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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 :) Keith > 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... how > > 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, you > can see extremely small diameter drums, inside of which there are very small > diameter pistons. > > In a car with 4 wheel disks, there is a practical lower limit on the piston > size, so on the 914, for example, they got the same diameter front pistons and > 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, but > 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 it's > unsprung weight,) but I don't think its accurate to say that drums are less > 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 assume > just to make sure that they seldom ran out of travel. This is most likely to > come up with drums, which take more fluid displacement as they wear, until they > 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 piston > will move until all the "free travel" has been taken out of BOTH circuits. Only > then will the fluid pressure start to rise, and it will riss equally in both > circuits. > > -- > ******************************* > Jim Adney, jadney@vwtype3.org > Madison, Wisconsin, USA > ******************************* > > > ------------------------------------------------ > To unsubscribe, E-mail to: <type3-off@vwtype3.org> > For more help, see http://vwtype3.org/list/ > ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/