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Why Do My Motorhome Brakes Hiss?

You’re going down the road in your awesome motorhome when you go to hit the brakes and hear a hissing noise. Do you have a snake hiding behind your pedals? Did you accidentally adopt a stray, angry cat? Chances are this isn't the case. So why do your motorhome brakes hiss?

There are two answers that are most likely the cause of the hissing noise. Your cause for alarm and course of action depend on what type of power brake system your motorhome has. There are two different types of brake booster assists: vacuum and hydroboost. While these brake booster assists are completely different systems, they have the same end goal when it comes to navigating the roadways in your motorhome!

Vacuum Assist

Vacuum brake systems are directly connected to the master cylinder of your braking system, and are fairly standard in a lot of vehicles. Class C motorhomes tend to usually have vacuum assist brake systems, as they have a less heavy load than Class A motorhomes. Vacuum pressure works to apply the brake in a fairly straightforward process, making your braking process easy and smooth.

If your motorhome uses this type of brake system, the reason you may be hearing a hissing noise is that your vacuum line could be leaking. If it is a small, short hiss, that could be normal, but if it is a longer-lasting hiss, you could be facing a leak. Because a large amount of pressure is needed to make the brake system function, even a small leak could cause an audible hissing noise. This is not a huge cause for alarm, as you will still be able to use your brakes until the seal goes bad completely. However, if you do wait for it to go bad, you won’t completely lose braking capabilities, but it will be very difficult for you to brake. In this case, it is not a bad idea to bring your motorhome into a mechanic to have them test, and if need be, replace the seal. Or if you are handy, you can replace it yourself!


Most commonly known as hydroboost, this brake booster assist is designed for vehicles that may not create enough vacuum pressure to assist the braking system, which is true for diesel, supercharged, and turbocharged engines. Since most Class A motorhome chassis fit these descriptions, it is generally assumed that they will have a hydroboost system, but you should double check to make sure you don’t have a bigger problem on your hands!

Hydroboost brake assist works in a similar way to vacuum assist, but instead of using vacuum pressure from the engine, it uses fluid from your power steering for more pressure and better braking performance. Therefore, its performance depends on a well-functioning power steering system. This brake system also depends on an electric motor that powers a pump on the master cylinder. This is used as a backup in case your vehicle should lose power or if your engine quits running, that way you can still use the brakes no matter what.

Unfortunately, a hissing sound coming from a hydroboost brake assist system is very common. On the other hand, that is an indication that nothing is wrong! You are just hearing the pump working to keep your brakes going! Again, if you have any doubts about this, you can always take it into your local mechanic to have them verify that this is normal, and that it is not a different issue.

Now that you know the possible causes of why your motorhome brakes hiss, you can take action if you need to! Luckily, if it is a problem, it is generally an easy fix! Just remember, when in doubt, have a professional check it out! Have you dealt with hissing brakes? Leave us a comment about your experience!

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