Steering box failed; now I hear air leaking when brakes applied

[FloridaCanuk]

My steering box failed in Kansas, leaking fluid heavily. After several phone calls I was still unable to find a mobile mechanic who would come out and meet us, so I limped to an RV park by constantly pulling over & replenishing the power steering fluid. However, I’m sure the fluid ran dry several times as I wasn’t always able to pull over right away. After the steering box was replaced we continued to make our way home to Florida.

The weird thing is that after the steering box was replaced, I kept hearing air hissing (leaking) whenever I had to apply the brakes to stop at a stop sign, red light, etc. It sounded like the air was leaking underneath the front of the RV more or less below me. Yet, the mechanic who installed the new steering box bled the air out of the system and as far as our brakes go, our Neptune doesn’t have air brakes. Could the air hissing mean that the power steering pump is failing because of it running dry several times, or could it be something else? Any help would be greatly appreciated.

[Dav L]

Is this an F53 Ford Chassis? With Hydroboost braking?
If so, there is no air. It's purely hydraulic.
If you apply the brakes while not moving...do you still hear the air hiss?
Can you have someone else apply the brake while you find the hiss source?
Are you sure it's air? There is an electric pump backup to the power steering hydraulic primary boost.

[speed racer]

This is pretty common with a hydrostatic brake system. It takes a long time for all the air to get purged from the system. I would leave it alone for a while and keep an eye on the fluid level.

[FloridaCanuk]

Originally Posted by Dav L

Is this an F53 Ford Chassis? With Hydroboost braking?
If so, there is no air. It's purely hydraulic.
If you apply the brakes while not moving...do you still hear the air hiss?
Can you have someone else apply the brake while you find the hiss source?
Are you sure it's air? There is an electric pump backup to the power steering hydraulic primary boost.

It’s a Roadmaster chassis; the brakes are not air brakes. I’m told they are “air over hydraulic”. I never did understand what that means...

[FloridaCanuk]

Originally Posted by speed racer

This is pretty common with a hydrostatic brake system. It takes a long time for all the air to get purged from the system. I would leave it alone for a while and keep an eye on the fluid level.

The power steering box is what was replaced. Yet the problem occurs when I step on the brakes. That’s what’s confusing me...

[FloridaCanuk]

Originally Posted by Dav L

Is this an F53 Ford Chassis? With Hydroboost braking?
If so, there is no air. It's purely hydraulic.
If you apply the brakes while not moving...do you still hear the air hiss?
Can you have someone else apply the brake while you find the hiss source?
Are you sure it's air? There is an electric pump backup to the power steering hydraulic primary boost.

I can check underneath, and will do so. The problem is that the park brake can’t be on when the service brakes are applied so if whoever is applying the service brakes screws up and stops applying them while I’m underneath the RV😧...

The sound is definitely air; The electric pump backup makes a very distinctive sound.

[Bubba1]

I have a 2003 Monaco Cayman, sister to your Neptune. Your coach does have a hydroboost style hydraulic 4 wheel disc brake system. It is not a true air over hydraulic brake system. The boost comes from the power steering pump. On my coach I will hear what sounds like air leaking when I have to step on the brakes hard and when I have to sit with the brakes held for long periods. I've owned this coach since new. I had similar concerns when I first got the coach in 2003. I was told it's like a pressure release valve because the power steering pump supplies more pressure than is sometimes needed for the braking system. That's not something I'd heard of before, but in sixteen years of ownership I've never had an issue with that part of the braking system. I change the power steering fluid and filter on mine every two years a long with the flushing and replacing the brake fluid at the same time.

I have had to replace the ABS controller and proportioning valve, 3 wheel sensors, both rear rotors and calipers and pads due to other issues with the braking system however.



Mike H

[Bubba1]

Also, the parking brake is totally separate from the service brakes and is the only true air brake on your coach. The air source comes from the engine compressor that supplies air for your suspension. If you have concerns about the parking brake just block your coaches rear wheels.


Mike H

[twinboat]

Air over hydraulic brakes use air chambers to push the master cylinder. The brake pedal send air to them.


If your brake pedal goes to a air valve, you have air over hyd. brakes. Look on the other side of the firewall, where the pedal is mounted.

Since there are air lines running from the brake valve to the " air over " clusters, they may have been nicked during the work.
The clusters look like this and there will be 2.

[FloridaCanuk]

Originally Posted by Bubba1

I have a 2003 Monaco Cayman, sister to your Neptune. Your coach does have a hydroboost style hydraulic 4 wheel disc brake system. It is not a true air over hydraulic brake system. The boost comes from the power steering pump. On my coach I will hear what sounds like air leaking when I have to step on the brakes hard and when I have to sit with the brakes held for long periods. I've owned this coach since new. I had similar concerns when I first got the coach in 2003. I was told it's like a pressure release valve because the power steering pump supplies more pressure than is sometimes needed for the braking system. That's not something I'd heard of before, but in sixteen years of ownership I've never had an issue with that part of the braking system. I change the power steering fluid and filter on mine every two years a long with the flushing and replacing the brake fluid at the same time.

I have had to replace the ABS controller and proportioning valve, 3 wheel sensors, both rear rotors and calipers and pads due to other issues with the braking system however.



Mike H

This is very reassuring. It explains the connection between the power steering & brake system. I was really scratching my head as to why a steering repair would affect the brakes. Hopefully this means that there’s nothing to worry about. Thanks for the information.

[FloridaCanuk]

Originally Posted by speed racer

This is pretty common with a hydrostatic brake system. It takes a long time for all the air to get purged from the system. I would leave it alone for a while and keep an eye on the fluid level.

Thanks, I’ll give it some time & monitor the fluid.

[FloridaCanuk]

Originally Posted by twinboat

Air over hydraulic brakes use air chambers to push the master cylinder. The brake pedal send air to them.


If your brake pedal goes to a air valve, you have air over hyd. brakes. Look on the other side of the firewall, where the pedal is mounted.

Since there are air lines running from the brake valve to the " air over " clusters, they may have been nicked during the work.
The clusters look like this and there will be 2.Attachment 257022

I’ll take a look in the generator compartment tomorrow ( the other side of the firewall). Offhand, I don’t recall ever seeing an air valve...

[Dav L]

Ok, just to restate...it sounds like the rig has Bosch Hydroboost braking on an F53 chassis. And, there is no air as part of the system. And the noise isn't Air at all. The association to steering to braking is the power steering pump provides boost to both the braking system and the steering box.

If there is any air in the braking system, it needs to be bled out of the braking system at the wheels. The brake pedal will feel spongy and the brakes will be less effective if any air is in the hydraulic portion.

Ensure that the power steering filters are clean and the reservoir is at the full mark with the proper fluid.

There is no air valves to look for. The thread went sideways due to the system not being identified in the first post.

[twinboat]

Its a Holiday Rambler Neptune on a Roadmaster chassis. A diesel pusher.

Far from a F53.

Originally Posted by Dav L

Ok, just to restate...it sounds like the rig has Bosch Hydroboost braking on an F53 chassis. And, there is no air as part of the system. And the noise isn't Air at all. The association to steering to braking is the power steering pump provides boost to both the braking system and the steering box.

If there is any air in the braking system, it needs to be bled out of the braking system at the wheels. The brake pedal will feel spongy and the brakes will be less effective if any air is in the hydraulic portion.

Ensure that the power steering filters are clean and the reservoir is at the full mark with the proper fluid.

There is no air valves to look for. The thread went sideways due to the system not being identified in the first post.