Brake Shuttle Valve - Install, use, and bleeding.

[vlad_d]

I just finished a total brake system install, which included a 2 circuit/line brake system and a brake Shuttle valve. There wasn't much online resources about this valve...in fact many online users deleting this valve because of complexity or ignorance. But it's actually an important safety feature and not that much of a mystery, when you get some key points. So, I thought I'd post here...since Google dumps you on RoversNorth forums 9 out of 10 times. Maybe this helps someone...

PDWL/Shuttle Valve - What is it?
The Shuttle Valve is a common valve in hydraulics systems where you can have 2 lines and if one line looses pressure, a "shuttle" plunger moves over and blocks the depressurized line. It makes it so that all your brake fluid doesn't squirt out onto the concrete if you tear a brake line. Car manufacturers use this feature to keep at least HALF (front or back) of your brake system working in a catastrophic leak. It makes a "2 circuit" system possible. So, deleting it just makes you go back to a 1 line system...and risks your brakes going out. Not great. It's worth having, and not that difficult.

Another name for this valve on Rovers is PDWL Valve for Pressure Drop Warning Light. That's because it has a switch on it that can be hooked up to show you when it has been tripped. The usefulness of this switch is debatable(you know when the brakes don't work very well!) but that is a SECONDARY benefit of this valve. Some people think the only thing the valve does is operate the light switch...but that's wrong. The valve is an emergency shut off for half the hydraulic system to keep pressure. The light switch is a bonus.

In modern cars, this is called a "Combination Valve" because it usually has a combination of Shuttle valve, failure switch AND a pressure regulator for different hydraulic pressure to the back wheels (for front disc brakes, back drum brakes setups where volume of fluid is different). Series Rovers have separate pressures from the lines out of the Brake Master Cylinder (more on this later) so they don't have a need for pressure adjustment in a combo valve. So, just Shuttle valve.

See a diagram of the parts below.

How it operates
The Shuttle valve has 2 lines coming in the top, and 2 lines coming out the bottom. Each set of lines is an IN/OUT setup, with the valve able to block the circuit. Along the cross axis, the valve has an access port where you can service the Shuttle plug and Seals. Sometimes, there is also another hole on the other side of the cross axis. This is just a duplicate of the front lines circuit. You can plug this up with a bolt (NRC4137), or run individual lines to the front left & right brakes...Basically like a T. There is also a center hole which is fitted with the PDWL switch. This switch is also removable to give access to the Shuttle valve when pressurized (more on this later) or to replace the switch.