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Mike in Va · 04-08-2021, 09:50 PM

I was returning home today in my 2001 Holiday Rambler I started down a mountain and as usual I tried to keep my speed to around 45-50 mph. When my speed got to around 50 I pushed on the brake pedal and it would not go down. It was like pushing on a solid piece of concrete no give at all. My speed picked up to faster then 60. Thank goodness I was able to weave in and out of traffic without causing an accident. I was able to pull up hard on the steering wheel and pushed on the brake pedal as hard as I could and was able to get SOME braking. Once I got to the bottom of the mountain I pulled into a rest area. After several minutes of realizing how lucky I had been. I read through the owners manual and found that I have a Hydro max boost brake pedal that worked off my power steering pump. I checked the reservoir and found it was a LITTLE low so I added approx 8 oz of fluid . After that the pedal worked and brakes worked like they are suppose to. This was the first time this happen and still don't know what caused it. Its hard to believe that 8 oz of fluid could have caused this when the container looks like it holds more then a 1/2 gal total. After driving it around the rest area several times, making sure the brakes worked ok. I may it home with no more problems. Is there any way to trouble shoot the boost pump. I'm not going to use it again until I can find out exactly what caused this to happen.Any suggestions on what caused this to happen are welcome.

Mike in Va · 04-08-2021, 09:54 PM

Forgot to add that my brake system is a air over hydraulic. Thanks

96 Wideglide · 04-08-2021, 09:56 PM

Don't know what you have, but you better try and get it to a qualified HD truck repair shop.

twinboat · 04-08-2021, 11:10 PM

You need to flush out the old fluid by breeding the brakes, If it hasn't been done in over 5 years.

Brake fluid is hydroscopic, meaning it absorbs water over time, and the water will lower the boiling point of the fluid.

The fluid gets above boiling point while braking hard.
When you let off the brake, water turns to steam and leaves air pocket in caliper.
Next application of brakes, If the fluid is still hot, like going down a long hill, your compressing air, not pushing fluid into caliper.

After a long stop the fluid cools and all seems normal.

You have air over hydraulic OR HydroMax brakes, not both.
One uses air to push the master cylinder plunger in, and the other uses steering pump pressure to help push the master cylinder plunger in.

In either case, fluid needs flushing every 5 years or so. Ford recommends every 2 years on Class A motorhome chassis.

JohnBoyToo · 04-09-2021, 04:33 AM

WOW, twinboat, I doubt my fluid has been swapped out - ever !

thank goodness no butt-puckering incidents like the OP had though...

OP, did you happen to hold the brakes on a long time and they heated up?
I use engine and gear braking mostly while coming down long passes...
just stabbing brakes hard every once in a while to quickly scrub speed and get off the brakes... if I'm on the brakes for 3 seconds, that's seems like a long time

fcmcelr · 04-09-2021, 01:48 PM

Back many years ago when I had a hydroboost system on a gasser, I also had an electric backup pump. Does your coach also have an electric backup and have you tested it to be sure you hear the motor run when the engine is off to simulate low hydro boost pressure?

wolfe10 · 04-09-2021, 01:57 PM

Hydraboost is hydraulic over hydraulic.

Air over hydraulic is very different.

Which system do you have?

And with either, indeed changing brake fluid is important.

BUT, that should not cause a hard pedal-- just the opposite were the brake fluid to heat to its (new lower, hydrated) boiling point. The pedal would go down and be spongy.

96 Wideglide · 04-09-2021, 05:29 PM

Quote:

Originally Posted by JohnBoyToo

WOW, twinboat, I doubt my fluid has been swapped out - ever !

thank goodness no butt-puckering incidents like the OP had though...

OP, did you happen to hold the brakes on a long time and they heated up?
I use engine and gear braking mostly while coming down long passes...
just stabbing brakes hard every once in a while to quickly scrub speed and get off the brakes... if I'm on the brakes for 3 seconds, that's seems like a long time

Don't you have air brakes?

Mike in Va · 04-10-2021, 08:37 AM

I posted the post when I got home after the incident and since then I've had time to sit back and think through what happened. The engine brake didn't work, but after thinking back I had down shifted down to first gear trying anything I could to get some slowed down, Don't know if this is why the engine brake didn't work. I have the hydro boost system on my DP motorhome. After trouble shooting I found the electric motor BACKUP doesn't have 12 volts going to one side of the relay. So it wasn't working at all. After reading the manual I've tested the system and the backup pump doesn't activate when the brake pedal is pushed with the key and motor turned off. I used a jumper wire and energized the second side of the relay and the motor came on as it is suppose to do. Don't know why I didn't notice this, the only thing I can say is that the system worked fine in flat and slow traffic and only when it was put on a heavy load did it show up. Another thing I noticed now is the brake pedal will not depress AT ALL when its pressed with the engine and key is off. I'm still getting to the bottom of everything but the brake pads look good, the fluid levels, both power steering and brake fluid, are full. I'm going to get the back up motor working correctly, test it, and then get it to a garage to make sure things are right. The engine brake worked as it is suppose all the way home after the incident. I guess it wouldn't down shift because I had shifted to first gear and it was protecting the engine. Still reading and trying to figure that one out. One thing that I didn't think to do was pull the air brake to stop. It may have caused some damage but a lot less then what could have happen. Thanks for all the information from everyone.

OldWEB · 04-10-2021, 09:22 AM

Here is a cut-out from the 2001 Holiday Rambler "Ambassador" manual, it looks like you should be fully covered. Also mentioned is an exhaust brake, you said engine brake, the same? How is that activated?

OldWEB · 04-10-2021, 09:54 AM

If you do not have it, here is a Bosch book on the Hydro-Max system. With a Trouble Shooting section on "Hard pedal".

http://1999southwind.com/DOWNLOAD/Bo...r%20Manual.pdf

96 Wideglide · 04-10-2021, 10:02 AM

Quote:

Originally Posted by Mike in Va

I guess it wouldn't down shift because I had shifted to first gear and it was protecting the engine. Still reading and trying to figure that one out.

You probably would have had to be down below 25mph for the transmission to downshift to 1st, to protect your engine from over-reving.

Xmcdog · 04-10-2021, 10:16 AM

Quote:

Originally Posted by wolfe10

Hydraboost is hydraulic over hydraulic.

Air over hydraulic is very different.

Which system do you have?

And with either, indeed changing brake fluid is important.

BUT, that should not cause a hard pedal-- just the opposite were the brake fluid to heat to its (new lower, hydrated) boiling point. The pedal would go down and be spongy.

Totally agree. The pedal would be soft and spongy with a long travel. Being rock hard is a different issue.

Mike in Va · 04-10-2021, 04:26 PM

I've been out today trouble shooting my problem. It seems that someone CUT the wires going to the electric motor on the hydro max pump under the dash board where the wires come through the front firewall. I found the wires I THINK attach to the motor but they have no power on either one. The pump hasn't work the entire time I"ve owned it. I did us a jumper wire and got it to work like its suppose to , so I know the pump is ok. Does anyone have any idea where the wires go to the fuse panel? If not I will have to cut all of the bundles loose and track the two wires. They are a yellow, hot, and green, ground, wire. Again its a 2001 holiday rambler ambassador. Thanks for all of your help.