design is settled in the final
> proportioning is measured and then a fixed proportioning valve is designed
> for the production cars.  

This seems quite reasonable. Makes for quick and easy adjustments, which would 
be good for getting the best final outcome.

> Most of the new cars have proportioning valves in them since it allows use
> of common brake parts across cars with different weight bias and lets the
> longer lead time components (rotors and calipers and knuckles) to be
> finalized and tooled early in the development.

This surprises me, because you pay a weight penalty with the proportioning 
valve. I wouldn't think it would be all that hard for Ford to get their 
manufacturer to turn out parts with variations in piston diameters. That would 
leave rotors, knuckles, and caliper castings all unchanged, so the fittings and 
everything else that went into the system could be settled early.

> >BTW, I'm not sure exactly what the advantages of disk brakes are (maybe it's
> >unsprung weight,) but I don't think its accurate to say that drums are less
> >efficient.

> While unsprung weight is an advantage of the disc brakes, I believe the real
> advantage is in performance.  Disc brakes shed heat much better than drum brakes
> and suffer less brake fade (reduce performance) under repeated hard braking and
> perform better when wet.   There are other advantages in terms of servicablility
> and cost as well.

This was what I had always read early on, but lately I seem to more often see 
comments about how the disk brakes actually shed heat more poorly because the 
caliper fits around the outside of the rotor. Frankly, since there really are 
so few true performance cars on the road, I don't think we would see so many 
disk brakes on cars unless they meant lower cost or lower weight (or both.)

-- 
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA


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