brake efficiency problem

For road racing, autocrossing, or just taking that curve in style. Oh yea, and stopping!
Ol'fogasaurus
Posts: 17881
Joined: Mon Nov 13, 2006 10:17 pm

Re: brake efficiency problem

Post by Ol'fogasaurus »

I wasn't going to post on this any more but: it is the situation that determines all on the same level. Sometimes you just can't accomplish it by normal means which means you have to get creative. Rules also determine the situation also.

For road and probably X-cross a level system probably should be the goal; I'm not sure about drifting mainly because of the extra manual brake setup use to get the rear of the car broken loose.

For trail and that you are going to have a mix of either way. For sand and other places that require big tires and turning brakes you are probably stuck with residual pressure valves. Engine swaps also may break the rules for flat mounting but not sure if that is occasionally or most of the time. Add to that the potential need for bias change, MC change, drum to disc or any or all.

Lee
jhoefer
Posts: 195
Joined: Wed Oct 05, 2011 2:30 pm

Re: brake efficiency problem

Post by jhoefer »

A level system isn't the ideal. There's two ways you can go for "ideal", and "ideal" only concerns how easy it is to bleed the system. First, if you don't use residual valves, then it is an open system that relies on gravity to keep the fluid where it needs to be. Fluid flows downhill, air bubbles flow uphill, so you'd want the calipers at the lowest point (You still need the caliper bleeders because the chamber inside the caliper is still a place air could be trapped.), the MC at some height above the calipers, and then the reservoir sitting somewhere above the MC such that the fluid level in it is the highest point in the system even with the car at an incline (this "incline" should probably include the effects of lateral forces during turns, etc as well). The lines should ideally slope upwards along their whole length from caliper to MC to reservoir. This would make the system self-bleeding over time as bubbles would naturally rise up and out the reservoir and it eliminates drainback as gravity ensures the fluid flows down towards the calipers. It would also work for the line from caliper to MC to form a single vertical U shape along its entire length as bubbles on one side of the U would naturally exit the MC/reservoir and bubbles on the other side would rise into the caliper for bleeding. Vertical humps or vertical loops however, will create local high spots that can trap air in the line and increase the bleeding difficulty. If you add a loop to the hard line for thermal expansion/stress relief it should ideally be horizontal with the low end of the loop on the caliper side (or where you want the fluid to go) and the high end of the loop on the MC side of the line (or where you want the air to go) to avoid this.

The second "ideal" case, with residual valves, you'd want the residual valve as the lowest point in the system, with the lines from it sloping upwards along their whole length to the caliper, this way air bubbles will want to rise up into the calipers where they can be easily bled out. If the valves are higher than the calipers, air would tend to be trapped in front of the valve increasing bleeding difficulty. The lines from the valve should also slope upwards along their whole length to the MC to prevent drainback issues between the valve and MC (the valves are already preventing drainback from the calipers) and air bubbles here would naturally rise up through the MC and out the reservoir. This drainback concern is typically avoided by mounting the valves as close as practical to the MC or being a part of the MC itself. It doesn't matter how high the MC is mounted in relation to the calipers as long as it's at or above the valves. As in the first case, you want the reservoir mounted above everything so the fluid level is always the high point of the whole system. This second layout could also work the same way without residual valves if the MC is the lowest point in the system, the calipers are higher than the MC, and the reservoir is higher than both.

Now these "ideal" and non-level setups are practically impossible to achieve in a car due to the necessary line routing and component placement creating local air traps so you will encounter some bleeding issues. But once completely bled and assuming no leaks, as long as the reservoir/fluid level is the high point, the component placement and line routing doesn't make a bit of difference to the actual hydraulic operation of the brakes. Mount the MC on the roof and spell out your name with the brake lines and it wouldn't matter.
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