Interesting problem with brakes

[flydude92]

I had an interesting experience with the motor home brakes yesterday.
We stayed four nights at Sauder Village in Archbold, Ohio. A place we regularly frequent.
Before we left on our trip I checked, among other things, the brake fluid level, verified there
were no leaks and that the brakes worked perfectly.

On our way home, shortly after we left our camping spot at about 5 mph as I applied the brakes
they pulsed badly as if the front rotors were extremely warped. By the time I got to the large
parking lot the brakes went almost completely to the floor but I was able to stop. I checked
everywhere for a problem. There was no loss of brake fluid, no leaks anywhere and nothing was
out of the ordinary. I moved it a few more feet with the same result.

The only place locally I could take it too was a Ford dealer that said they couldn?t get to it until
next week so I called AAA for a tow home. The Ford dealer thought it might be related to the
hydro boost system or even the ABS. While I waited I crawled under the RV looking for any
problems but found nothing wrong.

I decided to drive it around the parking lot again. It worked perfectly. No brake problems, no
pulsing, no bottoming out, nothing. I was tempted to drive it home but with a wife and three kids
it wasn?t a good idea and since AAA was on the way I had it towed home.

I never owned a Ford and don?t know anything about hydro boost systems.
I didn?t get a check engine light although I did find an error relating to the ABS (C1226) system.
I get different descriptions including Anti-Lock Brake System Power Valve Relay and warning
indicator output short circuit.

Any Ford experts out there?

 

[John Canfield]

That's really scary.  Which Ford chassis? 

 

[NY_Dutch]

Make sure your power steering fluid is topped off. It may seem odd, but the Hydro-Boost system uses the more powerful power steering pump and fluid as the brake booster instead of vacuum.

https://www.knowyourparts.com/technical-resources/brakes-and-brake-components/hydro-boost-the-non-vacuum-booster/

 

[flydude92]

John - E450 (added to signature)

Power steering is topped off. I noticed the connection between the power steering and brake booster while I was waiting for AAA. Never saw that before.
I have been researching it but I haven't seen anything related to my problem yet.
That is very informative  Thanks.

 

[John Canfield]

Moved from the Winnie board.

 

[Gary RV_Wizard]

That sounds like the classic signs of overheated brake fluid (boiling). Boiling fluid produces vapor and vapor in the brake lines is compressible, so no hydraulic action to move the calipers.  As soon as it cools a bit the function usually returns to normal.  However, this occurred before you had driven out of the campground, so overheating makes no sense at all.  Perhaps, though, something else caused a brief & temporary vaporization within the lines?  I can't imagine what, though.
I'm not familiar with the Ford hydroboost but generally those systems are a power assist. Loss of boost lets the pedal go low, but once it reaches the point where it mechanically pushes on the master cylinder to move brake fluid, the brakes work. Take a LOT of pedal effort, but they work.  Does that sound like what happened?  If so, could be as simple as a slipping belt on the power steering pump causing a brief loss of power boost.

 

[NY_Dutch]

Just to clarify a bit, Hydro-Boost brake boosters are not unique to Ford products. The systems from Bosch/Bendix are also used on Chevy/GMC, Chrysler products, and others where vacuum brake boosters are inadequate for hydraulic brake systems. They're often used on diesel trucks where there's virtually no engine vacuum to use with conventional boosters.

 

[flydude92]

I'm not familiar with the Ford hydroboost but generally those systems are a power assist. Loss of boost lets the pedal go low, but once it reaches the point where it mechanically pushes on the master cylinder to move brake fluid, the brakes work. Take a LOT of pedal effort, but they work.  Does that sound like what happened?  If so, could be as simple as a slipping belt on the power steering pump causing a brief loss of power boost.

That sounds possible. I was going so slow it didn't take much pressure to stop it.

I'm not sure why it initially felt like the rotors were badly warped. Maybe that was an early sign of slippage.

I will look at the serpentine belt, idlers and belt tensioner today for possible problems.

 

[TheBar]

Maybe a blockage in the line from the pump?

 

[84southwind]

That sounds possible. I was going so slow it didn't take much pressure to stop it.

I'm not sure why it initially felt like the rotors were badly warped. Maybe that was an early sign of slippage.

I will look at the serpentine belt, idlers and belt tensioner today for possible problems.

The pulsations you felt may have been from the antilock brake system, ii pulses the brakes on and off and will give the impression of warped rotors

 

[flydude92]

That makes sense.

