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Old 04-02-2003, 01:33 AM   #8
Scooby Specialist
Member#: 13486
Join Date: Dec 2001
Chapter/Region: W. Canada
Location: Calgary
06 Legacy GT wagon


Based on results from people who have actually done this, there seems to be no major problem - and actual improvements instead.

First, drum brakes get an advantage over discs since the friction material is Wedged into the drum. This means for the same force you get additional braking power with drums (to a point).

Second is the amount of fluid sent to the drums. If you had a car setup with drums and an equal car setup with discs the drum brakes would get FAR less fluid for the same braking power.
It's possible that Subaru uses the same proportioning valve, or keeps a very similar crack point (split point) and reducing ratio, on drums and disc models, but just sizes the drum piston accordingly, so as to get the same amount and pressure of fluid going to the rear brakes, and gets the same amount of brake torque. The WRX has split point of 285psi, ratio of 0.3. Anybody know the TS/OBS numbers?

Third is a valve that is present on disc/drum combo cars. At the moment I forgot the name(Im not referring adjustment of bias). In drum brake vehicles the pads are drawn away from the drum by a spring. Discs are basically in constant contact. Becuase of this a valve is installed that will send brake fluid to the rear FIRST, activating the rear brakes a short amount of time before the fronts. Since the rears need to take up the slack this pause usually means both brakes are activated at the same time.
This may very well be an issue. Under very light braking, the rear discs would activate first. Not good in really slippery conditions like iceracing. the valve is called the holdback valve: link

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Last edited by codger; 04-02-2003 at 02:19 AM.
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