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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/