legacycentral bbs

Anyone ever heard of a retrofit kit for changing your hydraulic brakes to pneumatic brakes?

I guess before you discredit this idea, you have to understand how air brakes work.

Two air lines run to each brake caliper, one is an emergency line and is pressurised all the time, the other is a supply line and it's what the brakes are activated on.

You charge the emergency line to release the brakes, then charging the supply line with air applies the brakes, removing the charge disengages the brakes.
if pressure zero's out in the emergency line, the brakes lock down by supplying the supply line with pressure through a tiny tank resivor just large enough to engage the brakes - a check valve keeps the pressure in the emergency supply tank and the pressure in the supply line from traveling back up and escaping through a leak.


The big advantages I can see:

Reduction in pedal fade because you can't really "boil" air. heat it enough and it just expands - increasing the braking effect and pad pressure.
Security feature, a switch activates which drains the pressure in the emergency line (but keeps the main pressure tank full) so that the car will lock all four brakes down when parked, therefore not moving period.

Safety, if an emergency line breaks, the car won't move.


anyone ever heard of a system like this? think it would be feasible or neat to have?

I wonder if the stock hydraulic calipers could be converted to work with air brakes, they're already exposed to tremendous fluid pressure...

Interesting, to say the least. Sounds expensive.

Binford wrote:Interesting, to say the least. Sounds expensive.

some subaru's came with the air suspension - which is basically an air compressor which is belt driven with a magnetic clutch. plus the resivor tank.

I'm sure a larger tank could be fitted, then it's a matter of running steel lines (or using the standard lines if they're big enough and strong enough) to the brakes, using a biasing valve for air situations, and having calipers that will respond to pneumatics.

You wouldn't need two actual supply lines running to each caliper, just some pretty intricate valving which can withstand the air pressure (somewhere around 40-60psi?)

I could draw a graphic how I would think it could work with one line to the caliper - but it's a little late.

Let someone else reinvent the wheel eh?

Air compresses though. Would this not result in an all-around mushy pedal feel until the compressor created the pressure needed?

I'd imagine the calipers would lose lubrication quite quickly with no brake fluid.

Having the brakes engaged at all times is actually a bad thing. It tends to warp rotors and leave uneven brake pad material on the rotor as well.

I think air brakes are not allowed in most cities due to their noise level. I see "compression brake use prohibited" signs all over the place.
Or are those different?

those would be engine brakes.

fundamentally different, they work by cutting off the fuel input when the driver is off the throttle, and modifiying the exhaust timing so that the piston draws fresh air in on every downstroke and releases it on every upstroke (so it works just like an air compressor, hence compression brake)

air brakes would be larger in all respects, that is the big disadvantage. I have air hoses from trucks right here and they are 3/4" OD or so, 1/2" ID. Other problems are leak detection (no visible fluid), corrossion of the internals, PV=nRT (not a problem with fluids), icing (big issue), and noise

basically a solution to problems that do not exist

I see absolutely no benefit in this.

The only real benefit I see is possibly the security one.

Boiling fluid doesn't happen that often IMO (except possibly Phil)

Air brakes do not work with disc brakes. You must have drum brakes.

I'm with Josh, there is no arena where airbrakes will significantly provide an advantage to discs.

Air compresses. Fluid does not. Compression is a sign of compliance. Compliance is something I want in my seat (barely), not in my brakes.

Oh, and airbrakes use anywhere from 90 to 120psi.