I checked the serpentine belt and pulleys. The belt shows minor some of wear and both idler pulleys accumulated something from the
back of the belt so I am replacing the belt, idler and tensioner assembly. Can't hurt.
There are no other signs of anything abnormal. The fitting at the bottom of the power steering pump is loose against the nut. It isn't
leaking and the dealer said that was normal. I don't know but no leaks has to be a good thing.

Brian

 

[John From Detroit]

John - E450 (added to signature)

Power steering is topped off. I noticed the connection between the power steering and brake booster while I was waiting for AAA. Never saw that before.
I have been researching it but I haven't seen anything related to my problem yet.
That is very informative  Thanks.

That is the "Hydro boost" system  You are used to vacuum assist. but your RV needs more help than that so they use Hydro Boost. This has a couple of ways it works.

Engine running PS pump working fluid flowing the PS system provides the brake BOOST.

Engine off or PS fluid not flowing a second back up electric pump is engaged.

Either way it works

I lost fluid due to putting off maintenance too long so repair work is being scheduled. NOT a big disaster as I'd planned on doing it... This summer.. Just not this week.  But in truth.  The timing may be excellent.

 

[Gary RV_Wizard]

The pulsations you felt may have been from the antilock brake system, ii pulses the brakes on and off and will give the impression of warped rotors

The ABS will indeed pulse like a warped rotor, but it seems unlikely that the ABS would engage at the [presumably] low speed or be coupled with a low pedal.  ABS has no effect on pedal travel or stopping effort. I just don't see it as a possible factor here.

 

[John From Detroit]

Only twice has the ABS on this rig kickesd in. Once on freeway. Once on wet leaves at about ... well pediatricians were passing me,, speed .

 

[ChasA]

Don't dismiss the master cylinder. They do go bad and leak internally.

 

[flydude92]

Update:

I finished installing the new serpentine belt, tensioner w/idler and separate idler.
The separate idler was difficult to turn which may explain the material on the
backside of the belt. The idler was turning when I originally checked it but it
may have been going to slow.

I tried some of the tests in the web site Dutch pointed too and they passed.

I decided to take it for a ride. I drove country roads for about an hour stopping at
two stores with speeds to 55 mph. It worked perfectly. No problems stopping.
The pedal felt normal. When I got back I climbed under it and looked for anything
abnormal but didn?t find anything.

Not sure what to do at this point but to replace the tires and move on.
I find it extremely difficult to repair something that is working. 

  I attached a picture of the belt layout on my 6.8L engine.
#1 is the idler that was difficult to turn.
#2 I don?t have an idler here so I guess it?s optional.
#3 is the power steering pump.

I will update if the problem reoccurs.

 

[Timmy_B]

That sounds like the classic signs of overheated brake fluid (boiling). Boiling fluid produces vapor and vapor in the brake lines is compressible, so no hydraulic action to move the calipers.  As soon as it cools a bit the function usually returns to normal...

That was the first thought that came to mind for me, as well.  This happened on my wife's classic MB SL 560.  Brakes went right to the floor, barely got it stopped.  Twenty minutes later, they acted like brand new!  Happened a couple of times before we finally figured out what was happening.  We had a bad wheel rotor; that aluminum wheel was so hot, you'd burn your hand if you touched it!!!

It doesn't make sense, as you said, if he had only just run it a short bit.

 

[flydude92]

Here are the pictures of the tire.

I attached them to the original post but they vanished.

 

[flydude92]

Update #2 with brake history:

Two years ago I had a seized caliper which warped the front/right rotor. Due to age I replaced the rotors,
calipers, pads, seals, bearings and rubber brake lines. I checked the rear brakes and they were perfect. Very
little wear on the rotors and probably 15000 miles left on the pads.

About 3 weeks ago I purchased a set of tires that the company wasn?t able to install due to the weight
of the RV and liability so I brought them two tires at a time and installed them at home.

I started with the driver?s rear first. With the tires off I checked the brakes. The rotors had very little wear
and a lot of pad material left. Nothing out of the ordinary.

However, on the passenger rear the outer pad was missing and the backing plate was riding along the rotor.
There wasn?t a lot of damage. When I removed the caliper the inner pad was separated from the backing plate.
The pad was still very thick. The caliper was not seized.

I wonder if the outer pad separated from the RV at some point shortly after leaving my spot.
When I tried to stop the brakes went to the floor since the caliper was compensating for the missing pad.
Once the backing plate contacted the rotor the brakes started working.

I am still in the process of replacing the rotors, calipers, pads, seals, bearings, and rubber brake lines along with the
metal line between the rear wheels. It?s amazing how long it takes to get the correct parts and the number of trips
to the parts places.

 

[uchu]

Thank you for the update...Quite an ordeal!

This is precisely why brake works are not in my DYI qualifications.