I posed your question to the Grok AI on X here's the response...it draws on previous posts from Steel Soldiers.
Adding a dual circuit air over hydraulic brake system to an M809 series military 5-ton truck involves significant modifications to the existing brake system. Here's how you might approach this conversion:
Planning and Preparation:
- Research and Design:
- Study the existing air-over-hydraulic system on the M809. Understand that this system uses air to assist hydraulic brakes but operates on a single circuit.
- Decide on the dual circuit setup: You'll want two independent circuits, one for the front brakes and one for the rear, to increase safety by allowing braking even if one circuit fails.
- Component Selection:
- Dual Circuit Master Cylinder: Choose one that can supply fluid to two independent systems. This might not be directly available for military vehicles, so look at similar systems in commercial heavy-duty trucks or adapt from other military truck series like the M939, which has full air brakes.
- Air Brake Chambers: You'll need to add or replace the existing air packs with dual-circuit compatible chambers if you're retaining the hydraulic part of the brakes.
- Valves: You'll need a dual-circuit air valve for the brake pedal. This could be a treadle valve from a commercial truck setup.
- Air Tanks: Two air tanks, one for each circuit, to maintain air pressure independently.
- Lines and Fittings: High-quality DOT-approved air lines and fittings for the new circuit.
Steps for Conversion:
- Remove Existing Components:
- Remove the existing single-circuit master cylinder and the air pack if it's not compatible with your new setup.
- Install New Master Cylinder:
- Mount the dual-circuit master cylinder. This might require fabricating a new bracket or modifying the existing one. Some have used parts from the M35A3 or M939 for this purpose.
- Air System Modifications:
- Install the dual-circuit air valve where the brake pedal would actuate. This valve should control air flow to both circuits independently.
- Install two air tanks if not already present, ensuring each circuit has its own air supply.
- Hydraulic System Setup:
- If you're keeping hydraulic actuation for the brakes, connect the new master cylinder's outputs to the hydraulic lines going to the front and rear brakes separately. This might require splitting the existing hydraulic line into two.
- Brake Chambers:
- If you're adding or replacing brake chambers, ensure they match the axle setup of the M809. The chambers should be dual-circuit capable, meaning they can operate on one circuit if the other fails.
- Air Line Routing:
- Route air lines from the tanks through the necessary valves to each brake chamber. Ensure each circuit's lines are separated to maintain independence.
- Bleeding and Testing:
- Bleed both the air and hydraulic systems to remove any air pockets, which could impair braking efficiency.
- Test the brakes thoroughly, checking for pressure loss, proper application, and emergency braking with one circuit disabled.
Considerations:
- Safety: Ensure the system meets safety standards, particularly for emergency braking. The dual circuit should allow for partial braking if one circuit fails.
- Regulations: Check local laws regarding vehicle modifications, especially for military surplus vehicles intended for civilian use.
- Maintenance: Dual circuit systems can be more complex to maintain, requiring attention to both air and hydraulic components.
Resources:
- Discussions on forums like SteelSoldiers offer insights into similar modifications, including part numbers and practical advice from those who've done it before.
This is a complex modification that should ideally be undertaken with a clear understanding of both air and hydraulic brake systems or with the help of professionals experienced in heavy vehicle brake conversions.
