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Re: [T3] Converting Single MC to Dual MC

Interesting... I think the big advantage of the disc brakes was their
superior ability to dissapate heat..
Ever try to bring something like a 66 Dodge charger down from say 100 with
drum front Brakes???
Memories like that dont FADE :)


> On 11 Dec 2002 at 19:02, Keith Park wrote:
> > But.. Jim, since you brake  about 2/3 on the front and the rest rear...
> > does this proportion stay the same with such a different type brake
> > (caliper vs Drum).  Drum brakes are much less effecient... I would think
> > youd need at the least a much different brake fluid pressure with them.
> The proportioning is done in the design stage of the car, by choosing what
> diameters of slave pistons you use AND at what radius the braking force is
> applied. Thus we got 42mm F caliper pistons and 3/4" (~19mm) rear pistons.
> These can't be compared directly since they are disks/drums. I'm sure the
> manufacturers have ways of making good educated guesses, however, and they
> certainly have the option to adjust those sizes in the prototype stage.
> On the Golf, where the rear wheels really have very little braking to do,
> can see extremely small diameter drums, inside of which there are very
> diameter pistons.
> In a car with 4 wheel disks, there is a practical lower limit on the
> size, so on the 914, for example, they got the same diameter front pistons
> the smallest rear pistons they could do, then they added the proportioning
> valve. Frankly I think they would have been better off with rear drums,
> there are plenty of people who think that 4 wheel disks MUST be better.
> BTW, I'm not sure exactly what the advantages of disk brakes are (maybe
> unsprung weight,) but I don't think its accurate to say that drums are
> efficient.
> > As to amount of fluid used... I could swear there were differences...
but I
> > bow to the master as he has hard numbers to back him up ;)
> I agree, there certainly must be differences, but this is just a matter of
> available MC stroke. VW adjusted the F/R stroke on our cars in 72, I
> just to make sure that they seldom ran out of travel. This is most likely
> come up with drums, which take more fluid displacement as they wear, until
> get adjusted. Disks just happen to be inherently self adjusting.
> If you think about it, you will see that in a tandem MC each internal
> will move until all the "free travel" has been taken out of BOTH circuits.
> then will the fluid pressure start to rise, and it will riss equally in
> circuits.
> --
> *******************************
> Jim Adney, jadney@vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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