parking brake valve leaking

Parking Brake Valve Leaking- Quick Troubleshooting


Is your RV parking brake valve causing trouble? Well, it can be because of a huge leak. 

So why is your parking brake valve leaking?

Well, the parking brake valve usually leaks air out for 3 common reasons. It can be a damaged exhaust port in your parking valve. The relay valve in your parking brake can also cause leaks if it’s plumbed wrong. Moreover, a leaking brake chamber can also be a reason behind it.

That’s not all. We have a more detailed answer to your questions. So head over to our segment to find out why your parking brake valve is leaking. 

Parking Brake Valve Leaking-  3 Common Causes 

A leaking valve is the most common concern of parking brakes of an RV. Parking brake valves can leak and release air due to different reasons. But it is important to understand what is causing the leak. Only then you can fix the leak. 

So here are a few common causes of a leaking parking brake valve. With this, you should be able to fix your problem. But before jumping into the causes, let’s first look at the few signs of a leaking parking brake valve –

  • Release of air
  • The parking brake makes a whistling noise
  • Rv may bounce or move 
  • Air pressure gauge falls

Cause 1 of 3: Leak in Exhaust port

A parking brake valve contains an exhaust port. If the exhaust port leaks or cracks, it can be the reason why air is leaking out. 

Now exhaust ports in any valve contain many delivery lines. These lines are again connected to the other valves of the brake. In most cases, one of these lines goes bad causing the exhaust port to leak. 

So check all the delivery lines by disconnecting all of them one by one from the exhaust port. Doing this will help you identify if it’s a faulty delivery line or a faulty exhaust port. If you hear air gushing out of one of the lines after disconnecting it, you know that’s the line that went bad

In case of no such sound or air coming out of the lines, then the exhaust port is definitely damaged. 


A leak in the exhaust port as mentioned can be either because of a bad exhaust port or the delivery lines. So if one of the lines is faulty, you just simply replace that with a new one. And that’ll be a quick and easy task. 

But if it’s the exhaust port that has gone bad, you’ll need to get yourself a whole new exhaust port. And then connect it to the parking valve. Moreover, you’ll have to connect and adjust all the delivery lines. Now doing this can be tricky because you must ensure all the delivery lines have been placed in the right positions. 

Cause 2 of 3: Relay Valve plumbed wrong

There is a high possibility that the relay valve may have been plumbed wrong in your RV system. Because of having too many ports within the parking brake valve. This is a major reason why the parking brake valve leaks air out of it. 

Chances are, the line from the dash valve has been plumbed into the supply circuit of the parking valve. 

You can also test this by disconnecting the line with the smallest diameter (typically the yellow-colored one) from the brake valve. If you find that air is coming out of the fitting, then the relay valve has been placed incorrectly. This is what causes the lines to back feed air to the dash valve.


If the relay valve is placed in the wrong position, you can just place it in the right place. Now doing this can be a tough job for you. 

So, make sure to take help from an expert. Place the valve accordingly and look for further leaks. If you find none, your problem is solved. 

Cause 3 of 3: Leaking Brake Chamber

Now the brake chamber can be leaked or damaged. This is a major reason behind a leaking parking brake valve. Most importantly, this one is hard to identify. The brake chamber in the RV has a diaphragm. 

This diaphragm, in most cases, can be cracked or torn causing air to leak from the parking valve. This is the reason why your air pressure gauge falls.


To repair the cracked diaphragm, you’ll need to cage the spring first. Make sure to fully insert the spring and then turn it 90 degrees. This ensures that the bolts are engaged in the parking brake. 

At this point, you’ll have to take out the clamp that’s holding the diaphragm. Make sure you do that carefully because it can seriously hurt you if done wrong. Once you’ve taken out the clamp, take out the cracked diaphragm. 

You can pull the slack adjuster back and use a vise grip to hold the small return spring compressed. This will help you install the new diaphragm easily. 

Once you’ve installed the new diaphragm, reinstall the clamp and assemble everything together again. Make sure to take out the cage bolt and reinsert the rubber plug.

By the way, here are our top choices of the diaphragm for brake chambers-

Troubleshooting these common components of the parking brake valve should help you fix the leak. If you still can’t find and fix the issue, you may want to take help from a mechanic. 


Question: What is a 30/30 brake chamber?

Answer:  A 30/30 brake chamber is a type of brake chamber that has 30 square inches of area in each chamber. Parking brake valves on the cab dash release air pressure in these chambers.

Question: What is crack pressure on the relay valve?

Answer: A crack pressure on the relay valve refers to the air pressure that is required at the input from the foot valve. This input is given before the relay valve sends the pressure to the brake. 

Question: What is a slack adjuster?

Answer: The slack adjuster is an assembly that transmits the braking torque to the S-cam. It facilitates the adjustment of the clearance between the brake lining and brake drum.


Parking brake valve leaking can be a serious issue if you don’t handle it properly. Moreover, the leak can lead to even further damage. So it is recommended to identify the issue and fix it immediately.

We hope we were able to help you through our detailed discussion on the parking brake issue. Let us know how well it worked for you in the comments below. 

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