Brake Valve Discussion (Proportioning, Metering and Combination Valves)
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- เผยแพร่เมื่อ 27 ส.ค. 2024
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Ever wonder how balance is achieved in your braking system. You have most likely heard of proportioning valves, combination valves and metering valves. But do you know what these valves do? In this training video, we discuss the evolution of brake valves over the years.
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Combination Valve
Before the turn of the century, vehicles with disc brakes in the front and drum brakes in the rear had a combination valve. Combination valves are commonly called proportioning valves. This valve is typically located below the master cylinder. The combination valve is a spring-operated device that has three key components:
1.) Metering Valve: The metering valve is located in-line with the front brakes. It holds off pressure to the front calipers until the rear brakes build up enough pressure. Once enough pressure builds up in the system (75-125 psi), the metering valve opens and allows the fluid to flow to the front calipers. Without the metering valve, the disc brakes would apply much quicker than the drum brakes. This would cause a nose dive during braking.
2.) Proportioning Valve: The proportioning valve is located in-line with the rear brakes. This valve prevents rear brake lockup during sudden and hard stops. This valve remains open until a panic braking situation. During sudden braking, high pressure from the master cylinder causes the proportioning valve to close. This restricts fluid pressure to the rear brakes and prevents them from locking up.
3.) Pressure Differential Switch: The pressure differential switch is located in the center of the combination valve. If the brake system loses pressure in the front or rear portion of the brake system, the switch grounds. This illuminates the warning light on the dashboard.
Height-Sensing Proportioning Valve
A height-sensing proportioning valve is found on many light trucks with disc brakes in the front and drum brakes in the rear. It's located in the hydraulic line leading to the rear drums.
Height-sensing proportioning incorporates a lever that is attached to the axle. As the load in the truck increases or decreases the lever moves the proportioning valve. If the load increases, the lever opens the valve to allow more pressure to the rear brakes. If the load decreases, the lever closes the valve to decrease pressure to the rear brakes.
Dynamic Rear Proportioning
Dynamic rear proportioning is the standard in late model vehicles. This electronic system is integrated into the ABS system. As you brake, the system monitors deceleration rates for each wheel. The system then reduces pressure at the rear wheels before they reach the point of lock up.
Since this system is dynamic, it is constantly monitoring and changing the brake pressure to the front and rear brakes. This provides optimum braking.
Thank you--I wondered how they divided the pressure as newer cars lack the 'proportioner valve' these days!
Great video, very informative!
Hello, We Have 2016 E450 cube van that the ABS system was not or very little braking to rear brakes all the time. We pulled fuse for ABS and still have very little brakes in rear and fronts lock up. Which makes the truck dangerious to drive in winter. I have taken the truck to two mechanic shops and both say pull the fuse and don't know what else to do for us.
Can anyone tell me the part number for the proportioning valve used as an example in this video? I have been looking for that style for a while now to no avail.
I have a very important question regarding my 2006 Toyota Tacoma that uses the anti-lock system, where is the proportioning valve that I cannot find? The power amplifier and the brakes and master cylinder are in excellent condition. Everything seems normal when I drive it, so far when I have to brake hard the front wheels do not lock. How can you help me with this problem, which is very worrying? I will be thanking you very much.
If proportioning valve not working rear or front brakes may lock.....
NOT so with a 2008 Ford Escape Hybrid I have 3 brakes that hardly work at all and 1 that will not stop working no matter what until i release the pressure on the front Driver side caliper. Ford really failed at life on this and now im faced with junk a beautiful running vehicle or custom brake system build and loose brake regeneration or cough up the $5291.00 price the Ford dealership quoted me for a replacement ECU/HCU. Being im not made of money and dont just have 6 grand laying around to blow on fords fail of building a reliable abs system for this vehicle Im going to bypass the junk abs braking system and hope it works well enough to not have to take it to the junk yard.
Thanks for the video Im looking into proportioning valves.
Hey, my buddy wants to put in a line lock in his 2003 jeep Rubicon because he wants to be able to hydraulically set his brakes and be able to get out while 4X4ing. I won't hold you to anything you say, I am just trying to figure out if it is possible. I think it is.
Interesting.
I have a 2002 town and country. can I just take off the ABS?
2003 Trailblazer 4.2L 4X4 no brake fluid coming to front brake calibers (or bleeders), help?!!!!
Master Cylinder, 2 Front Calibers, 2 Front Rotors, 2 Brake Pads are brand new/replaced.
Yes, Brake Fluid is in Brake Reservoir (new/bleeded-good) & pumped the Brake Pedal.
Again, still not getting any brake fluid coming out to the front.
Back brakes are fine.
Tip of the iceberg.
How to bleed Ford RABS Brakes th-cam.com/video/PbmQSXO9XHA/w-d-xo.html using a battery charger to operate the ABS system for RABS.