Solving Brake Swap Balancing Issues With a Brake Proportioning Valve

Dear Four Wheeler,

Reading through the November 2021 issue ofFour Wheelermagazine and seeing "Brake Time," a drum brake to disc article, put a smile on my face. How perfect, I thought, since I'm in the middle of doing this myself. The article took care of my loose ends on doing this job but left the question that I can't seem to get a grasp on: How do you decide on or what do you do for a metering valve to obtain the correct brake balance to the front and rear brakes? I have come to understand that disc and drum brakes use a different volume of fluid to operate. Can you use the same master cylinder that you used with drums? I was planning on putting an adjustable metering valve inline to adjust the rear brake more or less. How do you dial it in so your rear tires don't lock up way before your front tires, sending you into the fence on a turn? Any insights into this issue would be a great help. Thank you for the monthly inspiration I get through your pages.

Ryan,

via email

Four Wheeler Tech Editor Verne Simons' Response

Shown is a disassembled OEM (non-adjustable) brake proportioning valve from a Jeep TJ or XJ. on the right is the front brake inlet line and two front brake outlet lines. The yellowish gizmo on the bottom is a switch that probably turned on a dummy light if something in the brake hydraulics goes south, like if one of the brake circuits (front or rear) goes dry. On the left the spring and plunger almost certainly act as a residual pressure valve to keep some pressure on the rear drum brakes that these vehicles would have.

Dear Ryan,

This is an issue that rears its ugly head when swapping brakes around on vehicles (like swapping from drum brakes to discs) or when a different axle or axles (with different brakes) are swapped in place of the factory parts. It's a bit surprising and exciting when you're just barely on the brakes and the rear tires lock up. There are a few ways to make things right, some better than others. First you can try to swap more than just the actual brakes themselves between vehicles, and by that I mean also swapping the brake master and factory proportioning valve, but that may not work in all cases. It could work if you are upgrading brakes on an older vehicle using factory parts for a later version of the same vehicle. We're thinking of parts-swapping within similar-year Jeep CJs (disc brakes up front), Wranglers (rear disc brakes) or within Suzuki Samurais and Sidekicks/Trackers where many parts interchange, for example.

This is Wilwood PN 260-11179, an adjustable aftermarket proportioning valve. It's used to adjustably lower the amount of hydraulic pressure that gets sent to the rear brakes. That makes them lock up later than they would if the full pressure was sent to them from the master cylinder. This proportioning valve also comes with a pressure switch that can be used to turn your brake lights on when you pressurize the system (i.e. push the pedal).

After all, brake systems work because the size of the hydraulic cylinders in the brake master cylinder and the front or rear brakes (be they drum/drum, disc/drum, or disc/disc) are sized specifically to work in conjunction with each other. So if you just swap brakes around between manufacturers or different models, you'll almost certainly need to add other parts—aftermarket parts. That's because chances are the sizes of the brake cylinders for the discs or drums won't be the same as what you removed. As a result the brakes will either work too well or not as well. That could mean the front brakes doing all the work or the rear brakes locking up at the hint of applying the brakes. Luckily, aftermarket parts can fix this issue.

Adjustable Brake Proportioning Valve

The first part you mention is an adjustable proportioning valve, and this can be used to decrease the effectiveness of either the front or the rear brake circuit (wherever it is plumbed) to better match what the other end of the braking system is doing. In our case that has almost always meant the rear brakes lock up much sooner than the fronts do their job. The opposite is harder to notice (where the front brakes are doing all the work). What we've done when the rear brakes work too well is install an aftermarket adjustable proportioning valve in the rear brake circuit and then use it to "turn down" the effectiveness of those brakes. To do this you need to install the part and do some closed-course testing. (You can pretend you are a professional driver, and we hold no responsibility for the outcome of your tests.) Generally, while driving slowly on a gravel road, we want the rear brakes to lock up just a little bit before the fronts. Adjust accordingly for your application.

There are a few adjustable brake proportioning valves on the market, and they range in price correlating with the quality (or lack thereof) with which they are built. We've used a few from Wilwood and would solidly recommend them or parts from other big-name brake manufacturers. We've also used some cheaper adjustable proportioning valves with success, but this is one area of vehicle modification that you really don't want to compromise with cheap parts, especially if you are working on a vehicle that you road drive frequently, tow with, or generally fill with the lives of folks you care about. If it's a beater trail rig that gets trailered to the trail, "parts is parts."

After swapping axles in our 2001 Chevy Blazer and adding large disc brakes to the rear Ford 9-inch, the rear tires would lock up at the hint of applying the brakes. It's great that our brakes were super strong, but also basically undrivable. We were able to install the Wilwood PN: 260-11179 in the truck to solve this problem and also bypass the factory ABS, which wasn't working with our fancy new axles anyway.

We've used Wilwood PN: 260-11179and Wilwood PN: 260-8419 with success in the past. The first one even worked nearly perfectly to eliminate the factory ABS system on a 2001 S-10 Blazer that had a pair of Ford F-150 axles under it and disc brakes on the rear Ford 9-inch axle.

Residual Pressure Valves: Also Helpful

Another couple of parts that can be helpful, also from Wilwood, especially if you are not upgrading your master cylinder and a functional OEM brake proportioning valve or adjustable valve, are small inline residual pressure valves.

Related:Solid-Axle Chevy S10 Blazer

These small parts hold either 2 pounds or 10 pounds of brake pressure. That residual pressure helps keep the brake parts in position so when you hit the brakes, you don't have to pump the brakes to push the parts back in place. The 2-pound unit, PN: 260-13783, is used for disc brakes (to keep the pads close to the rotors), and the 10-pound unit, PN: 260-13784, is used to keep drum brake shoes close to the drums.

These are somewhat older versions of the Wilwood residual pressure valves that can be plumbed inline to help keep you from having to pump the brakes on some braking systems when you add drums or discs.

"Techline" is the monthly question and answer column byFour Wheelertech editor Verne Simons, who tries to answer any and all technical questions sent his way by readers. Verne's brain is generally focused on off-road tech, but he also has a background in geology, biology, some experience in cooking, music trivia, useless facts, and more, so don't be shy and he'll give you an answer—right or wrong! That is, unless it's completely off topic. Verne is available for Techline questions atverne_simons@motortrend.comor hit him up on Facebook or@Verne.Simonson Instagram.